Core body temperature rhythm
Circadian core body temperature (CBT) rhythm is established as a major influence on the sleep/wake cycle. CBT is measured using four iButtons (Humeau Laboratories, France) placed at each wrist and infraclavicular fossa, secured with a Comfell protective film. Recording begins in the middle of the afternoon and continues for 48 h with an acquisition frequency of one measurement every 10 min. Data collection is obtained from the Thermotrack software (ref: 303.000105.47) [The analysis of the circadian rhythm of CBT [acrophase (h:min), batyphase (h:min), period (h) and mesor (°C), amplitude (°C)] are carried out by a Cosinor technique (Time Series Analysis Seriel Cosinor, Version 6.3, Soft Technology Expert, Laboratory of Applied Statistics and BioMedical Computing, Richelieu, France). Acrophase and batypase are the measures of the time of overall high and low values recurring in each cycle. Period represents the duration of one cycle, MESOR (Midline Estimating Statistic Of Rhythm), is a rhythm-adjusted mean, and amplitude is a measure of half the extent of predictable variation within a cycle.