Abstract
We have modified a previously developed bed temperature monitor and used it to evaluate a sleeper's body movements. Sleep was monitored both at home and in the laboratory in normal subjects. From laboratory monitoring, a new algorithm to assess body movements using the sum of a square of temperature differences (SSD(t)) method was proposed, and the best conditions for detection of body movements are discussed. The experiment was performed with 12 normal male subjects and the body movement obtained from temperature changes was compared with that from video images. The sensitivity and positive predictive accuracy of body movement at the lower limbs with a sampling interval of 15 s and a threshold value of 0.2 °C2 were 88.7% and 95.4% respectively, over a total of 22 nights' observation. The results show that body movement can be accurately detected by placing one belt sensor under the lower limbs with a sampling interval of 15 s and a threshold value of 0.2 °C2 in SSD(t) analysis. We also found that body movement frequency is different among individuals during sleep, but has a certain range for an individual. No significant relationship between average body movement or average time in bed (TIB) and sleep profiles was observed among individuals for all subjects in one week of home monitoring. However, significant relationships between frequency of body movement or TIB and sleep profiles were observed in the long-term home monitoring for an individual. This suggests that body movements and TIB detected by bed temperature measurement can be used as indices for the assessment of sleep stability and continuity.