How much heat energy is given off by each exhalation from lungs?

Answer 1

Physiologically, exhalation is a passive event that occurs from the recoling of the expanded chest and flattened diaphram. So you do not have to expend energy to exhale.

If you want the energy lost by breathing out the warmed and humidified air in the lungs....you're gonna have to make some assumptions.

A) Room temp is 25oC
B) body temp is 37oC
C) average breath 500 mL
D) that the dead space in the lungs of 150mL does not count.

Constants:

Specific heat of air 1.012J/g/K
denisty of air 1.168 kg/m^3 = 0.000000001168 g/mL
saturated vapor desity at 37oC = 44 g/m^3.
specific heat of water vapor 1.864 J/kg/K (at 300K)


So by breathing out we move 500mL of air (0.000000584g). This means we heat 0.000000584g by 12oC(37-25oC) at a specific heat of 1.012J/g/K. Or 0.0000071J/breath. But we also humidify the air. So we'll have to account for the moisture and the energy used to heat it....to simplify, we'll just use the saturated vapor density (44 g/m^3 or 0.000044g per breath). This yields 0.00098 J/breath - not exactly neglible.

Total is 0.00098 J/breath by two significant figures. But this is just an estimate.

Answer 2

It depends: For a crying baby? A sleeping child? A marathoner or sprinter approaching the winning line? An injured person? An elderly woman with pneumonia?

These articles discuss techniques for measuring exhalation temperature.

- Matsui T, Gotoh S, Arai I, Hattori H, Fujita M, Obara K, Masuoka K, Nakamura S, Takase B, Ishihara M, Kikuchi M. Noncontact vital sign monitoring system for isolation unit (casualty care system).
Mil Med. 2006 Jul;171(7):639-43.

- Pless D, Keck T, Wiesmiller K, Rettinger G, Aschoff AJ, Fleiter TR, Lindemann J. Numerical simulation of air temperature and airflow patterns in the human nose during expiration.
Clin Otolaryngol Allied Sci. 2004 Dec;29(6):642-7.