Continuous positive airway pressure and lung inflation in sleep apnea patients

Background. It was shown in normals that an important decrease in upper air way resistance can be obtained with continuous positive airway pressure (CP AP). It was suggested that lung inflation in patients with sleep apnea synd rome (SAS) could also be a mechanism of action of CPAP. Objective: In the p resent study we wanted to evaluate the effects of nocturnal CPAP on the day time lung function pattern in patients with SAS. Methods: We measured arter ial blood gases and possible changes in static lung volumes in 57 SAS patie nts (37 with normal lung function, 10 with COPD and 10 with restrictive lun g disease) after at least one month of CPAP therapy. Results: A significant increase in PaO2 (from 79 to 84 mm Hg, p = 0.01) and a decrease in AaDO(2) (from 23 +/- 1 to 16 +/- 1, p < 0.01) was only observed in SAS patients wi th normal lung function. This improved gas exchange was parallelled by a sm all but non significant change in the FRC (from 96.5 +/- 3.2 to 105.4 +/- 3 .7%pred, p = 0.07) and TLC (from 101.3 +/- 1.7 to 104.1 +/- 1.4%pred, p = 0 .15). Similar changes in TLC and FRC were also observed in SAS patients wit h obstructive and restrictive lung disease. Conclusions: Chronic nocturnal CPAP therapy can improve daytime gas exchange and may influence lung inflat ion during the daytime. The small changes seem to be a functional effect bu t of no clinical relevance. Copyright (C) 2001 S. Karger AG, Basel.