title: Turbulent stress measurements downstream of three bileaflet heart valve designs in pigs.
abstract: OBJECTIVE
  Mechanical heart valves can cause thromboembolic complications, possibly due to abnormal flow patterns that produce turbulence downstream of the valve. The objective of this study was to investigate whether three different bileaflet valve designs would exhibit clinically relevant differences in downstream turbulent stresses.
  
  
  METHODS
  Three bileaflet mechanical heart valves (Medtronic Advantage), CarboMedics Orbis Universal and St. Jude Medical Standard) were implanted into 19 female 90 kg pigs. Blood velocity was measured during open chest conditions in the cross sectional area downstream of the valves with 10 MHz ultrasonic probes connected to a modified Alfred Pulsed Doppler equipment. As a measure of turbulence, Reynolds normal stress (RNS) was calculated at three different cardiac output ranges (3-4, 4.5-5.5, 6-7 L/min).
  
  
  RESULTS
  Data from 12 animals were obtained. RNS correlated with increasing cardiac outputs. The highest instantaneous RNS observed in these experiments was 47 N/m2, and the mean RNS taken spatially over the cross sectional area of the aorta during systole was between 3 N/m2 and 15 N/m2. In none of the cardiac output ranges RNS values exceeded the lower critical limit for erythrocyte or thrombocyte damage for any of the valve designs.
  
  
  CONCLUSIONS
  Reynolds normal stress values were below 100 N/m2 for all three valve designs and the difference in design was not reflected in generation of turbulence. Hence, it is unlikely that any of the valve designs causes flow induced damage to platelets or erythrocytes.
authors: Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Skejby Sygehus, Brendstrupgaardsvej, 8200 Aarhus, Denmark.
authors: Camilla
authors: C
authors: Nyboe
authors: Jonas A
authors: JA
authors: Funder
authors: Morten H
authors: MH
authors: Smerup
authors: Hans
authors: H
authors: Nygaard
authors: J Michael
authors: JM
authors: Hasenkam