Sinoaortic contribution to the adjustment of systemic resistance in exercising dogs

In conscious dogs instrumented with electromagnetic flow probes and miniature solid state pressure transducers, the cardiovascular response to treadmill exercise (6.5 km/h¹, 5% grade for 3 min) was studied before and after sectioning the carotid and aortic depressor nerves. Observations (75 expt, 5 dogs) indicate that after abrogation of sinoaortic reflexes, the hemodynamic response to exercise is qualitatively similar to that of the intact dog. However, significant quantitative differences are apparent after denervation. The cardiac output and heart rate responses are more sluggish, arterial pressure is more instable, particularly as exercise begins and ends, and finally the usual marked decline in systemic resistance is not sustained. These effects may be wholly or partly related to the absence of the arterial baroreceptors, and they indicate that the baroreceptors regulate the circulation during exercise in more complex fashion than previously recognized.