title: The relationship of normal and abnormal microstructural proliferation to the mitral valve closure sound.
abstract: BACKGROUND
  Many diseases that affect the mitral valve are accompanied by the proliferation or degradation of tissue microstructure. The early acoustic detection of these changes may lead to the better management of mitral valve disease. In this study, we examine the nonstationary acoustic effects of perturbing material parameters that characterize mitral valve tissue in terms of its microstructural components. Specifically, we examine the influence of the volume fraction, stiffness and splay of collagen fibers as well as the stiffness of the nonlinear matrix in which they are embedded.
  
  
  RESULTS
  To model the transient vibrations of the mitral valve apparatus bathed in a blood medium, we have constructed a dynamic nonlinear fluid-coupled finite element model of the valve leaflets and chordae tendinae. The material behavior for the leaflets is based on an experimentally derived structural constitutive equation. The gross movement and small-scale acoustic vibrations of the valvular structures result from the application of physiologic pressure loads. Material changes that preserved the anisotropy of the valve leaflets were found to preserve valvular function. By contrast, material changes that altered the anisotropy of the valve were found to profoundly alter valvular function. These changes were manifest in the acoustic signatures of the valve closure sounds. Abnormally, stiffened valves closed more slowly and were accompanied by lower peak frequencies.
  
  
  CONCLUSIONS
  The relationship between stiffness and frequency, though never documented in a native mitral valve, has been an axiom of heart sounds research. We find that the relationship is more subtle and that increases in stiffness may lead to either increases or decreases in peak frequency depending on their relationship to valvular function.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington 98195, USA. deinstein@chla.usc.edu
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Einstein
authors.forename: Karyn S
authors.initials: KS
authors.lastname: Kunzelman
authors.forename: Per G
authors.initials: PG
authors.lastname: Reinhall
authors.forename: Mark A
authors.initials: MA
authors.lastname: Nicosia
authors.forename: Richard P
authors.initials: RP
authors.lastname: Cochran
mesh_terms: D000818:Animals; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D006349:Heart Valve Diseases / Q000175:diagnosis* / Q000503:physiopathology*; D008943:Mitral Valve / Q000503:physiopathology*; D008955:Models, Cardiovascular; D010701:Phonocardiography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D013018:Sound Spectrography / Q000379:methods*; D013223:Statistics as Topic