Human cardiovascular and respiratory responses to graded muscle ischemia.

Responses of heart rate (HR), mean arterial blood pressure (MAP) ventilation (VE), and forearm blood flow (FBF) to different degrees of leg muscle ischemia were measured in eight subjects in a four-part experiment. Part I. Total circulatory occlusion (OCCL) of resting legs for 15 min had little or no effect on HR, MAP, VE, or FBF. Part II. OCCL of the legs for 3 min immediately after exercise at 50-250 W did not affect HR or end-tidal CO2; it lowered VO2 and VE and prevented recovery of MAP. Part III. OCCL beginning at end and 10, 20, 30 s before end of 7-min exercise (100-150 W) and continuing 3 min into recovery period produced sustained and graded increments (5-10 mmHg) in MAP, only small changes in HR, and accelerated recovery of VE while end-tidal CO2 remained constant. Part IV. OCCL at end and 30 s before end of exercise increased FBF 2.5-3.5 times; both skin and muscle vasodilated. Thus muscle ischemia preceded by exercise can raise MAP without affecting VE, whereas baroreflexes may lower HR and raise FBF. The results suggest the presence of muscle chemoreceptors whose major effect is on MAP.