title: The mechanism of the physiologic disappearance of the third heart sound with aging.
abstract: The third heart sound (S3) is often present in children and adolescents but is not present in most adults. Applying at the left ventricle a mathematical model, the mechanism of the disappearance of S3 was studied employing the frequency analysis of the sound and echocardiographic data. The existence of a significant correlation between the spectrum energy of S3 and the diameter and thickness of the left ventricle at the moment of S3 in 25 healthy subjects (aged 21 +/- 7 years) allowed us to interpret the origin of S3 based on a viscoelastic oscillating system. Once the left ventricle starts vibrating it behaves as a simple physical model composed of a mass (m), a spring (k) and a viscous element. The abrupt deceleration of the blood mass (m) against the left ventricular walls (k) triggers the vibration of the system according to the equation Fd = 1/2 pi.square root of k/m.square root of 1 - zeta 2, where Fd is the natural damped frequency and zeta is the damping factor. The equation shows that the vibrating system can oscillate only if zeta is < 1. During the growth of the individual the increased myocardial mass may lead to augmented viscous forces causing a gradual increase in zeta until the system becomes overdamped and consequently unable to vibrate causing the disappearance of S3.
authors.affiliation: Istituti di Medicina Interna I, Università di Ferrara, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Longhini
authors.forename: D
authors.initials: D
authors.lastname: Scorzoni
authors.forename: E
authors.initials: E
authors.lastname: Baracca
authors.forename: M C
authors.initials: MC
authors.lastname: Brunazzi
authors.forename: F
authors.initials: F
authors.lastname: Chirillo
authors.forename: D
authors.initials: D
authors.lastname: Fratti
authors.forename: G F
authors.initials: GF
authors.lastname: Musacci
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D004452:Echocardiography; D006347:Heart Sounds / Q000502:physiology*; D006801:Humans; D008955:Models, Cardiovascular; D008962:Models, Theoretical; D010701:Phonocardiography; D012815:Signal Processing, Computer-Assisted; D016277:Ventricular Function, Left / Q000502:physiology