Basic Concepts

The heart valves are mechanical devices that permit the flow of blood in one direction only. The two cuspid (atrio-ventricular) valves are located between the atria and ventricles, while the two semi-lunar valves are located at the entrance to the pulmonary artery and the great aorta. The cuspid valves prevent blood from flowing back into the atria from the ventricles and the semi-lunar valves prevent it from being regurgitated back into the ventricles from the aorta and pulmonary artery.

Any one of the four valves may lose its ability to close tightly; such a condition is known as valvular insufficiency or regurgitation. On the other hand, stenosis is an abnormality in which the fully open valvular orifice becomes narrowed by scar tissue that forms as a result of valvular disease; thereby the blood flow through the valve results in increased pressure drop across the valve orifice.

Here, we will address ourselves to aspects concerning the noninvasive assessment of valvular pathology, as characterized by its nonlinear constitutive property. In order to do so, we need to incorporate the noninvasive measurements of cardiac mechanical events, associated with valvular mechanics, that are available to us. One such set of measurements constitutes monitoring the geometry of cardiac structures by means of two-dimensional echocardiography. The heart sounds constitute yet another set of noninvasive data which can be utilized.

The acoustic waves (due to cardiac structual vibrations associated with cardiac mechanical events) that are transmitted to the chest contain information on the vibratory source.