Adaptation of anesthetized men to breathing through an inspiratory resistor.

Normal men anesthetized with methoxyflurane rebreathed carbon dioxide under two conditions. In one case they breathed most of the time through a low-resistance circuit and an inspiratory resistor of 40.4 cmH2O/1-s-1 was applied at intervals. In another case they breathed most of the time through the resistor and were allowed occasional free breaths. There were no differences between the two types of runs in tidal volume, respiratory frequency, duration of inspiration of loaded or unloaded breaths, or in amplitude or shape of occlusion pressure waves. It is concluded that the reaction of conscious men to an inspiratory resistive load, consisting of a compensatory augmentation of neural drive to respiratory muscles that does not depend on a chemical stimulus, is absent in anesthetized men.