Group 1	Unexposed and normoxic rats served as control
Group 2	Hypobaric hypoxia (HH) exposure (25,000 ft) for 6 h
Group 3	Hypobaric hypoxia (HH) exposure (25,000 ft) for 12 h
Group 4	Hypobaric hypoxia (HH) exposure (25,000 ft) for 24 h