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.