THE EFFECT OF EXTERNAL PRESSURE ON THE VASCULAR VOLUME OF THE FOREARM AND ITS RELATION TO CAPILLARY BLOOD PRESSURE AND VENOUS PRESSURE

Abstract

The pressure plethysmograph was used to determine the effect of graded external pressure on the vascular vol. of the forearm for the purpose of determining the usefulness of this procedure in estimating the blood pressure in the minute vessels collectively. In the normal forearm vascular vol. was greatest when external pressure was between 15 and 35 mm. Hg, becoming less at external pressures above and below this range. Three methods of determining "that external pressure at which the vis a tergo of the circulation was able to keep open the greatest collective vascular volume" were compared and yielded values of 27,21 and 21 mm. Hg respectively. In normal subjects this value had the same order of magnitude as capillary blood pressure under normal conditions, during venous congestion and when the forearm was placed above or below heart level. This plethysmographic method may be useful in studying the vol. of blood and the pressure in the minute vessels of the forearm in clinical conditions.