Studies on the relationship between peripheral heat flux and blood flow in the Korean diving women
The present investigation was undertaken to determine if the so-called vascular cold-adaptation is the main factor responsible for a greater maximal tissue insulation of ama for a given subcutneous fat thickness. To assess the vascular cold-adaptiation, regional skin heat flux and the concurrent limb blood flow were simultaneously measured.
The experiments were carried out in August of 1966 and in January of 1967 in Youg-Do Island in Pusan, 6 active ama and 6 nondiving control females who live in the same community were selected at random. Subcutaneous fat was determined by measuring skinfold thickness at ten representative body areas with a Best caliper.
Mean subcutaneous fat thickness and percentage of adiposity were estimated according to the formula described by Allen et al.,
The insure a uniform degree of cold exposure in all experiments, the subjects were immersed in a constant temperature water bath, the temperature of which could the regulated to within 0.01。C. They were clothed in cotton swim suits and immersed supine with only their faces above the water. O^^2 consumption was measured every 30min with a Collins spirometer. The subjects remained immersed for 2 hours in water of 30, 31 and 33。C. Calibrated gradient calorimeter discs were taped to the skin adjacent to the umbilicus, the upper and lower arm, the
mid-finger and the thigh and calf. The electromotive force generated by the heat flow discs was recorded by an Offner dynograph Operated at a sensitivity of 5μV/mm deflection. The calibration factor of the discs was 1.4kcal/hr/m^^3/μV.
The forearm and mid-finger blood flow was measured using Whitney circumference gauges.
To estimate the relative importance of convective heat transfer by blood flow and conduction of heat from limb interior to limb surface following immersion for 2 hours in water of 3 different temperatures, the arm or finger circulation was arrested for 10min and the relationship between the skin heat flux of limbs and the simultaneously measured limb blood flow was estimated.
Tissue insulation(Ⅰ) was computed from the formula Ⅰ=(rectal temp.-bath temp.)/rate of skin heat loss, using measurements obtained during the stea요 state conditions of the 2nd hour.
Among the results obtained from the present study, those obtained at 30。C water bath were most pominent, so that the author would like to describe mostly about them unless stated otherwise. The results may be summarized as follow:
(1) Rectal temperatures: In summer the rectal temperature of ama was averaged to 37.31。C before immersion and to 36.39。C at the end while that of non-divers averaged to 37.52。C and 36.65。C, respectively. The magnitude of decrease in rectal temperature by cold water immersion was comparable between the 2 groups, with some what lower final rectal temperatures in the ama. By contrast, in winter mean rectal temperatures of the ama were 37.15。C before immersion and 36.32 at the end, and the comparable figures observed in non-divers were 37.11 and 36.18。C.
Hence, in winter a greater decrease in rectal temperatures ws observed in non-divers, with higher final rectal temperatures for ama.
(2) Metabolic rate: After 2 hour immersion in 30。C water in summer, metabolic rate was averaged to 46.1kacl/hr/m**2 for ama and to 44.7 for non-divers. No significant differences between the 2 groups were observed. In winter the comparable figures were 53.6kacl/hr/m**2 in the ama and 48.8 in non-divers, showing a tendency for a higher metabolic rate in the ama.
(3) Limb blood flow: During summer the mid-0finger blood flow of ama in water of 30。C decreased to 1/3 of control values(from 19.2 to 6.6ml/min/100ml) while in non-divers it decreased at a smaller rate in summer as compared to non-divers with the resultant higher blood flow at the end of immersion in ama. The same changes of finger blood flow were also observed in winter. Forearm blood flow of both groups in summer decreased equally approximately by 40% at the end of 2 hour immersion in 30。C water(from 2.6 to 1.6 ml/min/100ml for ama and from 3.7 to 2.1 for non-divers). In winter both groups showed almost the same reduction(50%) of forearm blood flow by the end of 2 hour cold water immersion(from 6.3 to 3.0ml/min/100ml for ama and from 4.8 to 2.5 for non-divers). As a whole, the final values of forearm blood flow following immersion were higher for non-divers in summer whereas in winter they were higher in the ama.
(4) Relationship between skin heat flux and limb blood flow: During summer the finger skin heat flux and the finger blood flow decreased by the same proportion as subjects were immersed in cooler water. However, in winter, the finger skin heat flux or both groups fell during immersion more drastically while the finger blood flow showed a moderate change. The above tendency was more prominent for ama.
Although the forearm blood flow also decreased in both groups as water temperature dropped, the steady-state heat flux from the forearm skin remained unchanged in summer. This may imply that, in water as cold as 30。C, metabolic heat produced in the limbs is conducted directly to the skin surface to be lost to the water environment and that the limb circulation contributes little to limb heat loss. In winter, the forearm blood flow was higher while the steady forearm heat flux was lower as compared to summer, especially in ama. This again suggests that forearm blood flow contributes little to limb heat loss.
(5) Relationship between the subcutaneous fat thickness and the maximal tissue insulation: The maximal tissue insulation for a given subcutaneous fat thickness tended to be greater in ama in both seasons as compared to the control.
(6) Relationship between convective heat transfer and conductive heat loss in the limbs: As water temperature decreased, both convective and conductive heat loss tended to increase in both groups in summer whereas in winter were more pronounced in ama. In other words, the limb heat flux during whole body immersion in cold water does not seem to reflect the state of limb circulation.
These results indicate that, contrary to the earlier speculation, the process of cold acclimatization is not accompanied by a greater peripheral vasoconstriction. In other words, the greater tissue insulation as observed in ama can not be attributed to the development of vascular adaptation..