The relationship of the third and fourth heart sounds to transmitral flow

The third and fourth heart sounds in humans (S3 and S4) are believed to be caused by vibration of the ventricle and surrounding structures powered by the deceleration of transmitral blood flow during diastole. The authors modelled the kinematics of heart sound generation using a forced, damped, nonlinear harmonic oscillator with time-dependent stiffness. The oscillator´s forcing term utilized the deceleration portion of the clinical Doppler transmitral E (early) and A (atrial) wave. The model´s predictions are: (1) an S3 and S4 should always be present, (2) the higher the E and A wave deceleration, the more likely an S3 or S4 is audible, (3) a sufficient deceleration rate and coupling to the oscillator is required for audibility. Model based image processing and estimation theory permitted comparison to simultaneous transmitral Doppler and phonocardiographic data from patients with and without audible S3´s and S4´s and showed excellent agreement