Physiologic indexes in chronic insomnia during a constant routine: evidence for general hyperarousal?
Level 4 - case-series / case-control
Matched case-control physiological study.
What was done
Eleven individuals with clinically diagnosed chronic insomnia were compared to 13 matched healthy controls under a 24-hour constant-routine protocol involving continuous sleep deprivation in an isolated, sound-attenuated, temperature- and light-controlled laboratory. Researchers measured cardiovascular parameters, free cortisol, core body temperature, and cognitive performance. Differences in absolute levels and circadian parameters (amplitude and phase) were analyzed using mixed-model ANOVA and harmonic regression.
What was found
No statistically significant differences were found between the insomnia and control groups in absolute levels, circadian amplitude, or circadian phase for cardiovascular measures, free cortisol, or body temperature. Although physiologic markers of arousal were slightly elevated in the insomnia group, interindividual variability overwhelmed between-group differences. The abstract reports no exact numeric values, means, or p-values.
Why it matters
The findings challenge the hypothesis of sustained, 24-hour general physiological hyperarousal in chronic insomnia, suggesting that previously observed hyperarousal markers might be specific to the sleep state or bedtime rather than a constant trait.
Limits
The sample size was very small (n=24 total), leading to low statistical power to detect subtle physiological differences. The 24-hour constant-routine protocol with total sleep deprivation creates an artificial environment that does not reflect habitual sleeping conditions. Exact numerical data, effect sizes, and cognitive performance outcomes were not reported in the abstract.
Cited by
- contradicts Patients with sleep onset insomnia experience an abnormal continuous rise in cortisol around their bedtime.