Respiratory control during sleep and the development of nocturnal hypoxia in patients with obstructive sleep apnea hypopnea syndrome

Objective It is assumed that the reduced ventilatory control during sleep may be related to the nocturnal hypoxia in patients with obstructive sleep apnea hypopnea syndrome (OSAHS) and daytime CO_2 retention. Methods Oxygen desaturation index(ODI_4),sleep time spent when SaO_2 was below 90% (SIT_ 90 ),the lowest SaO_2(LSaO_2) and the mean SaO_2(MSaO_2) during sleep were measured in 24 OSAHS patients with daytime PaCO_2≥45 mm Hg and 39 with PaCO_245 mm Hg. Hypoxic(ΔP_ 0.1 /ΔSaO_2) and hypercapnic (ΔP_ 0.1 /ΔPaCO_2) responsiveness were measured in 11 eucapnic and 4 hypercapnic patients during wakefulness,NREM and REM sleep stages. Results Compared with the eucapnic patients,all the hypercapnic patients had more severe hypoxia during sleep ( P 0.05). Although both groups had similar chemical responsiveness during wakefulness,the hypercapnic patients had lower ΔP_ 0.1 /ΔSaO_2 and ΔP_ 0.1 /ΔPaCO_2 during both REM and NREM sleep ( P 0.05). Conclusion The depressed chemical responsiveness during sleep plays an important role in the development of nocturnal hypoxia in OSAHS patients with daytime CO_2 retention.