Factors affecting the physical performance of the rat in hyperbaric environments

Experiments were designed to partition the effect of inspired oxygen tension (PIO2), gas density (rho), and ambient pressure (P) at rest and during exercise in rats. At rest oxygen uptake (VO2) was reduced by 19.5% (P less than 0.01) in 3 ATA air and by 32.1% (P less than 0.01) in 10 ATA air from 1 ATA air control of 29.3 +/- 1.21 (SE) ml/min.kg; there was no difference in VO2 between 1, 3, and 10 ATA He mixtures containing 20% O2. During exercise, VO2 was depressed by 36.2% (P less than 0.01) in 3 ATA air from 1 ATA air value of 55.3 +/- 3.23 ml/min.kg; VO2 was unaffected in 3 ATA He containing 20% O2 as compared to that of 46.5 +/- 2.43 ml/min.kg at 1 ATA He-O2 ambient. These VO2 values were compared to that obtained from normoxic ambients for separation of effects of elevated PIO2, P, and rho on VO2 at rest and during exercise. The effect of PIO2 was deduced by comparing VO2 in normoxic and hyperoxic He and N2 at a given P and rho. The density effect was obtained by comparing the VO2 in various densities at a given P and PIO2. The P effect was obtained by comparing the VO2 in various ambient pressures at a given rho and PIO2. Summation of the effects of P, rho, and PIO2 sufficiently approximates the changes in VO2 at rest. The same procedure underestimates the actually measured VO2 in all N2 ambients.