Figure 1: Tissue structure of the Human Thorax Model. The numbers in the diagram indicate the thickness of the tissue layers in millimeters.
When the thorax is illuminated by the UWB signal emitted by a transmitter, the signal encounters various tissues. The signal propagates from the front through the pulsating heart and then leaves at the back of the thorax. A pulsating heart is subject to the variation of dimensions longitudinally towards its apex (pointed end) during diastole and systole of each cardiac cycle. 26 With reference to the transverse cross-section of human heart 19shown in Figure 2, the parts of the pulsating heart close to its apex and along its short axis the UWB signal is assumed to encounter during its propagation are, the right ventricle (RV) wall, RV cavity, inter ventricular septum, left ventricle (LV) cavity and LV wall. The instantaneous heart dimensions 19 calculated as the sum of the instantaneous dimensions of all the above parts during one cardiac cycle are shown in Figure 3.