Chemosensitivity and the ventilatory response to airflow obstruction during sleep

There is an accumulating body of evidence which suggests that chemical control of breathing can play a role in destabilizing respiratory rhythm during sleep. We hypothesized that the sleeping ventilatory response to hypercapnia (HCVR) and/or hypoxia (HVR) would predict respiratory events following release of inspiratory airway obstruction (IAO) in normal men during non-rapid-eye-movement (NREM) sleep. We therefore measured HCVR, HVR, and ventilation for three breaths preceding and eight breaths following three totally obstructed inspirations in eight normal subjects during NREM sleep. After IAO, we generally observed transient hyperventilation that resulted in hypocapnia and prolonged expiratory time. We found the initial increase in inspiratory minute ventilation (VI) following IAO to be correlated with HCVR (r = 0.72, P less than 0.05) but not HVR. In addition, the maximum decrease in PCO2 below base line was also related to HCVR (r = 0.83, P less than 0.05). This decrement in PCO2 predicted the subsequent prolongation in expiratory time (TE, r = 0.83, P less than 0.05) that was frequently observed. HCVR tended to predict the prolongation of TE, at the nadir of CO2 (r = 0.69, P = 0.057). In conjunction with this hypocapnia and prolongation of TE, hypoventilation with falling VI was often observed followed by periodic hyper- and hypoventilation. These results suggest that high HCVR may result in ventilatory overshoot following IAO and may contribute to ventilatory instability during sleep.