THE INFLUENCE OF VENOUS COLLECTING PRESSURE ON MEASUREMENTS OF CALF BLOOD FLOW BY VENOUS OCCLUSION PLETHYSMOGRAPHY.

The influence of different venous collecting pressures on blood flow measurements by venous occlusion phethysmography in the human calf at rest and during post-ischemic reactive hyperemia, has been studied in 7 normal subjects and 32 patients with different degrees and locations of atherosclerosis obliterans. Blood flow measurements were performed by using an airfilled rubber segment plethysmograph. The reproducibility of the blood flow measurements was tested in 12 normal subjects and 13 patients with atherosclerosis obliterans. The accuracy of the method was found acceptable. The different venous collecting pressures used in normal subjects were 50, 60, 70, 80, and 90 mm Hg and in patients 30, 40, 50, 60, and 70 mm Hg. In 7 patients with arterial obliterations and in 1 normal subject intra-arterial blood pressure measurements were made in the iliac or femoral artery simultaneously with blood flow measurements at 3 different venous collecting pressures. Systemic blood pressure was measured by conventional technique on the arm. In 5 patients the intraarterial blood pressure was measured distal to the main arterial obliterations and in 2 patients proximal to the obliterations. The venous collecting cuff was placed distally to the tip of the intraarterial catheter. The blood pressure distal to an arterial stenosis was found to be lower than the systemic blood pressure even at rest. During reactive hyperemia there was a considerable pressure fall both in the normal subject and in the patients. The intraarterial blood pressure during reactive hyperemia was found to increase during the flow measurements indicating hindrance of arterial inflow by inflation of the collecting cuff. In normal subjects the highest resting flow was measured at venous collecting pressures similar to or a little higher than the diastolic arm blood pressure, while in patients no significant differences were found between the values obtained at the different pressures used. During reactive hyperemia in the calf of normal subjects the optimal venous collecting pressure was found to be 50 mm Hg in the first 40 seconds of the hyperemia. The most valid measurements of post-ischemic reactive hyperemia in patients with atherosclerosis obliterans were made by using a venous collecting pressure of only 30 mm Hg throughout the study. Higher venous collecting pressures may give too low blood flow values, artificial delay of the peak flow value, and an altered configuration of the blood flow curves. [ABSTRACT FROM AUTHOR]