Time-varying pulmonary arterial input impedance via wavelet decomposition

Wavelet decomposition is proposed as a novel approach for determining pulmonary arterial input impedance throughout the breathing cycle. The canine pulmonary arterial input impedance was evaluated throughout the ventilatory cycle at 5, 10, and 15 cmH₂O of positive end-expiratory pressure. The impedance spectrum was obtained by Fourier transformation of wavelets generated by decomposing the pulmonary arterial pressure and flow waveforms. With wavelet decomposition, each heart beat is viewed individually as a transient pulse rather than as an interval within a continuous function of pressure and flow. The advantage of using this approach is the ability to obtain stable estimates of input impedance spectra with high-frequency resolution over the entire frequency range with only a limited data set of pressure and flow decomposed to wavelets as short as singular extrapolated cardiac cycles. This method was used to define the changes of input impedance that occur during the ventilatory cycle. Results show that the impedance spectrum undergoes notable changes during the breathing cycle and demonstrate the utility of the proposed method.