Department of Obstetrics and Gynecology, Medical University of Graz, Austria.
Physiol Meas. 2012 Jun;33(6):1015-26. doi: 10.1088/0967-3334/33/6/1015. Epub 2012 May 4.
Impedance cardiography (ICG) has been proposed to estimate the stroke volume (SV) and cardiac output (CO) in various medical indications. The aim of this study was to explore the reliability of ICG during pregnancy with respect to SV and CO measurements. Blood pressure, heart rate and thoracic impedance were monitored during the course of pregnancy and related ICG patterns analyzed. We determined thoracic impedance (Z(0)), left ventricular ejection time (LVET) and the maximum value of the first derivative of the impedance waveform (dZ/dt)(max) beat-to-beat. The two main components of non-invasive SV estimation, LVET and (dZ/dt)(max), decreased in week 35 relative to week 12 by 7.6% ± 4.8% and by 36.0% ± 14.0%, respectively, based on a decrease in R-R interval of 9.9% ± 9.7%, whereas changes in Z(0) did not play a significant role. Furthermore, the decrease of (dZ/dt)(max) was greater in the third compared to the second trimester of pregnancy. Taking into account an 18.2% ± 6.8% body weight increase, the calculated SV decreased in week 35 relative to week 12 by 19.2% ± 14.3%. The normalized term ((dZ/dt)(max))/Z(0) explained 85-94% of the variance of SV change after week 20. These results were confirmed for fixed R-R interval at a constant value across the repeated measurements. Based on beat-to-beat analysis of the main components of non-invasive SV estimation by ICG, measured repeatedly throughout normal pregnancy, we conclude that SV calculations render invalid data. Our findings strongly suggest that CO cannot be reliably assessed with ICG in pregnant women.
阻抗心动描记法（ICG）已被提议用于估计各种医学适应症下的每搏量（SV）和心输出量（CO）。本研究旨在探讨妊娠期间 ICG 在 SV 和 CO 测量方面的可靠性。在妊娠过程中监测血压、心率和胸阻抗，并分析相关的 ICG 模式。我们确定了胸阻抗（Z（0））、左心室射血时间（LVET）和阻抗波形的一阶导数的最大值（dZ/dt）（max）逐拍。非侵入性 SV 估计的两个主要组成部分，LVET 和（dZ/dt）（max），分别比第 12 周减少了 7.6%±4.8%和 36.0%±14.0%，这是基于 R-R 间隔减少了 9.9%±9.7%，而 Z（0）的变化并没有起到重要作用。此外，（dZ/dt）（max）的下降在孕晚期比孕中期更大。考虑到 18.2%±6.8%的体重增加，与第 12 周相比，第 35 周的计算 SV 减少了 19.2%±14.3%。在固定的 R-R 间隔不变的情况下，归一化项（（dZ/dt）（max））/Z（0）可以解释 SV 变化的 85-94%。这些结果在正常妊娠期间通过 ICG 对非侵入性 SV 估计的主要成分进行重复测量时得到了证实。基于对 ICG 测量的非侵入性 SV 估计的主要成分的逐拍分析，我们得出结论，SV 计算会产生无效数据。我们的研究结果强烈表明，在孕妇中不能可靠地使用 ICG 评估 CO。
