Maximum oxygen consumption and heat loss facilitation in small homeotherms by He-O2.

Abstract

ROSENMANN, MARIO, AND PETER MORRISON. Maximum oxygen consumption and heat loss facilitation in small homeotherms by He-02 . Am. J. Physiol. 226(3) : 490495. 1974.-The high thermal conductance of an 80% He-20y0 02 atmosphere was used to elicit maximum metabolism (Mmax) in moderate cold in species ranging from 7-g pygmy mice (Baiomys taylori) to 250-g white rats, including redpolls (Acanthis J?ammea), two vesper mice (Calomys d&la, C. callosus), tundra voles (Microtus oeconomus), and four strains of Mus musculus. Values slightly exceeded those in similar animals using other methods to confirm the low metabolic ratio (Mmax/M, in) in rodents (4-8 X). Submaximal values at higher temperatures defined thermal conductance in He-02 and air. In different species the ratios of these conductances ranged from 1.4 to 2.6, differences which relate to the extent and quality of the respective insulation. M,,, was obtained at 13-70°C warmer in He-02 than required in air for the same metabolic effort. Avoidance of low-temperature technology and freezing injury, elimination of treadmills and training in running, prompt attainment of M,,., (3-10 min after He-02 exposure), and obviation of shaving or wetting procedures are advantages of the present technique.