Exercise cardiac output has been measured by an indirect Fick technique in 94 normal subjects (48 men and 46 women) whose ages ranged from 20 to 85 years. With increasing age, exercise cardiac output was found to be greater despite no such trend in oxygen uptake; in consequence, exercise arteriovenous oxygen difference decreased with age. These trends were seen in both sexes, though the age effects were apparent a decade earlier in men. In addition, in men the heart rate was lower and stroke volume higher with increasing age. By contrast, no age effect on exercise pulse rate was noted in women. When the sexes were compared, exercise cardiac output was higher in women of the younger two decades (20 to 39 years), a difference which was not apparent in subsequent decades. sex differences in exercise cardiac output; age differences in exercise cardiac output; stroke volume during exercise; oxygen pulse during exercise Submitted on January 13, 1965

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