Fig. 1

Intermittent hypoxia treatment (IHT) protocols. a The apparatus for IHT was composed of a chamber, in which mice were habituated, connected with an injection tube and an evacuation tube. The injection tube was connected to bottled N₂ gas and an air pump through a switching apparatus with a solenoid valve and timers, by which gas was controlled for injection into the chamber. b Time course of fraction of inspired O₂ (FIO₂) during IHT. FIO₂ was reduced to 5% by 1 min of pure N₂injection, and FIO₂ was increased to 21% by 2 min of room air injection. The black box indicates the duration of N₂ injection, and the white box indicates the duration of room air injection. c The IHT protocol was composed of 3 min cycles, which included of 1 min of pure N₂ injection followed by 2 min of room air injection. Cycles were repeated from 9:00 to 17:00. The remainder of the day (16 h) was composed of normoxia treatment. The IH5D group was exposed to IHT for 5 days, and the IH5DR2 group was exposed to IHT for 5 days, followed by normoxia treatment for 2 days. The IH28D group was exposed to IHT for 28 days. The black box indicates repetition of the 3 min cycles for 8 h. The white box indicates normoxia treatment