Nocturnal body movements and sleep quality

Abstract

Nocturnal body motility and autonomic nervous system (ANS) activity as manifested in respiratory movements and the pumping action of the heart (ballistocardiogram, BCG) registered by using the static charge sensitive bed (SCSB) method were investigated in five studies. The SCSB data were classified into quiet (QS), intermediate (IS) and active (AS) states according to the frequency of small body movements and the regularity of the ANS parameters. These states and body movements per se were assessed as measures of sleep quality. QS, IS, and AS were also studied in relation to dreaming. Both visual (Study I) and automatic (Study ill) analyses revealed that the changes in different SCSB variables and in the activity states reflect the cyclic variation of the standard sleep stages. QS and IS were mainly related to NREM sleep, but while REM sleep was mostly scored as AS, the total nocturnal AS was a combination of wakefulness, stages 1 and 2, and REM sleep. The percentages of dream recall (Study 11) after QS (20%) and IS (25%) confirmed their association with NREM sleep, whereas the recall rate in AS (80%) was comparable with the percentages usually found after REM awakenings. Study IV using behavioral responsiveness as a measure of sleep depth showed similar kinds of differences between the SCSB activity states as were found between the standard sleep stages, the amount of QS appearing to be a useful indicator of deep sleep. Study V revealed significant inter-subject differences in the SCSB parameters but also a noteworthy intra-subject variation across 14 consequtive nights was found. The subjective sleep evaluations during the individual extremes of SCSB activity significantly differed from each other, quiet SCSB recording indicating subjectively good sleep. Studies I-IV indicate that SCSB activity analysis provides a simple and inexpensive method for assessing sleep quality and for dream research. According to Study V the validity of single-night recordings as measures of sleep quality should be questioned, especially as regards experimental settings with small number of subjects. Nevertheless, the SCSB appears to be a suitable method when repeated recordings are needed, as in follow-up studies.