Cardiac and respiratory effects of aortic arch baroreceptor stimulation.

The reflex cardiac and respiratory effects of stepwise pressure variations in the isolated aortic arch were determined in anesthetized dogs. Elevation of pressure in the aortic arch depressed respiratory movements, decreased heart rate in the unpaced heart, and diminished peak pressure in the paced, isovolumetric left ventricle preparation. The threshold for these reflex effects was an aortic arch pressure of approximately 100 mm Hg. The maximum rate of change of these variables as a function of aortic arch pressure occurred at a pressure of about 175 mm Hg. Aortic arch pressures of 300 mm Hg or more were necessary to achieve maximal reflex effects. Heart rate changes were mediated by parasympathetic pathways predominantly, although reciprocal sympathetic influences were also involved. Both divisions of the autonomic nervous system mediated the effects upon ventricular performance. ADDITIONAL