Fig. 2. Hypoxic ventilatory responses (AHRs) in 10 subjects measured during three different sessions. Session 1: run 1 = control AHR; run 2 = AHR during 0.1 minimum alveolar concentration (MAC) isoflurane inhalation; run 3: AHR during 0.1 MAC isoflurane inhalation but after pretreatment with antioxidants. Antioxidant pretreatment reverses the inhibiting effect of isoflurane on the hypoxic response in all subjects. Session 2: run 1 = control AHR; run 2 = AHR during 0.1. MAC isoflurane; run 3: AHR + isoflurane but after pretreatment with placebo. Placebo does not alter the inhibiting effect of isoflurane on the AHR. Session 3: run 1 = control AHR; run 2 = AHR during sham isoflurane; run 3: AHR during sham isoflurane but after pretreatment with antioxidant. There is no influence of sham isoflurane and antioxidant on the AHR.