Eighteen patients with OSA living at < @ m discontinued CPAP therapy during studies in Zurich ( @ m ) and during two sojourns of @ days in the Swiss Alps ( @ days at @,@ m and @ day at @,@ m ) separated by a @-week washout period at < @ m. Patients received acetazolamide ( @ @ mg/d ) or placebo at altitude in a randomized , double-blind , crossover design .