Objective: This study investigated the sleep-promoting, thermoregulatory, and circadian phase-shifting actions of passive body heating (PBH) in elderly insomniac patients (IPs) with mild-to-moderate vascular dementia.
Methods: Thirteen elderly IPs with vascular dementia (mean age 76.9 years; male/female ratio 2/11) were subjected to a PBH trial session. This session comprised a 3-day baseline period, 2-day PBH period, and 1-day post-PBH period. In the PBH period, the subjects received PBH (immersion in hot water about 40.0 degrees C to mid-thorax level) for 30 minutes beginning 2 hours before bedtime. Sleep-waking, estimated by actigraph, core body temperature (cBT), and heart rate variability were continuously monitored. Dim-light melatonin-onset time (DLMO) was determined in the baseline and post-PBH periods.
Results: PBH significantly improved subjects' sleep quality; sleep latency decreased; sleep efficiency increased; and wake time after sleep onset decreased. These trends were more prominent in the latter half of the sleep time. PBH induced a rapid cBT elevation of approximately 0.80 degrees C, on average, followed by enhanced heat loss (DeltacBT: difference in cBT between just after the PBH and bedtime), lasting 1.5 hours before sleep. There was a significantly positive correlation between DeltacBT and sleep latency. PBH induced no significant phase shift in DLMO. Heart-rate variability data showed that PBH induced parasympathomimetic action during sleep time in the subjects.
Conclusion: PBH may have a sleep-promoting effect by intervening in the thermoregulatory and autonomic systems in elderly IPs with vascular dementia.