Theoretical and Experimental Studies on Calculation Formula of Respiratory Heat Loss
1983 Volume 20 Issue 1 Pages 1-7
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1983 Volume 20 Issue 1 Pages 1-7
Respiratory heat loss, Qres [kcal/h], is calculated according to thermodynamic theory,
Qres = Veie - Vaia [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.
ia = 0.240Ta + Xa (597.3 + 0.441Ta) [kcal/kg dry air] (3)
ie = (0.200Feo2 + 0.204FeCO2 + 0.249FeN2) Te+ Xe (597.3 + 0.441Te) [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 Qres consisted of the following equation.
Qrea = Ve [575 (Xe-Xa) + 0.240 (Te - Ta) ] [kcal/h] (5)
Using equation (6) for Ve with total metabolic rate, M [kcal/h], he proposed equation (7) .
Ve = 0.0060M [kg dry air/h] (6)
Qres = 0.0023M (44 - Pa) + 0.0014M (34 - Ta) [kcal/h] (7)
where Pa - the partial pressure of water vapour in inspired gas [mmHg] . We measured Ve, Feo2, FeCO2, FeN2 and M with 33 Japanese males during resting and daily working activities. We derived a new equation (8) for Ve with M.
Ve = 0.01020M - 0.15992 [kg dry air/h] (8)
In such activities equation (6) underestimated Ve [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 Qres. If equation (5) would be adopted to calculate Qres, the value of Ve should be predicted from equation (8) instead of equation (6) .
