Attenuated thermoregulatory response to mild thermal challenge in subjects with sleep-onset insomnia

To determine if heat loss capacity of sleep onset insomniacs was different from that of healthy sleepers.

Measure skin temperature responses following brief exposure to a warm peripheral thermal challenge (PTC).

Sleep research laboratory in South Australia.

Eight primary insomniacs with sleep onset insomnia according to DSM-IV-TR criteria (SOI; 5 male, 3 female; mean age +/- SEM = 35.2 +/- 4.2 years) and ten healthy sleeping control subjects (HS; 7 male, 3 female; mean age = 28.2 +/- 2.8 years).

Two PTC conditions in counterbalanced order on non-consecutive days. During each condition, the subject's non-dominant forearm and hand were immersed for 3 minutes in Warm (45 degrees C) or Control water (i.e. same as the subject's non-dominant index finger temperature just prior to immersion, range 30-35 degrees C).

HS had a significantly higher maximum finger temperature response after immersion than SOI (P < 0.05). Expressed relative to Control PTC temperatures, the Warm PTC caused a significant increase in mean finger temperature for HS of 4.1 +/- 0.8 degrees C, compared with SOI of 0.9 +/- 0.4 degrees C. A significant negative relationship was observed between maximum finger temperature response and self-reported sleep onset latencies (R = -0.57, P < 0.05). There were no main effects of sleep status (SOI vs. HS) or interactions by time, in skin temperatures measured at either the back of hands or feet.

SOI were observed to have significantly attenuated thermoregulatory responses to a mild positive thermal challenge, providing evidence that impaired heat loss capacity from the periphery is associated with sleep onset insomnia.