Comparison of Dye-Dilution and Plethysmographic Blood Flow Measurements: An Evaluation of the Influence of Invasive Techniques on Blood Flow and on Arterial and Femoral Venous Substrate Variables in Man

Abstract

1. In eight healthy volunteers we compared leg blood flow, as determined in a calf segment by strain-gauge plethysmography, with the flow measured by a constant-rate infusion of Indocyanine Green dye into the femoral artery. The representativeness of the calf segment was evaluated by complementary measurements with additional strain gauges attached around the proximal and distal crural and the distal thigh segments (n = 6). Furthermore, we investigated the influence of the catheterization procedure and a simulated vascular puncture, as well as repeated venous occlusions, on blood flow and on arterial and femoral venous substrate concentrations and blood gases (n = 8). 2. The leg blood flow measured by dye dilution was 0.31 ± 0.03 litre/min (mean ± sem). The blood flow in the calf segments was 14.8 ± 1.6 ml min−1 litre−1 and no difference between the legs was observed. Extended to the whole leg the plethysmographic blood flow was 0.17 ± 0.01 litre/min and thus lower (43 ± 7%, P < 0.001) than the flow determined by the indicator-dilution method. Blood flow in the legs was not influenced by catheterization or sham punctures of the vessels or by repeated venous occlusions. 3. The concentrations of glucose, lactate and glycerol, as well as blood gas variables, in arterial and femoral venous blood did not change during the study or decreased so slightly (pH and lactate) that the arteriovenous difference was not influenced. 4. We conclude that the blood flow of the total leg cannot be satisfactorily estimated from strain-gauge plethysmography of a single calf segment. Strain-gauge plethysmography can therefore not be recommended for quantitative studies of substrate turnover in the leg tissues applying the Fick principle. Catheterization of the femoral vessels, or manipulations close to them with a thin cannula or repeated venous occlusions, has no significant effect on leg blood flow and substrate exchange.