THE VOLUME AND DISTRIBUTION OF BLOOD IN THE HUMAN LEG MEASURED IN VIVO. 1. THE EFFECTS OF GRADED EXTERNAL PRESSURE1 2

Journal/Book: THE JOURNAL OF CLINICAL INVESTIGATION VOI. XXXIII No. 5 pp. 798-806 May 1954. 1954;

Abstract: From the Department of Medicine Boston University School of Medicine and the Evans Memorial Massachusetts Memorial Hospitals Boston Mass. Submitted for publication July 1 1953 ; accepted January 27 1954 1This work was supported by a grant from the Life Insurance Medical Research Fund. 2 This paper was presented in part at a meeting of the New England Cardiovascular Society an February 19 1951. SUMMARY AND CONCLUSIONS 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. Small increases in external water pressure produced large decreases in the resting vascular volume which leveled off abruptly when the external pressure had risen to equal the venous (or venular) pressure. At that point the effective venous pressure was reduced to slightly greater than zero and the venous volume was at the "baseline value." The large decrease in vascular volume was attributed to the reduction in the effective venous (and venular) pressure. Further large increases in the external water pressure caused only small decreases in the vascular volume attributed to reductions in the effective pressures of the capillaries arterioles and arteries. It was concluded that 1. 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. 2. Changes in vascular volume produced by changes in external pressure are due almost entirely to changes in effective venous (and venular) pressure. 3. The combined volume of the capillaries arterioles and arteries is small regardless of the effective pressures in these vessels. 4. The volume and distribution of blood in the leg at rest are essentially functions of the effective venous pressure. ___MH

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