RESUMEN
The present study aimed to evaluate sleep architecture at 4300m in a sample of 10 healthy Indian lowlanders, mean age 25.7±5.1 yrs. Polysomnography on two consecutive nights each was performed at sea level and 4300 m, the first night for adaptation and the second one for actual recording. Total sleep time reduced from 433.33±8.95 to 412.06±13.13 minutes (P<0.0005), sleep latency increased from 11.56±6.85 to 22.22±7.95 minutes (P<0.0025), deep NREM sleep (S3+S4) reduced from 79.56±28.45 to 45.39±25.32 minutes (P<0.01), light NREM sleep (S1+S2) increased from 272.94±20.63 to 296.72±23.24 minutes (P<0.05), REM decreased from 80.89±7.65 to 69.94±11.30 minutes (P<0.02) and periodic breathing was present in 4 of 10 participants on the second night at 4300 m. Decreased sleep quality (P<0.0005) and increased sleep disturbances (P<0.0005) were reported in subjective ratings at high altitude. Changes in sleep architecture similar to but of a greater magnitude are present on the second night of staged induction to 4300 m, than reported at 3500 m in our earlier study.