Relationships between the circadian rhythms of finger temperature, core temperature, sleep latency, and subjective sleepiness.
Level 4 - case-series / case-control
Uncontrolled physiological observational study in a single cohort
PubMed 15038855 · doi:10.1177/0748730403261560
What was done
Fourteen healthy, young, good sleepers underwent a modified constant-routine protocol with 48 hours of continuous, enforced wakeful bed rest. Researchers took half-hourly measurements of palmar finger temperature, rectal (core) temperature, subjective sleepiness, and objective sleep latency. Individual time-series curves were aligned to the group mean core temperature minimum (05:00 h) and averaged. Cross-correlations among the four variables were calculated across phase lags ranging from -12 hours to +12 hours relative to the core temperature minimum.
What was found
Cross-correlation analyses indicated that finger temperature rhythm preceded the core temperature rhythm by 3 hours (r = -0.22). In turn, core temperature rhythm preceded subjective sleepiness by 0.5 hours (r = -0.33) and objective sleepiness (sleep latency) by 2 hours (r = 0.29).
Why it matters
These phase-lag relationships support the model that distal skin vasodilation and temperature changes precede core body temperature drops, which subsequently align with increases in subjective and objective sleepiness.
Limits
The study had a very small sample size (n = 14) limited to young, healthy, good sleepers. The findings are purely correlational, cross-correlation coefficients were relatively weak (|r| = 0.22 to 0.33), and the 48-hour enforced wakeful bed rest setting may not reflect natural daily sleep-wake dynamics.
Cited by
- context In order to wake up feeling refreshed and energized, human body temperature must increase by about 1 to 3 degrees.