Overshoot in mixed venous oxygen saturation during recovery from supine bicycle exercise in patients with recent myocardial infarction.

During recovery from dynamic exercise, systemic oxygen extraction rapidly decreases below the resting level in patients with heart failure, which leads to a subsequent increase in mixed venous oxygen saturation (SvO2) above its resting value (postexercise SvO2 overshoot). To evaluate the pathophysiologic basis of this phenomenon, postexercise SvO2 overshoot was evaluated in relation to hemodynamic, metabolic, and neurohumoral responses during recovery from maximal supine bicycle exercise in 22 patients with recent myocardial infarction. Postexercise SvO2 overshoot closely correlated with increased systemic vascular resistance (r = 0.79, p < 0.001) and reduced cardiac output (r = -0.74, p < 0.001), suggesting that SvO2 overshoot is primarily due to increased peripheral arteriovenous shunting caused by an enhanced peripheral vasoconstriction in the setting of reduced cardiac output. Postexercise SvO2 overshoot and systemic vascular resistance were significantly higher and cardiac output was significantly lower in New York Heart Association functional class 3 and 4 (8 patients) compared with class 1 and 2 (14 patients), whereas systemic arterial blood pressure was maintained at normal levels in both groups. Thus, postexercise SvO2 overshoot and, hence, decreased systemic oxygen extraction during recovery represent a compensatory response of an enhanced peripheral vascular tone that maintains systemic arterial blood pressure in the setting of reduced cardiac output by linking central and peripheral blood flow.