Base-line effects on response of stroke volume to leg exercise in the supine position

Abstract

Cardiac output was measured with dye dilution in normal subjects at rest in horizontal position, at rest supine with the legs on the pedals, and during increasing work loads. Experiments were designed to clarify the effect of leg raising on comparisons of stroke volume at various levels of exercise. Leg raising evoked a 19% increase in stroke volume and a decrease in heart rate. Oxygen uptake and A-V O₂ difference remained unaltered. In comparing stroke volume at mild exercise with leg-raised resting position, no change occurred contrasting the significant rise when compared with horizontal position. At mild exercise cardiac output response was relatively flat, whereas A-V O₂ difference rose sharply. At heavier exercise cardiac output rose more steeply and approximately linear to oxygen consumed. Stroke volumes at these loads were significantly higher than levels in both of the resting positions. Ignorance of the effect of leg raising results in misinterpretation of the stroke volume data at low levels of supine exercise when greatly enhanced tissue extraction of oxygen allows smaller blood flow increments. base line in exercise; exercise stroke volume; stroke volume, exercise; stroke volume, base line; supine exercise Submitted on December 13, 1963