This early physiological study demonstrated that the cardiac response to exercise in dogs is primarily mediated by increased heart rate rather than increased stroke volume.
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Exercise cardiac output rises mainly via heart rate in dogs; leaves open the relative role of stroke volume in humans.
Instantaneous blood flow through the thoracic aorta was monitored continuously during spontaneous activity in intact dogs by means of a new, pulsed, ultrasonic flowmeter. Integrated flow per stroke, accumulated flow per unit time and heart rate were simultaneously derived by means of electronic computers. During treadmill exercise at 3 mph on a 5% grade, the heart rate increased by two- or threefold, but the aortic flow per stroke was only slightly increased. This observation was confirmed by direct measurements, of left ventricular diameter. An increase in stroke volume is not an essential feature of the cardiac response to exercise in these experiments.
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Franklin et al. (1959) studied this question.
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