A Direct Measure Of Leg Blood Flow During Running: A Feasibility Case Study

Cardiac output and leg blood flow can be measured simultaneously with high accuracy using transpulmonary thermodilution and femoral vein thermodilution with a single bolus injection. These measurements have been performed during single leg kicking, cycling, and Nordic skiing, offering insights into competing blood flow demands during exercise. Running is the natural exercise modality of humans, however, to date there has been no direct measure of leg blood flow during running. PURPOSE: To determine the feasibility of the thermodilution technique to measure leg blood flow and conductance during high intensity running relative to cycling, in an exploratory case study. METHODS: A healthy, trained runner (30y male) completed an incremental test to exhaustion on a cycle ergometer, followed by an incremental test on a treadmill that progressed from walking to running. Leg blood flow and cardiac output were determined using the single bolus thermodilution technique. Throughout exercise, metabolic variables, femoral and venous pressures and temperatures were measured continuously, with regular sampling of arterial and venous blood. RESULTS: The participant reached a greater peak oxygen uptake during running relative to cycling (74 vs. 68 mL·kg-1·min-1). Peak limb blood flow was greater at peak running exercise (10.9 vs. 10.5 L·min-1); however, a greater peak cardiac output was observed during cycle exercise (28.6 vs. 30.2 L·min-1). The ‘beat phenomenon’ was apparent in femoral artery measures while running, and thereby produced large swings in leg conductance (62 - 90 mL·min-1·mmHg-1 @ 70 % VO2peak). Average leg vascular conductance was greater during walking relative to similar intensity cycling (36 vs. 25 mL·min-1·mmHg-1 @ ~25 % VO2peak) and remained greater during high intensity running (92 vs. 72 mL·min-1·mmHg-1 @ ~80 % VO2peak). CONCLUSION: We present the first direct measure of leg blood flow and conductance in a running human. Our findings corroborate several assumptions about leg blood flow during running compared to cycling. Crucially, we show that using thermodilution in running exercise can be completed safely. Natural Sciences and Engineering Research Council