Carotid chemoreceptor response to increases in CO 2 output

Abstract

The effect on carotid chemoreceptor activity of alterations in Pa CO 2 oscillations produced by venous CO 2 loading via the small intestines was studied in anaesthetised cats, which were paralysed and ventilated at constant frequency. Changes in Pa CO 2 oscillations were assessed from continuously recorded oscillations of arterial pH. Chemoreceptor activity was averaged over 20–50 pH cycles to determine the amplitude (csnd ampl) and mean level (csnd mean) of the respiratory fluctuation in discharge frequency during control and CO 2 loaded periods. Two groups of 5 cats were studied. In both group, the amplitude of the Pa CO 2 oscillations increased by an overall average of 74.5% (standard error, (SE = 9.2) with minimal change in mean Pa CO 2 (average increase 0.7 mm Hg), in response to an increase in V̇ CO 2 of 77.5% (SE = 7.4). When isoxia was maintained (Group 1) csnd ampl increased by 51.3% (SE = 11.1) and csnd mean by 17.3% (SE = 7.8). In Group 2, Pa O 2 rose by 16.7 mm Hg (SE =1.5) during CO 2 loading and both csnd ampl and csnd mean decreased by 7.4% (SE = 9.3) and 2.3% (SE = 13.3) respectively. The results demonstrate a sensitivity of chemoreceptors to changes in V̇ CO 2 which is influenced by small changes in Pa O 2 .