Influence of longterm CPAP therapy on CO(2) 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 study, CPAP therapy during 1 month did not seem to influence the HCVR [Verbraecken, J., De Backer, W., Willemen, M., De Cock, W., Wittesaele, W., Van de Heyning, P., 1995. Respir. Physiol. 101, 279-287]. It is, however, not well studied whether long term (1 year) CPAP therapy can influence HCVR in normocapnic patients. Therefore, we evaluated the effect of 1 year CPAP therapy on CO(2) drive in 20 OSA patients. The slope of HCVR (SHCVR) changed from 2.35+/-0.21 L min(-1) mmHg(-1) (control) to 1.66+/-0.16 L min(-1) mm Hg(-1) (P=0.04), but the mean within subject coefficient of variation in repeated measurements of SHCVR in treated and untreated OSA patients was not statistically different. Pa(O(2)) increased from 72+/-2 mm Hg to 80+/-2 (1 year) mm Hg. We conclude that CPAP therapy improves daytime gas exchange in normocapnic OSA and may possibly decrease CO(2) drive (slope) after a treatment period of 1 year.