title: In-vivo turbulent stresses of bileaflet prosthesis leakage jets.
abstract: OBJECTIVE
  Previous studies of leakage jet turbulence have been carried out in vitro, using a Newtonian fluid to simulate blood and large, rigid approximations to the chambers of the heart. The study aim was to apply an in-vivo method of quantifying leakage jet turbulence to a variety of bileaflet mechanical heart valves, and thereafter to determine the effects of exercise and valve design on turbulent shear stresses within leakage flow.
  
  
  METHODS
  Bileaflet prostheses sewn to a manual traversing device were implanted in the mitral position of 29 pigs of body weight ca. 90 kg. Pulsed Doppler ultrasound was used to acquire velocity measurements within the leakage jets detected 1 mm upstream of the housing. Analytical techniques were used to estimate peak velocities and maximum turbulent shear stresses from these velocity measurements.
  
  
  RESULTS
  Maximum turbulent shear stress was found to rise with increasing ventricular pressure. No leakage turbulence was found from a valve with relatively small leakage gap widths. The Medtronic Parallel valve was found to have considerable significant leakage flow disturbance, even under low ventricular pressure conditions. Similar maximum turbulent shear stress magnitudes were estimated in the leakage jets of the St. Jude Medical, CarboMedics and Sorin Bicarbon valves at medium ventricular pressure conditions. The maximum turbulent shear stresses estimated in these experiments were lower than those found in previous in-vitro measurements.
  
  
  CONCLUSIONS
  Exercise raises the turbulent shear stresses of leakage flow substantially. Hinge design and leakage gap width also affect the magnitudes of these stresses. Leakage flow turbulence may be less damaging to the blood than was previously thought, and is considerably less damaging than forward-flow turbulence.
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Arhus University Hospital, Skejby Sygehus, Arhus, Denmark. brandontravis2001@yahoo.com
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Travis
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Christensen
authors.forename: Morten
authors.initials: M
authors.lastname: Smerup
authors.forename: Morten S
authors.initials: MS
authors.lastname: Olsen
authors.forename: J Michael
authors.initials: JM
authors.lastname: Hasenkam
authors.forename: Hans
authors.initials: H
authors.lastname: Nygaard
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D005260:Female; D006350:Heart Valve Prosthesis; D019918:Heart Valve Prosthesis Implantation / Q000295:instrumentation / Q000379:methods; D008943:Mitral Valve / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D023421:Models, Animal; D008955:Models, Cardiovascular; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013552:Swine; D018608:Ultrasonography, Doppler; D017725:Ventricular Pressure / Q000502:physiology