Influence of longterm CPAP therapy on CO2 drive in patients with obstructive sleep apnea

According to recent publications, the values of the hypercapnic ventilatory responses (HCVR) in normocapnic obstructive sleep apnea (OSA) patients are highly variable, but they are usually within the normal range. In our stud y, CPAP therapy during 1 month did not seem to influence the HCVR [Verbraec ken, J., De Backer, W., Willemen, M., De Cock. W., Wittesaele, W., Van de H eyning, P., 1995. Respir. Physiol. 101, 279-287]. It is, however, not well studied whether long term (1 year) CPAP therapy can influence HCVR in normo capnic patients. Therefore, we evaluated the effect of 1 year CPAP therapy on CO, drive in 20 OSA patients. The slope of HCVR (SHCVR) changed from 2.3 5 +/- 0.21 L min(-1) mmHg(-1) (control) to 1.66 +/- 0.16 L min(-1) mmHg(-1) (P = 0.04), but the mean within subject coefficient of variation in repeat ed measurements of SHCVR in treated and untreated OSA patients was not stat istically different. Pa-O2 increased from 72 +/- 2 mmHg to 80 +/- 2 (1 year ) mmHg. We conclude that CPAP therapy improves daytime gas exchange in norm ocapnic OSA and may possibly decrease CO2 drive (slope) after a treatment p eriod of 1 year. (C) 2000 Elsevier Science B.V. All rights reserved.