Automated measurement and frequency analysis of the pneumocardiogram

The flow pneumocardiogram (PnCG), ie, measurement of cardiogenic gas movement in and out of the lung during apnea, was transduced by an in-line, high-gain pneumotachograph. A portion of the differentiated PnCG, the dPn/dt IJ wave, has been shown previously to correlate closely with left ventricular function. A simple analog device was designed and tested to measure the dPn/dt IJ amplitude on a practical beat-to-beat basis. Frequency-power spectral analysis showed the PnCG to be a low frequency phenomenon with the systolic component in the 9-to-10-Hz range. Appropriate band-pass filtering of the PnCG and its applicability as an intraoperative monitoring device are presented.