RESPIRATORY VARIATIONS OF BARORECEPTOR REFLEX TRANSMISSION AND THEIR EFFECTS ON SYMPATHETIC ACTIVITY AND VASOMOTOR TONE

The reflex effects of short bilateral sinus nerve stimulation are dependent on the time of stimulation within the respiratory cycle. Stimulation during the expiratory phase produces greater vasodilatation in the perfused m. gracilis and stronger inhibition of lumbar sympathetic activity than does stimulation during the inspiratory phase. The time course of reflex sympathetic inhibition during the respiratory cycle, measured by the reflex pause of sympathetic activity after sinus nerve stimulation, is described. Continuous stimulation of both sinus nerves intensifies the respiratory grouping of sympathetic activity. This phenomenon can be explained by the respiratory oscillation of reflex transmission. The respiratory grouping of sympathetic activity and the respiratory vasomotor oscillations cannot be abolished by baroreceptor denervation and/or elimination of respiratory movements with neuromuscular blocking agents. If the baroreceptor nerves are intact the respiratory variations are modified also by respiratory blood pressure waves. The significance of the findings with respect to the central functional organization of respiratory and cardiovascular centers and the various factors responsible for the respiratory grouping of sympathetic activity are discussed. © 1968 Springer-Verlag.