验证一个不依赖呼吸商的能量消耗方程。
Validation of an equation for energy expenditure that does not require the respiratory quotient.
机构信息
Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, Washington United States of America.
Department of Medicine, University of Washington, Seattle Washington, United States of America.
出版信息
PLoS One. 2019 Feb 1;14(2):e0211585. doi: 10.1371/journal.pone.0211585. eCollection 2019.
BACKGROUND
Energy expenditure (EE) calculated from respirometric indirect calorimetry is most accurate when based on oxygen consumption (VO2), carbon dioxide production (VCO2) and estimated protein metabolism (PM). EE has a substantial dependence of ~7% on the respiratory quotient (RQ, VCO2/VO2) and a lesser dependence on PM, yet many studies have instead estimated EE from VO2 only while PM has often been ignored, thus reducing accuracy. In 1949 Weir proposed a method to accurately calculate EE without using RQ, which also adjusts for estimated PM based on dietary composition. This RQ- method utilizes the calorimeter airflow rate (FR), the change in fractional O2 concentration (ΔFO2) and the dietary protein fraction. The RQ- method has not previously been empirically validated against the standard RQ+ method using both VO2 and RQ. Our aim was to do that.
METHODS
VO2 and VCO2 were measured repeatedly in 8 mice fed a high protein diet (HPD) during exposure to different temperatures (n = 168 measurements of 24h gas exchange). The HPD-adjusted RQ+ equation was: EE [kcal/time] = VO2 [L/time]×(3.853+1.081RQ) while the corresponding RQ- equation was: EE = 4.934×FR×ΔFO2. Agreement was analyzed using the ratios of the RQ- to RQ+ methods along with regression and Bland-Altman agreement analyses. We also evaluated the standard equation using the dietary food quotient (FQ) of 0.91 as a proxy for RQ (FQ+ method).
RESULTS
Ratio analysis revealed that the mean error of the RQ- method was only 0.11 ± 0.042% while the maximum error was only 0.21%. Error using the FQ+ method was 4 -and 10-fold greater, respectively. Bland-Altman analysis demonstrated that the RQ- method very slightly overestimates EE as RQ decreases. Theoretically, this error can be eliminated completely by imposing an incurrent fractional oxygen concentration at a value only slightly greater than the atmospheric level.
CONCLUSIONS
The Weir 'RQ-free' method for calculating EE is a highly valid alternative to the 'gold standard' method that requires RQ. The RQ- approach permits reduced cost and complexity in studies focused on EE and provides a way to rescue EE measurement in studies compromised by faulty CO2 measurements. Practitioners of respirometry should consider adjusting EE calculations for estimated protein metabolism based on dietary composition.
背景
基于耗氧量（VO2）、二氧化碳生成量（VCO2）和估计的蛋白质代谢（PM）计算得出的能量消耗（EE）通过呼吸测热间接量热法计算时最为准确。EE 对呼吸商（RQ，VCO2/VO2）的依赖性约为 7%，对 PM 的依赖性较小，但许多研究仍仅根据 VO2 估计 EE，而常常忽略 PM，从而降低了准确性。1949 年，Weir 提出了一种无需使用 RQ 即可准确计算 EE 的方法，该方法还根据饮食成分调整估计的 PM。该 RQ-方法利用量热计气流率（FR）、氧分数变化（ΔFO2）和饮食蛋白分数。该 RQ-方法以前并未根据同时使用 VO2 和 RQ 的标准 RQ+方法进行过实证验证。我们的目的是做到这一点。
方法
在暴露于不同温度下（24 小时气体交换测量 168 次），8 只喂食高蛋白饮食（HPD）的老鼠中反复测量 VO2 和 VCO2。HPD 调整的 RQ+方程式为：EE[kcal/time]=VO2[L/time]×（3.853+1.081RQ），而相应的 RQ-方程式为：EE=4.934×FR×ΔFO2。使用 RQ-与 RQ+方法的比值以及回归和 Bland-Altman 一致性分析来分析一致性。我们还使用 0.91 作为 RQ 替代值的饮食食物商（FQ）评估了标准方程（FQ+方法）。
结果
比率分析显示，RQ-方法的平均误差仅为 0.11±0.042%，最大误差仅为 0.21%。使用 FQ+方法的误差分别为 4 倍和 10 倍。Bland-Altman 分析表明，随着 RQ 的降低，RQ-方法略微高估 EE。从理论上讲，通过将传入的氧分数设定为仅略高于大气水平的值，可以完全消除这种误差。
结论
Weir 用于计算 EE 的无 RQ 方法是一种高度有效的替代“金标准”方法，该方法需要 RQ。RQ-方法可以降低研究 EE 时的成本和复杂性，并为因 CO2 测量错误而导致 EE 测量受损的研究提供一种方法。呼吸测热法的从业者应考虑根据饮食成分调整基于估计的蛋白质代谢的 EE 计算。
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