Control of arterial pressure in conscious, sinoaortic-denervated sheep in normoxia and hypoxia

The contribution of the sinoaortic reflexes to the control of both the mean level and variability of arterial pressure (Pa) and heart rate (HR) was studied in five adult ewes after chronic section of the carotid sinus and aortic depressor nerves (SAD). SAD group responses were compared with a sham-operated group (n = 6). Pa was 15% lower in the SAD group due to a reduction of total peripheral resistance. The standard deviations and coefficients of variation for both Pa and HR obtained by continuous 16-h monitoring (10-s intervals) in the SAD sheep were not significantly different from those of the sham group. Arterial hypoxia (arterial PO₂ = 40 mmHg for 96 h) had no significant influence on the mean values or variability for Pa and HR for either group, although both groups spent more time lying down. Ventilation was unchanged in the SAD group. Thus mean Pa is lower after removal of baroreceptor and chemoreceptor inputs, but the variabilities of both HR and Pa are unaltered during both normoxia and hypoxia in this sedentary species.