The Development of Circadian Rhythms in Human Infants

1.5.2 Circadian Rhythms in Temperature
The pattern of change in core body temperature within a 24 hour period has been well
described in adult chronobiology research. The tight control of core body temperature
is thought to be part of the mechanism which determines the sleep/wake cycle
(Aschoff, 1981).
During the day it had been well documented that body temperature is high with a
gradual fall over the first few hours after the onset of sleep based largely on work in
the adult population (Minors, 1981). Early summary reports investigating the
development of circadian rhythms with regard temperature control in infancy and
childhood, showed a drop occurring through the night before a gradual increase
towards day time values based on the analysis of data from 100 children (Hellbrügge,
1960). The maximum drop was reported to occur later in the night for older children
and earlier in infants. However the time of onset of sleep was not taken into account.
Therefore the finding of a later drop occurring in older children, per say, when
compared to an infant, is likely to be related to a later bed time, rather than denoting a
change in maturity state. Another method of determining the timing of temperature
circadian rhythmicity relates that the measurement of the depth of fall in the first four
hours of sleep at any age, as being more important. Normalising the data to timing of
sleep onset reveals the maximum drop occurring in the first few months of life, not
the first few years. This technique was used by Lodemore et al in their description of
the development core body temperature rhythms. To be more precise the timing of
the maturity in infancy of core body temperature changes occurred, at 2-3 months of
age. This is described in more detail below as it is the method selected in this study as
a marker of physiological maturity (Lodemore et al., 1991).
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