Respiratory heat loss, Q
res [kcal/h], is calculated according to thermodynamic theory,
Q
res = V
ei
e - V
ai
a [kcal/h] (1)
where V = air rate [kg dry air/h], i = enthalpy [kcal/kg dry air] and subscript e and a represent expired and inspired gas respectively.
i
a = 0.240T
a + X
a (597.3 + 0.441T
a) [kcal/kg dry air] (3)
i
e = (0.200F
eo2 + 0.204F
eCO2 + 0.249F
eN2) T
e+ X
e (597.3 + 0.441T
e) [kcal/kg dry air] (4)
where F = ratio of each gas weight to total gas weight [-], T = temperature [°C] and X = humidity ratio [kg/kg dry air] .
Fanger (1970) presented a formula to estimate Q
res consisted of the following equation.
Q
rea = V
e [575 (X
e-X
a) + 0.240 (T
e - T
a) ] [kcal/h] (5)
Using equation (6) for V
e with total metabolic rate, M [kcal/h], he proposed equation (7) .
V
e = 0.0060M [kg dry air/h] (6)
Q
res = 0.0023M (44 - P
a) + 0.0014M (34 - T
a) [kcal/h] (7)
where P
a - the partial pressure of water vapour in inspired gas [mmHg] . We measured V
e, F
eo2, F
eCO2, F
eN2 and M with 33 Japanese males during resting and daily working activities. We derived a new equation (8) for V
e with M.
V
e = 0.01020M - 0.15992 [kg dry air/h] (8)
In such activities equation (6) underestimated V
e [mean relative error (MRE) = 25.88%] . Using present 387 data we compared equation (1) with equation (5) . Each value from equation (5) was lower than that of equation (1) (MRE=5.45%) . It was concluded that under relatively low metabolic level equation (6) caused considerable errors. Equation (7) which is based on equation (6) can never estimate an accurate value of Q
res. If equation (5) would be adopted to calculate Q
res, the value of V
e should be predicted from equation (8) instead of equation (6) .
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