Biomedical Engineering Reference
In-Depth Information
mm/s
0.00
0.38
0.78
1.16
1.56
(a)
(b)
FIgure 23.8
(See color insert.)
(a) Simulated blood perfusion of the human hand. (Reproduced from
Shao HW et al.,
Computer Methods in Biomechanics and Biomedical Engineering
, 2012. With permission.)
(b) Vasculature in the human hand. (From http://www.zcool.com.cn/ZMjEzNjg4.html.)
Figure 23.8a represents the distribution of Darcy's velocity at the steady state. The distribution of
Darcy's velocity indicates that (a) blood flow in the tissue has a high velocity near the arteries, and
(b) in the fingertip the perfusion rate, which is directly proportional to Darcy's velocity, is higher
than in other parts of the hand due to the large number of microvessels in the fingertip. Figure 23.8b
shows a casting specimen of the human hand, whereby it can be seen that the predicted blood perfu-
sion is in favorable agreement with the microvasculature.
23.5 FInIte element analySIS oF blood Flow and
temPerature durIng dIgItal thermal monItorIng
In the DTM test, hyperemic blood flow for healthy people can reach a peak value that is higher
than that for people who are at risk of cardiovascular events, since higher hyperemic blood perfu-
sion values correspond to arteries that are capable of experiencing larger levels of vasodilatation.
In order to simulate the fingertip temperature in the DTM test in this work, three sets of inputs for
the pressures in the larger arteries and veins of the hand during vessel occlusion and reperfusion
were used as shown in Figure 23.9. For all three sets of inputs, an occlusion time period of 180 s
was chosen to be consistent with the occlusion time that is used in a majority of clinical trials after a
period of steady state lasting 80 s. After occlusion, three kinds of recovery conditions during reper-
fusion were assumed to simulate different levels of RH: (1) an instantaneous pressure overshoot that
was three times higher than that at the steady state and exponential decay back to the steady level,
(2) an instantaneous pressure overshoot that was two times higher than that at the steady state and
exponential decay back to the steady level, and (3) a direct exponential recovery back to the steady
level without overshoot.
The dynamic variation curves for fingertip temperatures are plotted in Figure 23.10, corre-
sponding to the three levels of RH. It can be seen that fingertip temperature variation is closely
related to the pressure changes in larger arteries. In comparison with the predicted temperature
variation, the measured fingertip temperatures in the DTM tests, which represent the average val-
ues of five healthy subjects, are plotted (Wang and He 2010). The simulation results showed good
agreement with the experimental results at the rest and occlusion stages. At the recovery stage,
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