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Respiratory heat loss during work at various ambient temperatures
J B Cain1, S D Livingstone, R W Nolan
1Defence Research Establishment Ottawa, Environmental Protection Section, Ontario, Canada.
Respiration Physiology
|February 1, 1990
Summary
Respiratory heat loss in extreme cold was quantified. Expired air temperature remained consistent across metabolic rates, while humidity neared saturation, accounting for significant heat loss.
Area of Science:
- Environmental Physiology
- Human Metabolism
Background:
- Understanding respiratory heat loss is crucial for individuals working in cold environments.
- Previous research has not fully quantified heat loss across various metabolic rates in extreme cold.
Purpose of the Study:
- To determine the temperature and humidity of expired air at different metabolic rates in cold ambient temperatures (-40°C to 20°C).
- To calculate the resulting respiratory heat loss in these conditions.
Main Methods:
- Five subjects had their expired air temperature and water vapor content measured while standing or walking.
- Measurements were taken in controlled ambient temperatures ranging from -40°C to 20°C.
Main Results:
- Expired air temperature showed minimal variation with ambient temperature and was unaffected by metabolic rate, respiration rate, or breathing frequency.
- Relative humidity of expired air approached saturation in extreme cold.
- Respiratory heat loss constituted 25-30% of resting metabolic rate and 15-20% of working metabolic rate.
Conclusions:
- Expired air temperature is a stable physiological parameter in cold environments.
- Respiratory heat loss is a significant factor in energy expenditure during cold exposure, regardless of metabolic activity level.