Sinus Nerve Stimulation in the Chloralose Anesthetized Cat: Effect on Blood Pressure, Heart Rate, Muscle Blood Flow and Vascular Resistance

In the chloralose anesthetized cat short duration stimuli (0.05—0.1 msec.) of the sinus nerve produce a pressor response. This preparation was utilized to examine the relation between frequency of direct chemoreceptor fiber stimulation and change in blood pressure, heart rate, muscle blood flow and muscle vascular resistance. Blood pressure, heart rate and muscle vascular resistance increased during sinus nerve stimulation proportional to the frequency. Muscle blood flow remained essentially constant despite the pressure rise. Responses were detected at 0.5 cps. Maximum response occurred at 16—20 cps. The range of frequency response for vascular resistance and heart rate is similar to that obtained by stimulating sympathetics directly. Thus both limbs of a cardiovascular reflex are have similar frequency response characteristics. The likelihood that the data obtained represents an approximation of the chemoceptor responses which in other preparations are masked by predominance of baroceptor function is discussed.