노인의 한냉환경에서의 체온조절상에 관한 실험적 연구 : 특히 물리적조절상에 관하여

Abstract

[한글]

[영문]

It has been suggested by Krag and kountz(1950), Horvath et al.(1955) and Spurr et al.(1955) that the mechanism for prevention of heat loss is less efficient in the aged than in the young. In addition, they observed that peripheral vasoconstriction occurred more rapidly and more intensively in the aged people in response to the cold stimulus.

Although it is not clear on the basis of these reports whether the physical insulation of the aged people in cold would be different from the younger, it is evident that the vascular reactivity in response to cold seems to be altered in the aged people. Hence this investigation was undertaken to investigate the physical insulation of the aged people in a systemic manner by water immersion method which has been successfully applied to the Easkimos an Korean diving women by Rennie et al.

Methods

Prior to the onset of the experiments, a careful physical examination was given to all volunteers and those with findings suggestive of any cardiopulmonary diseases were excluded. The subjects consisted of healthy Korean men and women over 60 years old and about 30 years old as control group. The number of old subjects was 17 men and 17 women, while that of young subjects was 11 men and 21 women.

The subcutaneous fat was determined by measuring skinfold thickness at 10 representative body areas with a Best caliper. 40mm was substracted from the total to allow for skin thickness and the remainder divided by 20 to determine mean subcutaneous fat thickness. Percent body fat was estimated from the relationship between skinfold thickness and adiposity described by Allen et al. The mean subcutaneous fat thickness and percent body fat were not statistically significant between males and females in old subjects. However, young females were significantly greater than young males(P＜0.01).

To insure a uniform degree of cold exposure in all experiments, the subjects were immersed in a constant temperature water bath consisting of an 84×30×28 in. plywood box. Water was stirred by two centrifugal pumps, each delivering 20 liters/min. One of these was directed so as to pump from head to feet; the other

pumped from feet to head. 1,000 watt heating elements, actuated by a mercury switch, extended the length of the bath 6 in. from the bottom. By means of a variable thermostat(Yellow Springs Insturument Co.) water temperature could be regulated to within 0.01℃ at any arbitrarily selected temperature above that of

room air.

The subjects were clothed in cotton swim suits and immersed supine on the plastic mesh with only their faces above the water. rectal temperatures were measured to within 0.01℃ with a thermistor calibrated over the range 35-40℃. Oxygen consumption was measured for 6 out of every 30 min. with a Collins spirometer. The subjects remained immersed for 3 hours in water at a constant temperature for each experiment. The bath temperature chosen for each experiment varied between 28∼33℃.

Tissue insulation (Ⅰ) was computed from the formula Ⅰ=(rectal temp. bath temp.)/rate of skin heat loss, using measurements obtained during the steady state conditions of th 3rd hour of immersion. Skin heat loss was assumed to equal metabolic rate minus respiratory heat loss (8% of meatboilc rate). In those

instances where rectal temperature continued to decline, the net loss of body heat(0.83×rectal temp.×0.6×body wt.) was added to metabolic rate in estimating skin heat loss.

Results and discussion

Thermal and metabolic responses were studied in the aged subjects while they were immersed in water of 28∼33℃ for a period of 3 hours. In addition, the values of maximal tissue insulation was compared during the third hour of immersion at the

critical water temperature.

Results obtained in this study may be summarized as follows:

(1) the critical water temperature was within the range of 28∼33℃ and there was no difference between males and females in the aged subjects. However, in the young subjects, the critical water temperature was 1-2℃ lower in the females than in the

males even when a comparison was made at a similar subcutaneous fat thickness. Thus the water temperature at which 50% of subjects shivered was 29.9℃ in young females in contrast to 31.1℃ in males. In the older subjects, the corresponding value was 31.2℃ for both males and females. From these results, it is evident that the elevated shivering threshold as seen in young females is no longer in existence in the older females. However, why the shivering threshold is so elevated in the younger females alone is not known at present. It can be only said that it is not

entirely due to the difference in subcutaneous fat thickness.

(2) The final rectal temperature at a given water temperature is lower in the aged than in the younger. This was particularly so in the older males an older females. When the final rectal temperatures of both young an old subjects at 31℃ water were plotted as a function of the mean subcutaneous fat thickness, it was evident that the final rectal temperature were higher in fatter subjects regardless of their ages. In other words, one would not expect to find any difference between the young and the old subjects in the level of final rectal temperature if a comparison were made at a comparable subcutaneous fat thickness.

(3) Despite the difference in the level of final rectal temperature between younger subjects and older subjects, the skin heat loss was not significantly different between them. Hence the mean insulation value was significantly greater in the females as compared to the males (P＜0.05). However, this difference was not

observed when individual insulation values were plotted against the mean subcutaneous fat thickness, indicating that the difference in the insulation values between two groups is entirely due to the difference in the subcutaneous fat thickness.

(4) Critical water temperature and maximal tissue insulation obtained in this study were compared to other data reported from the available literatures. It suggested that the Korean has an ability to tolerate greater body cooling than those of Americans, Caucasians, Athapascan Indians or Eskimos, which might be taken

as evidence for the racial difference in physical regulation if temperature.

(5) The results obtained in the present investigation do not support the earlier contention that the maximal insulation in cold is perhaps greater in the aged. It can be concluded that there is no difference in maximal tissue insulation between

the aged and the young man provided a due consideration is given to the difference in subcutaneous fat thickness of each individual.