Axillary temperature: a circadian marker rhythm for shift workers

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Abstract
This study was designed to test the usefulness of the axillary temperature as a circadian marker rhythm, e.g. for shift workers in field experiments, where recordings may be required over extended periods. Axillary and rectal temperatures were recorded automatically at 5 or 15min intervals (Δt) using a ‘Chronotherm’ ambulatory system. Conventional (t-test, analysis of variance (ANOVA), correlation) and curve-fitting (cosinor) methods as well as power spectra were used for statistical analyses, (a) Rectal and axillary temperature rhythms were compared in five subjects over a 36 h span in laboratory conditions. Apart from rather small but constant differences in respective mesors (24 h mean) and acrophases (peak time location on the 24 h scale), rectal and axillary temperature recordings gave similar results in each individual. (b) In analyses of axillary temperatures recorded over periods of up to 15 days in a further five subjects (a field study with usual activities), only minor changes in circadian rhythm parameters were found to result from manipulation of the sampling interval over the range Δt= 15 min to Δt= 240 min, with or without data during sleep, (c) The axillary temperature recorded at Δt= 15 min over a 13 day span in a 32 year old worker on a 3-4 day rotating shift schedule had a prominent period (τ) of 22.3 h, although the prominent period of the rhythms of both wrist activity and the sleep-wake cycle remained unaltered at 24 h. Thus internal desynchronization was shown to have occurred in this subject.

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