Effects of Bedroom Environment on Average Heart Rate During Sleep in Temperate Regions: Winter Conditions in Healthy Males in Their Twenties with Average BMI

The nocturnal average heart rate was found to correlate more strongly with mortality rates than the resting heart rate or 24-hour average heart rate. This study aimed to identify the environmental factors that most significantly affect the day-to-day variability of average heart rate during sleep (SHR[1]) during winter. Measurements were conducted in the participants' usual bedrooms of nine healthy male participants in their twenties with an average BMI, living in a temperate region. The measurement periods were from December 1, 2022, to March 8, 2023, and from December 1, 2023, to February 6, 2024. In addition to the heart rate, body movement, room, radiant, and bed microclimate temperatures, carbon dioxide concentration, relative humidity, and illuminance were measured. The results demonstrated that the average room and radiant temperatures during the measurement period had a significant negative correlation with the average SHR during the measurement period, with correlation coefficients of -0.83 and -0.91, respectively. Using a multilevel structural equation model, the most explanatory factors for SHR were found to be body movement, operative temperature, bed microclimate temperature, carbon dioxide concentration, and the interaction term between the bed microclimate temperature and carbon dioxide concentration. Overall, a deeper understanding of the impact of environmental conditions in winter on sleep heart rate could facilitate the design of environments that stabilize SHR.