Influence of oral clonidine on the ventilatory response to acute and sustained isocapnic hypoxia in human males

Abstract

Animal studies suggest that α2 agonists inhibit the chemoreceptor response to hypoxia. We have examined the effect of oral clonidine on the ventilatory response to sustained, isocapnic hypoxia (Sp(O2) 79.7% (SD 1.1%) for 20 min) in eight male subjects. The hypoxic ventilatory response was measured before and after both clonidine and placebo. Clonidine had no significant effect on baseline ventilation or gas exchange. After clonidine, the acute hypoxic response (AHR) (mean 5.81 (95% confidence limits 1.94, 9.68) litre min-1) was significantly less than control (10.40 (5.97, 14.83) litre min-1) and hypoxic ventilatory decline (HVD) (3.42(2.35, 4.49)litre min-1) was also significantly less than control (6.49(3.92, 9.06) litre min-1) (P < 0.05). After placebo, AHR was similar to control but HVD was significantly larger (6.82(5.28, 8.36) litre min-1) than control (4.79(3.03, 6.55) litre min-1) (P<0.05). Thus clonidine reduced both AHR and HVD but the absolute level of ventilation at the end of hypoxia was unchanged.