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 passing that in a case of seeming coma where albumin 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.