Effects of exposure to carbon dioxide and human bioeffluents on sleep quality and physiological responses

Abstract

Twenty-four subjects were exposed to two levels of occupant pollution in a thermally neutral sleeping environment, as indicated with average carbon dioxide (CO2) concentrations of 800 ppm and 2000 ppm during the night. Sleep quality was measured by polysomnography and a wrist-type actigraphy sensor simultaneously, and also assessed by a questionnaire. Physiological parameters indicating responses of cardiovascular and pulmonary function were measured repeatedly prior to sleep and after waking up in the morning. The results show that when exposed to the high level of occupant pollution with the average CO2 concentration being 2000 ppm, subjects reported lower satisfaction on sleep and less easiness of awakening, and experienced a shorter duration of total sleep and deep sleep stage, which indicates a worse sleep quality. Furthermore, fractional CO2, end-tidal CO2 and systolic blood pressure measured in the morning were significantly higher. The change of LF/HF ratio of heart rate variability was significantly more at the onset of sleep and less during arousal. This suggests that when sleeping in an occupant-polluted environment, subjects experienced a slower automatic nervous system transition from a sympathetically dominated state to a parasympathetically dominated state at night, and vice versa in the morning.