The Development of Circadian Rhythms in Human Infants

11.8 Choice of physiological measurements in human infants
Were the measurements taken an appropriate choice of for the study of
physiological development in human infants?
Temperature measurements
Rectal temperature is a method of measurement of core body temperature, which has
been widely published and is an accepted method for investigation within the
postnatal period (Jackson et al., 2004, Lodemore et al., 1992, Wailoo et al., 2003,
Wailoo et al., 1989, Messaritakis et al., 1990, Brown et al., 1992, Morley et al.,
1992). It is found to be safe, with risk of perforation by probe being quoted as low as
1 in 2 million in older studies, using mercury in glass thermometers (Morley et al.,
1992) which have now been superseded by use of soft flexible probes. It has been
shown by Craig et al 2002 (Craig et al., 2002) to have high agreement with core body
temperature measurements taken with more invasive methods used in monitoring
critically ill children in intensive care which would be ethically and socially
unacceptable for use in research involving healthy volunteers, such as pulmonary
artery site use, distal oesophagus or tympanic membrane using a thermistor probe.
Other methods have not been shown to reflect core body temperature accurately
(axillary or infrared tympanic membrane).
Temperature within the body is closely regulated to a very narrow range of values.
This is essential for normal metabolism, and enzymatic function at a cellular level. It
allows direct outcome measure of a robust physiological diurnal rhythm.
The data loggers used were robust and small enough to allow reasonably easy carriage
alongside the infant during routine care within the home. The rectal probes were
tolerated well by the infants. However the use of smaller loggers or alternative
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