Nguyen T, de Jonge L, Smith S R, Bray G A
Pennington Biomedical Research Center, Baton Rouge, Louisiana, USA.
Med Biol Eng Comput. 2003 Sep;41(5):572-8. doi: 10.1007/BF02345320.
A robust algorithm for pull-calorimeters that provides a rapid response to changes in respiratory gas exchange has been implemented. Metabolic plateaus (over 20 min), such as that generated by steady treadmill exercise, can be measured accurately (< 2.0% error for an energy expenditure level of 16.7 kJ min(-1)). The time resolution for changes between plateaus can be accurately found with 1 min discrimination. Implementation required only software changes but no structural or instrumentation changes to the chamber. The algorithm was based on the one developed for the push-calorimeter at the Sahlgrenska Hospital in Sweden. The method utilises published equations for the rate of O2 consumption and CO2 production in the chamber, along with techniques for suppressing noise and identifying trends. Using the exact solution of the equations for steady state, the O2 concentrations from the preceding 30 min period are fitted to two connected exponential segments, of variable length, using the least-squares method. The smoothed O2 concentration and associated time derivative are then determined for the time point 15 min earlier and substituted into the respiration equations. The CO2 concentrations are subjected to the same analysis. The process is repeated every minute, and the newly computed rates of O2 consumption and CO2 production, as well as metabolic rate, are then presented. Gas injection tests proved that the chamber can respond instantaneously to a change from one steady state of respiration to another and correctly averages repeated changes in respiration with periods less than 15min (< 1.4% error for simulated, alternating O2 consumption levels of 0.81 min (-1) and 0.01 min). The successful integration of the algorithm into the Pennington chambers allows for traditional 24 h energy expenditure measurements and various metabolic experiments requiring rapid responses.
已实现一种用于拉式热量计的强大算法，该算法能对呼吸气体交换的变化做出快速响应。代谢平台期（超过20分钟），比如由稳定的跑步机运动产生的平台期，可以被精确测量（对于16.7 kJ min⁻¹的能量消耗水平，误差<2.0%）。平台期之间变化的时间分辨率可以通过1分钟的辨别准确得出。实施该算法仅需软件更改，而无需对测试舱进行结构或仪器更改。该算法基于瑞典萨尔格伦斯卡医院为推式热量计开发的算法。该方法利用已发表的关于测试舱内氧气消耗率和二氧化碳产生率的方程，以及抑制噪声和识别趋势的技术。使用稳态方程的精确解，采用最小二乘法将前30分钟期间的氧气浓度拟合为两个长度可变的相连指数段。然后确定提前15分钟时间点的平滑氧气浓度及其相关的时间导数，并代入呼吸方程。二氧化碳浓度也进行同样的分析。每分钟重复此过程，然后呈现新计算出的氧气消耗率、二氧化碳产生率以及代谢率。气体注入测试证明，测试舱能够瞬间响应从一种呼吸稳态到另一种呼吸稳态的变化，并能正确平均周期小于15分钟的重复呼吸变化（对于模拟的交替氧气消耗水平0.81 min⁻¹和0.01 min，误差<1.4%）。该算法成功集成到彭宁顿测试舱中，使得传统的24小时能量消耗测量以及各种需要快速响应的代谢实验成为可能。
