Hornby L, Coates A L, Lands L C
Division of Respiratory Medicine, Montreal Children's Hospital-McGill University, Quebec, Canada.
J Appl Physiol (1985). 1995 Sep;79(3):1032-8. doi: 10.1152/jappl.1995.79.3.1032.
Cardiac output (CO) during exercise can be determined noninvasively by using the indirect Fick CO2-rebreathing technique. CO2 measurements for this technique are usually performed with an infrared analyzer (IA) or mass spectrometer (MS). However, IA CO2 measurements are susceptible to underreading in the face of high O2 concentrations because of collision broadening. We compared an IA (Ametek model CD-3A) with a MS (Marquette model MGA-1100) to see the effect this would have on mixed venous PCO2 (PVCO2) and CO measurements. After calibration with room air and a gas mixture of 5% CO2-12% O2-83% N2, both devices were tested with three different gas mixtures of CO2 in O2. For each gas mixture, IA gave lower CO2 values than did the MS (4.1% CO2: IA, 3.85 +/- 0.01% and MS, 4.13 +/- 0.01%; 9.2% CO2: IA, 8.44 +/- 0.07% and MS, 9.19 +/- 0.01%; 13.8% CO2: IA, 12.57 +/- 0.15% and MS, 13.82 +/- 0.01%). Warming and humidifying the gases did not alter the results. The IA gave lower values than did the MS for eight other medical gases in lower concentrations of O2 (40-50%). Equilibrium and exponential rebreathing procedures were performed. Values determined by the IA were > 10% higher than those determined by the MS for both rebreathing methods. We conclude that all IAs must be checked for collision broadening if they are to be used in environments where the concentration of O2 is > 21%. If collision broadening is present, then either a special high O2-CO2 calibration curve must be constructed, or the IA should not be used for both arterial PCO2 and PVCO2 estimates because it may produce erroneously low PVCO2 values, with resultant overestimation of CO.
运动期间的心输出量（CO）可通过使用间接Fick二氧化碳重呼吸技术进行无创测定。该技术的二氧化碳测量通常使用红外分析仪（IA）或质谱仪（MS）进行。然而，由于碰撞加宽，在高氧浓度情况下，IA二氧化碳测量容易出现读数偏低的情况。我们将一台IA（阿美特克CD - 3A型号）与一台MS（马奎特MGA - 1100型号）进行比较，以观察这对混合静脉血二氧化碳分压（PVCO2）和心输出量测量的影响。在用室内空气和5%二氧化碳 - 12%氧气 - 83%氮气的混合气体校准后，两台设备用三种不同的氧气中二氧化碳混合气体进行测试。对于每种混合气体，IA得出的二氧化碳值均低于MS（4.1%二氧化碳：IA为3.85±0.01%，MS为4.13±0.01%；9.2%二氧化碳：IA为8.44±0.07%，MS为9.19±0.01%；13.8%二氧化碳：IA为12.57±0.15%，MS为13.82±0.01%）。对气体进行加热和加湿并未改变结果。对于其他八种低氧浓度（40 - 50%）的医用气体，IA得出的值也低于MS。进行了平衡和指数重呼吸程序。对于两种重呼吸方法，IA得出的值比MS得出的值高>10%。我们得出结论，如果要在氧气浓度>21%的环境中使用，所有IA都必须检查是否存在碰撞加宽。如果存在碰撞加宽，那么要么必须构建一条特殊的高氧 - 二氧化碳校准曲线，要么IA不应用于动脉血二氧化碳分压和PVCO2估计，因为它可能会产生错误的低PVCO2值，从而导致心输出量的高估。
