[RESULTS] The median ( quartiles ) apnea-hypopnea index at 490 m was 4.6 / h ( 2.3 ; 7.9 ) , values at 1,630 and 2,590 m , day 1 and 2 , respectively , were 7.0 / h ( 4.1 ; 12.6 ) , 5.4 / h ( 3.5 ; 10.5 ) , 13.1 / h ( 6.7 ; 32.1 ) , and 8.0 / h ( 4.4 ; 23.1 ) ; corresponding values of mean nocturnal oxygen saturation were 96 % ( 95 ; 96 ) , 94 % ( 93 ; 95 ) , 94 % ( 93 ; 95 ) , 90 % ( 89 ; 91 ) , 91 % ( 90 ; 92 ) , P < 0.05 versus 490 m , all instances .