The relation between carotid body chemoreceptor discharge, carotid sinus pressure and carotid body venous flow.

1. Activity in forty-two single chemoreceptor afferent fibres from the carotid body in thirty-nine cats was measured when the carotid body was naturally and artificially perfused. In nine of these cats, carotid body venous flow was also measured.2. When pressure within the carotid sinus segment was suddenly raised or lowered, chemoreceptor activity changed in the opposite direction within the first 5-10 sec by an amount which was significantly greater than the variation of activity in the control period. Thereafter activity stabilized at a level which was not different from control.3. Whether the carotid body was naturally or artificially perfused, carotid body chemoreceptor activity, following this initial transient change, was unaffected in eight out of twelve fibres by alterations in carotid sinus pressure within the range 60-160 mm Hg and carotid body venous flow 10-60 mul./min, blood gas tensions and pH being maintained constant. In the four remaining fibres, chemoreceptor activity increased slightly but significantly as pressure was lowered in this range. Chemoreceptor activity increased in all fibres tested when pressure was lowered below 50-60 mm Hg.4. Chemoreceptor response curves to changes in P(a,O2) (30-450 mm Hg), P(a,CO2) (27-62 mm Hg) or [H(+)](a) (3-7 x 10(-5) m-equiv/l.) were not significantly different whether the carotid body was perfused (a) naturally at the prevalent systemic pressure, (b) artificially at the same pressure, or (c) artificially at one higher pressure, 130 or 140 mm Hg.5. These results indicate that the carotid body chemoreceptors are relatively unaffected by sustained changes in arterial pressure or in total carotid body flow within the physiological range.