Fig. 4. Comparative effects of 1 minimum alveolar concentration (MAC) sevoflurane (SEVO; current study) and 1 MAC halothane 7(HAL) on peak expiratory neuronal activity (ΔFcon, left bars ) and peak phrenic nerve activity (ΔPPA (right bars ). The depression of Fconby 1 MAC sevoflurane was not different (n.s.) from the depression by 1 MAC halothane. The depression of PPA by the anesthetic was significantly larger than the depression of Fcon, both for 1 MAC halothane (##P < 0.01) and for 1 MAC sevoflurane (§§§P < 0.001). In addition, the depression of PPA was significantly larger with 1 MAC sevoflurane than with 1 MAC halothane (**P < 0.01).