24-Hour Metabolic Rate in Insomniacs and Matched Normal Sleepers

Groups of 10 objectively defined insomniacs and age-, sex- and weight-matched normal sleepers were evaluated on sleep, performance, mood, personality and metabolic measures over a 36-hour sleep laboratory stay. Insomniacs were defined to have increased wake time during the night but also had decreased stage 2 and rapid eye movement sleep. As expected insomniacs reported increased confusion, tension and depression and decreased vigor on the profile of mood states mood scale throughout the evaluation period as compared to the normals. Insomniacs also had decreased memory ability on the short-term memory test and the MAST. These performance and mood differences were not secondary to sleepiness because the insomniacs also had significantly increased multiple sleep latency test (MSLT) values throughout the evaluation period. In conjunction with the consistent mood, performance and MSLT differences during the day and the sleep differences at night, whole body VO2, measured at intervals across the day and throughout one night of sleep, was consistently elevated at all measurement points in the insomniacs as compared to the normals. The nocturnal increase in metabolic rate remained even after metabolic values from periods during the night containing wake time or arousals were eliminated from the data set. It was concluded that patients who report chronic insomnia may suffer from a more general disorder of hyperarousal (as measured here by a 24-hour increase in metabolic rate) that may be responsible for both the daytime symptoms and the nocturnal poor sleep. Future studies need to explore 24-hour insomnia treatment strategies that decrease hyperarousal.