Goran M I, Poehlman E T, Nair K S, Danforth E
Department of Medicine, College of Medicine, University of Vermont, Burlington 05405.
Am J Physiol. 1992 Dec;263(6):E1119-24. doi: 10.1152/ajpendo.2006.263.6.E1119.
Physiological sources of variation in the 2H-to-18O dilution space ratio (DSR) were examined in 34 males and 20 females (4-78 yr; 14.7-143.2 kg; 1.8-61.0% body fat). Dilution spaces were obtained by time 0 extrapolation of isotope washout over 10-14 days, and body composition was obtained by underwater weight (adults) or bioelectrical impedance (children). The mean DSR was 1.050 +/- 0.015 (range 1.029-1.111), significantly higher (P < 0.001) than the traditionally assumed value of 1.029 based on exchange over 4 h. Use of the value 1.029 causes a systematic 8% overestimate of energy expenditure from doubly labeled water, relative to use of the value 1.05. The DSR was not related to body composition or age but was significantly higher (P < 0.05) in males (1.052 +/- 0.016) than in females (1.044 +/- 0.012). This gender effect was not explained by differences in the number of exchangeable hydrogens in the body. We conclude 1) variation in the 2H-to-18O DSR is not explained by body composition but is influenced by the chemical availability of exchangeable hydrogens to undergo exchange; 2) because the DSR is not easily predicted, use of the observed dilution spaces are recommended; 3) if a fixed DSR is used, values of 1.044 and 1.052 are recommended in females and males, respectively.
在34名男性和20名女性（年龄4 - 78岁；体重14.7 - 143.2千克；体脂率1.8 - 61.0%）中研究了2H与18O稀释空间比（DSR）的生理变异来源。通过对10 - 14天内同位素洗脱进行时间0外推获得稀释空间，通过水下称重法（成人）或生物电阻抗法（儿童）获得身体成分。平均DSR为1.050±0.015（范围1.029 - 1.111），显著高于（P < 0.001）基于4小时交换得出的传统假设值1.029。相对于使用1.05的值，使用1.029会导致双标记水能量消耗系统性高估8%。DSR与身体成分或年龄无关，但男性（1.052±0.016）显著高于（P < 0.05）女性（1.044±0.012）。这种性别效应无法通过体内可交换氢数量的差异来解释。我们得出结论：1）2H与18O DSR的变异不能用身体成分来解释，而是受可交换氢进行交换的化学可用性影响；2）由于DSR不易预测，建议使用观察到的稀释空间；3）如果使用固定的DSR，建议女性和男性分别使用1.044和1.052的值。
