Study objectives: The purpose of this study was to determine the consistency of situational insomnia across several stressful conditions, including the first night in the sleep laboratory, phase advance of sleep time by 3 hours, phase advance of sleep time by 6 hours, and administration of 400 mg of caffeine. The impact of situational insomnia on alertness, metabolic rate, and cardiac measures on the following day was also measured.
Design and setting: Subjects spent 5 to 7 nights and the following days in the laboratory. Standard polysomnographic recordings were made on each night. On each day, subjects had a Multiple Sleep Latency Test, performance testing, and metabolic and heart-rate observation periods.
Participants: Fifty adult normal sleepers.
Interventions: Subjects had 1 night with their sleep phase advanced by 3 hours, 1 night with sleep phase advanced by 6 hours, and 1 night with the administration of 400 mg of caffeine 30 minutes prior to lights out.
Measurement and results: Sleep efficiency was reduced and variability was increased in each of the stressful conditions, as predicted. Those subjects with the greatest sleep efficiency on the adaptation night (top 25%) were compared with those subjects with the lowest sleep efficiency on the adaptation night (bottom 25%). Those subjects with the poorest sleep on the adaptation night (situational insomnia) had normal sleep on the baseline night that followed but had significantly reduced sleep efficiency when their sleep was advanced or they were given caffeine. Those same subjects had a significant decrease on their Multiple Sleep Latency Test on the day following the 6-hour advance and a significant increase in their Multiple Sleep Latency Test on the day following caffeine administration. The good sleepers had no significant change in their Multiple Sleep Latency Test during any of the study conditions. In terms of demographic variables, the situational insomnia group used less alcohol and tended to include a higher percentage of men. The situational insomnia group also had an elevated heart rate and increased low-frequency and decreased high-frequency electrocardiographic spectral power compared to the good sleepers. Significant differences were not found on personality or historical reports of poor sleep.
Conclusions: Normal young adults have a consistent response to various types of situational stress. Those individuals who respond with poor sleep may display increased sleepiness associated with their poor sleep but may also be more sensitive to the effects of caffeine. These individuals have cardiac changes consistent with sympathetic nervous system activation, and they may be at risk for developing insomnia and other associated disorders.