The ventilatory response to arousal from sleep is not fully explained by differences in CO2 levels between sleep and wakefulness

1. Arousal from sleep is associated with transient stimulation of ventilati on above normal waking levels that predisposes to subsequent breathing inst ability and central apnoea. The transient hyperpnoea at. arousal is normall y explained by differences in arterial partial pressure of CO2 (P-a,P-CO2) between sleep and wakefulness, with a, higher P-a,P-CO2 in sleep leading to stimulation of ventilation at arousal according to the awake ventilatory r esponse to CO2. Surprisingly, however, the validity of this current model i n fully explaining the increased ventilation at arousal from sleep has not, been directly tested. 2. This study tests the hypothesis that. the level of ventilation at. arous al from non-rapid eye movement (non-REM) sleep is greater than that produce d by elevating P-a,P-CO2 in wakefulness to the sleeping level, i.e. the ven tilation predicted by the current model. 3. Studies were performed in five clogs. Inspired CO2, was used to increase end-tidal partial pressure of CO2 (P-ET,P-CO2) in wakefulness amp measure the ventilators response. The same P-ET,P-CO2 was then maintained in non-RE M sleep. Ventilation was measured for 10 breaths before and after arousal f rom non-REM sleep induced by a 72 dB tone. 4. Arousal from sleep produced a transient surge in ventilation of 1.42 +/- 0.35 l min(-1) (P = 0.005). This increased ventilation was due to arousal from sleep per se as the tone alone produced no change in awake ventilation . In support of the hypothesis, ventilation at. wake onset from sleep was g reater by 0.83 +/- 0.28 l min(-1) (P = 0.031) than the ventilation elicited in wakefulness by raising P-ET,P-CO2 to the sleeping level. 5. The results show that >50% of the increase in ventilation at wake onset. from deep is not attributable to the awake ventilatory response to the ele vated P-a,P-CO2 that was previously present in sleep. This result leads to important modifications of the physiological model currently used to explai n the ventilatory consequences of arousal from sleep.