Emission rate of carbon dioxide by older adults while sleeping

Humans emit carbon dioxide (CO₂) as a product of their metabolism. No measurements of CO₂ emission rates (CERs) of elderly sleeping people have yet been reported. This study performed such measurements and examined the possible mechanisms impacting CERs. Sixteen participants (8 males) aged ≥65 years old slept alone for a whole night under each of the four conditions in a 2 × 2 design: air temperatures of 27 °C and 30 °C and ventilation rates of 5 m³/h per person and 28 m³/h per person (resulting in an average indoor CO₂ concentration of about 1200 ppm and 760 ppm, respectively). Physiological responses were recorded during sleep. Indoor parameters including CO₂ concentration were continuously measured during and after sleep period. The CERs were calculated using a mass-balance model. The results show that the average CER was 9.0 ± 1.6 L/h per person. It was ca. 20% higher for males than for females, probably due to higher body mass, body surface area, and longer time awake during sleep. Compared with 27 °C, the CER was about 10% higher at 30 °C probably due to longer time awake and higher heart rate and skin temperature at this condition. No significant differences in CERs were observed between the two ventilation rates. The CERs measured in the present study for elderly are slightly lower than recently reported for young adults and 10–12 year old children. They all provide information required for estimating ventilation rates in bedrooms assuming that the ventilation is achieved with clean outdoor air.