Fingertip Model for Blood Flow and Temperature - Computational Biomechanics of the Musculoskeletal System - page 303

Time t, s

Time t, s

120 240 360 480 120 240 360 480

35
34
33
32
31
30
29
28
27
26
25
24
23
22

39

Te mperature of water T w = 10 ° C
Te mperature of air T air = 22° C

36

33

30

T w = 10°C
T air = 22°C

27

24

21

Experimental result

18

4 ω dermis
ω dermis

4ω dermis
ω dermis

15

12

0 400 800 1200 480 600 720 840

Time t, s Time t, s

(a) (b)

FIgure 23.3 (a) Predicted average skin temperature under cold water stimulation. (b) Comparison between
predicted average skin temperature and experimental data. (From Clark RP and Edholm OG, Man and his
thermal environment , Edward Arnold (Publishers) Ltd., London, 1985.)

In the simulation, the following computational conditions were set up. The environmental
temperature was 22°C and the wind velocity was 0.1 m/s. After immersion in 10°C cold water for
1 min, the finger was then exposed to indoor air at 22°C. The arterial temperature was considered
to be constant at 37°C. The venous temperature was set to be equal to the tissue temperature. The
predicted average skin temperature is plotted in Figure 23.3a. It can be seen that the skin tempera-
ture became the same as that at the resting stage within 5 min, when the blood perfusion of the
dermis was four times as large as that at the resting stage. If the blood perfusion in the recovery
stage remained the same as that of the resting perfusion, the skin temperature could not recover
even up to 10 min later. Figure 23.3b clearly shows that the predicted temperature with larger
blood perfusion after cold-water stimulation was in a good agreement with the experimental
values.
We can also see that there was a fluctuation in the measured skin temperature that was not
revealed in the prediction, and that the fluctuation was not different from the heart rate. Hence, the
fluctuation may have been related to regulation of the autonomic nervous system (ANS).

23.3 thermal regulatIon modelIng
In order to simulate the temperature oscillation, we coupled a model of regulation of the ANS
(Zhang et al. 2010). We developed an ANS model on the basis of earlier studies by Liang (2007)
and Xu et al. (2008). The peripheral thermoregulation pathway comprises sensory nerves, recep-
tors, the central nervous system (CNS), efferent nerves, and effectors. Receptors are located in the
hypothalamus, efferent nerves are sympathetic vasoconstrictors, and effectors adhere to arteriole
smooth muscle. A flow chart for signal transport is shown in Figure 23.4.
The thermoregulation signal is considered to start from the current through the opening of ion
channels in the sensory nerves, and the intensity of the current is related to the environmental tem-
perature and the subject's comfort threshold. The receptors receive the frequency of impulses from