CHAPTER III

PHYSIOLOGY OF THE CIRCULATION

No attempt will be made to cover the entire subject of the physiology of the circulation. Only in so far as it relates to arteriosclerosis and blood pressure and has a bearing on the probable explanation of blood pressure phenomena will it be discussed.

"The heart and the blood vessels form a closed vascular system, containing a certain amount of blood. This blood is kept in endless circulation mainly by the force of the muscular contractions of the heart; but the bed through which it flows varies greatly in width at different parts of the circuit, and the resistance offered to the moving blood is very much greater in the capillaries than in the large vessels. It follows, from the irregularities in size of the channels through which it flows, that the blood stream is not uniform in character throughout the entire circuit--indeed, just the opposite is true. From point to point in the branching system of vessels the blood varies in regard to its velocity, its head of pressure, etc. These variations are connected in part with the fixed structure of the system and in part are dependent upon the changing properties of the living matter of which the system is composed." (W. H. Howell.)

If the vascular system were composed of a central pump, projecting at every stroke a given amount of liquid into a series of rigid tubes, the aggregate cross sections of which were equal to the cross section of the main pipe, then the velocity at the openings would be the same as at the source (making allowances for friction). The problem would then be a simple one. In the circulation of the blood no such simple condition obtains. The capillary beds is an enormous area through which the blood flows slowly. From the time the blood is thrown into the aorta the velocity begins to diminish until it reaches its minimum in the capillaries. In no two persons is the initial velocity at the heart the same, nor in the same person is it the same at all times of day. The size of the heart, the actual strength of the muscle, the amount of blood ejected at every beat, and the size and elasticity of the aorta are some of the factors which determine the velocity of blood at the aortic orifice. When to these factors are added the differences in arterial tissue, the activity or resting stage of the various organs, etc., the question becomes exceedingly complicated. In spite of these many disturbing elements, attempts more or less successful have been made to estimate the velocity of the blood in animals. Thus, in the carotid of the horse the velocity was found to be 300 mm. per second (Volkman) and 297 mm. (Chauveau); in the carotid of the dog, 260 mm. (Vierordt). In the jugular vein of the dog Vierordt found the velocity to be 225 mm. per second. These figures do not represent the actual velocity of the blood in all horses or all dogs, but they do give us some general idea of the rate of flow of the blood. For man it has been calculated that the velocity in the aorta is about 320 mm. per second. The velocity is not uniform in the large arteries, where at every heart beat there is a sudden increase followed by a decrease as the heart goes into diastole. The farther away from the heart the measurements are made the more even is the flow.

Observations by W. H. Luedde with the Zeiss binocular corneal microscope on the rate of flow in the conjunctival capillaries must modify somewhat our former conceptions. He finds that "The rate varies in the different arteries, capillaries, and veins from a barely perceptible motion to a little more than 1 mm. per second. Further, some parts of the capillary network are ordinarily supplied with blood elements only occasionally. This is shown by the passage of a column of corpuscles along a certain line, followed after an interval of seconds, during which no corpuscles pass, by another column in the same line as before."

The vessels of the conjunctiva probably are quite like superficial vessels in the skin and mucous membranes. Therefore, we must be free to admit that the circulation in them is not absolutely steady. Luedde found further that in syphilitics there were tortuosities, irregularities, minute aneurysmal dilatations and even obliterations of capillaries. Some of the changes occurred as early as one month after infection.

The rate in the capillaries of man is estimated to be between 0.5 mm. and 0.9 mm. per second. As the blood is collected into the veins and the bed becomes smaller, the velocity increases until at the heart it is almost the same as in the aorta. That the velocity could not be exactly the same is evident from the fact that the cross section of the veins, which return the blood to the right auricle, is greater than is the cross section of the aorta.

The volume of the bed is subject to rapid and wide fluctuations, which are dependent on many causes, both physiologic and pathologic. The call of an actively functionating organ or group of organs causes a widening of a more or less extensive area, and the velocity necessarily varies. In states of great relaxation of the vessels there may be a capillary pulse. In order to force blood at the same rate through dilated vessels as through normal vessels, there must be more blood or there must be a more rapid contraction of the central pump. What actually happens, as a rule, is an increase in the rate of the heart beat. There are conditions--such, for example, as aortic insufficiency--where actually more blood is thrown into the circulation at every beat, so that the rate is not changed.

It has been calculated that the average amount of blood thrown into the aorta at every systole of the heart is from 50 to 100 c.c. This is forcibly ejected into a vessel already filled (apparently) with blood. In order to accommodate this sudden accession of fluid, the aorta must expand. The aortic valves close, and during diastole the blood is forced through the vascular system by the forcible, steady contraction of the highly elastic aorta. Other large vessels which branch from the aorta also have a part in this steady propulsion of blood. From seventy to eighty times a minute the aorta is normally forcibly expanded to accommodate the charge of the ventricle. It is not difficult to understand the great frequency of patches of sclerosis in the arch when these facts are borne in mind.

What relationship the viscosity of the blood has to the rate and volume of flow is not fully understood. As yet there is not much known about the subject, and no one has devised a satisfactory means of measuring the viscosity. It is thought by some that an increased viscosity assists in producing an increased amount of work for the heart.

=Blood Pressure=

Blood pressure is the expression used for a series of phenomena resulting from the action of the heart. As every heart beat is actual work done by the heart in overcoming resistance to the outflow of blood, this force is approximately measurable in a large artery such as the brachial. It has been determined that the pressure in the brachial artery is almost equal to the intraventricular pressure in the left ventricle. In animals it is easy to attach manometers to the carotid artery and to measure the blood pressure accurately. Formerly the method consisted in attaching a tube and allowing the blood to rise in the tube. The height to which the blood rose measured the maximum pressure. This is a crude method and has been replaced by the U-tube of mercury with connection made to the artery by saline or Ringer's solution. This apparatus is familiar to all physiologists.

In man the measurement is most conveniently made from the brachial artery. There is some difference in the pressure in the femoral and the brachial and some use both arteries. However, the difficulty of adjusting instruments to the upper leg, the great force which must be used to compress the femoral artery and the relative inaccessibility of the leg as compared to the arm, make the leg an inconvenient part for use in blood pressure determinations. It is not to be recommended.

Blood pressure is a valuable aid in diagnosis and of material help in many cases in prognosis, but it is not infallible neither can it be used alone to diagnose a case. Blood pressure is only one of many links in a chain of evidence leading to diagnosis. It has been badly used and much abused. It has been condemned unjustly when it did not furnish _all_ the evidence. It has been made a fetish and worshipped by both doctors and patients. A sane conception of blood pressure must be widely disseminated lest we find it being discarded altogether.

Blood pressure consists of more than the estimation of the systolic pressure. The blood pressure picture consists of (1) the systolic pressure, (2) the diastolic pressure, (3) the pulse pressure which is the difference between the systolic and diastolic pressure, (4) the pulse rate. Expressed in the literature it should read thus: 120-80-40; 72. That tells the whole story in a brief, accurate form. This is recommended in history reporting. It must be ever kept in mind that a blood pressure reading represents the work of the heart at the _moment when it was taken_. Within a few minutes the pressure may vary up or down. There is no normal pressure as such, but an average pressure for any group of people of the same age living under similar conditions. The habit of speaking of any systolic figure as normal should be broken. A pressure picture may be normal but a systolic reading, whatever it may be, is not accurately designated as normal. This distinction is worth insisting upon.

=Blood Pressure Instruments=

There are several instruments which are in common use for the purpose of recording blood pressure in man.

Historically, the determination of blood pressure for man began with the attempt of K. Vierordt in 1855 to measure the blood pressure by placing weights on the radial pulse until this was obliterated. The first useful instrument, however, was devised by Marcy in 1876. He placed the hand in a closed vessel containing water connected by tubing with a bottle for raising the pressure and by another tube with a tambour and lever for recording the size of the pulse waves. He maintained that when pressure on the hand was made, the point where oscillations of the lever ceased was the maximal pressure, the point where the oscillations of the recording lever was largest, was the minimal pressure.

This pioneer work was practically forgotten for twenty-five years. It was not until 1887 that V. Basch devised an instrument which was used to some extent. This instrument recorded only maximum pressure. It consisted of a small rubber bulb filled with water communicating with a mercury manometer. The bulb was pressed on the radial artery until the pulse below it was obliterated and the pressure then read off on the column of mercury. V. Basch later substituted a spring manometer for the mercury column. Potain modified the apparatus by using air in the bulb with an aneroid barometer for recording the pressure. These instruments are necessarily grossly inaccurate. Moreover, they do not record the diastolic pressure.

In 1896 and 1897 further attempts were made to record blood pressure by the introduction of a flat rubber bag encased in some nonyielding material, which was placed around the upper arm. Riva-Rocci used silk, while Hill and Barnard used leather. The latter used a bulb or Davidson syringe to force air into the cuff around the arm and palpated the radial artery at the wrist, noting the point of return of the pulse after compression of the upper arm, and reading the pressure on a column of mercury in a tube.

Except that the width of the cuff has been increased from 5 cm. to 12 cm., this is the general principle upon which all the blood pressure instruments now in use are based. Most of the apparatuses make use of a column of mercury in a U-tube to record the millimeters of pressure. As the mercury is depressed in one arm to the same extent as it is raised in the other arm the scale where readings are made is .5 cm. and the divisions represent 2 mm. of mercury but are actually 1 mm. apart.

The cuff was made 12 cm. in diameter because it was shown (v. Recklinghausen) that with narrow cuffs much pressure was dissipated in squeezing the tissues. Janeway has shown that with the use of the 12 cm. cuff accurate values are obtained independently of the amount of muscle and fat around the brachial artery. In other words if an actual systolic blood pressure of 140 mm. is present in two individuals, the one with a thin arm, the other with a thick arm, the instrument will record these pressures the same where a 12 cm. arm band is used. We need have no fear of obtaining too high a reading when we are taking pressure in a stout or very muscular individual. Janeway also was the first to call attention to the fact that the diastolic or minimal pressure was at the point where the greatest oscillation of the mercury took place. This is difficult to estimate in many cases as the eye can not follow slight changes in the oscillation when the pressure in the cuff is gradually reduced. Practically this is the case in small pulses.

The Riva-Rocci instrument was modified by Cook. (See Fig. 13.) He used a glass bulb containing mercury into which a glass tube projected. The bulb was connected by outlet and tubing to the cuff and syringe. The glass tube was marked off in centimeters and millimeters and for convenience was jointed half way in its length. The instrument could be carried in a box of convenient size. This instrument is fragile and more cumbersome, although lighter in weight, than others and is very little used at present.

Stanton's instrument (Fig. 14) is practically Cook's made more rigid in every way but without the jointed tube. The cuff has a leather casing, the pressure bulb is of heavy rubber, the glass tube in which the mercury rises is fixed against a piece of flat metal and there are stopcocks in a metal chamber introduced between the bulb and mercury with which to regulate the in- and out-flow of air. The pressure can be gradually lowered conveniently without removing the pressure bulb.

The most accurate mercury manometer is that of Erlanger. (Fig. 15.) The instrument is bulky and is not practicable for the physician in practice. The principle is that used by Riva-Rocci. There is an extra T-tube introduced between the manometer and air bulb connecting with a rubber bulb in a glass chamber. The oscillations of this are communicated to a Marey tambour and recorded on smoked paper revolving on a drum. There is a complicated valve which enables the operator to reduce the pressure with varying degrees of slowness. The mercury is placed in a U-tube with a scale alongside it. The instrument is expensive and not as easy to manipulate as its advocates would have us believe. Hirschfelder has added to the usefulness (as well as to the complexity) of the Erlanger instrument, by placing two recording tambours for the simultaneous registering of the carotid and venous pulses. In spite of its complexity and necessary bulkiness, very valuable data are obtained concerning the auricular contractions.

One of the best of the mercury instruments is the Brown sphygmomanometer. In this (Fig. 16) the mercury is in a closed, all-glass tube so that it can not spill under any sort of manipulation. It is in this sense "fool-proof." The cuff, however, is poorly constructed. It is too short and there are strings to tie it around the arm. I have found that this causes undue pressure in a narrow circle and renders the reading inaccurate. In the clinic we use this mercury instrument with a long cuff like that provided by the Tycos instrument.

The Faught instrument (Fig. 17) is larger than the Brown, but is less easily broken and is not too cumbersome to carry around. The substitution of a metal air pump for the rubber makes the apparatus more durable.

The v. Recklinghausen instrument is not employed to any extent in this country. It is both expensive and cumbersome, and has no advantages over the other instruments.

Several other instruments have been devised and new ones are constantly being added to the already large list. With those employing mercury the principle is the same. The aim is to make an instrument which is easily carried, durable, and accurate.

In all the mercury instruments the diameter of the tube is 2 mm. One would suppose that there would be noticeable differences in the readings of the different mercury instruments depending upon the amount of mercury used in the tube. By actual weight there is from 35 to 45 gms. of mercury in the several instruments. After many trials, no noticeable differences in blood pressure readings can be made out between a column weighing 35 gm. and one weighing 45 gm.

There is, however, the inertia of the mercury to be overcome, friction between the tube and the mercury, and vapor tension. The mercury is therefore not as sensitive to rapid changes of pressure in the cuff as a lighter fluid would be. The mercury must be clean and the tube dry so that there is no more friction than what is inherent between the mercury and glass. In making readings on a rapid pulse the oscillations of the mercury column are apt to be irregular or to cease now and then, due to the fact that the downward oscillation coincides with a pulse wave, or an upward oscillation receives the impact of two pulse waves transmitted through the cuff. Instruments have been devised to obviate this difficulty, but they have not come into favor. They are usually too complicated and at present can not be recommended.

An instrument devised by Dr. Rogers (the "Tycos") has met with considerable popularity. (Fig. 18.) This is not an instrument which operates with a spring and lever. The instrument is composed essentially of two metal discs carefully ground and attached at their circumferences to the metal casing below the dial. There is an air chamber between these discs through the center of which air is forced by the syringe bulb. When air is forced into the space between these two discs, they are forced apart to a very slight extent, with the highest pressures only 2-3 mm. of bulging occurs. From data gathered after extensive use for five years these discs were not found to have sprung. A lever attached to a cog which in turn is attached to the dial needle magnifies to an enormous extent the slightest expansion of the discs. Every dial is handmade and every division is actually determined by using a U. S. government mercury manometer of standard type. No two dials therefore are alike in the spacing of the divisions of the scale but every one is calibrated as an individual instrument. There is no doubt in the author's mind that for the general practitioner the instrument has some advantages over the mercury instruments. It reveals the slightest irregularity in force of the heart beat. The oscillation of the dial needle is more accurately followed by the eye than is that of the column of mercury. The needle passes directly over the divisions of the scale, while with usual mercury instruments the scale is an appreciable distance (sometimes .5 cm.) from the column of mercury at the side. (Fig. 19.) The diastolic pressure is more easily read on the "Tycos." It is where the maximum oscillation of the needle occurs as the pressure is slowly released from the cuff. Although it does not appear that this instrument, if properly made and standardized, could become inaccurate, nevertheless it is advisable to check it every few months against a known accurate mercury manometer instrument.

Another perfectly satisfactory dial instrument is the Faught (Figs. 20 and 21). The general plan of this differs in some minor points from the "Tycos." I have compared the two and have found no difference in the readings. Both can be recommended.

One or two other cheaper dial instruments are on the market. The Sanborn seems to be quite satisfactory. (Fig. 22.) It is cheaper than the other dial instruments. There is this much to be said, no instrument using a spring as resistance to measure pressure can be recommended.

=Technic=

The same technic applies to all the mercury instruments. The patient sits or lies down comfortably. The right or left arm is bared to the shoulder, the cuff is then slipped over the hand to the upper arm. (See Fig. 23.) At least an inch of bare arm should show between the lower end of the cuff and the bend of the elbow. The rubber is adjusted so that the actual pressure from the bag is against the inner side of the arm. The straps are tightened, care being taken not to compress the veins. The upper part of the cuff should fit more snugly than the lower part. The part of the instrument carrying the mercury column is now placed on a level surface; the two arms of the mercury in the tube must be even, and at _0_ on the scale. With the fingers of one hand on the radial pulse, the bag is compressed until the pulse is no longer felt. (See Fig. 24.) One should raise the pressure from 10-12 mm. above this, and close the stopcock between the bulb and the mercury tube. In a good instrument the column should not fall. If it does there is a leak of air in the system of tubing and arm bag. Now with the finger on the pulse, or where the pulse was last felt, gradually allow air to escape by turning the stopcock so that the column of mercury falls about 2 mm. (one division on the scale) for every heart beat or two. One must not allow the column of mercury to descend too slowly as it is uncomfortable for the patient and introduces a psychic element of annoyance which affects the blood pressure. On the other hand, the pressure must not be released too rapidly, else one runs over the points of systolic and diastolic pressure and the readings are grossly inaccurate. It is impossible to say how rapidly the mercury must fall. Every operator must find that out for himself by practice. The first perceptible pulse wave felt beneath the palpating finger at the wrist, represents on the scale the systolic pressure. This can be seen to correspond to a sudden increase in the magnitude of the oscillation of the mercury column. The systolic pressure, thus obtained, is from 5-10 mm. lower than the real systolic pressure. The more sensitive the palpating finger, the more nearly does the systolic pressure reading approach that found by using such an instrument as Erlanger's, where the first pulse wave is magnified by the lever of the tambour.

The pressure is now allowed to fall, until the palpating finger feels the largest possible pulse wave, which is coincident with the greatest oscillation of the mercury. This is the diastolic pressure. Beyond this point there is no oscillation of the mercury column. The difference between the two is the pulse pressure. Thus the pulse is felt after compression at 120 on the scale, and the maximum oscillation occurs at 80. The systolic pressure is 120 mm., the diastolic is 80 mm., and the pulse pressure is 40 mm.

With the "Tycos" or Faught the arm band is snugly wound around the arm, the bag next to the skin and the end tucked in, so that the whole band will not loosen when air is forced into the bag. The cuff is blown up until the pulse is no longer felt. One should raise the pressure not more than 10 mm. above the point of obliteration of the pulse. The valve is then carefully opened so that the needle gradually turns toward zero. At the first return of the pulse wave felt at the wrist, the needle is sure to give a sudden jump. This is the systolic pressure and is read off on the scale. The needle is now carefully watched until it shows the maximum oscillation. This is the diastolic pressure. The difference between the two is, as above, the pulse pressure.

In taking pressure one should take the average of several, three or four. Moreover, one must not take consecutive readings too quickly and one must be sure that between every two readings all the air is out of the cuff and that the mercury or dial is at zero. _It has been repeatedly shown that in a cyanosed arm the systolic pressure is raised so that even slight cyanosis between readings must be carefully avoided._

The only accurate method of determining both the systolic and diastolic pressure, but especially the diastolic, is by the so-called auscultatory method. (See Fig. 25.) The cuff is adjusted in the usual way and one places the bell of a binaural stethoscope over the brachial artery from one to two centimeters below the lower edge of the cuff.[3] Care must be taken that the bell is not pressed too firmly against the arm and that the edge of the bell nearest the cuff is not pressed more firmly than the opposite end. For this purpose, one can not use the ordinary Bowles stethoscope or any of the other much lauded stethoscopes, because the surface of the bell is too large. The diameter of the bell must not be more than twenty-five millimeters, twenty is still better. It is advisable before beginning the observation to locate with the finger the pulse in the brachial artery just above the elbow, so that the stethoscope may be placed over the course of the artery. (Fig. 26.) The first wave which comes through is heard as a click, and occurs at a point on the manometer or dial scale from 5-10 mm. higher than can usually be palpated at the radial artery. This is the true systolic pressure. By keeping the bell of the stethoscope over the brachial artery while the pressure is falling, one comes to a point when all sound suddenly ceases. This is said to be the diastolic pressure. This is incorrect as will be shown later.

[3] A firm makes a stethoscope so that the bell is clamped on the arm leaving both the operator's hands free.

=Arterial Pressure=

The arterial pressure in the large arteries undergoes extensive fluctuations with every heart beat. The maximum pressure produced by the systole of the left ventricle of the heart is known as the =maximum= or =systolic pressure=. It practically equals the intraventricular pressure. The minimum pressure in the artery, the pressure at the end of diastole, is called the =diastolic pressure=. The difference between the systolic and diastolic pressures is known as the =pulse pressure=. There is yet another term known as the =mean pressure=. For convenience, this may be said to be the arithmetical mean of the systolic and diastolic pressures. Actually, however, this can not be the case, owing to the form of the pulse wave, which is not a uniform rise and fall--the upstroke being a straight line, but the downstroke being broken usually by two notches. We do not make use of the mean pressure in recording results. It is of experimental interest and needs only to be mentioned here.

It has been shown that the mean pressure is quite constant throughout the whole arterial system. The maximum pressure necessarily falls as the periphery of the vascular system is approached. In general it may be said that the minimal pressure is quite constant. Too little attention is paid to minimal and pulse pressure. The minimal pressure is important, for it gives us valuable data as to the actual propulsive force driving the blood forward to the periphery at the end of diastole.

It is readily understood how the maximum pressure falls as the periphery is approached, until in the arterioles the maximum and minimum pressures are about equal. The pressure then in these arterioles is practically the same as the diastolic pressure. Actually it is a few millimeters less. The diastolic blood pressure would, therefore, measure the peripheral resistance and, as the maximum for systolic pressure represents approximately the intraventricular pressure, the difference between the two, the pulse pressure, actually represents the force which is driving the blood onward from the heart to the periphery. It is hence very evident that the mere estimation of the systolic pressure gives us but a portion of the information we are seeking.

The pulse pressure is subject to wide fluctuations but as a rule for any one normal heart it remains fairly constant as the rate varies. In a rapidly beating heart the diastole is short and the diastolic pressure rises. If the systolic pressure does not also rise, as in a normal heart following exercise, we will say, the pulse pressure falls. We know that when the pulse rate is constant, vasodilatation causes a fall in diastolic pressure and a rise in pulse pressure. On the contrary, vasoconstriction causes a rise in diastolic pressure and a fall in pulse pressure.

It is very probably the case that with two individuals of equal age and equal pulse rate, and equal systolic pressure of 160 mm., the one with a diastolic pressure of 110 mm. and, therefore, a pulse pressure of 50 mm. is much worse off than the other with a diastolic pressure of 90 mm. and a pulse pressure of 70 mm. The latter may be normal for the age of the person especially when certain forms of fibrous arteriosclerosis accompanied by enlarged heart are present.

The former is not normal for any age. Low pulse pressure usually means a weak vasomotor control and is only found in failing circulation or in markedly run down states, such as after serious illness or in tuberculosis. Therefore, it is most important to estimate accurately the diastolic pressure as well as the systolic pressure, for only in this way can we obtain any data of value regarding the driving power of the heart and the condition of the vasomotor system. A high systolic pressure does not necessarily mean that a great deal of blood is forced into the capillaries. Actually it may mean that very little blood enters the periphery. The heart wastes its strength in dilating constricted vessels without actually carrying on the circulation adequately.

=Normal Pressure Variations=

The systolic pressure varies considerably under conditions which are by no means abnormal. Thus, the average for men at all ages is about 127 mm. Hg. (All measurements are taken from the brachial artery, with the individuals in the sitting posture.) For women the average is somewhat lower, 120 mm. Hg. The pressure is lowest in children. In children from 6-12 years the average systolic pressure is 112 mm. Normally, there is a gradual increase as age comes on, due, as will be shown in the succeeding chapter, to physiologic changes which take place in the arteries from birth to old age. In the chart here appended is graphically shown the normal variations in the blood pressure at different ages compiled from observations made on one thousand presumably normal persons. (Fig. 28.)

The diastolic pressure has been estimated to be about 35 to 45 mm. Hg lower than the systolic pressure, and consequently these figures represent the pulse pressure in the brachial artery of man. This is equivalent to saying that every systole of the left ventricle distends this artery by a sudden increase in pressure equal to the weight of a column of mercury 2 mm. in diameter and 35 to 45 mm. high. Naturally, at the heart the pressure is highest. As the blood goes toward the capillary area the pressure gradually decreases until, at the openings of the great veins into the heart, the pressure is least. At the aorta (A) the pressure (systolic) is approximately 150 mm. Hg, at the brachial artery (B) it is 130 mm., in the capillary system (C) it is 30 mm., in the femoral vein (F) it is 20 mm., at the opening of the inferior vena cava (I) it is 3 mm.

Attention has been called to the normal systolic pressure at different ages. This is not the only cause for variations in the blood pressure. Normally, it is greater when in the erect position than when seated, and greater when seated than when lying down. During the day there are well-recognized changes. The pressure is lowest during the early morning hours, when the person is asleep. In women there are variations due to menstruation. Muscular exercise raises the blood pressure markedly. The effect of a full meal is to raise the blood pressure. The explanation is that during and following a meal there is dilatation of the abdominal vessels. This takes blood from other parts of the body, provided that the other factors in the circulation remain constant. A fall of pressure would necessarily occur in the aorta. To compensate for this, there is increased work on the part of the heart, which reveals itself as increased pressure and pulse pressure. It is well known that the interest in the process taken by an individual upon whom the blood pressure is estimated for the first time tends to increase the rate of the heart and to raise the blood pressure. For this reason the first few readings on the instrument must be discarded, and not until the patient looks upon the procedure calmly can the true blood pressure be obtained. As a corollary to this statement, mental excitement, of whatever kind, has a marked influence on the pressure. The patient must remain absolutely quiet. Raising the head or the free arm causes the pressure to rise. Another important physiologic variation is produced by concentrated mental activity. This tends to hurry the heart and increase the force of the beat. In short, it may be stated as a general rule that any active functioning of a part of the body which naturally requires a great excess of blood tends to elevate the blood pressure. At rest the pressure is constant. Variations caused by the factors mentioned act only transitorily, and the pressure shortly returns to normal.

=The Auscultatory Blood Pressure Phenomenon=

Since the first description of the auscultatory blood pressure sounds by Korotkov in 1905, this method has been more and more employed until today it is the standard, recognized method of determining the points in the blood pressure reading. When one applies the 12 cm. arm band over the brachial artery and listens with the bell of the stethoscope about one cm. below the cuff directly over the brachial artery near the bend of the elbow, one hears an interesting series of sounds when the air in the cuff is gradually reduced. The cuff is blown up above the maximum pressure. As the air pressure around the arm gradually is lowered, the series of sounds begins with a rather low-pitched, clear, clicking sound. This is the first phase. This only lasts through a few millimeters fall when a murmur is added and the tone becomes louder. This click and murmur phase is the second phase. A few millimeters more of drop in pressure and a clear, sharp, loud tone is audible. Usually this tone lasts through a greater drop than any of the other tones. This is the third phase. Rather suddenly the loud, clear tone gives place to a dull muffled tone. In general the transition is quite sharp and distinct. This is the fourth phase. The tone gradually or quickly ceases until no tone is heard. This is the fifth phase (Ettinger.)

The first phase is due to the sudden expansion of the collapsed portion of the artery below the cuff and to the rapidity of the blood flow. This causes the first sharp clicking sound which measures the systolic pressure.

The second, or murmur and sound phase, is due to the whorls in the blood stream as the pressure is further released and the part of the artery below the cuff begins to fill with blood.

The third tone phase is due to the greater expansion of the artery and to the lowered velocity in the artery. A loud tone may be produced by a stiff artery and a slow stream or by an elastic artery and a rapid stream. This tone is clear cut and in general is louder than the first phase.

The fourth phase is a transition from the third and becomes duller in sound as the artery approaches the normal size.

The fifth phase, no sound phase, occurs when the pressure in the cuff exerts no compression on the artery and the vessel is full throughout its length.

It is generally conceded that the sounds heard are produced in the artery itself and not at the heart.

The tones vary greatly in different hearts. A very strong third tone phase or prolongation of this phase usually means that the heart which produces the tone is a strongly acting one, although allowances must be made for a sclerosed artery in which there is a tendency to the production of a sharp third phase.

Weakness of the third phase, as a rule, indicates weakness of the heart and this dulling of the third phase may be so excessive that no sound is produced. Goodman and Howell have carried this method further by measuring the individual phases and calculating the percentage of each phase to the pulse pressure. Thus, if in a normal individual the systolic pressure is 130 mm., the diastolic 85 mm., and the pulse pressure 45 mm., the first phase lasts from 130 to 116 or 14 mm., the second from 116 to 96, or 20 mm., the third from 96 to 91 or 5 mm., the fourth from 91 to 85, or 6 mm. The first phase would then be 31.1 per cent of the total pulse pressure, the second phase 44.4 per cent, the third phase 11.1 per cent, and the fourth phase 13.3 per cent. They consider that the second and third phases represent cardiac strength (C. S.) and the first and fourth represent cardiac weakness (C. W.). They believe that C. S. should normally be greater than C. W. In the example above C. S.:C. W. = 55.5:44.4. In weak hearts, especially in uncompensated hearts, the conditions are reversed and C. W. > C. S. This is often the case. As a heart improves C. S. again tends to become greater than C. W. They think that the phases should be studied in respect to the sounds and also to the encroachment of one sound upon another.

These observations are interesting but we have not found the division into phases as helpful as it was thought to be. We spent a great deal of time on this question. All that can be said, in my opinion, is that a loud, long third phase is usually evidence of cardiac strength.

A further interesting feature which can be heard in all irregular hearts is a great difference in intensity of the individual sounds. Goodman and Howell call this phenomenon tonal arrhythmia. Irregularities can be made out by the auscultatory method which can not be heard at the heart.

In anemia the sounds are very loud and clear and do not seem to represent the actual strength of the heart.

The general lack of vasomotor tone in the blood vessels together with some atrophy and flabbiness of the coats probably explains the loud sounds.

In polycythemia the sounds have a curious, dull, sticky character and can not be differentiated accurately into phases, a condition which was predicted from the knowledge of the sharp sounds in anemia.

In not all cases can all phases be made out. It is usually the fourth phase which fails to be heard.

In such cases the loud third tone almost immediately passes to the fifth phase or no sound phase. The importance of this will later be taken up.

"In arteriosclerosis, with hardening and loss of elasticity of the vessel walls, the auscultatory phenomena, according to Krylow, are apt to be more pronounced, since the back pressure at the cuff probably causes some dilatation of the vessel above it, while the lumen of the vessel is smaller than normal. Both of these factors cause an increased rapidity in the transmission of the blood wave when pressure in the cuff is released, which in time favors the vibration of the vessel walls.

"In high grade thickening of the arterial walls, however, especially where calcification had occurred, Fischer found that the sounds were distinctly less loud than normal, the more so in the arm, which showed the greater degree of hardening. According to Ettinger's experience, the rapidity of the flow distinctly increases the auscultatory phenomenon." (Gittings.)

The sounds depend upon the resonating character of the cuff, upon the size and accessibility of the vessel, upon the force of the heart beat, and upon the velocity of the blood.

=The Maximum and Minimum Pressures=

The maximum (systolic) pressure is read at the point where the first audible click is heard after the cuff is blown up and the pressure gradually reduced by means of the needle valve in the hand bulb or on the upright of the glass containing the mercury. All are agreed upon this point. There has been some dispute as to the place where the diastolic pressure should be read. Korotkov considered that the diastolic pressure should be read at the fourth phase when the loud tone suddenly becomes dulled. Others held that the diastolic pressure should be read at the fifth phase, the absence of all sound. Experiments carried out to determine this point were made by me with the assistance of Prof. Eyster and Dr. Meek at the Physiological Laboratory of the University of Wisconsin. We arranged apparatus making it possible to hold the pressure in the carotid artery of dogs at maximum or minimum. A femoral artery was then dissected and an instrument devised to compress the artery with a water jacket. The whole was connected up with a kymograph. A time marker was put in so as to record the place where changes in sound were heard while listening below the cuff around the femoral artery. Two sets of records were taken. One with pressure greater than minimum pressure and a falling pressure over the femoral artery (Fig. 29), the other with pressure at zero and gradually raised to minimum pressure (Fig. 30). Both sets of records showed the same result; viz., that at a point corresponding to the sudden change of tone the pressure on the artery corresponded to the minimum pressure. It was therefore concluded that experimentally in dogs the point where diastolic pressure should be read is at the tone change from clear to dull, not at the point where all sound disappears.

Erlanger showed some years ago, that with his instrument, the point at which diastolic pressure should be read was at the instant when the maximum oscillation of the lever suddenly became smaller. While checking up the graphic with the auscultatory method using Erlanger's instrument, it was noticed that the disappearance of all sound did not correspond with the sudden diminution of the oscillation of the lever connected with the brachial artery. A series of records were carefully made on patients. It was seen that during the period of the third tone phase the oscillations of the lever on the drum reached a maximum (Fig. 31) and remained at approximately the same height for some millimeters while the pressure was gradually falling. At a point at which the third tone, clear and distinct, became dull, there was an appreciable decrease in the height of the pulse wave. From this point to the disappearance of all sound there was a gradual diminution of the size of the pulse waves.

For normal pressures the difference between the fourth (dull) tone and the fifth (disappearance of all tone) phase, amounted to 4 to 10 mm. Occasionally the difference was so little, the change from sharp third tone through fourth dull tone to disappearance of all sound was so abrupt, that one could take the disappearance of all sound as the diastolic pressure, with an error of not more than 2 to 4 mm. This is within the limits of normal error and practically may be used by those who have difficulty in noting the change from third to fourth phase. For high pressures, however, the difference between fourth and fifth phases was never less than 8 mm., and was found as much as 16 mm. The diastolic, therefore, should always be taken at the fourth phase if possible.

It was found that with the dial instrument the greatest fling of the lever corresponded to the third phase and the sudden lessened amplitude of the oscillation was at the fourth phase and was coincident with the change of tone from sharp to dull. Thus the diastolic pressure may be read off on the dial scale by watching the fling of the hand and with some practice one might acquire considerable accuracy. It is better, simpler, and, for most observers, more accurate to use the stethoscope and hear the change of sound.

=The Relative Importance of the Systolic and Diastolic Pressures=

The systolic pressure represents the maximum force of the heart. It is measured by noting the first sound audible over the brachial artery using the auscultatory method. It is the summation of two factors largely; the force expended in opening the aortic valves (potential) and the force expended from that point to the end of systole, the force which is actually driving the blood to the periphery (kinetic). To start the blood in motion, the heart must overcome a dead weight equal to the sum of all the forces holding the aortic valves closed. This sum of factors, called the peripheral resistance, must be reached and passed by the force of the ventricular beat before one drop of blood is set in motion along the aorta. This factor of resistance assumes a great importance.

The systolic pressure is always fluctuating as it depends upon so many conditions, and the calls of the body except during sleep are many and various. In a study of diurnal variations in arterial blood pressure it has been found that--(1) A rise of maximum pressure averaging 8 mm. of Hg. occurs immediately on the ingestion of food. A gradual fall then takes place until the beginning of the next meal. There is also a slight general rise of the maximum pressure during the day. (2) The range of maximum pressure varies considerably in different individuals, but the highest and lowest maximum pressures are practically equidistant from the average pressure of any one individual.[4]

[4] Weyse, A. W., and Lutz, B. R.: Diurnal Variations in Arterial Blood Pressure, Am. Jour. Physiol., 1915, xxxvii, 330.

The pressure is lowest during sleep and gradually rises near the end of sleep, so that on awakening the pressure was the same as before sleep.

Physiologically there are many conditions which modify the systolic pressure. Sleep, position, meals, exercise, emotional states cause often wide fluctuations which may be very sudden. It should be constantly borne in mind, that the systolic pressure reading which is made, is the maximum effort of the heart at that moment only.

The diastolic pressure measures the peripheral resistance. It measures the work of the heart, the potential energy, up to the moment of the opening of the aortic valves. It is the actual pressure in the aorta. The diastolic pressure is not very variable; it is not subject to the same influences which disturb the systolic pressure. It fluctuates as a rule, within a small range. It is not affected by diet, by mental excitement, by subconscious psychic influences, to anything like the extent to which the systolic pressure is affected by the action of these factors. The diastolic pressure is determined by the tone in the arterioles and is under the control of the vasomotor sympathetic system. Any agent which causes chronic irritation of the whole vasomotor system produces increase in the peripheral resistance with consequent rise in the diastolic pressure. Any agent which acts to produce thickening of the walls of the arterioles, narrowing their lumina, produces the same effect.

Such states naturally result in increased work on the part of the heart, which as a result, hypertrophies in the left ventricle. The increase in size and strength is a compensatory process in order to keep the tissues supplied with their requisite quota of blood. Conversely, paralysis of the vasomotor system produces fall of diastolic pressure which, if long continued, results in death.

The diastolic pressure then is of importance for the following reasons:

1. It measures peripheral resistance.

2. It is the measure of the tonus of the vasomotor system.

3. It is one of the points to determine pulse pressure.

4. Pulse pressure measures the actual driving force, the kinetic energy of the heart.

5. It enables us to judge of the volume output, for pulse pressure which is only determined by measuring both systolic and diastolic pressure, is such an index.

6. It is more stable than the systolic pressure, subject to fewer more or less unknown influences.

7. It is increased by exercise.

8. It is increased by conditions which increase peripheral resistance.

9. The gradual increase of diastolic pressure means harder work for the heart to supply the parts of the body with blood.

10. Increased diastolic pressure is always accompanied by increased pulse pressure, and increased size of the left ventricle, temporarily (exercise) or permanently.

11. Decreased diastolic pressure goes hand in hand with vasomotor relaxation, as in fevers, etc.

12. Low diastolic pressure is frequently pathognomonic of aortic insufficiency.

13. When the systolic and diastolic pressures approach, heart failure is imminent either when pressure picture is high or low.

When all these factors are taken into consideration, it becomes apparent that the diastolic pressure is most important, if not the most important part of the pressure picture.

Up to within a very brief time all the statistical evidence of blood pressure was based on systolic readings alone. This data is most valuable and much has been learned as to diagnosis and prognosis, but it is a mass of data based on a one-sided picture and can not be as valuable as the statistics which will undoubtedly be published later when all the pressure picture figures can be analyzed.

=Pulse Pressure=

The pulse pressure is the actual head of pressure which is forcing the blood to the periphery. At every systole a certain amount of blood 75-90 c.c. (Howell) is thrown violently into an already comfortably filled aorta. The sudden ejection of this blood instigates a wave which rapidly passes down the arteries as the pulse wave. The elastic recoil of the aorta and large arteries near the heart contract upon the blood and keep it moving during diastole. Normally the blood-vessels are highly elastic tubes with an almost perfect coefficient of elasticity. The pulse pressure varies under normal conditions from 30 to 50 mm. Hg. There is a very definite relationship between the velocity of blood and the pulse pressure which is expressed thus; velocity = pulse rate x pulse pressure.[5]

Further it has been demonstrated that under normal conditions and during various procedures--the pulse pressure is a reliable index of the systolic output.[6]

[5] Erlanger and Hooker: An Experimental Study of Blood Pressure and of Pulse Pressure in Man, Johns Hopkins Hosp. Rep., 1904, xii, 145.

[6] Dawson and Gorham: The Pulse Pressure as an Index of Systolic Output, Jour. Exper. Med., 1908, x, 484.

Increased pulse pressure therefore goes hand in hand with greater systolic output. Physiologically this is most ideally seen during exercise. Following exercise the pulse rate increases, the systolic pressure rises greatly, the diastolic slightly or not at all. The pulse pressure therefore is increased. The velocity also is much increased. The call comes for more blood and the heart responds. In the chronic high pulse pressures there are four correlated conditions which, so far as I have studied them, are always present. These are: (1) An increase in size of the cavity of the left ventricle. The ventricle actually by measurement contains more blood than normal, and therefore throws out more blood at every systole. The volume output is greater per unit of time. (2) There is actual permanent increase in diameter of the arch of the aorta. This is a compensating process to accommodate the increased charge from the left ventricle. (3) There are on careful auscultation over the manubrium, particularly the lower half, breath sounds which vary from bronchial to intensely tubular, depending upon the anatomic placing of the aorta, the shape of the chest, and the degree of dilatation. Often there is very slight impairment of the percussion note as well. (4) There is increase in size of all the large distributing arteries, carotids, brachials, femorals, renals, celiac axis, etc., with fibrous changes in the media, loss of some elasticity, and increase in size of the pulse wave. Increased pulse pressure means increased volume output, but does not always mean increased velocity. The proper distribution of blood to the various organs of the body is regulated by the vasomotor system acting upon the small arteries which contain considerable unstriated muscle. When fibrous arteriosclerosis is present there is loss of elasticity in the distributing arteries and a greater volume of blood must be thrown out by the ventricle at every systole in order that every organ shall have its full quota of blood. A force which is sufficient to send blood through elastic normal distributing tubes becomes totally insufficient to send the same amount of blood through tortuous and more or less inelastic tubes.

It is evident then that pulse pressure is exceedingly important. It can only be determined by measuring both the _systolic_ and _diastolic_ pressure. The pulse rate must also be known in order to compute the velocity. It is essential to have the whole pressure picture for all cases if correct conclusions are to be drawn.

In an irregular heart, especially in the cases due to myocardial disease, it is quite impossible to determine the true diastolic pressure. One can only approximate it and say that the pulse pressure is low or high. As a matter of fact the real systolic pressure can not be determined. For this figure the place on the scale where most of the beats are heard may be taken for the average systolic pressure. No one can seriously maintain that he can measure the diastolic pressure under all circumstances.

By means of the auscultatory method of measuring blood pressure we are able to determine irregularities of force in the heart beats more easily than by listening to the heart sounds. A pulsus alternans is readily made out. The irregular tones heard over the brachial artery in cases of irregular heart action have been called "tonal arrhythmias."

=Blood Pressure Variations=

A recent study of diurnal variations in blood pressure has shown that while the maximum pressure rises after the ingestion of food and steadily rises slightly throughout the day, the minimum blood pressure is very uniform throughout the day, and is little affected by the ingestion and digestion of meals. When it is affected, a rise or a fall may take place. Throughout the day, it tends to become slightly lower. The pulse pressure then is greater towards evening.

Weysse and Lutz in a study of this question draw the following conclusions:

1. A rise of maximum pressure averaging 8 mm. of Hg occurs immediately on the ingestion of food. A gradual fall then takes place until the beginning of the next meal. There is also a slight general rise of the maximum pressure during the day.

2. The average maximum blood pressure for healthy young men in the neighborhood of 20 years of age is 120 mm. of Hg. This pressure obtains commonly one hour after meals. The higher maximum pressures occur immediately after meals, and the lower, as a rule, immediately before meals.

3. The range of maximum pressure varies considerably in different individuals, but the highest and lowest maximum pressures are practically equidistant from the average pressure of any one individual.

4. The minimum blood pressure is very uniform throughout the day, and is little affected by the ingestion and digestion of meals. When it is affected a rise or fall may take place. There is a tendency for a slight general lowering of the minimum pressure throughout the day.

5. The average minimum blood pressure for healthy young men in the neighborhood of 20 years of age is 85 mm. of Hg. Thus we get an average pulse pressure of 35 mm. of Hg.

6. Pulse pressure, pulse rate, and the relative velocity of the blood flow are increased immediately upon the ingestion of meals. They attain the maximum, as a rule, in half an hour, and then decline slowly until the next meal. There is a general increase in each throughout the day.

These measurements were made upon persons at rest. Almost any form of exercise would have made the variations much greater. No account is taken of the psychic variations which for the physician are the most important to bear in mind. Neglect to take this variation into account will inevitably lead to false conclusions.

THE AVERAGE DIURNAL BLOOD PRESSURE RECORD OF THE TEN SUBJECTS

==========+=======+=======+=======+=======+========+=======+=============== TIME |MAXIMUM|MINIMUM| MEAN | PULSE | PULSE |PP x PR| NOTES | | | | |PRESSURE| RATE | ----------+-------+-------+-------+-------+--------+-------+--------------- |_mm._Hg|_mm._Hg|_mm._Hg|_mm._Hg| | | 4:30 p.m. | 119.5 | 84.1 | 101.8 | 35.4 | 72.0 | 2549 | 5:00 p.m. | 117.7 | 83.5 | 100.6 | 34.2 | 71.1 | 2432 | 6:00 p.m. | 118.0 | 84.0 | 101.0 | 34.0 | 74.9 | 2547 |Before dinner 6:45 p.m. | 127.2 | 88.2 | 107.7 | 39.0 | 78.1 | 3046 |After dinner 7:00 p.m. | 124.7 | 87.7 | 106.2 | 37.0 | 76.0 | 2812 | 7:30 p.m. | 122.0 | 83.4 | 102.7 | 38.6 | 76.0 | 2934 | 8:00 p.m. | 122.4 | 85.5 | 103.4 | 36.9 | 71.2 | 2527 | 8:30 p.m. | 120.0 | 85.0 | 102.5 | 35.0 | 69.7 | 2439 | 9:00 p.m. | 120.5 | 84.7 | 102.5 | 35.8 | 65.2 | 2334 | 9:30 p.m. | 118.2 | 84.4 | 101.6 | 33.8 | 64.4 | 2177 | 7:30 a.m. | 118.4 | 87.6 | 103.0 | 30.8 | 70.3 | 2165 | 8:00 a.m. | 116.4 | 86.4 | 101.4 | 30.0 | 69.8 | 2094 Before breakfast 8:30 a.m. | 124.2 | 85.4 | 104.8 | 38.8 | 79.4 | 3081 |After breakfast 9:00 a.m. | 123.8 | 84.4 | 104.1 | 39.4 | 84.1 | 3313 | 10:00 a.m.| 118.2 | 83.6 | 100.9 | 34.6 | 70.7 | 2446 | 11:00 a.m.| 116.2 | 84.8 | 100.5 | 31.4 | 67.7 | 2126 | 12:00 m | 114.4 | 83.2 | 98.8 | 31.2 | 66.2 | 2065 |Before luncheon 12:30 p.m.| 122.8 | 83.2 | 103.0 | 39.6 | 70.9 | 2808 |After luncheon 1:00 p.m. | 122.3 | 82.0 | 102.1 | 40.3 | 79.7 | 3212 | 2:00 p.m. | 118.4 | 81.4 | 99.9 | 37.0 | 77.6 | 2871 | 3:00 p.m. | 118.8 | 82.6 | 100.7 | 36.2 | 75.1 | 2719 | 4:00 p.m. | 115.8 | 82.0 | 98.9 | 33.8 | 71.9 | 2420 | 5:00 p.m. | 117.2 | 83.4 | 100.3 | 33.8 | 69.6 | 2352 | 6:00 p.m. | 117.4 | 84.4 | 100.9 | 33.0 | 72.8 | 2402 |Before dinner 6:45 p.m. | 124.6 | 83.1 | 103.8 | 41.5 | 80.4 | 3337 |After dinner 7:00 p.m. | 125.2 | 84.2 | 104.7 | 41.0 | 76.1 | 3120 | 7:30 p.m. | 122.0 | 84.0 | 103.0 | 38.0 | 73.7 | 2801 | 8:00 p.m. | 119.6 | 85.0 | 102.3 | 34.6 | 72.3 | 2502 | 8:30 p.m. | 119.7 | 84.0 | 101.3 | 34.7 | 69.0 | 2394 | 9:00 p.m. | 120.0 | 86.2 | 103.1 | 33.8 | 68.0 | 2298 | +-------+-------+-------+-------+--------+-------+ Average | 120.0 | 85.0 | 102.5 | 35.0 | 72.0 | 2550 | ----------+-------+-------+-------+-------+--------+-------+--------------- (Taken from Weysse and Lutz.)

In some experiments to determine the changes upon the blood pressure induced by hot and cold applications on and within the abdomen, Hammett, Tice and Larson found that heat applied to the outside of the abdomen raises the blood pressure. The application of cold produces no change. Either hot or cold saline introduced within the abdomen causes a fall in blood pressure.

Experimentally, certain drugs such as adrenalin, barium chloride, nicotine, digitalis, strophanthus and the infundibular portion of the pituitary body known as pituitrin raise the maximum pressure. In the clinic it is difficult to conclude always whether the drug alone is responsible for rise in maximum pressure. Adrenalin given intravenously will raise the pressure. So will digitalis and strophanthus. I have watched the maximum pressure rise within three minutes following an intravenous injection of gr. 1/100 (0.0006 gm.) strophanthin 20 mm. of Hg: I have seen the subcutaneous injection of 10 minims of adrenalin repeated several times daily for six months fail to have the least effect on the blood pressure picture.

Elevation of the foot of the bed about nine inches proved so efficacious in steadying failing hearts in acute infectious diseases, particularly typhoid, that a study was made of the effect upon blood pressure. Many observations were made, but no instrumental proof of rise in blood pressure could be adduced.

Exercise always raises blood pressure, the maximum much more than the minimum. In athletes the minimum pressure may actually fall, the maximum rise so that a greater volume output results from the greater pulse pressure.

Shock and hemorrhage lower it. Hemorrhage lowers also the pulse pressure, and it may be possible to prognosticate internal hemorrhage by frequent estimations of the systolic and diastolic pressures (Wiggers). Compression of the superior mesenteric artery or the celiac axis in dogs raises the blood pressure measured in the carotid artery for a period of at least an hour. This seems to be dependent on purely mechanical causes, and is not a reflex vasomotor phenomenon. (Longcope and McClintock.)

Experimentally blood pressure can be increased by direct compression of the brain as Cushing has shown. It was thought at one time that in man the same effect would result from tumor of the brain or especially from subdural or extradural hemorrhage following head injuries. This, however, is not the case. No information of great value can be obtained by the measurement of blood pressure in these states. We do know that too high and too prolonged compression of the medulla brings about exhaustion of the cardiac center accompanied with rapid pulse, low pressure and eventual death.

=Hypertension=

All the conflict during the past few years over the subject of blood pressure has revolved around this much overworked word. Hypertension means high pressure, and yet it carries with it a suggestion of high pressure which is harmful to the individual. As a matter of fact hypertension is a compensatory process, it is often a saving process in spite of the fact that it carries possibilities of harm in its possessor. It has been made a fetish, a god to fall down before and worship and it has been the means of holding a torch of fear over a patient which has not been lost on the charlatans. Popularization of blood pressure has brought its crop of evils, no one of which has been as fruitful in dollars to unprincipled quacks as hypertension.

Hypertension is the expression on the part of the circulation to meet new conditions in the tissues so that all tissues will be nourished and all will be enabled to function. Looked at from that point of view it is a conservative process and in many cases it is. It is not an average normal state, but it is normal state for the man who has it in chronic form. Hypertension should be viewed rationally and its proper place in the whole make-up of the patient determined. Hypertension is a relative term. What might be high pressure in a man of sedentary habits who reaches the age of fifty, might not be high pressure in a full blooded formerly athletic man of the same age. Temporary hypertension due to excitement, exercise, etc., must be kept in mind. It is not intended to convey the impression that hypertension is of no moment. It is a matter for investigation, but not a matter to worship as the all-in-all.

Hypertension is, after all, a physiologic response on the part of the organism in order to maintain the circulation in equilibrium in the face of conditions which tend to produce vasoconstriction in large areas and, therefore tend to deprive these areas of blood. That there must be some substance in the blood stream which causes this constriction seems certain. What it is, is not at present known. Recently, Voegtlin and Macht[7] have isolated a crystalline substance from the blood of man and other mammals which they regard as a lipoid and closely related to cholesterin. This substance was recovered by them from the cortex of the adrenal gland. This becomes of added interest in the light of observations made by Gubar (quoted by Voegtlin and Macht). He noted "that the vasoconstricting properties of blood serum vary in different pathologic conditions, being increased in nephritis, for instance, and diminished in others." In some experiments made in the summer of 1913, we found there was no marked difference in the anaphylactic shock produced in half-grown rabbits by the injection of normal and uremic blood serum. As lipoids do not cause anaphylaxis, there should be no difference in the reaction of normal and uremic sera unless in one there was some form of protein not in the other. This does not seem to be the case. The presence of something in the circulation, therefore, produces constriction of vessels. This calls for more force in contraction on the part of the heart. This substance may be of lipoid nature. The continued presence of this hypothetical substance naturally would lead to hypertrophy of the heart.

[7] Isolation of a New Vasoconstrictor Substance from the Blood and the Adrenal Cortex, Jour. Am. Med. Assn., 1913, lxi, 2136.

What makes hypertension of significance is not the hypertension itself, but the fact that it is the expression of processes going on in the body which demand exhaustive investigation. To attach a blood pressure cuff to the arm, find the pressure, and diagnose hypertension is like putting a thermometer under the tongue, noting a rise in the mercury, and diagnosing fever. What causes the hypertension? Can the causes be removed? Those are the really vital questions after the symptom hypertension has been discovered.

All states of hypertension are accompanied by more or less increase of pulse pressure. In other words the systolic pressure is always increased to greater degree than the diastolic pressure. In studies carried out in the wards and Pathological Laboratory of the Milwaukee County Hospital, Milwaukee, we found that in all of the cases of chronic high blood pressure with resulting high pulse pressure four correlated factors were found. If any one of these factors is present, the other three are found.

1. In all high pulse pressure cases there is increase in the size of the cavity of the left ventricle. The ventricle actually contains more blood when it is full, and throws out, therefore, more blood at each systole. The actual volume output is greater per unit of time. Such hearts always show increase in thickness of the ventricular wall. I quite agree with Stone,[8] who says, "It is merely to be emphasized that when the pulse pressure persistently equals the diastolic pressure (high pressure pulse, in other words) with a resulting 50 per cent, _overload_, which means the expenditure of double the normal amount of kinetic energy on the part of the heart muscle, cardiac hypertrophy has occurred." They are found in aortic insufficiency, in chronic nephritis, in the diffuse fibrous type of arteriosclerosis, and in some cases of exophthalmic goiter. Such a condition occurs temporarily after exercise.

[8] Stone, W. J.: The Differentiation of Cerebral and Cardiac Types of Hyperarterial Tension in Vascular Diseases, Arch. Int. Med., November, 1915, p. 775.

2. In all high pulse pressure cases there is actual permanent increase in diameter of the arch of the aorta. This is a compensating process to accommodate the increased charge from the left ventricle. Smith and Kilgore[9] have shown this to be true in cases of chronic nephritis with hypertension. Their research confirms my own observations. They found dilatation of the arch in (1) syphilis (that is, aortitis); (2) age over 50 (that is, probable factor of arteriosclerosis); (3) other serious cardiac enlargement, and (4) hypertension (with more or less hypertrophy, as in chronic nephritis).

[9] Smith, W. H., and Kilgore, A. R.: Dilatation of the Arch of the Aorta in Chronic Nephritis with Hypertension, Am. Jour. Med. Sc., 1915, cxlix, 503.

In ten cases showing arches at the upper limit of normal (that is, 6 cm. in diameter) and hypertrophy of the heart, three were chronic mitral endocarditis; one was chronic aortic endocarditis; three were chronic mitral and aortic endocarditis, and there was one each of hyperthyroidism, pericarditis and adherent pericardium.

In fourteen cases of hypertension (highest systolic 270 mm., average systolic, 215 mm.), all showed cardiac hypertrophy. "All but three of these cases had great vessels whose transverse diameters measured over the normal limit of 6 cm., and in one of those measuring 6 cm. the Roentgen-ray diagnosis was 'slight dilatation' of the arch." Smith and Kilgore are at a loss to explain the three exceptions. They did not give diastolic pressures, so pulse pressures are not known. Possibly the three exceptions were cases of high diastolic pressure in which the pulse pressure possible was not over 60 mm. Such cases might show "slight dilatation of the arch," but not marked dilatation, such as was found in the other, evidently high pulse pressure cases.

We have found that only the high pulse pressure cases show dilatation of the arch. Certain high tension cases which have had a very high diastolic pressure do not reveal any accurately measurable dilatation of the aortic arch. An empty aorta after death is quite different from a functionating aorta during life. Hence the dilatation which is found postmortem must have been considerable during life. And conversely, a dilatation which was present during life might not be looked on as such after death.

3. In all high pulse pressure cases one will find on careful auscultation over the manubrium, particularly its lower half, breath sounds which vary from bronchial to intensely tubular. At times the percussion note will be slightly impaired, as McCrae[10] has shown in dilatation of the arch of the aorta. This auscultatory sign is evidence of some more or less solid body in the anterior mediastinum which is lying on the trachea and permits the normal tubular breathing in the trachea to be audible over the upper part of the sternum. It is found in cases of dilated aortic arch. Fluoroscopic examination has confirmed the findings on auscultation.

[10] McCrae, Thomas: Dilatation of the Arch of the Aorta, Am. Jour. Med. Sc., 1910, cxl, 469.

4. In all high pulse pressure cases, in which the pulse pressure is over 70 mm. of mercury, there is increase in the size of all large distributing arteries, carotids, brachials, femorals, renals, celiac axis, etc., with fibrous changes in the media, loss of some of the elasticity, and in the palpable superficial arteries, increase in size of the pulse wave.

Increased pulse pressure means increased volume output, but does not always mean increased velocity. The proper distribution of blood to the various organs of the body is regulated by the vasomotor system acting on the small arteries which contain considerable unstriated muscle. In order that there may be enough blood at all times and under varying conditions of rest and function, there must be a proper supply coming through the distributing vessels, the large arteries, those containing much elastic tissue, and only a very small amount of unstriated muscle tissue or none whatever. Fibrous sclerosis of these vessels causes them to become enlarged and tortuous and to lose much of their elasticity, which is essential for the even distribution of blood. A greater blood volume is therefore necessary in order that the organs may receive their quota of blood. A force which is sufficient to send blood through elastic normal distributing tubes becomes totally insufficient to send the same amount of blood through tortuous and more or less inelastic tubes. As a compensatory process the pulse pressure increases. For this to increase, the left ventricular cavity dilates, the arch dilates, and as a greater force must be exerted to keep the increased mass in motion, the heart responds by hypertrophy of its left ventricle and becomes itself the subject of fibrous changes in the myocardium. The mass movement of blood is therefore greater in high pulse pressure cases than in cases of normal pulse pressure.

In cases of chronic interstitial nephritis--contracted granular kidney--it may well be that the sclerosis of the arteries is a secondary process caused, as Adami thinks, by the hypertension itself. In aortic insufficiency the situation is somewhat different. The high pulse pressure is due to a very low diastolic pressure, for in my experience with uncomplicated aortic insufficiency the systolic pressure is, as a rule, not much increased above the normal for the individual's age. Here peripheral resistance is so low that a capillary pulse is common. The volume output per unit of time is greatly increased, the arch of the aorta is dilated, and the pulse is large. The fact that a large part of the blood regurgitates during diastole back into the ventricle, and the fact that the diastolic pressure is low means that there is no increased resistance to overcome, and the systolic pressure is not raised.

Stone[11] has divided the cases of hypertension into the cerebral and cardiac types. He finds that there is a difference in prognosis and in the mode of death in the two groups. He has further attempted to judge of the work placed upon the heart by calculating what he calls the heart load or pressure-ratio. For example, he takes a normal pressure at 120-80-40. The relation between 80 and 40 is 1/2 or 50 per cent. That he considers normal. When the heart load increases so that the pulse pressure equals or exceeds the diastolic pressure, the heart load is 100 per cent or more, he considers the danger of myocardial exhaustion graver than when the heart load is normal or less than 50 per cent.

[11] Stone, W. J.: Arch. Int. Med., 1915, xvl, 775.

It is his opinion, in which I heartily concur, "that an individual with a systolic pressure of 200 and a diastolic pressure of 140, is in greater danger of cerebral death than an individual with a systolic pressure of 200 and a diastolic pressure of 100." He is "likewise certain that the individual with a systolic pressure of 200 and a diastolic of 90 to 100 is in greater danger of a cardiac death. It is apparently the constant high diastolic pressure rather than the intermittently high systolic pressure which predisposes to cerebral accident."

I have not been able to confirm all of Stone's conclusions. His contention holds good for some cases, but not, in my experience, for the great majority of the hypertension cases. I feel that in the classification of the chronic high pressure case we can go one step farther and split his first group into two usually differentiable groups. Syphilis is not an etiological factor in any of these groups. It is not considered that these groups are absolutely distinct and can always be rigidly separated. There are variations and combinations which render an exact separation impossible. But bearing this in mind the following classification is proposed as a working classification.

Group A. Chronic nephritis.

Group B. Essential hypertension.

Group C. Arteriosclerotic hypertension.

Group A. _Chronic Nephritis._ These are the cases with a high-pressure picture, that is to say, high systolic (200+) and high diastolic (120-140+). The pulse pressure is much increased. The palpable arteries are hard and fibrous. There is puffiness of the under eyelids, which is more pronounced in the morning on arising. Polyuria with low specific gravity and nycturia are present. There are almost constant traces of albumin in the urine, with hyaline and finely granular casts.

Functionally these kidneys are much under normal. The functional capacity determined by Mosenthal's modification of the Schlayer-Hedinger method shows a marked inability to concentrate salts and nitrogen. The phthalein output is below normal. As the case advances the phthalein output becomes less and less, until a period is reached when there are only traces or complete suppression at the end of a two-hour period. Such patients may live for ten weeks (one of our cases) or longer, all the time showing mild uremic symptoms, and suddenly pass into coma and die.

The natural end of patients in this group is either uremia or cardiac decompensation (so-called cardiorenal disease). Cerebral accidents may happen to a small number. It is only to this group, in my opinion, that the term cardiorenal disease should be applied. Formerly I believed that all high systolic pressure cases were cases of chronic nephritis of some definite degree. From the purely pathologic standpoint that is true, but from the important, functional standpoint it is far from being the true state of the cases.

In this group there is marked hypertrophy and moderate dilatation of the left ventricle with dilatation and nodular sclerosis of the aorta. The kidneys are firm, red, small, coarsely granular, the cortex much reduced, the capsule adherent. Cysts are common. It is the familiar primary contracted kidney. Mallory calls this capsular-glomerulonephritis. The etiology is obscure. Often no cause can be found. Again, there is a history of some kidney involvement following one of the acute infectious diseases, or it may follow the nephritis of pregnancy. Usually, however, these cases fall into the group of secondary contracted kidneys, chronic parenchymatous nephritis.

Illustrative Case.--R. Z., a woman, aged thirty-six years, was seen July 26, 1916, in coma. There was a history of typhoid fever at nineteen years, but no other disease. She had had nine full-term pregnancies, the last one thirteen months previously. For a week before the onset of the present illness she had complained of severe headaches and dizziness. There were no heart symptoms. For the past year she has had nycturia. Physical examination revealed tubular breathing beneath the manubrium, a few rales in the chest, an enlarged heart (left side), with a systolic murmur over the aortic area. Blood pressure was 178-125-53, the pulse rate 96, leucocytes 27,250. Venesection of 500 c.c. of blood and intravenous injections of 500 c.c. of 5 per cent NaHCO_3 in normal saline were employed. Lumbar puncture withdrew 60 c.c. of clear fluid under pressure with 6 cells per cubic millimeter. The eye grounds showed distinct haziness of the disks and dilatation of the veins. Blood pressure after venesection was 164-122-42, pulse 76, but in a few days rose to 222-142-80, pulse 70. A second venesection of 400 c.c. and proctoclysis of 1000 c.c. saline solution was tried. The blood-pressure now was 198-140-58. The pH of the blood was 7.6, the alkaline reserve was 35 volume per cent (van Slyke), and the CO_2 tension of the alveolar air (Marriott) was 25 mm. The phthalein on the day following the second venesection was 45 per cent in two hours. The urine at first showed 500 c.c. in twenty-four hours, specific gravity 1016, albumin and casts. Later she passed 1300 to 1600 c.c. with specific gravity around 1010. The blood-pressure fluctuated considerably, reaching as low as 138-98-40, pulse 88. She was discharged improved September 10, 1916. She had constant headache but managed to keep up. In June, 1917, she suddenly died in an uremic coma.

Group B. This one might designate as the hereditary type, although there is not always a history in the antecedent. This group includes the robust, florid, exuberantly healthy people. They often are heard to boast that they have never had a doctor in their lives. They are usually thick-set or very large, fleshy people. The pressure picture is exceedingly high. The pulse pressure is moderately increased. The arteries are rather large, fibrous, and often quite tortuous, although this is not always the case. Some persons have hard, small, fibrous arteries. There is no puffiness beneath the eyes, no polyuria, and no nycturia as a rule. The urine is of normal amount, color, and specific gravity. Albumin is only rarely found and then in traces, but careful search of a centrifuged specimen invariably reveals a few hyaline casts. The phthalein excretion is normal or only slightly reduced. The kidneys excrete salt and nitrogen normally. It is in this group that apoplexy is found most frequently. The rupture of the vessel occurs when the victim is in perfect health, often without any warning. Occasionally when such a case recovers sufficiently to be around, cardiac decompensation sets in later and he dies then of the cardiac complications.

Pathologically the hearts of such persons are found to have the most enormous hypertrophy of the wall of the left ventricle. The cavity is somewhat enlarged, as is always the case when the pulse-pressure is increased, but the size of the cavity is not the striking feature. The aorta is fibrous, thick walled, and the arch is slightly dilated. There are patches of arteriosclerosis. One such case seen only at autopsy had a rupture of the aorta just above the sinus of Valsalva and died of hemopericardium. The kidneys are of normal size, dark red, firm, the capsule strips readily, the surface is smooth or finely granular, the cortex is not decreased. The pyramids are congested and red streaks extend into the cortex. Microscopically the capsules of the glomeruli are a trifle thickened; a few show hyaline changes. There is rather diffuse, mild, round-cell infiltration between the tubules. The tubular epithelium shows little or no demonstrable changes. The arterioles are generally the seat of a moderate thickening of the intima and media, but it is not usual to find obliterating endarteritis. There is evidently a diffuse fibrous change which has not affected either the tubules or glomeruli to any great extent.

Illustrative Case.--L. C., a man, aged fifty-six years, stonemason by trade, is a stocky, thick-necked individual. He had never been ill in his life until a year ago, when he fell from his chair unconscious. He had a right-sided hemiplegia which has cleared up so completely that except for a very slight drag to his foot he walks perfectly well. He came in complaining of shortness of breath and cough. There was no swelling of the feet. Here evidently was left-heart decompensation. Examination showed the blood pressure to be 240-130-110, pulse irregular, 104 to the minute. There were cyanosis and rales throughout both chests. The urine was normal in color, specific gravity 1025, small amount of albumin, few casts, hyaline and granular. The phthalein elimination was 65 per cent in two hours. Under rest, purgatives, and digitalis he was much improved. He has since had two other apoplectic strokes, the last of which was fatal.

When these patients are seen with acute cardiac decompensation, there are, of course, much albumin and many casts in the urine, and the phthalein output is, for the time being, decreased.

Group C. This might be called the arteriosclerotic high-tension group (Stone's cardiac group). The cases are usually over fifty years old. They are men and women who have lived high and thought hard. Often they have had periods of great mental strain. Many men in this group were athletes in their young manhood. Many have been fairly heavy drinkers, although never drinking to excess. They are usually well nourished and inclined to stoutness. The pressure picture is high systolic with normal or only slightly increased diastolic and large pulse pressure. The arteries are large, full, fibrous, usually tortuous. The heart is very large, the apex far down and out. There is no polyuria; nycturia is uncommon, quite the exception. The urine is normal in color, amount, and specific gravity. Albumin is only rarely found and hyaline casts are not invariably present. The phthalein excretion is quite normal and the excretions of salt and nitrogen are also normal. The terminal condition in most of the patients in this group is cardiac decompensation. They may have several attacks from which they recover, but after every attack the succeeding one is produced by less exertion than the preceding one, and it becomes more and more difficult to control attacks. Eventually the patients become bed- or chair-ridden, and finally die of acute dilatation of the heart.

Occasionally patients in this group may have a cerebral attack, but in my experience this is uncommon. Pathologically the heart is large, at times true _cor bovinum_, dilated and hypertrophied. The cavity of the left ventricle is much dilated. The aorta is dilated and sclerosed.

The kidneys are increased in size, are firm, dark red in color, with fatty streaks in the cortex. The capsule strips readily and the cortex is normal in thickness or only slightly increased. The organ offers some resistance to the knife. The microscope shows small areas scattered throughout where the glomeruli are hyalinized, the stroma full of small round cells, the tubules dilated, and the cells are almost bare of protoplasm. Naturally the tubules are full of granular cast material. Also the arterioles show extensive intimal thickening, fibrous in character, with occasional obliterating endarteritis. One gets the impression that the small sclerotic lesions are the result of anemia and gradual replacement of scattered glomeruli by fibrous tissue. For the most part the kidney, except for the chronic passive congestion, appears quite normal. One can readily understand that in such a kidney function could not have been much interfered with.

Illustrative Case.--C. K., an active, stout, business man, aged fifty-six years, consulted me on account of shortness of breath and swelling of the feet in May, 1915. He had just returned from a hospital in another city, where he had gone with what was apparently cardiac decompensation. In his early manhood he had been a gymnast and a prize winner. He has worked hard, often given way to violent paroxysms of temper, has eaten heavily but drunk very moderately. The heart was greatly enlarged, the arch of the aorta dilated, a mitral murmur was audible at the apex. The radials and temporals were large, tortuous, and fibrous. The blood pressure picture ranged around 180-90-90. He was easily made dyspneic and had a tendency to swelling of the lower legs. The urine was acid, of normal specific gravity, normal in amount, normal phthalein, normal concentration of salt and nitrogen, contained albumin only when he was suffering from decompensation of the heart. Casts were always found. He finally died, after sixteen months, with all the symptoms of chronic myocardial insufficiency. The heart was enormous, a true _cor bovinum_. The kidneys were typical of this condition, possibly somewhat larger than usual.

=Hypotension=

When the pressure is constantly below the normal, it is called hypotension. This may be transient--as in fainting--it may be a normal state of the individual, it occurs in most fevers and in a great variety of diseases, including anemias.

In arteriosclerosis, especially the diffuse (senile) type, the blood pressure is invariably low, and may be spoken of as hypotension. The heart in such a case is small, the muscle is flabby, there is brown atrophy of the fibers, and some replacement of the muscle cells by connective tissue. The same causes which have produced general arteriosclerosis have also produced sclerosis of the coronary arteries, and probably the lessened blood supply accounts for much of the atrophy of the heart muscle.

In typhoid fever the maximum blood pressure during beginning convalescence may be as low as 65 mm. Hg. I have frequently seen hypotension of 80 mm. This is common.

Meningitis is the only acute infectious disease in which the blood pressure is more often high than low. This is accounted for by the increased intracranial tension.

Following large hemorrhages the blood pressure is reduced. In venesection the withdrawal of blood may not affect the blood pressure. The procedure is done to relieve overdistension of the heart.

In pleurisy with effusion and in pericarditis with effusion there is hypotension.

Collapse, whether from poisoning by drugs or as the result of dysentery, cholera, or profuse vomiting from whatever cause, reduces the blood pressure.

In cachectic states, such as cancer, the blood pressure is low. General wasting of the whole musculature includes that of the heart and the heart muscle shows the condition known as "brown atrophy."

A most interesting and important condition in which hypotension occurs is pulmonary tuberculosis. Haven Emerson has recently gone over the whole subject in a careful piece of work and his summary is as follows:

"Hypotension or subnormal blood pressure is universally found in advanced pulmonary tuberculosis, in which condition emaciation may play a part in its causation. Hypotension is found in almost all cases of moderately advanced tuberculosis, or in early cases in which the toxemia is marked except when arteriosclerosis, the so-called arthritic or gouty diathesis, chronic nephritis, or diabetes complicate the tuberculosis and bring about a normal pressure or a hypertension. Occasionally the period just preceding a hemoptysis or during a hemoptysis may show hypertension in a patient whose usual condition is that of hypotension.

"Hypotension has been found by so many observers in early, doubtful or suspected cases with or before physical signs of the disease in the lungs, and is considered by competent clinicians so useful a differential sign between various conditions and tuberculosis, that it should be sought for as carefully as it is the custom at present to search for pulmonary signs.

"Hypotension when found persistently in individuals or families or classes living under certain unhygienic conditions should put us on our guard against at least a predisposition to tuberculosis. Most unhygienic conditions, overwork, undernourishment and insufficient air, are of themselves causes of a diminished resistance, and it seems likely that a failure of normal cardiovascular response to exercise or change of position may be found to indicate this stage of susceptibility, especially to tuberculous infection.

"... Hypotension, when it is present in tuberculosis, increases with an extension of the process. Recovery from hypotension accompanies arrest or improvement. Return to normal pressure is commonly found in those who are cured. Continuation of hypotension seems never to accompany improvement. Prognosis can as safely be based on the alteration in the blood pressure as on changes in the pulse or temperature...."

There are a few drugs which lower the blood pressure, but, as a rule, their effects are more or less transitory. We know of no drug, unless it be iodide of potassium, which has the property of causing changes in the blood (decrease in viscosity?), which tends to reduce the blood pressure when it is excessive. This drug fails us many times.

SOME DRUGS WHICH INFLUENCE THE BLOOD PRESSURE

=Pressure Raisers=

Adrenalin, when injected directly into a vein or deep into the muscles. The action is transitory.

Caffeine, preferably in the form of caffeine-sodium-benzoate. A good drug.

Strychnine, which does not act directly but seemingly through the higher centers.

Ergot, somewhat uncertain.

Nicotine, not used therapeutically.

Camphor, used in sterile olive oil and injected deeply into the muscles.

Digitalis, when the cardiac tone is low and decompensation is present. Its action is prolonged but slow. Injections of the infundibular portion of the pituitary body. Not in use clinically.

=Pressure Depressors=

Nitroglycerine and amyl nitrite, action transitory but rapid.

Sodium nitrite and erythrol tetranitrate. Action somewhat more prolonged.

Aconite, veratrum viride, chloral, etc. These depress the heart.

Purgatives, drastic and hydragogue.

Potassium and sodium iodide may lower blood pressure. When they do, the action is prolonged.

Diuretin and theocin-sodium-acetate.

=Venous Pressure=

Comparatively little work has been done upon the determination of the pressure in the veins in man. It is conceivable that this procedure may, at times, be of great value. A number of attempts have been made to measure the venous pressure by compressing the arm veins and noting on a manometer the force necessary to obliterate the vein. As the pressure is so slight, water is used instead of mercury, and readings have been given in centimeters of water.

In the apparatus shown in the figure (Fig. 33), Drs. Hooker and Eyster succeeded in making estimations of the venous pressure. The box _B_ is held in position by the tapes _A_, so that the vein is visible through the rectangular opening in the thin rubber covering the bottom. The box is connected with the water manometer _G_, by a rubber tube, from which a T-tube enters the rubber bulb _E_. When the bulb _E_ is compressed between the plates _D_, by the coarse thumbscrew _C_, air is forced into the box _B_, exerting a pressure on the vein lying exposed beneath. This pressure is transmitted directly to the manometer =G=, and may be read off in centimeters of water on the accompanying scale. The veins of the back of the hand are used and there must be no obstruction between them and the heart. The rubber-covered box is accurately and lightly fitted over a vein and pressure made until it is obliterated. By measuring the distance above or below the heart level that the hand was when the observation was made, and subtracting or adding these figures to the manometer reading, we obtain the venous pressure at the heart level.

Eyster has modified this instrument so that it is now much simpler to operate. He uses a small glass cup with a flaring edge and a diameter of about 2 cm. This is sealed to the skin directly over a vein on the back of the hand by means of collodion. The stem of the cup has a rubber tube leading to a small hand bulb and to the manometer tube which contains colored water. Slight compression of the hand bulb obliterates the vein which can be seen through the glass cup. The pressure in centimeters of water is then read off. (Fig. 34.) The principle is the same as in the earlier instrument, but the application is easier.

Practically Hooker and Eyster found that the normal variation in healthy subjects was from 3 to 10 cm. of water. The pressure rose in cases of decompensated hearts with dyspnea and venous stasis, and returned to normal with improvement in the condition of the patient. It might be possible with this instrument to foretell an oncoming decompensation by the rise in venous pressure.

The venous pressure may also be estimated roughly by slowly elevating the arm and noting the instant at which a particular vein collapses. By measuring the height of the vein above the heart some idea may be obtained of the pressure within the right auricle.

=The Pulse=

There is nothing characteristic about the pulse of a person suffering from arteriosclerosis, except it be the difference in the pulse of high tension and of low tension. The pulse of high tension has a gradual rise, a more or less rounded apex, and the dicrotic wave is slightly marked and occurs about half-way down on the descending limb. In arteriosclerosis with low tension the radial artery is usually so rigid that very little pulse wave can be obtained. The general form of a low tension pulse is a sharp upstroke, a pointed summit, and a secondary wave on the base line, which corresponds to the dicrotic wave. Such a pulse can be easily palpated, and is known as a dicrotic pulse. However, such a pulse can occur only when the artery still retains all or a large part of its elasticity; hence in arteriosclerotic low tension we would never see such a pulse as the typical dicrotic.

=The Venous Pulse=

It would carry us too far to discuss fully the character of the venous pulse, but a brief summary of the essential features of the normal venous pulse is presented. The venous pulse is a term used to express the tracing obtained from the internal or external jugular vein at the root of the neck. Normally a very characteristic curve is produced, which can be readily analyzed into a series of waves corresponding to the fluctuations in the cardiac cycle. To understand these waves and their values, the accompanying figure is helpful. (Fig. 35.)

Bachmann summarizes the normal waves in the venous pulse tracing as follows:

"The physiological or so-called venous pulse consists of three positive and three negative waves, bearing a more or less definite relation to the events of the cardiac cycle, and having their origin in the various movements of the chambers and structures of the right heart. The first positive wave (_a_) is presystolic in time, and is due to the contraction of the auricle, causing a slowing of the venous current and producing a centrifugal wave through a sudden arrest of the inflowing blood. The second positive wave (_S_) is presystolic in time, and originates in the sudden projection of the tricuspid valve into the cavity of the auricle during the quick, incipient rise in the intraventricular pressure occurring in the protosystolic period. The third positive wave (_v_) occurs toward the end of ventricular systole. It consists of two lesser waves separated by a shallow notch. The factors entering into its formation are the relaxation of the papillary muscle at a time when the intraventricular is still higher than the intraauricular pressure, resulting in an upward movement of the tricuspid leaflets and a return of the auriculoventricular septum to its position of rest.

"The first negative wave (between positive wave _a_ and _S_) is due to the relaxing auricle. The second negative wave (_Af_) occurs during the diastole of the auricle. It is due to the dilatation of its walls, to the displacement of the auriculoventricular septum toward the apex occurring at the time of ventricular systole, and to the pull of the papillary muscles on the tricuspid valve leaflets. The third negative wave (_Vf_) appears during ventricular diastole and in the common pause of the heart chambers. Its cause is found in the passage of the blood from the auricle into the ventricle. It is somewhat modified possibly by the continual ascent of the auriculoventricular septum and by a wave of stasis due to the accumulation of blood coming from the periphery." (Fig. 36.)

Hirschfelder has described another wave which he calls the "h" wave, which is due to the floating up of the tricuspid valve by the blood in the ventricle before the complete filling of the ventricle following the auricular systole. (Fig. 37.)

=The Electrocardiogram=

In the past few years an immense amount of work has been done by numerous observers on the changes in the electrical potential of the various portions of the heart during contraction. The very elaborate and delicate electrocardiograph with the string galvanometer devised by Einthoven is used. It has been definitely determined that the impulse to cardiac contraction originates in the sinus node, a collection of differentiated nerve cells situated at the junction of the superior vena cava with the right auricle. From there the impulse travels in certain fibers in the interauricular wall, passes through another node, the auriculoventricular or Tawara node, situated in the auricular wall just above the auriculoventricular ring, thence via the Y-bundle, or bundle of His to the ventricles. This sequence is orderly, regular, and normally invariable. (Fig. 38.)

The sino-auricular (s-a) node is the most irritable portion of the heart, it is endowed with the greatest amount of rhythmicity as well. It is under the control of the vagus nerve. Its inherent rate of rhythmicity is probably more rapid than the usual numbers of impulses per minute, but it is inhibited by the vagus. Paralysis of the vagus endings increases the rate of impulse formation and therefore the rate of the heart.

The electrocardiogram is a graphic representation on a photographic film or sensitive bromide paper of the changes of electrical potential during muscular activity. The lines are made by the highly magnified string of the galvanometer as it moves across the slit in the photographic apparatus in response to the induction currents set up in the heart magnified by the special galvanometer.

The record is made in three so-called Leads.

Lead I

The electrodes are attached to right arm and left arm.

Lead II

The electrodes are attached to right arm and left leg.

Lead III

The electrodes are attached to left arm and left leg.

A series of regular figures is normally obtained in which are depressions and elevations and regular spacing of these elevations and depressions. The waves so-called have been arbitrarily designated _P_, _Q_, _R_, _S_, _T_. There is some difference in the three leads. "The wave _P_ is positive in _all leads_. _P_ to _R_ interval varies slightly in the _three leads_. All the waves of _Lead II_ are greater than those of _Leads I_ and _III_. The wave _R_ is positive in _all leads_. _T_ is usually positive in _all leads_, but is occasionally negative in Lead III. Even in normal individuals there is a considerable range of variation in the electrocardiogram which is within the limits of the normal." (Hart.) (Fig. 39.)

The _P_ wave is admitted to be the wave of auricular contraction. _Q_, _R_, _S_, is the ventricular complex caused, it is thought, by the current passing over the ventricles. _T_ wave is not yet definitely settled. It has been thought by some that it represented actual ventricular contraction and its height and shape had some meaning in heart force. This is denied by others. Hart defines it as "The final activity of the ventricle." The _T_ wave is usually increased in size during exercise.

The _P-R_ interval is almost the most important feature of the tracing. It is the actual conduction time in fractions of a second of the impulse from s-a node to the ventricles. Normally this is about 0.2 second or slightly less. Much that was hoped for from the electrocardiograph in the clinic has not been forthcoming. Its greatest value is in states of abnormal conductivity, such as various grades of heart block, extrasystoles, whether originating in auricles or in either ventricle, abnormalities of rhythm, as flutter and fibrillation. It has, however, aided materially in the intelligent interpretation of many phenomena heretofore not well understood, and has enormously increased our knowledge of the physiology and pathologic physiology of the heart.

It is not possible to enter farther into the subject here. This brief discussion must suffice. The reader is referred to works on this subject in connection with diseases of the heart.