Department of Biomedical Engineering, Tampere University of Technology, Biokatu 6, FIN-33520 Tampere, Finland.
Physiol Meas. 2011 Mar;32(3):337-45. doi: 10.1088/0967-3334/32/3/005. Epub 2011 Feb 14.
The transthoracic electrical impedance signal originates from the cardiac and respiratory functions. In impedance pneumography (IP) the lung function is assessed and the cardiac impedance signal, cardiogenic oscillations (CGOs), is considered an additive noise in the measured signal. In order to accurately determine pulmonary flow parameters from the signal, the CGO needs to be attenuated without distorting the respiratory part of the signal. We assessed the suitability of a filtering technique, originally described by Schuessler et al (1998 Ann. Biomed. Eng. 26 260-7) for an esophageal pressure signal, for CGO attenuation in the IP signal. The technique is based on ensemble averaging the CGO events using the electrocardiogram (ECG) R-wave as the trigger signal. Lung volume is known to affect the CGO waveforms. Therefore we modified the filtering method to produce a lung volume-dependent parametric model of the CGO waveform. A simultaneous recording of ECG, IP and pneumotachograph (PNT) was conducted on 41 healthy, sitting adults. The performance of the proposed method was compared to a low-pass filter and a Savitzky-Golay filter in terms of CGO attenuation and respiratory signal distortion. The method was found to be excellent, exhibiting CGO attenuation of 35.0±12.5 dB (mean±SD) and minimal distortion of the respiratory part of the impedance signal.
经胸电阻抗信号源于心脏和呼吸功能。在阻抗容积描记法（IP）中，肺功能得到评估，而心脏阻抗信号，心源性震荡（CGO），被认为是测量信号中的附加噪声。为了从信号中准确确定肺流量参数，需要衰减 CGO，而不使信号的呼吸部分失真。我们评估了一种滤波技术的适用性，该技术最初由 Schuessler 等人描述（1998 年，《生物医学工程年鉴》26 260-7），用于食管压力信号中的 CGO 衰减。该技术基于使用心电图（ECG）R 波作为触发信号对 CGO 事件进行集合平均。众所周知，肺容积会影响 CGO 波形。因此，我们修改了滤波方法，以产生与肺容积相关的 CGO 波形参数模型。对 41 名健康、坐姿成年人同时记录心电图（ECG）、IP 和呼吸量计（PNT）。从 CGO 衰减和呼吸信号失真的角度，将所提出的方法与低通滤波器和 Savitzky-Golay 滤波器进行了比较。结果表明，该方法性能优异，CGO 衰减为 35.0±12.5 dB（平均值±标准差），对阻抗信号的呼吸部分的失真最小。
