Balouch Jamal, Olfert I Mark, Wagner Peter D, Hopkins Susan R
Department of Medicine, Division of Physiology, University of California, San Diego, La Jolla, California 92093-0623, USA.
Respir Physiol Neurobiol. 2007 Feb 15;155(2):177-83. doi: 10.1016/j.resp.2006.04.009. Epub 2006 May 22.
The open circuit acetylene uptake method is a useful non-invasive means of measuring cardiac output. However, because of accumulation of inhaled acetylene in tissues, the cardiac output uptake is underestimated, if residual acetylene is not allowed to wash out completely in between measurements. We determined the effect of applying a correction factor that estimates mixed venous acetylene concentration from endtidal values to the calculation of cardiac output. This accounts for mixed venous acetylene present during measurements made before complete washout. Six healthy subjects performed steady-state exercise at approximately 30% and 60% of V(O2 max). Cardiac output measurements were made at each exercise intensity using the open circuit acetylene uptake method (inspired [acetylene] approximately 1%), with the first and last measurements having no detectible levels of acetylene in expired gas (reference measurement). Data were also obtained with immediate pre-measurement endtidal concentrations ranging from 3% to 15% of the inspired [acetylene], in random order in between. Oxygen consumption, carbon dioxide production and heart rate did not change significantly during testing at each exercise intensity. Reference cardiac output also did not change significantly and averaged 11.1+/-0.8 L/min at 30% of V(O2 max) and 16.5+/-2.0 L/min at 60% of V(O2 max). Uncorrected cardiac output measurements progressively underestimated cardiac output by 15% at the 3% of inspired endtidal [acetylene] and by over 50% at 15% [acetylene] (p<0.0001). However, when corrected for residual endtidal [acetylene], cardiac outputs were not significantly different from the reference measurements. The results of this study suggest that by accounting for residual endtidal acetylene in mixed venous blood, cardiac output can be accurately measured even when washout of acetylene is incomplete, allowing measurements as often as every 10-15 s.
开路乙炔摄取法是一种有用的非侵入性心输出量测量方法。然而，由于吸入的乙炔在组织中蓄积，如果在测量之间不允许残留的乙炔完全清除，心输出量摄取会被低估。我们确定了应用校正因子的效果，该校正因子根据潮气末值估算混合静脉血乙炔浓度，并将其应用于心输出量的计算中。这考虑了在完全清除之前进行测量时存在的混合静脉血乙炔。6名健康受试者在约30%和60%的最大摄氧量（V(O2 max)）下进行稳态运动。在每个运动强度下，使用开路乙炔摄取法（吸入[乙炔]约为1%）测量心输出量，第一次和最后一次测量时呼出气体中没有可检测到的乙炔水平（参考测量）。在测量前还随机获取了潮气末浓度为吸入[乙炔]的3%至15%的数据。在每个运动强度测试期间，耗氧量、二氧化碳产生量和心率没有显著变化。参考心输出量也没有显著变化，在30%的V(O2 max)时平均为11.1±0.8 L/分钟，在60%的V(O2 max)时平均为16.5±2.0 L/分钟。未校正的心输出量测量在吸入潮气末[乙炔]为3%时逐渐低估心输出量15%，在[乙炔]为15%时低估超过50%（p<0.0001）。然而，当对残留的潮气末[乙炔]进行校正后，心输出量与参考测量值没有显著差异。本研究结果表明，通过考虑混合静脉血中残留的潮气末乙炔，即使乙炔清除不完全，也能准确测量心输出量，允许每隔10 - 15秒进行一次测量。
