Study objectives: This study documents both the incidence and effects of central apnea on diagnosis and treatment of OSA at different altitudes in the Mountain West and substantiates the clinical impression that individuals living at altitude with moderate to severe OSA are significantly more difficult to treat with PAP.
Methods: Split-night polysomnography was compared between sites for patients with a diagnostic AHI > 15 living at 1421 meters (Site 1; N = 150), at 1808 m (Site 2; N = 150) and at 2165 m (Site 3; N = 142). The quality of PAP titration obtained was rated, based on AASM clinical guidelines, from 1 = optimal to 4 = unacceptable. Patients developing central apneas during PAP therapy (CAI > 5.0) were titrated with an alternative O(2) > CPAP/Bilevel PAP protocol.
Results: The mean number of central apneas in the diagnostic portion of studies was significantly higher (p < 0.01) at Sites 2 (19.26) and 3 (12.36) than at Site 1 (3.11). Mean numbers of central apneas/h developing on treatment with PAP varied from 4.8/h at Site 1, to 9.79/h at Site 2, to 19.25/h at Site 3 (p < 0.001). At Site 1, 10.6% had a central apnea index (CAI) > 5.0, while 22% met this criterion at Site 2 and 38.7% at Site 3 (Site 3 vs Site 1, p = 0.01; Site 2 vs Site 1, p = 0.02). Rated titration quality varied significantly between sites. At Site 1, mean titration quality was 1.437 (SD 0.821); for Site 2, 1.569 (SD 0.96), and for Site 3, 1.772 (SD 1.025). Titration quality at Site 3 was significantly worse than at Site 1 (t = 3.22, p < 0.01) and at Site 2 (t = 2.55, p < 0.02). Repeat titration requirement differed significantly (p = 0.025). Analysis of covariance comparing titration across 3 altitude levels, controlling for age, was significant for the effect of altitude (p = 0.017). Utilizing the alternative O(2) > C-PAP/Bi-PAP protocol in patients with CAI > 5.0 developing on PAP treatment, an overall optimal or good titration (AASM criteria) was attained in 75/79 (95%) of titrated patients.
Conclusions: This study demonstrates that central apnea becomes significantly more common at increasing altitude in both diagnostic and treatment portions of split-night polysomnography in patients with significant OSA. An apparent exponential increase in the percentage of OSA patients with a CAI > 5.0 occurs with increasing altitude. Altitude associated central apnea has a significant negative effect on the quality of OSA treatment obtained during PAP titration for patients living at the altitudes addressed in this study.
Keywords: CPAP; Obstructive sleep apnea; altitude; central apnea; oxygen.