=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 stopc.o.c.k 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 stopc.o.c.k 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.

[Ill.u.s.tration: Fig. 23.--Method of taking blood pressure with a patient in sitting position.]

[Ill.u.s.tration: Fig. 24.--Method of taking blood pressure with patient lying down.]

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.

[Ill.u.s.tration: Fig. 25.--Observation by the auscultatory method and a mercury instrument. One hand regulates the stop c.o.c.k which releases air gradually.]

[Ill.u.s.tration: Fig. 26.--Observation by the auscultatory method and a dial instrument. The right hand holds the bulb and regulates the air valve.]

=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.

[Ill.u.s.tration: Fig. 27.--Schema to ill.u.s.trate the gradual decrease in pressure from the heart to the vena cava: (a), arteries; (c), capillaries; (v), veins; (A), aorta, pressure 150 mm.; (B), brachial artery, pressure 130 mm.; (F), femoral vein, 20 mm.; (IVC), inferior vena cava, 3 mm. (Modified from Howell.)]

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.)

[Ill.u.s.tration: Fig. 28.--Chart showing the normal limits of variation in systolic blood pressure. (After Woley.)]

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 m.u.f.fled 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 pa.s.ses 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 p.r.o.nounced, 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."