EFFECTS OF HEART RATE AND CARDIAC FUNCTION ON OXYGEN UPTAKE AFTER EXERCISE

Abstract

During recovery from exercise, there is an exponential decrease in the oxygen uptake (Vo₂), which is composed of one fast and one slow component. We evaluated the effect of heart rate (HR) and cardiac function on the fast component. Vo₂ was measured during treadmill exercise and in the recovery period in 8 patients with implanted rate-responsive pacemaker, 7 patients with mild chronic heart failure and 8 healthy men. Two sequential exercise tests were performed at random in 8 patients with the pacemaker programmed to either the fixed rate (VVI, 60bpm) or rate-responsive (VVI-R, peak HR 104bpm) mode. In the VVI-R mode, the rate of decrease in Vo₂ is faster than in the VVI mode. In patients with VVI-R pacing and those with heart failure, the rates of decrease in Vo₂ were similar, but were significantly prolonged compared with the healthy men. HR decreased more slowly in patients with heart failure than in healthy men. Thus, heart rate and cardiac function are important determinants of the rate of decrease in Vo₂> after exercise.