Role of the carotid bodies in ventilatory acclimation to chronic hypoxia by the awake cat.

Steady-state breathing patterns during air and hypoxia (PIO2 = 84 Torr) were measured in awake cats in the following conditions: (1) during 7 months of exposure to air following carotid body resection (CBR; N = 6); (2) during 7 months of hypobaric hypoxia (PIO2 = 84 Torr; N = 5) following CBR; (3) during 5 months of exposure to hypobaric hypoxia (N = 4) while intact and then following CBR. Also, in groups (1) and (2) the aortic nerves were sectioned (ANX) at the end of the acclimation periods. The results show that the awake cat hypoventilates if the carotid bodies have been removed, and hypoxic sensitivity is reduced during long-term exposures to either hypoxia or normoxia. ANX caused a slight increase in respiratory frequency, indicating a minor role for the aortic bodies. CBR after acclimation to hypoxia resulted in decreased tidal volume but no change in respiratory frequency. The slight ventilatory acclimation to hypoxia in CBR cats was solely due to increased respiratory frequency. The phenomenon of 'hypoxic tachypnea' was modulated by acclimation, indicating that the effect of hypoxic acclimation upon respiratory frequency is due to central mechanisms.