The effect of altitude descent on obstructive sleep apnea.

BACKGROUND The present requirement for "at facility" polysomnograms requires many residents in mountain communities to descend in elevation for sleep testing, which may cause misleading results regarding the severity of obstructive sleep apnea (OSA). DESIGN Eleven patients with previously undiagnosed sleep apnea living at an altitude > 2,400 m (7,900 feet) in Colorado underwent diagnostic sleep studies at their home elevation and at 1,370 m (4,500 feet), and 5 of the 11 patients were also studied at sea level. RESULTS The mean (SE) apnea-hypopnea index (AHI) fell from 49.1 (10.5)/h to 37.0 (11.2)/h on descent to 1,370 m (p = 0.022). In the five patients who traveled to sea level, the AHI dropped from 53.8 (13.2)/h at home elevation to 47.1 (14.8)/h at 1,370 m, and to 33.1 (12.6)/h at sea level (p = 0.018). The reduction in AHI was predominantly a reduction in hypopneas and central apneas, with little change in the frequency of obstructive apneas. Duration of the obstructive apneas lengthened with descent. Of eight patients with an AHI < 50/h at their home elevation, two patients had their AHI fall to < 5/h at 1,370 m, and a third patient dropped to < 5/h at sea level, ie, below many physicians' threshold for providing therapy. Patients with the most severe OSA had the least improvement with descent. CONCLUSIONS Because AHI decreases significantly with descent in altitude, polysomnography is most accurately done at the home elevation of the patient. Descent to a sleep laboratory at a lower elevation may yield false-negative results in patients with mild or moderate sleep apnea.