CAPILLARY BLOOD PRESSURE IN MAN. COMPARISON OF DIRECT AND INDIRECT METHODS OF MEASUREMENT. 1

Abstract

In the course of studies of the peripheral cir-culation in hypertensive subjects it became de-sirable to make measurements of the capillary blood pressure. Previous studies by others (1, 2, 3) had indicated that the capillary blood pres-sure is at approximately the same level in normal and hypertensive subjects. The accuracy of the indirect methods of measurement employed in these earlier studies has never been actually estab-lished. Indeed there is reason to suspect their reliability (4). It seemed necessary, therefore, before attempting to determine capillary blood pressure in hypertensive subjects, to analyze critically some of the available methods of meas-urement, in order to select one which would yield trustworthy results. Two methods were chosen for analysis: (1) the direct microinjection method of Landis (5), and (2) the indirect, pressure-capsule method of Danzer and Hooker (6). Heretofore, no attempt has been made to com-pare in the same individual the results obtained by the direct and indirect methods. The present investigation has led to the conclusion that the two methods do not give comparable results, and that, of the two, only the direct method gives accurate readings. METHODS Because of their size, accessibility and position parallel to the skin surface, the capillaries in the nail -folds are, in man, the most suitable for blood pressure determina-tions. All of the following observations were made upon capillaries in the nail folds of the fingers of quiet, re-cumbent subjects with normal systemic venous pressures. The capillary bed was always at the level of the heart, i.e., 2 to 5 cm. below the level of the anterior chest wall at the third intercostal space. The observations were made in a quiet, warm room, the temperature of which was usually 240 to 260 C. In none of the experiments was the room temperature higher than 28° C. or lower