If the block is functional, depending upon some temporary overstimulation of the vagus nerve, atropin, which paralyzes the endings of the vagus, will naturally lift the block. If the block is due to some actual lesion of the bundle of His, such as fibrosis, gumma, or other lesion, then atropin will have no influence to terminate the block. In this manner we are able to distinguish between functional and organic heart block.

CHAPTER V

BLOOD PRESSURE IN ITS CLINICAL APPLICATIONS

It is well to bear constantly in mind the point made over and over in this work, that blood pressure is only one of many methods of acquiring information. He who worships his sphygmomanometer as a thing apart and infallible will sooner or later come to grief. Judgment must be used in interpreting changes in blood pressure just as judgment is essential in properly evaluating any instrumental help in diagnosis. One must not forget the personal equation which enters into even accurate instrumental recording in medicine and surgery.

In this chapter there will be no attempt to quote largely from what others have said or thought. Every one has his own opinion as to the value of certain methods after he has worked with them for a long time.

The ideas here expressed, except in cases where no opportunity has offered to make personal studies, are those gathered from personal experience.

=Blood Pressure in Surgery=

Careful estimation of the blood pressure in surgical cases has, at times, great value. In all surgical diseases the most important fact to know is not the systolic pressure, but the pulse pressure. If the pulse pressure keeps within the range of normal, does not drop much below 30 mm. in an adult, then so far as we can tell the circulation is being carried on. When the systolic pressure is gradually falling and the diastolic remains the same, the circulation is failing and unless the pulse pressure can be established again the patient will die. Again we see the value of the pulse pressure.

All prolonged febrile diseases tend to produce a lowering of the blood pressure picture. The diastolic does not fall to the same extent as the systolic so that there is a pulse pressure smaller than normal. This is to be expected from what we know of the general depression of the circulation in fevers. The blood pressure reading is only a graphic record of what we have long known, and enables us from day to day accurately to measure the general circulation.

=Head Injuries=

It was claimed that in fracture of the skull or in concussion much could be gained by frequent estimations of the blood pressure. This seemed probable in the light of experiments on compressing the brains of dogs by the use of bags inserted through trephine openings (Cushing). In the clinic, however, it has not been found of any material value. It has a value in differentiating a simple fracture, let us say, from a case of uremia which is picked up on the street with a b.u.mp on the head. There the high pressure usually found would at once direct attention to the kidneys and the newer methods of blood examination would at once settle the question. Naturally uremics may also have skull fracture. There the diagnosis would be complicated. A decompression done at once would be indicated. If the skull fracture happened in a uremic, the decompression would probably do no harm. In fact, there are some who advise decompression for uremia.

=Shock and Hemorrhage=

In shock the blood pressure picture is low but the pulse pressure drops to abnormally low figures. It seems to me that the blood pressure instrument has its greatest value in surgery in the warning it gives to the operating surgeon in cases of impending shock.

It is well known that the first effect of ether, the commonly used anesthetic, is to raise the blood pressure and quicken the pulse rate.

The whole blood pressure picture is at first elevated (Fig. 54). Soon the whole pressure falls slightly but continues at a higher level than normal. The diastolic pressure drops back nearly to normal and the increased pulse pressure is due almost entirely to the slight rise in the systolic pressure. Now the whole duty of the anesthetist is to administer the ether so that this ratio of systolic and diastolic is maintained throughout the operation. Warning comes to him of impending shock before it comes to any one in the neighborhood (Fig. 55). Any sudden change in the pressure is a signal for increased watchfulness.

Should the pressure all at once drop he can immediately notify the surgeon and inst.i.tute measures to resuscitate the patient.

[Ill.u.s.tration: Fig. 54.--Blood pressure record from a normal reaction to ether. Note that the systolic and diastolic rise and fall together. At the end of the anesthetization the pulse pressure is practically the same as at the beginning. Compare this with the record in Fig. 55, where the operation had to be discontinued on account of the onset of shock.]

[Ill.u.s.tration: Fig. 55.--Beginning of operative shock. Chart showing the method of recording blood pressure during operation.

Note that the pulse and respiration show no remarkable changes, but the blood pressure steadily fell, the systolic more than the diastolic so that the pulse pressure was gradually reaching the danger point. Further work on this case was stopped following the warning given by the blood pressure. The patient was returned to the ward and a week later anesthesia was again given, the operation was completed, and the patient had a satisfactory convalescence.]

A method which is widely used is as follows: The anesthetist wraps the cuff of one of the dial instruments around the patient's arm, and arranges the dial so that it can easily be seen by him at all times.

This does not in any way interfere with the work of the surgeon. Over the brachial artery below the cuff is the bell of a binaural stethoscope held in place by the strap attachment now on the market. The tubes of the stethoscope are long enough to reach conveniently to the ear pieces.

A watch is pinned to the sheet of the table. He has a chart, as ill.u.s.trated (Fig. 56) on a board and makes a dot in every s.p.a.ce for five minute intervals. By joining the lines a curve is obtained which tells at a glance what the circulation is doing. I feel sure that more attention and care exercised on the part of the anesthetist would be the means of conserving many lives lost from shock following operation.

[Ill.u.s.tration: Fig. 56.--Showing method of using blood pressure instrument during operation without interfering with the operator or a.s.sistants. Sheet thrown back to show cuff on arm of patient.

Anesthetist has chart on table beside him, dial pinned to pad in full view, bulb near hand. Extra tubing must be put on the blood pressure instrument.]

A sudden drop in the pressure picture may mean a large hemorrhage. The gradual return of the pressure picture means that the vasomotor mechanism has acted to keep up the pulse pressure. Should the diastolic pressure continually fall, it may mean that the hemorrhage is still taking place (Wiggers).

=Blood Pressure in Obstetrics=

One might affirm almost without fear of contradiction that the constant determination of blood pressure during pregnancy is more important than the examination of the urine. Within recent years a number of observers having access to a large material, have given the results of their findings. There is a striking unanimity of opinion, although now and then a difference in minor details.

The blood pressure should be taken frequently during pregnancy. The usual and highly essential precautions in taking pressure in general apply most particularly in these cases. Towards the end of pregnancy the pressure should if possible be taken daily and oftener if necessary.

Pressure in women is usually below 120 mm. Many patients have a temporary rise in blood pressure during pregnancy, due oftenest to constipation, without developing other symptoms. This is common to all conditions and has no significance. Some think that an abnormally low pressure, that is, a systolic below 90 mm., suggests that the patient is likely to react unduly to the strain of labor. This is denied by others.

Among 1000 cases (Irving) the pressure was below 90 in only one case. A gradually rising pressure precedes alb.u.minuria, as a rule. If there is alb.u.min without change in pressure the alb.u.min may usually be disregarded. Some think that a pressure over 130 mm. systolic should be carefully watched. The danger limit is set by some at 150 mm. If the blood pressure from the very first is high, it may mean only that that was the patient's normal pressure. This calls for increased watchfulness. It is held by some that high blood pressure favors hemorrhage and probably explains the hemorrhagic lesions in the placenta and some viscera in eclampsia and alb.u.minuria.

All are agreed that the most significant change is the gradual but sure rise from a low pressure. When this is combined with alb.u.minuria the danger of toxemia is imminent. The high blood pressure in those under thirty years of age seems to be a more certain sign of approaching toxemia than the same pressure in those older. The pressure falls within a few days to its normal after delivery in the toxic cases.

Although the emesis gravidarum is held to be a sign of a toxemia of some unknown nature, the blood pressure is never raised even in the pernicious form.

=Infectious Diseases=

In all infectious diseases the blood pressure tends to be lower than normal. During chills the systolic may rise to great height due to the violent muscular contractions.

We found the blood pressure of great value in giving information concerning the circulation. Again we repeat that it is not the systolic alone or the diastolic alone but the pulse pressure which we wish to keep informed about. In pneumonia we have tried out Gibson's law only to discard it. This so-called law is that in pneumonia the systolic pressure in millimeters should remain above the figure for the pulse rate. When the figure in mm. of pressure is equalled by or exceeded by the pulse rate the prognosis is grave.

In typhoid fever we have made many estimations at various stages of the disease. We can only say that the pressure picture tends to fall during the course. The systolic falls more than the diastolic so that it is not uncommon to see pulse pressures of 20 mm. at the beginning of convalescence in spite of the high caloric feeding practiced. At the time of perforation the systolic pressure may be raised. This is only the reflex from the initial pain. Soon the pressure falls and if peritonitis sets in, the pressure is exceedingly low and the pulse pressure gradually falls until the circulation can no longer be carried on. In large hemorrhage the pressure suddenly falls. If only one hemorrhage has occurred a gradual rise takes place, but the general pressure picture remains at a lower level for days, gradually returning where it was before the hemorrhage.

In beginning failure of the circulation we found elevation of the foot of the bed about nine inches to be of such value that we felt there must be some increase in blood pressure. Numerous readings were made covering a period of several months. Although we felt certain that the circulation was improved, we rarely needed cardiac stimulation, we never could prove any increase of blood pressure with the sphygmomanometer.

In all infectious diseases there is no help offered by blood pressure estimations in diagnosis. The sole and important use is that of keeping track of the circulation.

=Valvular Heart Disease=

No rules can be laid down for blood pressure in valvular heart disease.

Aortic stenosis, the rarest of the valvular lesions, is practically always accompanied by high pressure picture. Mitral stenosis on the contrary usually shows a low pressure picture. Mitral insufficiency may show an exceedingly low picture or an exceedingly high picture. Aortic insufficiency also may be accompanied by a high systolic or by a normal systolic pressure. It depends on the etiology. Practically all the rheumatic cases have low pressure, the syphilitic cases have a high pressure. It is characteristic of all cases of aortic insufficiency that the diastolic pressure is low, even as low as 30 mm. The pulse pressure is invariably high. Usually there is no difficulty in determining the diastolic pressure. The intense third tone suddenly becomes dull at the point of diastolic pressure and frequently the dull sound can be distinctly heard over the artery down to the zero of the scale. If difficulty is found in reading the diastolic as the pressure is reduced, the estimation may be reversed and the pressure gradually increased from zero to the point where the dull tone suddenly becomes loud and clear.

These points always coincide.

=Kidney Diseases=

This has already been discussed somewhat fully in Chapter III and will receive more consideration later. It might be remarked in pa.s.sing that in a case of seeming coma where alb.u.min is found in the urine but where the blood pressure is low or normal, I have found at autopsy in several cases pyonephrosis and not chronic nephritis. The blood pressure may be useful in differentiating uremic coma from the coma of pyonephrosis.

Also in the cases of coma with anasarca, either the acute, subacute or chronic form the blood pressure is not raised as a rule. Other diseases of the kidney, as tuberculosis, cancer, infection with pyogenic organisms, are not accompanied with any notable changes in blood pressure.

=Other Diseases, Liver, Spleen, Abdomen, etc.=

Blood pressure is only of value in the above diseases in affording information concerning the state of the circulation. There is nothing characteristic about the pressure in any of these diseases.