The apparent conductance (K(ss), in W · m-2 · °C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (T(w)) 22-23°C] (K(ss) = H(ss)/(T(sf) - T(sk)) where H(ss) is the skin-to-water heat flow directly measured by heat flow transducers and T(sf) and T(sk) are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (q(c)) through the superficial shell was then estimated as q(c) = (T(sf) - T(sk)) · (K(ss) - K(ss,min)), assuming that at rest K(ss) was minimal (K(ss,min)) and resting q(c) = 0. The duration of immersion was set to allow rectal temperature (T(re)) to reach ~37°C at the end of rest and ~38°C at the end of exercise. Except at the highest T(w) used, K(ss) at the start of exercise was always K(ss,min) and averaged 51 W · m-2 · °C-1 (range 33-57 W · m-2 · °C-1) across subjects, and q(c) was zero. At the end of exercise at the highest T(w) used for each subject, K(ss) averaged 97 W · m-2 · °C-1 (range 77-108 W · m-2 · °C-1) and q(c) averaged 53% (range 48-61%) of H(ss) (mean H(ss) = 233 W · min-2). The threshold for cutaneous vasodilation (TCV) was defined as the combinations of the highest T(re) and T(sk) at which K(ss) = K(ss,min) and q(c) = 0. T(sk) at the TCV was found to be negatively related to T(re): T(sk) = 285.9 - 6.88 T(re); r = -0.90; n = 11. Above the TCV, q(c) increased by 271 ± 84 W · min-2 · °C-1 of increase in T(sk). It is concluded that a given change of T(re) has 7- to 9-fold stronger effects than the same change of T(sk) on the TCV and on the increase of q(c) beyond the TCV.
Conductive and convective heat flows of exercising humans in cold water / G. Ferretti, A. Veicsteinas, D. Rennie. - In: JOURNAL OF APPLIED PHYSIOLOGY. - ISSN 8750-7587. - 67:6(1989 Dec), pp. 2473-2480.
Conductive and convective heat flows of exercising humans in cold water
A. VeicsteinasSecondo
;
1989
Abstract
The apparent conductance (K(ss), in W · m-2 · °C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (T(w)) 22-23°C] (K(ss) = H(ss)/(T(sf) - T(sk)) where H(ss) is the skin-to-water heat flow directly measured by heat flow transducers and T(sf) and T(sk) are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (q(c)) through the superficial shell was then estimated as q(c) = (T(sf) - T(sk)) · (K(ss) - K(ss,min)), assuming that at rest K(ss) was minimal (K(ss,min)) and resting q(c) = 0. The duration of immersion was set to allow rectal temperature (T(re)) to reach ~37°C at the end of rest and ~38°C at the end of exercise. Except at the highest T(w) used, K(ss) at the start of exercise was always K(ss,min) and averaged 51 W · m-2 · °C-1 (range 33-57 W · m-2 · °C-1) across subjects, and q(c) was zero. At the end of exercise at the highest T(w) used for each subject, K(ss) averaged 97 W · m-2 · °C-1 (range 77-108 W · m-2 · °C-1) and q(c) averaged 53% (range 48-61%) of H(ss) (mean H(ss) = 233 W · min-2). The threshold for cutaneous vasodilation (TCV) was defined as the combinations of the highest T(re) and T(sk) at which K(ss) = K(ss,min) and q(c) = 0. T(sk) at the TCV was found to be negatively related to T(re): T(sk) = 285.9 - 6.88 T(re); r = -0.90; n = 11. Above the TCV, q(c) increased by 271 ± 84 W · min-2 · °C-1 of increase in T(sk). It is concluded that a given change of T(re) has 7- to 9-fold stronger effects than the same change of T(sk) on the TCV and on the increase of q(c) beyond the TCV.Pubblicazioni consigliate
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.