Verschoor N, Woltjer H H, van der Meer B J, de Vries P M
Department of Pulmonary Medicine, Free University Hospital, Amsterdam, Netherlands.
Physiol Meas. 1996 Feb;17(1):29-35. doi: 10.1088/0967-3334/17/1/003.
Impedance cardiography is a reliable method for estimating stroke volume (SV). Breathing, however, causes artefacts, which can be avoided by measuring during breath holding. This study investigated whether SV determination is accurate during breath holding. Twelve healthy subjects were tested in the supine position at rest and during two levels of exercise: 100 and 200 W. Averaged SV values were monitored by means of impedance cardiography before and after endexpiratory breath holding. During breath holding, SV measurement was on a beat-to-beat basis. An obvious decrease in SV during breath holding was noticed, being significant only during exercise (mean decrease of 38% at 100 W and 58% at 200 W). The rest measurements were repeated with open and closed glottis, which yielded the same results. This indicates that the SV decrease was not caused by a Valsalva-like manoeuvre. The mean SV value calculated by means of impedance cardiography for the total breath hold period was significantly lower than the SV during breathing, both at rest (91.7 +/- 2.4%) and at 100 W (90.5 +/- 7.0%). From this study it can be concluded that averaging of the impedance signal, measured while the subject is breathing, is preferential to measuring during breath holding, because the latter condition systematically underestimates SV.
阻抗心动图是一种估算每搏输出量（SV）的可靠方法。然而，呼吸会产生伪影，通过在屏气期间进行测量可以避免这种情况。本研究调查了屏气期间SV测定是否准确。对12名健康受试者在静息仰卧位以及两种运动水平（100瓦和200瓦）下进行了测试。在呼气末屏气前后，通过阻抗心动图监测平均SV值。在屏气期间，逐搏测量SV。注意到屏气期间SV明显下降，仅在运动期间显著（100瓦时平均下降38%，200瓦时平均下降58%）。在声门开放和闭合的情况下重复进行静息测量，结果相同。这表明SV下降不是由类似瓦尔萨尔瓦动作引起的。通过阻抗心动图计算的整个屏气期间的平均SV值显著低于呼吸期间的SV，无论是在静息时（91.7±2.4%）还是在100瓦时（90.5±7.0%）。从这项研究可以得出结论，对受试者呼吸时测量的阻抗信号进行平均，比屏气期间测量更可取，因为后一种情况会系统性地低估SV。
