Enhanced skin blood flow
response to hyperthermia after endurance training is mainly caused by plasma
volume expansion in humans
Shigeki
Ikegawa, Yoshi-ichiro Kamijo, Kazunobu Okazaki, Shizue Masuki, Yoshiyuki Okada,
and Hiroshi Nose
Department
of Sports Medical Sciences, Shinshu University Graduate School of Medicine,
Matsumoto 390-8621, Japan.
We
tested the hypothesis that enhanced skin blood flow (SkBF) response to
hyperthermia after endurance training (ET) was mainly caused by plasma volume
(PV) expansion in humans. Seven young men performed ET at 70% peak oxygen
consumption rate (VO2 peak) at 30 C, 30 min/day, 5 days, while
monitoring daily food intake. Before and after ET, we measured esophageal
temperature (Tes) and forearm vascular conductance (FVC) during
30-min exercise at pre-training 65% VO2 peak in the same environment
as in ET in 2 conditions; normovolemia (Nor) and acute hypovolemia (Hypo) with
a diuretic. ET lowered Tes threshold for an increase in FVC (THFVC)
by 0.28 C and elevated the sensitivity of an increase in FVC at a given rise
in Tes (¢FVC/¢Tes) by 32% with ~10% PV expansion. In Hypo before ET,
THFVC increased by 0.13 C and ¢FVC/¢Tes decreased by 5%
compared with those in Nor before ET with ~10% PV loss. Similarly, in Hypo
after ET, THFVC increased by 0.22 C and ¢FVC/¢Tes
decreased by 38 % compared with those in Nor after ET with ~20% PV loss. We
found that the effects of a given change in PV on THFVC and ¢FVC/¢Tes
after ET were not different from those by Hypo (P>0.05). Thus, enhanced SkBF
response after ET might be mainly caused by PV expansion.
Key words: fluid,
exercise, skin