Environmental parameters in the experimental evaluation of a respiratory aggression

Acute nitrogen normobaric hypoxic challenges, resulting in an approximately 50% overall survival, were performed in young adult male and female heterozygous OF1 mice under various environmental conditions. The time required to obtain 50% survival was 20 min for a constant pO2 of 42 Torr, and 151 min when pO2 was progressively lowered by nitrogen flushing from 159 to 16.5 Torr. In LD12:12 synchronized animals, survival was significantly (P less than 0.001) less when hypoxia was performed during the light (L) than during the dark (D) phase. Lowering the ambient temperature from 33.8 to 13.2 degrees C increased the length of the progressive hypoxia necessary to obtain a 50% survival of the mice by 1.7 times, and diminished the final pO2 from 35 to 12 Torr. Grouping and crowding both decreased hypoxic survival. A previous stress (starvation) diminished hypoxic resistance of mice, while a preceding hypoxia, carbon monoxide inhalation, or sodium cyanide injection had the opposite effect. In all instances, OF1 females were more resistant than males. Most of these variations can be related to differences in respiratory exchanges, locomotor activity and aggressiveness, which are dependent upon the various experimental environmental parameters.