Optimal time-window duration for computing time/frequency representations of normal phonocardiograms in dogs.
The optimal duration of the time-window used to compute the time-frequency representation (spectrogram) of the phonocardiogram was studied in four dogs by using intracardiac and thoracic measurements of the PCG. The power and cross-spectrograms of the intracardiac and thoracic PCGs were computed using a fast Fourier transform algorithm and a sine-cosine window with 10 per cent decaying functions. A coherence spectrogram was also computed for each dog to study the linear relationship between the two signals and determine the optimal time-window duration. Results show that the optimal range of the time-window duration is between 16 and 32 ms. A time-window shorter than 16 ms spreads out low-frequency components into the higher frequencies and generates a spectrographic representation with poor frequency resolution (> or = 62.5 Hz). A window larger than 32 ms increases the frequency resolution but smears the spectrographic representation of the signal in the time domain and thus cannot correctly reflect the time-varying properties of the signal. In both cases, the amplitude of the coherence function computed between the left ventricular and the thoracic phonocardiograms is overestimated.
Jamous
G
G
Laboratory of Biomedical Engineering, University of Montreal, Quebec, Canada.
Durand
L G
LG
Langlois
Y E
YE
Lanthier
T
T
Pibarot
P
P
Carioto
S
S
D000818:Animals; D004285:Dogs; D008955:Models, Cardiovascular; D010701:Phonocardiography / Q000379:methods*; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors