THE VOLUME AND DISTRIBUTION OF BLOOD IN THE HUMAN LEG MEASURED IN VIVO. I. THE EFFECTS OF GRADED EXTERNAL PRESSURE 12

Abstract

The leg was rendered as bloodless as possible by pressurizing it in a water-filled plethysmograph at a suprasystolic pressure. Blood was prevented from reentering the leg by a cuff at suprasystolic pressure proximal to the plethysmograph while the water pressure in the plethysmograph was readjusted to an exact (low) level. The circulation was then restored and the volume of blood that entered the leg at this external pressure was measured after reactive hyperemia had subsided. Such measurements were repeated over a wide range of external water pressures. Results of these expts. led to the following conclusions. A constant baseline of venous volume at an effective pressure slightly greater than zero is obtained when an external pressure equal to or greater than the natural local venous pressure is applied to the leg. Changes in vascular volume produced by changes in external pressure are due almost entirely to changes in effective venous (and venular) pressure. The combined volume of the capillaries, arterioles, and arteries is small regardless of the effective pressures in these vessels. The volume and distribution of blood in the leg at rest are essentially functions of the effective venous pressure.