2007, Piran, Slovenia

Modelling
(T , T , V&
, ) = 1.
0 + α (T T , ) if Tc,th < Tc (2)
DILAT C s O r
c −
2 c th
= 1.0 if Tc < Tc,th
α is a gain constant. Experimental studies since 1970 established that Tc,th decreases
approximately 0.1 o C for each degree C increase in T s . The effect of O r , V& on Tc,th was
2
controversial until Taylor, et al. (1988) and Smolander, et al. (1991) showed rather clearly
that Tc,th is not affected by moderate levels of O r , V& (say 2
O r , V& < 0.5) when T 2
s is less than
34 o C. At higher intensities of exercise, Tc,th increases with O r , V& , as shown in Figure 1. The
2
solid line in Fig. 1 is a graph of the relationship
2
ΔTc
, th = 1.41 ΔV − 0.194 ΔV + 0.01
(3)
V&
, − V&
, / 1.0 − V&
,
& = 0.5.
in which ( ) ( )
THRESHOLD CENTRAL TEMPERATURE
INCREASE: C
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
ΔV = O 2 r O2
crit
O2
crit , and O crit , V 2
40 50 60 70 80 90 100
OXYGEN CONSUMPTION RATE: % VO2 max
Figure 1. Δ Tc,th for active vasodilation as a function of O r , V 2
& when TS < 33.0 . Filled and
open circles identify plethysmographic and laser-Doppler data, respectively, of Smolander, et
al., 1991; open triangles identify data of Taylor, et al., 1988. Also shown is the graph of
Eqn. 3.
While Eqn. 2 accounts for the effect of heavy exercise on SkBF at normal skin temperatures,
it fails to account for the effect of moderate exercise on Δ Tc,th at high skin temperatures. For
example, Eqn. 1 yields Δ Tc,th = 0 o C for V& , r ≈ 0.
5,
which is at variance with the threshold
O2
increments of 0.29 o C observed by Johnson and Park (1981) and 0.28 o C observed by
Kellogg et al. (1991). However, those studies were carried out with s T = 38 o C. A possible
solution for that dilemma is to assume that V& decreases with increasing T s , which is not
O2 , crit
unreasonable, because cutaneous blood flow and volume both increase when the skin
temperature is high. We simply assume that V& decreases linearly from V& = 0.5 for
T s ≤ 33 o C to
O2 , crit
O2 , crit
O2 , crit
V& = 0 for 38 o C. Then, if s T = 38 o C and & = 0.
5 , as in the study of
V O2 , r
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