Quantitation of the turbulent stress distribution downstream of normal, diseased and artificial aortic valves in humans

Abstract

Damage to blood corpuscles seems to be related to the magnitude and exposure time of the turbulent shear stresses (TSS). According to in vitro studies the critical TSS level for lethal erythrocyte and thrombocyte damage is 150-400 N/m2, for exposure times within physiological ranges. To study the distribution of TSS in the human ascending aorta, a hot-film anemometer needle probe was used to register blood velocities at 41 evenly distributed measuring points in the cross-sectional area 5-6 cm downstream of the aortic annulus. Measurements were made in the ascending aorta after normal aortic valves (prior to coronary bypass surgery), after stenotic aortic valves, and after implantation of either St. Jude Medical or Starr Edwards Silastic Ball valves. Three-dimensional visualization of velocity profiles were performed and Reynolds normal stresses (RNS) were calculated within 50-ms overlapping time windows in systole. By coordinating the mean RNS for each time window and for all 41 measuring points, 2-dimensional color-coded mapping of the RNS distribution was made. Based on the velocity profiles and the RNS distribution a relative blood damage index (RBDI) was calculated to incorporate the magnitude and exposure time for RNS in the entire cross-sectional area into one parameter. Turbulent shear stresses were estimated by using a previously determined correlation equation between RNS and TSS. After normal aortic valves, RNS was below 4 N/m2.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro assessment of flow patterns and turbulence intensity in prosthetic heart valves using generalized phase‐contrast MRI

“…Modalities such as thermal anemometry, intra-luminal pulsed Doppler and laser Doppler anemometry can provide high quality velocity information but are either highly invasive or impossible to use in vivo (11)(12)(13). In clinical practice, the gold standard for assessment of prosthetic heart valves are two-dimensional (2D) ultrasound and uni-directional Doppler, but these modalities are limited in the assessment of turbulent flow.…”

Turbulent stress measurements downstream of three bileaflet heart valve designs in pigs☆

“…This means that even though turbulent shear stress values are lower than the critical threshold level alteration may still occur. RNS values measured preoperatively in human beings by Nygaard et al [9] were below 4 N/m 2 . The mean RNS values for all three valve types in this study are similar to the mean RNS values measured in native valves in 17 pigs by Hasenkam et al [14].…”

“…While the St. Jude Medical and the Carbomedics valves have been tested widely through the past years [9,13,14,22] turbulent stresses have so far not been measured in the newer Medtronic Advantage valve.…”

“…In healthy individuals with normal valves Reynolds normal stresses (RNS) have been measured to be below 4 N/m 2 [9].…”

“…Several studies have tested different mechanical valves in order to identify optimal design and orientation to minimize interference with blood flow [9,[13][14][15][16]. In order to minimize formation of TSS it is necessary to identify a valve design that interferes minimally with the blood flow.…”