Howard L S, Barson R A, Howse B P, McGill T R, McIntyre M E, O'Connor D F, Robbins P A
University of Oxford, University Laboratory of Physiology, United Kingdom.
J Appl Physiol (1985). 1995 Mar;78(3):1088-91. doi: 10.1152/jappl.1995.78.3.1088.
Although techniques for the short-term control of end-tidal gases exist, the lack of a satisfactory technique for longer-term control of the end-tidal gases has limited protracted physiological experiments of this nature. We have constructed a chamber in which subjects can be comfortable for many hours while having their end-tidal gas composition monitored and controlled. The system for controlling the end-tidal gas composition is based on a principle described by Swanson and Bellville (J. Appl. Physiol. 39: 377-385, 1975) in which end-tidal PO2 (PETO2) and PCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 from the desired values are corrected by a feedback mechanism that adjusts the inspired gas composition accordingly. End-tidal and inspired gas tensions are measured via a nasal catheter connected to a mass spectrometer. A computer averages the end-tidal and inspired gas tensions and, at 5-min intervals, adjusts the gas composition inside the chamber. During 8 h of isocapnic hypoxia, the system held the 5-min average value for PETO2 within 2 Torr of the desired value (55 Torr) and the value for PETCO2 within 0.35 Torr of the desired value (the resting value for each subject) in four subjects.
虽然存在用于短期控制呼气末气体的技术，但缺乏一种令人满意的用于长期控制呼气末气体的技术，这限制了此类长期生理实验。我们构建了一个舱室，受试者在其中可以舒适地待上数小时，同时其呼气末气体成分会受到监测和控制。用于控制呼气末气体成分的系统基于斯旺森和贝尔维尔（《应用生理学杂志》39: 377 - 385, 1975）所描述的原理，即监测呼气末氧分压（PETO2）和二氧化碳分压（PETCO2），并且监测实际的PETO2和PETCO2与期望值的偏差，通过一种反馈机制进行校正，该机制会相应地调整吸入气体成分。呼气末和吸入气体张力通过连接到质谱仪的鼻导管进行测量。一台计算机对呼气末和吸入气体张力进行平均，并每隔5分钟调整舱室内的气体成分。在4名受试者进行8小时等碳酸血症性低氧过程中，该系统使PETO2的5分钟平均值保持在期望值（55 Torr）的2 Torr范围内，使PETCO2的值保持在期望值（每个受试者的静息值）的0.35 Torr范围内。
