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Mechanism of Overshoot in Cardiac Function During Recovery From Submaximal Exercise in Man*
Background: A sudden increase (overshoot) in the left ventricular ejection fraction during the recovery from maximal exercise has been reported in patients with coronary artery disease, but its mechanism has not been fully clarified. We investigated whether this phenomenon may occur in normal subjects, and whether it depends on the intensity of exercise.
Methods: Thirteen normal subjects (mean [+/- SD] age, 59 +/- 8 years old) performed two levels (25 W and 50 W) of mild-intensity, constant-work-rate exercise for 6 min on a cycle ergometer. Left ventricular function was monitored continuously during the recovery from exercise using a computerized cadmium telluride detector.
Results: An overshoot was observed in the ejection fraction during the first minute of recovery compared with the end-exercise value. The overshoot in the ejection fraction during recovery after the 50-W exercise was greater than that seen after the 25-W exercise. An overshoot phenomenon in stroke volume was also observed during the recovery from 50-W exercise.
Conclusions: The overshoot in cardiac function observed during the early phase of recovery, which was caused mainly by an immediate decrease in end-systolic volume, occurred even after exercise of mild intensity. This phenomenon appears to suggest the existence of a transient mismatch between cardiac contractility and afterload reduction during the recovery from mild-intensity exercise, even in normal subjects. (CHEST 1999;116:868-873)
Key words: ejection fraction; mild-intensity exercise; overshoot phenomenon; stroke volume
Abbreviation: CdTe = cadmium telluride
Although there are numerous reports1-6 on the time course of cardiac function during exercise, the change in cardiac function during the recovery from exercise is not well understood. A sudden increase (overshoot) in the left ventricular ejection fraction during the recovery from maximal exercise has been reported7 in patients with coronary artery disease. However, its mechanism has not been fully clarified. It is also not known whether this phenomenon may occur in normal subjects. Further, there is no report on whether this phenomenon may occur even after exercise of submaximal or mild intensity.
We continuously monitored cardiac function after two levels of submaximal mild-intensity exercise performed at a constant work-rate in normal subjects. Our objectives included the following: (1) to determine whether the overshoot phenomenon of cardiac...