ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Table 1: Computed slice measurements for average characteristic diameter, oxygen concentration, and the
corresponding Sh number.
Position of
cross-section
Average diameter (mm)
AWA* Oxygen mass
fraction concentration
Sherwood number (Sh)
Proximal 3.59 0.0021187 63.24
Middle 3.61 0.0021235 63.60
Distal 3.81 0.0021218 66.82
* Area-weighted average
5. DISCUSSION
Physiological WSS in porcine arterial vasculature ranges between 0.4 < τ < 1.5 Pa [3]. It
has been proposed that the local value of WSS affects the overall physiological state of
the arterial wall. Locations exposed to shear stress within the physiological range are
thought to atheroprotective and thus cells in these regions remain in their quiescent
state. While endothelium exposed to shear stresses lower than τ, and in zones of
recirculation, are thought to be more susceptible to injury and disease [3].
The current study evaluates the variation of fluid dynamics and oxygen transport (WSS,
helicity, and oxygen concentration) along the stented geometry. It can be seen
qualitatively that regions in the proximal and distal cross-sections with an overall higher
magnitude of WSS (>0.3 Pa) have less NIH (fig. 2). However, it is important to note
that, these locations are at the extremes of the stent, and from the limited data presented
it is impossible to discount the possibility that the tissue response may be influenced by
the physical impact of stent into the arterial wall. Future analysis of additional sections
may provide more insight in this respect.
The Sh numbers in Table 1 indicate that there is a lower overall distribution of oxygen
within the proximal section. We are working towards further representation of the
oxygen gradient from entry to exit of the stent by means of a point-wise plot of Sh along
the axial length of the stent. In addition, the value obtained for the oxygen concentration
(Table 1) is lower in the proximal section when compared with the two successive (mid
and distal) sections (fig. 3a). This may be due to the sudden expansion caused by the
stent, which results in flow separation at the expansion point [9].
As there is evidence of disturbed flow patterns adjacent to the struts, a greater number
of struts may also affect the Sh value [10]. In addition, noticeable helicity, shown as
positive- or negative-direction Dean vortices, were observed in the proximal and middle
sections of the domain (fig. 3b); this occurrence may be enhanced due to the presence of
the over-expanded stent within the volume. It is important to note that the regions with a
positive helical directional flow are observed near zones with less NIH, while the
locations with negative (opposite) helical directional flow may induce larger regions of
disturbed flow and thus greater NIH. The identification of Dean vortex patterns within
stented geometries have been demonstrated in previous studies [6], but the correlation
with oxygen concentration patterns remains unclear.