Blood flow in relationship to muscular contraction were studied in hindlimb of rabbits anesthetized with urethane and electricity.
Exercise hyperemia (EH), postexercise hyperemia (PEH) and hematocrit (Hct) were measured with time intervals. Under a blood pressure of 100/70 mmHg by urethan anesthesia, EH with stimulation of 5 to 10 Hz was exponentially increased to a 2-3 times more than the control level. But, EH produced by stimulation of 20 to 50 Hz decreased from the start to the first 20 sec of exercise, then increased gradually to a peak within 60 sec after exercise. Recovery time in PEH was prolonged as the intensity of the stimulation increased ; about 4 min by 5 Hz, 6-7 min by 10 Hz, and 8-13 min by 20-50 Hz. On the other hand, under a blood pressure of 150/100 mmHg by electroanesthesia, a rapid increase in EH was observed, and a shorter recovery time in PEH was obtained with an equal stimulation ; about 2 min by 5 Hz, and 4 min by 20 Hz.
An increase in Hct occurred at the first 15 to 20 sec of exercise, and in strenuous muscle contraction it was approximately 3% higher than the resting level. In PEH, Hct decreased gradually as the degree of hyperemia fell.
Muscle blood flow and Hct increase in response to the muscular activity evoked. The data suggest that these changes depend on the complex mechanism of arteriolar dilatation, capillary bed enlargement, an increase of capillary permeability and water shift.