title: Monodimensional estimation of maximum Reynolds shear stress in the downstream flow field of bileaflet valves.
abstract: OBJECTIVE
  Turbulent flow generated by prosthetic devices at the bloodstream level may cause mechanical stress on blood particles. Measurement of the Reynolds stress tensor and/or some of its components is a mandatory step to evaluate the mechanical load on blood components exerted by fluid stresses, as well as possible consequent blood damage (hemolysis or platelet activation). Because of the three-dimensional nature of turbulence, in general, a three-component anemometer should be used to measure all components of the Reynolds stress tensor, but this is difficult, especially in vivo. The present study aimed to derive the maximum Reynolds shear stress (RSS) in three commercially available prosthetic heart valves (PHVs) of wide diffusion, starting with monodimensional data provided in vivo by echo Doppler.
  
  
  METHODS
  Accurate measurement of PHV flow field was made using laser Doppler anemometry; this provided the principal turbulence quantities (mean velocity, root-mean-square value of velocity fluctuations, average value of cross-product of velocity fluctuations in orthogonal directions) needed to quantify the maximum turbulence-related shear stress.
  
  
  RESULTS
  The recorded data enabled determination of the relationship, the Reynolds stresses ratio (RSR) between maximum RSS and Reynolds normal stress in the main flow direction. The RSR was found to be dependent upon the local structure of the flow field.
  
  
  CONCLUSIONS
  The reported RSR profiles, which permit a simple calculation of maximum RSS, may prove valuable during the post-implantation phase, when an assessment of valve function is made echocardiographically. Hence, the risk of damage to blood constituents associated with bileaflet valve implantation may be accurately quantified in vivo.
authors.affiliation: Laboratory of Biomedical Engineering, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Grigioni
authors.forename: Carla
authors.initials: C
authors.lastname: Daniele
authors.forename: Giuseppe
authors.initials: G
authors.lastname: D'Avenio
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barbaro
mesh_terms: D015150:Echocardiography, Doppler; D006350:Heart Valve Prosthesis; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008955:Models, Cardiovascular; D008962:Models, Theoretical; D011474:Prosthesis Design; D011673:Pulsatile Flow / Q000502:physiology*; D013314:Stress, Mechanical