INFLUENCE OF ORAL CLONIDINE ON THE VENTILATORY RESPONSE TO ACUTE AND SUSTAINED ISOCAPNIC HYPOXIA IN HUMAN MALES

Animal studies suggest that alpha(2) agonists inhibit the chemorecepto r response to hypoxia. We have examined the effect of oral clonidine o n the ventilatory response to sustained, isocapnic hypoxia (Sp(o2) 79. 7% (so 1.1 %) for 20 min) in eight male subjects. The hypoxic ventilat ory response was measured before and after both clonidine and placebo. Clonidine had no significant effect on baseline ventilation or gas ex change. After clonidine, the acute hypoxic response (AHR) (mean 5.81 ( 95% confidence limits 1.94, 9.68) litre min(-1)) was significantly les s than control (10.40 (5.97, 14.83) litre min(-1)) and hypoxic ventila tory decline (HVD) (3.42(2.35, 4.49) litre min(-1)) was also significa ntly less than control (6.49(3.92, 9.06) litre min(-1)) (P < 0.05). Af ter placebo, AHR was similar to control but HVD was significantly larg er (6.82(5.28, 8.36) litre min(-1)) than control (4.79(3.03, 6.55) lit re 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.