title: The effects of altitude associated central apnea on the diagnosis and treatment of obstructive sleep apnea: comparative data from three different altitude locations in the mountain west.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Family Medicine, University of Colorado School of Medicine, Southern Colorado Residency Program, Pueblo, CO, USA. pueo34@earthlink.net
authors.forename: J F
authors.initials: JF
authors.lastname: Pagel
authors.forename: Carol
authors.initials: C
authors.lastname: Kwiatkowski
authors.forename: Bennet
authors.initials: B
authors.lastname: Parnes
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000531:Altitude; D000704:Analysis of Variance; D015331:Cohort Studies; D003120:Colorado; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D017286:Polysomnography / Q000379:methods; D011175:Positive-Pressure Respiration / Q000379:methods; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D017678:Sex Distribution; D020182:Sleep Apnea, Central / Q000175:diagnosis* / Q000453:epidemiology / Q000628:therapy*; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis* / Q000453:epidemiology / Q000628:therapy*; D016896:Treatment Outcome