Neural control of airflow profile during hypoxia in sleep and wakefulness

Airflow profile is often overlooked when characterizing respiratory pattern, although some profiles are theoretically more efficient than others. We studied airflow profiles, diaphragmatic activity (DIA) and the activity of augmenting inspiratory (I_AUG) neurons in the ventral medulla of unanesthetized cats breathing either 21% O₂ or 10-12% O₂ in N₂ during wakefulness (W), non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. We hypothesized that a change in airflow profile might be an adaptive response to hypoxia. During hypoxia in W and NREM sleep, the sawtooth profile characteristic of normoxia changed to a more efficient constant flow profile in inspiration and expiration. In REM sleep, expiratory airflows were not constant but instead decayed throughout the phase. The efficient airflow profile can be explained by DIA and I_AUG neural activity both of which showed (1) an early onset while there was still expiratory flow, (2) an increase in inspiration and (3) persistence during early expiration. In REM sleep persistence of activity during early expiration was less. We conclude that reshaped neural activity causes more efficient airflow profiles in response to hypoxia.