Time-frequency representations of the diaphragmatic movement measured by a surface piezoelectric contact sensor in dogs

The diaphragm movement (DM) signal acquired by means a surface piezoelectric contact sensor (HP21050A) applied on the costal wall is analyzed in this work. For this purpose, the DM signal was related with the diaphragm length changes, measured using a pair of piezoelectric crystals implanted into the costal diaphragm (sonomicrometry). Experiments were performed in three pentobarbital-anesthetized mongrel dogs, during spontaneous ventilations with an inspiratory load. Time-frequency characteristics of diaphragm muscle movement (DM) signal were analyzed by means of eight time-frequency representations (TFRs): the spectrogram (SPEC), two scalograms using a Morlet wavelet (SCALl) and a wavelet generated from the DM signal (SCAL2), the Wigner-Ville distribution (WVD), the Choi-Williams distribution (CHWD), two generalized exponential distributions (GED1 and GED2), and the Born-Jordan distribution (BJD). The contraction velocity of the diaphragm muscle, estimated with the diaphragm length (DL) signal was related with the instantaneous frequency of the DM signal, estimated using bilinear TFRs (WVD, CHWD, GEDs and BJD). Moderate relationship was found using classical TFRs (SPEC and SCALs). The GEDl was the TFR that shown the best results for this specific application.