Loeppky J A
Lovelace Respiratory Research Institute, Albuquerque, NM 87108, USA.
Aviat Space Environ Med. 1998 Apr;69(4):368-73.
Measurements of pulmonary gas exchange are especially sensitive to low levels of CO2 in the environment; this is an important consideration in measurements in enclosed spaces.
In order to determine the responses to these low levels, subjects were exposed in five studies to partial pressures of inspired CO2 (PICO2) of 5.7 and 7.5 mmHg for 30 min during basal conditions at rest and to 5.4, 9.4 and 15 mmHg during a progressive exercise to VO2max on a cycle ergometer.
In the two resting studies, total pulmonary ventilation and alveolar ventilation were increased by 19% at 7.5 mmHg (1.1% sea level equivalent) and 10% at 5.4 mmHg (0.8% equivalent), with clear evidence of CO2 retention in both studies. During exercise at 15 mmHg the VO2max was reduced significantly by 13%, compared with air at about the same maximal ventilation, but VO2max was not reduced at 9.4 mmHg. A 6% decrease in VO2max at a PICO2 of 5.4 mmHg may have resulted from these subjects being less fit. The maximal CO2 output and respiratory exchange ratio in the three exercise studies was always lower with CO2 than corresponding air measurements, indicating CO2 storage. Evaluation of submaximal measurements provided an equation for predicting ventilation as a function of PICO2 and VO2/VO2max and demonstrated that ventilation during submaximal exercise is increased significantly by the lowest CO2 level. BP and heart rate responses during submaximal and maximal work were not predictably altered by CO2 at these levels.
These studies demonstrate that minimal CO2 levels have significant influences on pulmonary ventilation during rest and exercise and must be considered in acute studies in confined spaces such as space cabins. The inspired CO2 should be stated when ventilation measurements are reported under these conditions.
肺气体交换测量对环境中低水平的二氧化碳特别敏感；这是在封闭空间测量时的一个重要考虑因素。
为了确定对这些低水平二氧化碳的反应，在五项研究中，让受试者在静息基础状态下暴露于吸入二氧化碳分压（PICO2）为5.7和7.5 mmHg的环境中30分钟，以及在使用自行车测力计进行递增运动至最大摄氧量（VO2max）期间暴露于5.4、9.4和15 mmHg的环境中。
在两项静息研究中，总肺通气量和肺泡通气量在7.5 mmHg（相当于海平面的1.1%）时增加了19%，在5.4 mmHg（相当于海平面的0.8%）时增加了10%，两项研究中均有明显的二氧化碳潴留证据。在15 mmHg运动时，与大约相同最大通气量的空气相比，VO2max显著降低了13%，但在9.4 mmHg时VO2max没有降低。在PICO2为5.4 mmHg时VO2max降低6%可能是由于这些受试者身体状况较差所致。在三项运动研究中，二氧化碳条件下的最大二氧化碳排出量和呼吸交换率总是低于相应的空气测量值，表明有二氧化碳潴留。对次最大测量值的评估提供了一个根据PICO2和VO2/VO2max预测通气量变化的方程，并表明在次最大运动期间最低水平的二氧化碳会显著增加通气量。在这些水平下，次最大和最大运动期间的血压和心率反应不会因二氧化碳而发生可预测的改变。
这些研究表明，最低水平的二氧化碳对静息和运动期间的肺通气有显著影响，在诸如太空舱等封闭空间的急性研究中必须予以考虑。在这些条件下报告通气测量值时应说明吸入二氧化碳的情况。
