Impact of arousal threshold and respiratory effort on the duration of breathing events across sleep stage and time of night.

PURPOSE

The frequency and duration of breathing events are influenced by sleep stage and time of day. In the present study we examined if these modifications are linked to adaptations in the arousal threshold and/or the magnitude of respiratory effort during and immediately after breathing events.

METHODS

Participants with sleep apnea slept for 3h in the evening and morning. For breathing events detected during these sessions the rate of change of respiratory effort, maximum respiratory effort immediately prior to termination of an event, and the maximum tidal volume and the minimum partial pressure of end-tidal carbon dioxide (PCO) immediately following an event were measured.

RESULTS

The rate of change of respiratory effort was similar in N2 compared to N1 but the maximum respiratory effort immediately prior to event termination was greater (-10.7±1.2 vs. -9.6±1.0cmHO/s, P<0.05). Likewise, tidal volume was increased (1169±105 vs. 1082±100ml, P<0.05) and PCO was decreased (37.0±0.8 vs. 37.7±0.8mmHg P<0.05) following events in N2 compared to N1. A similar tidal volume and PCO response was evident following events in the morning compared to the evening independent of sleep stage.

CONCLUSIONS

We conclude that alterations in the arousal threshold, reflected by an increase in respiratory effort at event termination, coupled to increases in tidal volume and reductions in PCO contribute to modifications in event duration and frequency associated with variations in sleep state or time of night.