99 Int. J . B i o m e t e o r . 1975, vol. 19, n u m b e r 2, pp. 99-107
Thermoregulatory Responses to Heat and Exercise in Japanese and Caucasians by K. Ohara*, N. Okuda and S. Takaba A B S T R A C T . - R e s p o n s e s to h e a t and e x e r c i s e w e r e s t u d i e d in 9 m a l e J a p a n e s e s u b j e c t s who w a l k e d on a t r e a d m i l l at a s p e e d of 4 . 4 - 4 . 8 k m / h at 0 g r a d e f o r 2 h o u r s in a c l i m a t i c c h a m b e r in J u l y 1973, in Nagoya J a p a n . T h e r e s u l t s w e r e c o m p a r e d w i t h t h o s e o b t a i n e d in a s i m i l a r s t u d y m a d e in J u l y 1966 in C i n c i n n a t i , Ohio. T h e following r e s u l t s w e r e o b t a i n e d : (1) J a p a n e s e s h o w e d a 1 . 8 ' t i m e s h i g h e r r a t e of s w e a t i n g than C a u c a s i a n s . T o t a l s w e a t f r o m the w h o l e body d u r i n g 2 h o u r s w a l k w a s a l s o h i g h e r in J a p a n e s e . (2) J a p a n e s e e x h i b i t e d l o w e r c h l o r i d e c o n c e n t r a t i o n in local s w e a t than C a u c a s i a n s in s p i t e of t h e i r h i g h e r d i e t a r y s a l t intake, h i g h e r s e r u m c h l o r i d e c o n c e n t r a t i o n and h i g h e r r a t e of s w e a t i n g . While in C a u c a s i a n s t h e s w e a t c h l o r i d e c o n c e n t r a t i o n s h o w e d a t e n d e n c y to c o n t i n u e to r i s e d u r i n g t h e l a t e r p e r i o d of the walk in s p i t e of d e c r e a s i n g s w e a t r a t e a f t e r s w e a t s u p p r e s s i o n o c c u r r e d , in J a p a n e s e it t e n d e d to fall in p a r a l l e l w i t h the s w e a t r a t e . No d i f f e r e n c e w a s o b s e r v e d in t h e l e n g t h of the l a t e n t t i m e of s w e a t s u p p r e s s i o n . (3) T h e r e w e r e no d i f f e r e n c e s in r e c t a l t e m p e r a t u r e o r h e a r t r a t e , both at t h e p e r i o d of e q u i l i b r i u m r e c t a l t e m p e r a t u r e and at t h e end of the w a l k . (4) M e a n skin t e m p e r a t u r e d u r i n g the w a l k w a s s i g n i f i c a n t l y h i g h e r in J a p a n e s e than in C a u c a s i a n s . It w a s c o n c l u d e d t h a t the J a p a n e s e g r o u p w a s b e t t e r h e a t a c c l i m a t i z e d than C a u c a s i a n s , though the two g r o u p s w e r e c o n s i d e r e d to h a v e b e e n n a t u r a l l y h e a t e x p o s e d by s e a s o n to t h e s a m e e x t e n t . INTRODUCTION it is a c o m m o n l y a c c e p t e d fact that t r a n s i t o r y h e a t a c c l i m a t i z a t i o n t a k e s p l a c e by s e a s o n a l o r a r t i f i c i a l h e a t e x p o s u r e s . H o w e v e r , it r e m a i n s s t i l l u n c l e a r w h e t h e r o r not t h e i n h e r e n t f a c t o r s p l a y any r o l e in the e n v i r o n m e n t a l a d a p t a t i o n in i n d i v i d u a l s , and if so, to w h a t extent, e s p e c i a l l y in highly d e v e l o p e d a n i m a l s p e c i e s i n c l u d i n g m a n . Only v e r y l i t t l e knowledge h a s h i t h e r t o b e e n a c c u m u l a t e d on t h i s topic f r o m the a s p e c t of c o m p a r a t i v e p h y s i o l o g y of t h e r m o r e g u l a t i o n in m a n . A c c o r d i n g to W y n d h a m et al. (1964), u n a c c l i m a t e d B a n t u a r e s u p e r i o r in t h e i r p e r f o r m a n c e in h e a t to the C a u c a s i a n s . A f t e r a c c l i m a t i z a t i o n , t h e d i f f e r e n c es in r e c t a l t e m p e r a t u r e , h e a r t r a t e and s w e a t r a t e w e r e not s i g n i f i c a n t b e t w e e n the two g r o u p s , w h i c h i n d i c a t e s that the B a n t u d o e s not a p p e a r to h a v e an i n h e r e n t a d v a n t a g e in the a b i l i t y to r e g u l a t e body t e m p e r a t u r e in h e a t . W e i n e r (1950) a l s o could not find a b e t t e r s t a t e of a c c l i m a t i z a t i o n in B a n t u m i n e w o r k e r s than in E u r o p e a n s . On the o t h e r hand, it w a s r e p o r t e d by B a k e r (1958) that N e g r o e s h a v e a h i g h e r p h y s i o l o g i c a l t o l e r a n c e than A m e r i c a n W h i t e s u n d e r h o t - w e t c o n d i t i o n s and that t h e d i f f e r e n c e i s g e n e t i c in o r i g i n . A c c o r d i n g to R o b i n s o n et ai. (1941), N e g r o s h a r e c r o p p e r s a r e s u p e r i o r in t e m p e r a t u r e r e g u l a t i o n to w h i t e m e n . Dill, Hail and v a n B e a u m o n t (1966) s u g g e s t e d the p o s s i b i l i t y of i n b o r n f a c t o r s a f f e c t i n g the s w e a t c h l o r i d e c o n t e n t f r o m c r o s s - s e c t i o n a l as w e l l as l o n g i t u d i n a l o b s e r v a tions of f a m i l i a r r e l a t i o n s h i p s . A c c o r d i n g to Kuno (1956), n a t i v e s in the t r o p i c s *) D e p a r t m e n t of Physiology, Nagoya City U n i v e r s i t y M e d i c a l School, M i z u h o - k u , M i z u h o - e h o , Nagoya 467 J a p a n . R e c e i v e d 3 D e c e m b e r 1973
100 (The P h i l i p p i n e I s l a n d s , F o r m o s a and Siam) exhibit a l o w e r s e n s i t i v i t y of the s w e a t c e n t e r , a l o w e r c h l o r i d e c o n c e n t r a t i o n in s w e a t and a l a r g e r n u m b e r of a c t i v e s w e a t g l a n d s than i m m i g r a n t J a p a n e s e . Wyndham et al. (1952) found a notably s m a l l e r s w e a t r a t e in a c c l i m a t i z e d n o n - E u r o p e a n A f r i c a n l a b o u r e r s w h e n c o m p a r e d w i t h E u r o p e a n s . A l a r g e r n u m b e r of a c t i v e s w e a t g l a n d s in I n d o n e s i a n s than in J a p a n e s e w a s a l s o r e p o r t e d by Toda (1968). Kawahata and Sakamoto (1951) r e p o r t e d the s m a l l e s t n u m b e r of a c t i v e s w e a t glands in Ainu a m o n g t h e v a r i o u s r a c e s studied, n a m e l y , J a p a n e s e in Japan, J a p a n e s e b o r n in the t r o p i c s , F i l i p i n o s and R u s s i a n s . It w a s pointed out by Kuno (1956), h o w e v e r , that t h e r a c i a l d i f f e r e n c e s in the n u m b e r of a c t i v e s w e a t g l a n d s as w e l l a s in s w e a t i n g f u n c t i o n s including c e n t r a l r e s p o n s i v e n e s s a r e c o n s i d e r e d to be e s s e n t i a l l y a c q u i r e d o n e s . It is v e r y difficult f r o m t h e m e t h o d o l o g i c a l point of view to m e a s u r e the g e n e t i c a d a p t a t i o n s e p a r a t e l y f r o m p h y s i o l o g i c a l adaptation, b e c a u s e of the m i x e d c o n t r i b u t i o n s of the a n t h r o p o m e t r i c , p s y c h o l o g i c a l o r b e h a v i o r a l f a c t o r s a s e x p r e s s e d by L a d e l l (1964) as " c l i m a t i c know h o w " . Thus the p r e v i o u s r e p o r t s m a d e on t h i s topic r e v e a l e d no d e c i s i v e d i f f e r e n c e s in heat adaptation a m o n g ethnic g r o u p s , i n s o f a r as the i n b o r n and a c q u i r e d c h a r a c t e r i s t i c s of the heat r e s p o n s e s a r e c o n c e r n e d . In the p r e s e n t study, h e a t r e s p o n s e s w e r e e x a m i n e d on J a p a n e s e s u b j e c t s u n d e r a l m o s t the s a m e e x p e r i m e n t a l c o n d i t i o n s as in the study p r e v i o u s l y m a d e on C a u c a s i a n s by one of the p r e s e n t a u t h o r s in t h e y e a r 1966 in Cincinnati, Ohio (Ohara, 1968). The r e s u l t s o b t a i n e d w e r e c o m p a r e d with t h o s e in C a u c a s i a n s f r o m the q u a n t i t a t i v e as w e l l as q u a l i t a t i v e ( r e s p o n s e p a t t e r n a s a whole) a s p e c t of the r e s p o n s e s , in o r d e r to find out the r a c i a l d i f f e r e n c e s in h e a t a c c l i m a t i z a tion b e t w e e n t h e two g r o u p s . METHOD AND MATERIALS E x p e r i m e n t s w e r e c a r r i e d out on 9 v o l u n t e e r s , J a p a n e s e h e a l t h y m a l e s ( m e d i c a l s t u d e n t at an u n i v e r s i t y ) f r o m 16 to 31 J u l y 1973 in Nagoya (Table 1). TABLE 1.
P h y s i c a l c h a r a c t e r i s t i c s of the two ethnic g r o u p s
Japanese Age, y e a r 17-25 Subject
Caucasian Age, year 17-21
n=9
Height
Weight
cm
kg
Surface area m2
55.7
1.55
K.A.
165
Y.M.
166
62.4
H.N.
157
64.2
S.M.
176
61.0
H.T.
176
60.5
Subject
n = 8
Height
Weight
cm
kg
Surface area m2
G.J.
164
57.5
1.64
1.65
P.K.
188
77.4
2.04
1.61
B.L.
175
73.6
1.89
1.70
T.L.
182
63.5
1.82
1.69
W.D.
183
79.6
2.01 1.88
S.T.
167
63.3
1.67
D.K.
184
62.7
N.K.
165
56.9
1.58
K.R.
169
66.5
1.76
D.S.
188
76.2
2.05
179.1 + 8.9
69.6 +8.1
1.89 +0.15
¥.J.
154
55.3
1.49
M.N.
164
59.0
1.60
mean + s.d.
165.6 + 6.1
59.8 +3.3
1.62 +0.ii
101 T h e s u b j e c t s w a l k e d on a t r e a d m i l l at a s p e e d of 4 . 4 - 4 . 8 k m / h at 0 g r a d e f o r 2 h o u r s in a c l i m a t i c c h a m b e r of 4 5 . 0 o c , RH 37-38% and a i r v e l o c i t y of 0 . 4 m / s . W a l k i n g w a s i n t e r r u p t e d e v e r y 20 rain f o r about 1 m i n f o r l o c a l s w e a t s a m p l i n g . T h e following m e a s u r e m e n t s w e r e m a d e d u r i n g the w a l k : (1) R e c t a l t e m p e r a t u r e (Tre) w a s r e c o r d e d c o n t i n u o u s l y w i t h a m u l t i - p o i n t r e c o r d e r (CHINO m o d e l E T - 1 2 0 0 ) by u s i n g a c o p p e r - c o n s t a n t a n t h e r m o e l e m e n t i n s e r t e d in t h e r e c t u m to a d e p t h of 11 c m . T h e t h e r m o e l e m e n t w a s m o u n t e d in a W a r n e baloon c a t h e t e r ( W a r n e S u r g i c a l P r o d u c t L t d . ) and fixed at the r e q u i r e d d e p t h in the r e c t u m by e x p a n d i n g the b a l o o n i n s i d e t h e anal s p h i n c t e r . (2) Skin t e m p e r a t u r e (Ts) w a s m o n i t o r e d c o n t i n u o u s l y w i t h t h e m u l t i p o i n t r e c o r d e r by u s i n g Y - s h a p e d c o p p e r c o n s t a n t a n t h e r m o e l e m e n t s fixed to t h e s k i n w i t h a d h e s i v e p l a s t e r in 5 body r e g i o n s , the f o r e h e a d , left c h e s t , left s c a p u l a r r e g i o n , left f o r e a r m and left thigh. Simple m e a n s of skin t e m p e r a t u r e s in 5 r e g i o n s w e r e c s l e u l a t e d . (3) H e a r t r a t e (HR) w a s r e c o r d e d c o n t i n u o u s l y by t e l e m e t e r i n g , and h e a r t r a t e p e r m i n u t e w a s c a l c u l a t e d f r o m the r e c o r d i n g s u s i n g 20 b e a t s f o r e a c h 5 rain in s u c c e s s i o n . (4) Sweating: Ca) T o t a l s w e a t v o l u m e f r o m t h e w h o l e body w a s m e a s u r e d by body w e i g h t l o s s w i t h a h u m a n s c a l e (Kobe Scale Co.) w i t h a n a c c u r a c y of 2 g. (b) L o c a l s w e a t r a t e and e l e c t r o l y t e c o n c e n t r a t i o n in s w e a t w e r e m e a s u r e d by the m e t h o d p r e v i o u s l y r e p o r t e d by O h a r a (1968). S a m p l i n g of l o c a l s w e a t w a s m a d e w i t h a n i n t e r v a l of 20 m i n in body a r e a s of r i g h t c h e s t , r i g h t s c a p u l a r r e g i o n and r i g h t f o r e a r m , u s i n g t h e s w e a t e u p - f H t e r p a p e r m e t h o d c o v e r i n g a skin a r e a of 1 2 . 6 e m 2 . Sweat r a t e w a s m e a s u r e d g r a v i m e t r i c a l l y on f i l t e r p a p e r d i s c s and e x p r e s s e d in m g / ( c m 2 . m i n ) . T h e f i l t e r p a p e r d i s c s w e r e e x t r a c t e d w i t h 40 m l d i s t i l l e d w a t e r f o r 24 h o u r s and t h e e l e c t r o l y t e c o n c e n t r a tion in s w e a t w a s m e a d u r e d in Na and K by t h e f l a m e p h o t o m e t r i e m e t h o d and in CI w i t h a C h l o r i d e m e t e r ( H i r a n u m a Sangyo CL-1), r e s p e c t i v e l y . P e a k s w e a t r a t e as w e l l a s p e a k c h l o r i d e c o n c e n t r a t i o n in s w e a t w e r e o b t a i n e d in i n d i v i d u a l s ; A v e r a g e v a l u e s of l o c a l s w e a t in t h e c h e s t and f o r e a r m w e r e u s e d f o r the a n a l y s i s of t h e r e s u l t s , b e c a u s e t h e s e two a r e a s w e r e a l s o u s e d in the c o m p a r a t i v e s t u d y m a d e in C i n c i n n a t i on A m e r i c a n W h i t e s . F o r t h e s a m e r e a s o n , c h l o r i d e c o n c e n t r a t i o n in s w e a t w a s c h o s e n to r e p r e s e n t the s a l t c o n c e n t r a t i o n in s w e a t . (5) S e r u m e l e c t r o l y t e c o n c e n t r a t i o n w a s m e a s u r e d on c u b [ t a l v e n o u s blood f o r Na, K and C1 b e f o r e and a f t e r the w a l k . C h l o r i d e c o n c e n t r a t i o n w a s u s e d f o r a c o m p a r i s o n Of s e r u m e l e c t r o l y t e c o n c e n t r a t i o n b e t w e e n the Nagoya and C i n c i n n a t i experiments. RESULTS R e c t a l t e m p e r a t u r e w a s e l e v a t e d s u b s e q u e n t to the s t a r t of t h e w a l k C0 rain) and r e a c h e d a m o r e o r l e s s s t a b l e l e v e l at w h i c h h e a t b a l a n c e w a s c o n s i d e r e d to be newly e s t a b l i s h e d , showing e q u i l i b r i u m r e c t a l t e m p e r a t u r e . R e c t a l t e m p e r a t u r e r o s e a g a i n t h e r e a f t e r w i t h i n d i v i d u a l v a r i a t i o n of the g r a d i e n t . T o t a l s w e a t f r o m the w h o l e body in two h o u r s walk w a s g i v e n f o r u n i t body s u r f a c e a r e a c a l c u l a t e d by the f o r m u l a of F u j i m o t o et al. (1968) ( T a b l e 2). R e s p o n s e s of l o c a l s w e a t as w e l l a s c h l o r i d e c o n c e n t r a t i o n in s w e a t showed r e m a r k a b l e i n d i v i d u a l v a r i a t i o n s ( T a b l e 2). L o c a l sweat, e x p r e s s e d in m g / ( c m 2 . m i n ) , i n c r e a s e d d u r i n g the walk, r e a c h i n g its p e a k r a t e and d e c l i n e d t h e r e a f t e r in the l a t t e r p e r i o d of the w a l k . T h e l a t e n t t i m e of t h e o c c u r r e n c e o f s w e a t s u p p r e s s i o n and t h e slope of t h e s u p p r e s s i o n ( e x p r e s s e d in p e r c e n t d e c r e a s e of s w e a t r a t e p e r 10 min) showed c o n s i d e r a b l e i n d i v i d u a l v a r i a t i o n . C h l o r i d e c o n c e n t r a t i o n in s w e a t i n c r e a s e d in p a r a l l e l w i t h s w e a t r a t e b e f o r e the s w e a t r a t e r e a c h e d i t s peak, and u s u a l l y d e c r e a s e d w i t h s w e a t r a t e a f t e r s w e a t s u p p r e s s i o n o c c u r r e d . However, t h e r e w a s s o m e v a r i a t i o n a m o n g i n d i v i d u a l s , a n d in s o m e p e r s o n s t h e c h l o r i d e c o n c e n t r a t i o n c o n t i n u e d to i n c r e a s e in s p i t e of d e c r e a s i n g sw e a t r a t e .
102 TABLE 2.
Heat r e s p o n s e s in J a ~anese and C a u c a s i a n s Japanese Mean + SD
Body w e i g h t l o s s in 2 h r s w a l k ( g / m 2) P e a k s w e a t r a t e , SR ( m g / ( c m 2 . rain)) P e a k c h l o r i d e c o n c . in sweat,
1088.7
+ 150.9
1.78
+
32.4 scl (meq/1) L a t e n t t i m e of s w e a t s u p p r e s s i o n 64.1 Ss (min) Slope of change in SR a f t e r Ss, 2.34 (% c h a n g e / 1 0 min) Slope of change in Sel a f t e r Ss, + 1.54 (% c h a n g e / 1 0 mill)
+
R e c t a l t e m p e r a t u r e (Tre) b e f o r e walk, (°C) T r e at equil, p.*, (°C) R i s e in T r e at equil, p*, (oc) R i s e in T r e at the end of walk,
(oc)
Slope of c h a n g e in T r e a f t e r equil. p.*, ( A o c / 1 0 min) +
Serum chloride concentration b e f o r e walk, (meq/1) a f t e r walk, (meq/1) I n c r e a s e , (%)
685.4 1.00
0.57 17.4
+ 23.4
3.63
2.73
+ 7.59
37.69 38.41 0.72
+ + +
0.35 0.50 0.36
1.07
+
0.40
36.8 37.1 105.0 109.2 + 4.46
< 0.01
0.13
+
+
0.033
+
65.4 -
0.074 +
< 0. 001
+ 19.9
3.12
P
+ 62.5
40.5
+
H e a r t r a t e (HR) at t h e s t a r t of 118.2 walk, ( b e a t s / m i n ) 131.9 HR at equil, p.*, ( b e a t s / m i n ) HR at the end of walk, ( b e a t s / 144.1 min) R i s e in HR at equil, p.*, ( A beats/min) 13.7 R i s e in HR at t h e end of walk, ( a beats/rain) 25.9 Slope of change in HR a f t e r equil, p.*, (5 b e a t s / m i n . 10 rain)) + 2.38 Mean skin t e m p e r a t u r e (Ts) at equil, p.*, (°C) T s at t h e end of walk, (oc)
Caucasian Mean + SD
+
18.9 3.45
+ 4.63
< 0.01
37.01 38.31 1.32
+ + +
0.79 0.30 0.71
< 0.05
1.53
+
0.65
+ 0.052 +
< 0.05
0.071
+ +
12.8 16.6
99.8 129.6
+ 10.3 ¥ 15.8
+
15.8
140.8
+ 18.4
+
12.7
29.9
+ 16.5
+
14.3
41.0
+ 20.4
Thermoregulatory Responses to Heat and Exercise in Japanese and Caucasians by K. Ohara*, N. Okuda and S. Takaba A B S T R A C T . - R e s p o n s e s to h e a t and e x e r c i s e w e r e s t u d i e d in 9 m a l e J a p a n e s e s u b j e c t s who w a l k e d on a t r e a d m i l l at a s p e e d of 4 . 4 - 4 . 8 k m / h at 0 g r a d e f o r 2 h o u r s in a c l i m a t i c c h a m b e r in J u l y 1973, in Nagoya J a p a n . T h e r e s u l t s w e r e c o m p a r e d w i t h t h o s e o b t a i n e d in a s i m i l a r s t u d y m a d e in J u l y 1966 in C i n c i n n a t i , Ohio. T h e following r e s u l t s w e r e o b t a i n e d : (1) J a p a n e s e s h o w e d a 1 . 8 ' t i m e s h i g h e r r a t e of s w e a t i n g than C a u c a s i a n s . T o t a l s w e a t f r o m the w h o l e body d u r i n g 2 h o u r s w a l k w a s a l s o h i g h e r in J a p a n e s e . (2) J a p a n e s e e x h i b i t e d l o w e r c h l o r i d e c o n c e n t r a t i o n in local s w e a t than C a u c a s i a n s in s p i t e of t h e i r h i g h e r d i e t a r y s a l t intake, h i g h e r s e r u m c h l o r i d e c o n c e n t r a t i o n and h i g h e r r a t e of s w e a t i n g . While in C a u c a s i a n s t h e s w e a t c h l o r i d e c o n c e n t r a t i o n s h o w e d a t e n d e n c y to c o n t i n u e to r i s e d u r i n g t h e l a t e r p e r i o d of the walk in s p i t e of d e c r e a s i n g s w e a t r a t e a f t e r s w e a t s u p p r e s s i o n o c c u r r e d , in J a p a n e s e it t e n d e d to fall in p a r a l l e l w i t h the s w e a t r a t e . No d i f f e r e n c e w a s o b s e r v e d in t h e l e n g t h of the l a t e n t t i m e of s w e a t s u p p r e s s i o n . (3) T h e r e w e r e no d i f f e r e n c e s in r e c t a l t e m p e r a t u r e o r h e a r t r a t e , both at t h e p e r i o d of e q u i l i b r i u m r e c t a l t e m p e r a t u r e and at t h e end of the w a l k . (4) M e a n skin t e m p e r a t u r e d u r i n g the w a l k w a s s i g n i f i c a n t l y h i g h e r in J a p a n e s e than in C a u c a s i a n s . It w a s c o n c l u d e d t h a t the J a p a n e s e g r o u p w a s b e t t e r h e a t a c c l i m a t i z e d than C a u c a s i a n s , though the two g r o u p s w e r e c o n s i d e r e d to h a v e b e e n n a t u r a l l y h e a t e x p o s e d by s e a s o n to t h e s a m e e x t e n t . INTRODUCTION it is a c o m m o n l y a c c e p t e d fact that t r a n s i t o r y h e a t a c c l i m a t i z a t i o n t a k e s p l a c e by s e a s o n a l o r a r t i f i c i a l h e a t e x p o s u r e s . H o w e v e r , it r e m a i n s s t i l l u n c l e a r w h e t h e r o r not t h e i n h e r e n t f a c t o r s p l a y any r o l e in the e n v i r o n m e n t a l a d a p t a t i o n in i n d i v i d u a l s , and if so, to w h a t extent, e s p e c i a l l y in highly d e v e l o p e d a n i m a l s p e c i e s i n c l u d i n g m a n . Only v e r y l i t t l e knowledge h a s h i t h e r t o b e e n a c c u m u l a t e d on t h i s topic f r o m the a s p e c t of c o m p a r a t i v e p h y s i o l o g y of t h e r m o r e g u l a t i o n in m a n . A c c o r d i n g to W y n d h a m et al. (1964), u n a c c l i m a t e d B a n t u a r e s u p e r i o r in t h e i r p e r f o r m a n c e in h e a t to the C a u c a s i a n s . A f t e r a c c l i m a t i z a t i o n , t h e d i f f e r e n c es in r e c t a l t e m p e r a t u r e , h e a r t r a t e and s w e a t r a t e w e r e not s i g n i f i c a n t b e t w e e n the two g r o u p s , w h i c h i n d i c a t e s that the B a n t u d o e s not a p p e a r to h a v e an i n h e r e n t a d v a n t a g e in the a b i l i t y to r e g u l a t e body t e m p e r a t u r e in h e a t . W e i n e r (1950) a l s o could not find a b e t t e r s t a t e of a c c l i m a t i z a t i o n in B a n t u m i n e w o r k e r s than in E u r o p e a n s . On the o t h e r hand, it w a s r e p o r t e d by B a k e r (1958) that N e g r o e s h a v e a h i g h e r p h y s i o l o g i c a l t o l e r a n c e than A m e r i c a n W h i t e s u n d e r h o t - w e t c o n d i t i o n s and that t h e d i f f e r e n c e i s g e n e t i c in o r i g i n . A c c o r d i n g to R o b i n s o n et ai. (1941), N e g r o s h a r e c r o p p e r s a r e s u p e r i o r in t e m p e r a t u r e r e g u l a t i o n to w h i t e m e n . Dill, Hail and v a n B e a u m o n t (1966) s u g g e s t e d the p o s s i b i l i t y of i n b o r n f a c t o r s a f f e c t i n g the s w e a t c h l o r i d e c o n t e n t f r o m c r o s s - s e c t i o n a l as w e l l as l o n g i t u d i n a l o b s e r v a tions of f a m i l i a r r e l a t i o n s h i p s . A c c o r d i n g to Kuno (1956), n a t i v e s in the t r o p i c s *) D e p a r t m e n t of Physiology, Nagoya City U n i v e r s i t y M e d i c a l School, M i z u h o - k u , M i z u h o - e h o , Nagoya 467 J a p a n . R e c e i v e d 3 D e c e m b e r 1973
100 (The P h i l i p p i n e I s l a n d s , F o r m o s a and Siam) exhibit a l o w e r s e n s i t i v i t y of the s w e a t c e n t e r , a l o w e r c h l o r i d e c o n c e n t r a t i o n in s w e a t and a l a r g e r n u m b e r of a c t i v e s w e a t g l a n d s than i m m i g r a n t J a p a n e s e . Wyndham et al. (1952) found a notably s m a l l e r s w e a t r a t e in a c c l i m a t i z e d n o n - E u r o p e a n A f r i c a n l a b o u r e r s w h e n c o m p a r e d w i t h E u r o p e a n s . A l a r g e r n u m b e r of a c t i v e s w e a t g l a n d s in I n d o n e s i a n s than in J a p a n e s e w a s a l s o r e p o r t e d by Toda (1968). Kawahata and Sakamoto (1951) r e p o r t e d the s m a l l e s t n u m b e r of a c t i v e s w e a t glands in Ainu a m o n g t h e v a r i o u s r a c e s studied, n a m e l y , J a p a n e s e in Japan, J a p a n e s e b o r n in the t r o p i c s , F i l i p i n o s and R u s s i a n s . It w a s pointed out by Kuno (1956), h o w e v e r , that t h e r a c i a l d i f f e r e n c e s in the n u m b e r of a c t i v e s w e a t g l a n d s as w e l l a s in s w e a t i n g f u n c t i o n s including c e n t r a l r e s p o n s i v e n e s s a r e c o n s i d e r e d to be e s s e n t i a l l y a c q u i r e d o n e s . It is v e r y difficult f r o m t h e m e t h o d o l o g i c a l point of view to m e a s u r e the g e n e t i c a d a p t a t i o n s e p a r a t e l y f r o m p h y s i o l o g i c a l adaptation, b e c a u s e of the m i x e d c o n t r i b u t i o n s of the a n t h r o p o m e t r i c , p s y c h o l o g i c a l o r b e h a v i o r a l f a c t o r s a s e x p r e s s e d by L a d e l l (1964) as " c l i m a t i c know h o w " . Thus the p r e v i o u s r e p o r t s m a d e on t h i s topic r e v e a l e d no d e c i s i v e d i f f e r e n c e s in heat adaptation a m o n g ethnic g r o u p s , i n s o f a r as the i n b o r n and a c q u i r e d c h a r a c t e r i s t i c s of the heat r e s p o n s e s a r e c o n c e r n e d . In the p r e s e n t study, h e a t r e s p o n s e s w e r e e x a m i n e d on J a p a n e s e s u b j e c t s u n d e r a l m o s t the s a m e e x p e r i m e n t a l c o n d i t i o n s as in the study p r e v i o u s l y m a d e on C a u c a s i a n s by one of the p r e s e n t a u t h o r s in t h e y e a r 1966 in Cincinnati, Ohio (Ohara, 1968). The r e s u l t s o b t a i n e d w e r e c o m p a r e d with t h o s e in C a u c a s i a n s f r o m the q u a n t i t a t i v e as w e l l as q u a l i t a t i v e ( r e s p o n s e p a t t e r n a s a whole) a s p e c t of the r e s p o n s e s , in o r d e r to find out the r a c i a l d i f f e r e n c e s in h e a t a c c l i m a t i z a tion b e t w e e n t h e two g r o u p s . METHOD AND MATERIALS E x p e r i m e n t s w e r e c a r r i e d out on 9 v o l u n t e e r s , J a p a n e s e h e a l t h y m a l e s ( m e d i c a l s t u d e n t at an u n i v e r s i t y ) f r o m 16 to 31 J u l y 1973 in Nagoya (Table 1). TABLE 1.
P h y s i c a l c h a r a c t e r i s t i c s of the two ethnic g r o u p s
Japanese Age, y e a r 17-25 Subject
Caucasian Age, year 17-21
n=9
Height
Weight
cm
kg
Surface area m2
55.7
1.55
K.A.
165
Y.M.
166
62.4
H.N.
157
64.2
S.M.
176
61.0
H.T.
176
60.5
Subject
n = 8
Height
Weight
cm
kg
Surface area m2
G.J.
164
57.5
1.64
1.65
P.K.
188
77.4
2.04
1.61
B.L.
175
73.6
1.89
1.70
T.L.
182
63.5
1.82
1.69
W.D.
183
79.6
2.01 1.88
S.T.
167
63.3
1.67
D.K.
184
62.7
N.K.
165
56.9
1.58
K.R.
169
66.5
1.76
D.S.
188
76.2
2.05
179.1 + 8.9
69.6 +8.1
1.89 +0.15
¥.J.
154
55.3
1.49
M.N.
164
59.0
1.60
mean + s.d.
165.6 + 6.1
59.8 +3.3
1.62 +0.ii
101 T h e s u b j e c t s w a l k e d on a t r e a d m i l l at a s p e e d of 4 . 4 - 4 . 8 k m / h at 0 g r a d e f o r 2 h o u r s in a c l i m a t i c c h a m b e r of 4 5 . 0 o c , RH 37-38% and a i r v e l o c i t y of 0 . 4 m / s . W a l k i n g w a s i n t e r r u p t e d e v e r y 20 rain f o r about 1 m i n f o r l o c a l s w e a t s a m p l i n g . T h e following m e a s u r e m e n t s w e r e m a d e d u r i n g the w a l k : (1) R e c t a l t e m p e r a t u r e (Tre) w a s r e c o r d e d c o n t i n u o u s l y w i t h a m u l t i - p o i n t r e c o r d e r (CHINO m o d e l E T - 1 2 0 0 ) by u s i n g a c o p p e r - c o n s t a n t a n t h e r m o e l e m e n t i n s e r t e d in t h e r e c t u m to a d e p t h of 11 c m . T h e t h e r m o e l e m e n t w a s m o u n t e d in a W a r n e baloon c a t h e t e r ( W a r n e S u r g i c a l P r o d u c t L t d . ) and fixed at the r e q u i r e d d e p t h in the r e c t u m by e x p a n d i n g the b a l o o n i n s i d e t h e anal s p h i n c t e r . (2) Skin t e m p e r a t u r e (Ts) w a s m o n i t o r e d c o n t i n u o u s l y w i t h t h e m u l t i p o i n t r e c o r d e r by u s i n g Y - s h a p e d c o p p e r c o n s t a n t a n t h e r m o e l e m e n t s fixed to t h e s k i n w i t h a d h e s i v e p l a s t e r in 5 body r e g i o n s , the f o r e h e a d , left c h e s t , left s c a p u l a r r e g i o n , left f o r e a r m and left thigh. Simple m e a n s of skin t e m p e r a t u r e s in 5 r e g i o n s w e r e c s l e u l a t e d . (3) H e a r t r a t e (HR) w a s r e c o r d e d c o n t i n u o u s l y by t e l e m e t e r i n g , and h e a r t r a t e p e r m i n u t e w a s c a l c u l a t e d f r o m the r e c o r d i n g s u s i n g 20 b e a t s f o r e a c h 5 rain in s u c c e s s i o n . (4) Sweating: Ca) T o t a l s w e a t v o l u m e f r o m t h e w h o l e body w a s m e a s u r e d by body w e i g h t l o s s w i t h a h u m a n s c a l e (Kobe Scale Co.) w i t h a n a c c u r a c y of 2 g. (b) L o c a l s w e a t r a t e and e l e c t r o l y t e c o n c e n t r a t i o n in s w e a t w e r e m e a s u r e d by the m e t h o d p r e v i o u s l y r e p o r t e d by O h a r a (1968). S a m p l i n g of l o c a l s w e a t w a s m a d e w i t h a n i n t e r v a l of 20 m i n in body a r e a s of r i g h t c h e s t , r i g h t s c a p u l a r r e g i o n and r i g h t f o r e a r m , u s i n g t h e s w e a t e u p - f H t e r p a p e r m e t h o d c o v e r i n g a skin a r e a of 1 2 . 6 e m 2 . Sweat r a t e w a s m e a s u r e d g r a v i m e t r i c a l l y on f i l t e r p a p e r d i s c s and e x p r e s s e d in m g / ( c m 2 . m i n ) . T h e f i l t e r p a p e r d i s c s w e r e e x t r a c t e d w i t h 40 m l d i s t i l l e d w a t e r f o r 24 h o u r s and t h e e l e c t r o l y t e c o n c e n t r a tion in s w e a t w a s m e a d u r e d in Na and K by t h e f l a m e p h o t o m e t r i e m e t h o d and in CI w i t h a C h l o r i d e m e t e r ( H i r a n u m a Sangyo CL-1), r e s p e c t i v e l y . P e a k s w e a t r a t e as w e l l a s p e a k c h l o r i d e c o n c e n t r a t i o n in s w e a t w e r e o b t a i n e d in i n d i v i d u a l s ; A v e r a g e v a l u e s of l o c a l s w e a t in t h e c h e s t and f o r e a r m w e r e u s e d f o r the a n a l y s i s of t h e r e s u l t s , b e c a u s e t h e s e two a r e a s w e r e a l s o u s e d in the c o m p a r a t i v e s t u d y m a d e in C i n c i n n a t i on A m e r i c a n W h i t e s . F o r t h e s a m e r e a s o n , c h l o r i d e c o n c e n t r a t i o n in s w e a t w a s c h o s e n to r e p r e s e n t the s a l t c o n c e n t r a t i o n in s w e a t . (5) S e r u m e l e c t r o l y t e c o n c e n t r a t i o n w a s m e a s u r e d on c u b [ t a l v e n o u s blood f o r Na, K and C1 b e f o r e and a f t e r the w a l k . C h l o r i d e c o n c e n t r a t i o n w a s u s e d f o r a c o m p a r i s o n Of s e r u m e l e c t r o l y t e c o n c e n t r a t i o n b e t w e e n the Nagoya and C i n c i n n a t i experiments. RESULTS R e c t a l t e m p e r a t u r e w a s e l e v a t e d s u b s e q u e n t to the s t a r t of t h e w a l k C0 rain) and r e a c h e d a m o r e o r l e s s s t a b l e l e v e l at w h i c h h e a t b a l a n c e w a s c o n s i d e r e d to be newly e s t a b l i s h e d , showing e q u i l i b r i u m r e c t a l t e m p e r a t u r e . R e c t a l t e m p e r a t u r e r o s e a g a i n t h e r e a f t e r w i t h i n d i v i d u a l v a r i a t i o n of the g r a d i e n t . T o t a l s w e a t f r o m the w h o l e body in two h o u r s walk w a s g i v e n f o r u n i t body s u r f a c e a r e a c a l c u l a t e d by the f o r m u l a of F u j i m o t o et al. (1968) ( T a b l e 2). R e s p o n s e s of l o c a l s w e a t as w e l l a s c h l o r i d e c o n c e n t r a t i o n in s w e a t showed r e m a r k a b l e i n d i v i d u a l v a r i a t i o n s ( T a b l e 2). L o c a l sweat, e x p r e s s e d in m g / ( c m 2 . m i n ) , i n c r e a s e d d u r i n g the walk, r e a c h i n g its p e a k r a t e and d e c l i n e d t h e r e a f t e r in the l a t t e r p e r i o d of the w a l k . T h e l a t e n t t i m e of t h e o c c u r r e n c e o f s w e a t s u p p r e s s i o n and t h e slope of t h e s u p p r e s s i o n ( e x p r e s s e d in p e r c e n t d e c r e a s e of s w e a t r a t e p e r 10 min) showed c o n s i d e r a b l e i n d i v i d u a l v a r i a t i o n . C h l o r i d e c o n c e n t r a t i o n in s w e a t i n c r e a s e d in p a r a l l e l w i t h s w e a t r a t e b e f o r e the s w e a t r a t e r e a c h e d i t s peak, and u s u a l l y d e c r e a s e d w i t h s w e a t r a t e a f t e r s w e a t s u p p r e s s i o n o c c u r r e d . However, t h e r e w a s s o m e v a r i a t i o n a m o n g i n d i v i d u a l s , a n d in s o m e p e r s o n s t h e c h l o r i d e c o n c e n t r a t i o n c o n t i n u e d to i n c r e a s e in s p i t e of d e c r e a s i n g sw e a t r a t e .
102 TABLE 2.
Heat r e s p o n s e s in J a ~anese and C a u c a s i a n s Japanese Mean + SD
Body w e i g h t l o s s in 2 h r s w a l k ( g / m 2) P e a k s w e a t r a t e , SR ( m g / ( c m 2 . rain)) P e a k c h l o r i d e c o n c . in sweat,
1088.7
+ 150.9
1.78
+
32.4 scl (meq/1) L a t e n t t i m e of s w e a t s u p p r e s s i o n 64.1 Ss (min) Slope of change in SR a f t e r Ss, 2.34 (% c h a n g e / 1 0 min) Slope of change in Sel a f t e r Ss, + 1.54 (% c h a n g e / 1 0 mill)
+
R e c t a l t e m p e r a t u r e (Tre) b e f o r e walk, (°C) T r e at equil, p.*, (°C) R i s e in T r e at equil, p*, (oc) R i s e in T r e at the end of walk,
(oc)
Slope of c h a n g e in T r e a f t e r equil. p.*, ( A o c / 1 0 min) +
Serum chloride concentration b e f o r e walk, (meq/1) a f t e r walk, (meq/1) I n c r e a s e , (%)
685.4 1.00
0.57 17.4
+ 23.4
3.63
2.73
+ 7.59
37.69 38.41 0.72
+ + +
0.35 0.50 0.36
1.07
+
0.40
36.8 37.1 105.0 109.2 + 4.46
< 0.01
0.13
+
+
0.033
+
65.4 -
0.074 +
< 0. 001
+ 19.9
3.12
P
+ 62.5
40.5
+
H e a r t r a t e (HR) at t h e s t a r t of 118.2 walk, ( b e a t s / m i n ) 131.9 HR at equil, p.*, ( b e a t s / m i n ) HR at the end of walk, ( b e a t s / 144.1 min) R i s e in HR at equil, p.*, ( A beats/min) 13.7 R i s e in HR at t h e end of walk, ( a beats/rain) 25.9 Slope of change in HR a f t e r equil, p.*, (5 b e a t s / m i n . 10 rain)) + 2.38 Mean skin t e m p e r a t u r e (Ts) at equil, p.*, (°C) T s at t h e end of walk, (oc)
Caucasian Mean + SD
+
18.9 3.45
+ 4.63
< 0.01
37.01 38.31 1.32
+ + +
0.79 0.30 0.71
< 0.05
1.53
+
0.65
+ 0.052 +
< 0.05
0.071
+ +
12.8 16.6
99.8 129.6
+ 10.3 ¥ 15.8
+
15.8
140.8
+ 18.4
+
12.7
29.9
+ 16.5
+
14.3
41.0
+ 20.4
