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.