Holloway J C, Geiser F
Department of Zoology, School of Biological Sciences, University of New England, Armidale, New South Wales 2351, Australia.
Physiol Biochem Zool. 2001 Mar-Apr;74(2):219-25. doi: 10.1086/319666.
Helox (79% helium and 21% oxygen) has often been used for thermobiological studies, primarily because helium is thought to be metabolically inert and to produce no adverse effects other than increasing heat loss. However, these assumptions have been questioned. As basal metabolic rate (BMR) represents maintenance energy requirements for vital body functions, potential physiological effects of helox should be reflected in changes of BMR. In this study, sugar gliders were subjected to both air and helox atmospheres over a wide range of T(a)'s, including the thermoneutral zone (TNZ), to determine (1) whether helox has any influence other than on heat loss and (2) the maximum heat production (HP(max)) and thermal limits of this species. Although thermal conductance in the TNZ increased in helox, BMR was similar in air and helox (0.55+/-0.07 and 0.57+/-0.06 mL g(-1) h(-1), respectively). The TNZ in helox, however, was shifted upwards by about 3 degrees C. Below the TNZ, sugar gliders were able to withstand an effective temperature of -24.7+/-7.3 degrees C with an HP(max) of 3.14+/-0.36 mL g(-1) h(-1). The low effective temperature tolerated by sugar gliders shows that they are competent thermoregulators despite their apparent lack of functional brown fat. Similarities of BMRs in air and helox suggest that the effect of helox is restricted to an increase of heat loss, and, consequently, helox represents a useful tool for thermal physiologists. Moreover, the lack of increase of BMR in helox despite an increase in thermal conductance of sugar gliders suggests that BMR is not a function of body surface.
氦氧混合气（79%的氦气和21%的氧气）常被用于热生物学研究，主要是因为人们认为氦气在代谢上是惰性的，除了增加热量散失外不会产生其他不良影响。然而，这些假设受到了质疑。由于基础代谢率（BMR）代表维持身体重要功能所需的能量，氦氧混合气的潜在生理效应应反映在BMR的变化上。在本研究中，蜜袋鼯在包括热中性区（TNZ）在内的广泛环境温度（Ta）范围内分别处于空气和氦氧混合气环境中，以确定（1）氦氧混合气除了对热量散失有影响外是否还有其他影响，以及（2）该物种的最大产热（HP(max)）和热极限。尽管在氦氧混合气环境中热中性区的热传导增加，但在空气和氦氧混合气环境中的基础代谢率相似（分别为0.55±0.07和0.57±0.06 mL g(-1) h(-1)）。然而，氦氧混合气环境中的热中性区向上移动了约3摄氏度。在热中性区以下，蜜袋鼯能够承受-24.7±7.3摄氏度的有效温度，最大产热为3.14±0.36 mL g(-1) h(-1)。蜜袋鼯能耐受较低的有效温度，这表明尽管它们明显缺乏功能性褐色脂肪，但仍是有能力的体温调节者。空气和氦氧混合气环境中基础代谢率的相似性表明，氦氧混合气的作用仅限于增加热量散失，因此，氦氧混合气是热生理学家的一个有用工具。此外，尽管蜜袋鼯的热传导增加，但在氦氧混合气环境中基础代谢率并未增加，这表明基础代谢率不是体表的函数。
