Role of chemosensitivity in intrathoracic pressure changes during obstructive sleep apnea.

We tested the hypothesis that the awake ventilatory response to hypoxia and hypercapnia may contribute to the variability of respiratory effort developed in response to upper airway obstruction in obstructive sleep apnea syndrome. The polygraphic recordings of 38 patients diagnosed as having obstructive sleep apnea on the basis of an apnea+hypopnea index greater than 10 were examined. All subjects received hypoxic and hypercapnic ventilatory tests the day before the nocturnal polysomnography. Thirty apneas during non-rapid eye movement (NREM) sleep and at least 10 apneas during rapid eye movement sleep were analyzed. For each considered apnea, we measured esophageal pressure (Pes) swings during the first three breaths preceding apnea and during the first three and last three occluded efforts occurring during the apnea. We considered as indices of respiratory effort the overall increase from the minimum to the maximum Pes (delta Pes), the rate of increase of Pes during apnea (RPes), and the maximal respiratory effort at the end of apnea (Pes max fin). In NREM sleep, all three indices of respiratory effort were correlated positively with the awake ventilatory response to hypoxia or hypercapnia and with the apnea index. No correlation was found between the indices of respiratory effort and body mass index, age, pulmonary function tests, awake blood gases, apnea duration, and apnea desaturation. In rapid eye movement sleep, none of the considered variables predicted the degree of respiratory effort. In conclusion, our results suggest that the degree of ventilatory response to upper airway occlusion in obstructive sleep apnea may be influenced by the sensitivity of central neural drive to chemical stimuli.