Effects of exhaustive submaximal exercise on cardiovascular function during sleep

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Abstract
The influence of an afternoon bout of exhaustive submaximal exercise on cardiovascular function and catecholamine excretion during sleep was examined in 5 female and 4 male subjects. Subjects walked on a treadmill for successive 50-min periods at 50, 60 and 70% maximal O2 consumption, separated by 10-min rest periods. Exercise terminated with volitional exhaustion. Following an adaptation night, EEG and impedance cardiographic measures were obtained during 3 successive nights of sleep, with exercise preceding night 3. Relative to the base-line night (night 2), exhaustive exercise resulted in a sustained elevation of heart rate and cardiac output throughout the entire night''s sleep. The magnitude of these elevations was unaffected by sleep stage but decreased over the night. The typical pattern of circadian decline in cardiac output was unaltered. The decline in heart rate with sleep onset was greater on the exercise night. Changes in impedance dZ/dt and R-Z interval suggested an enhanced myocardial contractility during the first 3 h of sleep postexercise. Analysis of morning urine samples revealed that in 7 of 9 subjects norepinephrine excretion increased, epinephrine excretion decreased and dopamine excretion was unchanged during sleep on the exercise night. Evidently, these cardiac changes reflect a sustained increase in myocardial .beta.-receptor activity.

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