The Influence of Bed Partners on Movement During Sleep

Sleep. 17(4):308-315 © 1994 American Sleep Disorders Association and Sleep Research Society The Influence of Bed Partners on Movement During Sleep F. P. Pankhurst and J. A. Home Sleep Research Laboratory, Loughborough University, Leicestershire, u.K. Summary: Two related studies are reported. Both involved the use of wrist actimetry and morning sleep logs in subjects 23-67 years of age. In the first study, 46 pairs of bed partners were monitored for 8 nights to assess the extent and concordance of their body movements, and whether the latter exhibited age and gender differences. The second study concentrated on the presence or absence of a bed partner, and included subjects who either habitually . slept alone or whose usual partner was absent for at least 1 night. Men showed a significantly greater number of discrete movements during sleep than did women. Overall, 5-6% of all 30-second sleep epochs contained such movements, with about IIJ of these movements being common (within the same epoch) to both partners. This concordance was highest in younger couples. Female bed partners reported being disturbed more often by their partner than was the case for male partners. Subjects sleeping with a partner showed a greater number of discrete movements than matched subjects who slept alone. Movements decreased during temporary absence of the usual bed partner. Couples seemed unaware of the similarity in the timing of their movements during sleep, and most reported sleeping better when their bed partner was present. Key Words: Actimetry-Sleep disturbance-Body movements - Bed partners - Gender differences. Little research has been conducted into the effects bed partners have on sleep. The best known study, by Monroe (1), examined the effects on the sleep electroencephalogram (EEG) when the usual sleeping arrangements for 28 married (for> 12 months) good sleepers (aged 21-25 years) were changed. They slept for 3 consecutive nights in the laboratory. The first night was for adaptation, and the other two nights were randomized for sleep-with-spouse and sleep-alone. During the latter, both partners averaged 20 minutes extra stage 4 sleep, 16 minutes less stage REM sleep and fewer awakenings. All these findings were significant. Women had significantly more total sleep for all conditions. Subjective estimates of sleep quality did not differ between the conditions. Monroe concluded that sleeping alone gave better sleep. Aaronson et al. (2) used time-lapse photography to monitor a couple (44 and 46 years of age) sleeping at home for 7 nights. Sixty percent of the man's movements were matched by the woman, and 70% of the woman's movements were matched by the man. Using similar recording methods, these authors (3) reported Accepted for publication January 1994. Address correspondence and reprint requests to J. A. Horne, Sleep Research Laboratory, Human Sciences Department, Loughborough University, Leicestershire LEI I 3TU, U.K. earlier on the effects of a pet sleeping on a bed with its owner. There was a marked amount of movement synchrony during the first part of the night. There is a growing body of literature on the application of actimetry to sleep, which has been reviewed elsewhere (cf. reference 4). Actimeters provide an attractive method for examining the association of body movements between bed partners during sleep. We were able to do this as part of a larger study (4) that monitored 15 nights of home sleep in 400 people (2070 years) living near U.K. airports. It appeared from objective (actimetry) and subjective (sleep log) findings that even for airports having a relatively large number of flights at night (most were not very loud) the effect of aircraft noise on sleep was minor (4), and very little of our data were affected by sleep disturbance due to aircraft noise. Here we report the results of two studies. The first, the more substantial of the two, concerned the monitoring of sleep in 46 pairs of bed partners to assess the extent and concordance of body movements between them, and to see whether there were gender and age differences in this respect. The second study used other subjects from the main study (4) and looked both at subjects who habitually slept alone and subjects who usually slept with a partner, but whose partner was absent for at least I night out of the 15 nights monitored. 308 BED PARTNERS AND BODY MOVEMENT IN SLEEP sample) or those who suffered from pain that seriously disrupted sleep were excluded. Poor sleepers not on hypnotics were included. During this interview subjects were asked to volunteer for a major study on sleep habits. Of the 447 who agreed, 400 were selected randomly. At four of the sites, subjects who always slept in the same bed as their partner were asked if the partner would take part as well. If so, the latter was also interviewed, and the same selection criteria were applied. Twelve bed partners for each of these four sites were chosen, making 46 couples in all (two couples dropped out). All subjects were paid £5 (about U.S. $8) per actimeter night. The couples were 23-67 years of age (see Table 1); each slept together in either a double (84%) or king-size (16%) bed. Eighty percent had slept together in the same bed for > 5 years, 1'7% for between 1 and 5 years. TABLE 1. Distribution of bed partners by age and gender. Percentages in parentheses Age group Sex 20-34 years 35-49 years 50-70 years Total Male Female Total 11 (23.9) 16 (34.8) 27 (29.3) 18(39.1) 17 (37.0) 35 (38.0) 17 (37.0) 13 (28.3) 30 (32.6) 46 46 92 309 METHODS Subjects Subjects lived near one of four major U.K. airports (Heathrow, Gatwick, Stansted and Manchester) and had been living in their homes for at least 1 month. Subject selection for the main study is detailed elsewhere (4). In brief, at each of two sites per airport interviewers knocked on doors and continued interviewing until a quota of 200 was obtained. Interviewees were informed that this was a Government survey into living conditions, and one member per household was interviewed. The sample reflected the age and gender distribution of the local populations, based on the latest U.K. census data (i.e. about equal numbers of men and women, evenly distributed across the three age ranges: 20-34, 35-49 and 50-70 years). They were invited to be interviewed further about their sleep habits, and 614 agreed. Subjects on hypnotics (4.4% of our Actimetry The "Swiss-type" actimeters (Gaehwiler Electronics, Hombrechtikon, Switzerland) were used. These react to accelerations > 0.1 g and are unresponsive to normal passive movements of the bed caused by movement of a bed partner. Actimeters were set for 30second epochs and synchronized to within ± 5 seconds of each other. Actigrams (the sequential accumulations of movements per 30 seconds) were read into a com- <> I I 22 I I I I 23 I I I I 24 I I I I 01 I I I I I I I 02 I 03 I I I I 04 I I I I 05 I I I I 06 (...truncated)