Study objectives: The objectives of this study were (1)
to evaluate the way in which nasal continuous positive airway pressure
(CPAP) therapy influences the relative humidity (rH) of inspired air;
and (2) to assess the impact on rH of the addition of an integrated
heated humidifier or a full face mask to the CPAP circuitry.
Design: The studies were performed in 25 patients with
obstructive sleep apnea syndrome receiving long-term nasal CPAP therapy
and complaining of nasal discomfort. During CPAP administration,
temperature and rH were measured in the mask either during a night’s
sleep for 8 patients or during a daytime study in which the effects of
mouth leaks were simulated in 17 patients fitted with either a nasal
mask (with or without humidification) or a face mask alone.
Setting: University hospital sleep disorders center.
Measurements and results: Compared with the values obtained
with CPAP alone, integrated heated humidification significantly
increased rH during the sleep recording, both when the mouth was closed
(60 ± 14% to 81 ± 14%, p < 0.01) and during mouth leaks
(43 ± 12% to 64 ± 8%, p < 0.01). During the daytime study, a
significant decrease in rH was observed with CPAP alone. Compared with
the values measured during spontaneous breathing without CPAP
(80 ± 2%), the mean rH was 63 ± 9% (p < 0.01) with the mouth
closed and 39 ± 9% (p < 0.01) with the mouth open. The addition
of heated humidification to CPAP prevented rH changes when the mouth
was closed (82 ± 12%), but did not fully prevent the rH decrease
during simulation of mouth leaks (63 ± 9%) compared with the
control period (80 ± 2%, p < 0.01). Finally, attachment of a
face mask to the CPAP circuitry prevented rH changes both with the
mouth closed (82 ± 9%) and with the mouth open (84 ± 8%).
Conclusions: These data indicate that inhaled air dryness
during CPAP therapy can be significantly attenuated by heated
humidification, even during mouth leaks, and can be totally prevented
by using a face mask.