Estimation of Acoustic Transfer Function of the Heart by Analyzing the Heart Sounds Simultaneously Detected on the Chest Wall and in the Esophagus

This paper proposes a new method to estimate a time varying acoustic transfer function of a heart by using the two acoustic transfer functions. One is a transfer function from the wall surface of a chest to the esophagus through a chest and a heart. The transfer function is estimated by calculating the cross spectra between the applied vibration signal and the heart sound detected in the esophagus, each of which is picked up while the vibration is applied to the wall surface of a chest. The other transfer function also Indicates the transfer characteristics from the wall surface of a chest to the esophagus through a chest and a heart. However, this transfer function Is estimated from the two heart sounds simultaneously detected on the chest wall and in the esophagus while the vibration is not applied, By using these signals and the transfer functions between them, we obtain a transfer function of a heart by removing the influence due to the transfer function of a chest. This time varying transfer function of a heart obtained by the proposed method is available in various fields such as noninvasive measurement of internal pressure of a heart and medical treatments of hypertrophic cardiomyopathy and myocardial infarction.