Hsia C C, Herazo L F, Ramanathan M, Johnson R L
Department of Medicine, University of Texas Southwestern Medical Center, Dallas 75235-9034, USA.
J Appl Physiol (1985). 1995 Apr;78(4):1612-6. doi: 10.1152/jappl.1995.78.4.1612.
In dogs during exercise, respiratory rate can reach 200 breaths/min, blood temperature can exceed 42 degrees C, and hematocrit can approach 60%. To determine whether these changes significantly affect the measurement of cardiac output by the acetylene rebreathing method (QcRB), we compared estimates of QcRB with those measured by thermodilution and Fick (QcFI) techniques in nine dogs at rest and during steady-state exercise on a treadmill up to near-maximal workloads. Solubility of acetylene in blood was corrected to the simultaneously measured blood temperature and hematocrit. Results were also adjusted for mixing efficiency. Up to a QcFI of 20 l/min, QcRB was not significantly different from QcFI (P > 0.05). However, cardiac output measured by thermodilution was consistently higher than those measured by the other techniques (P < 0.0001). We conclude that the overall agreement between QcRB and QcFI estimates supports the validity of the rebreathing technique under exercise conditions where body temperature and hematocrit are changing rapidly and the breathing pattern is unrestrained. Systematic error by the thermodilution technique may be related to a variety of methodological issues as well as possible dissipation of cooling into the myocardial tissue and subsequent incomplete washout.
在运动的犬类中，呼吸频率可达200次/分钟，体温可超过42摄氏度，血细胞比容可接近60%。为了确定这些变化是否会显著影响乙炔重呼吸法（QcRB）测量心输出量，我们在9只犬处于静息状态以及在跑步机上进行稳态运动直至接近最大负荷时，将QcRB的估计值与通过热稀释法和菲克法（QcFI）测量的值进行了比较。根据同时测量的体温和血细胞比容对乙炔在血液中的溶解度进行了校正。结果也针对混合效率进行了调整。在QcFI达到20升/分钟之前，QcRB与QcFI没有显著差异（P>0.05）。然而，通过热稀释法测量的心输出量始终高于通过其他技术测量的值（P<0.0001）。我们得出结论，QcRB和QcFI估计值之间的总体一致性支持了在体温和血细胞比容快速变化且呼吸模式不受限制的运动条件下重呼吸技术的有效性。热稀释技术的系统误差可能与多种方法学问题以及冷却可能消散到心肌组织中并随后冲洗不完全有关。
