The Development of Circadian Rhythms in Human Infants

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The discussion will then seek to critique the selection of methods used in the study, in order to justify the data collection undergone. Finally the implications of the work, particularly in terms of developmental physiology and areas of future work will be outlined. Each of the seven questions posed in the introduction of this study are addressed in turn in this section of the discussion. 206
11.1 Physiological development - age related changes in core body temperature during night time sleep What is the pattern of physiological development in human infants in terms of age related change in overnight core body temperature during sleep and what is the nature of the change (gradual versus abrupt)? In this study, the cohort of infants investigated demonstrated the characteristic change in deep body temperature during sleep with age that has been previously well described in the literature (Lodemore et al., 1991, Wailoo et al., 1989). The infants in the initial weeks, exhibited a small drop in core body temperature just before the onset of sleep, during the first four hours of the night time temperature recording. This was followed by a gradual rise in temperature towards day time values by the end of the night. The depth of the drop in core temperature within the first four hours of sleep deepened with increasing postnatal age. This process has been described by researchers, involving the infant moving from neonatal physiology, to an infant state of pre-maturation in terms of physiological development (Jackson, 2000, Atkinson, 1995). The infants are said to exhibit a mature rhythm (similar to that of an adult) at a particular and specific age, which can be determined when the maximal fall occurs in deep body temperature during sleep to below 36.5 0 C. This occurs on average at around 3 months of age. No further fall occurs with increase age, denoting stability of the circadian rhythm (unless infant is ill or vaccinated). The overnight temperature readings for the infants studied in this project showed the characteristic changes in core body temperature with sleep as described above, with a fall in minimum temperature recorded within the first four hours of sleep with age (see results section 4.2). These data were analysed to see whether there was a gradual 207
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The Development of Circadian Rhythm
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Table of Contents LIST OF FIGURES .
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7.1 Analysis of infant sleep measur
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List of Figures Figure 1.1 - Diagra
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List of Tables Table 3.1 - Descript
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1 Introduction Happiness is not a m
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Each of these independently is impo
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There is general agreement, that al
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Summary 1. Development encompasses
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Figure 1.1 - Diagram illustrating c
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A phase shift is used to describe a
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1.4 Ontogeny in Human Infants Well
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1.5.2 Circadian Rhythms in Temperat
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1.5.4 Factors affecting Temperature
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1.6 Melatonin (Reviewed in Cardinal
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mechanism by which this occurs is n
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It is at this time that infant slee
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1.7 Cortisol Cortisol is a hormone,
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1.7.3 Circadian pattern of Cortisol
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In a separate study, Weerth et al u
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Summary 1. Cortisol is crucial to a
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NREM sleep has 4 stages. It occupie
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1.8.1 Functions of Sleep The functi
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1.8.3 Ontogeny of Sleep in Infants
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Sleep can clearly be used as marker
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For the purpose of this study, the
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Summary 1. Sleep is defined by lack
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Overall the SCN generates signals (
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Figure 1.2 - The mammalian circadia
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1.9.3 Molecular Components of the C
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Figure 1.3 - Mechanisms from SCN to
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1.9.7 Melatonin and Clock Melatonin
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The links between the central clock
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Chapter 2 Methods
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There were strict inclusion and exc
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This personal contact on the postna
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2.1.3 Home monitoring visits The fi
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2.1.4 Further monitoring informatio
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Core body temperature was taken sim
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2.3 Collection of urine samples Pai
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were read against air at 429 nm aft
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allowed the display and comprehensi
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2.8.1 RNA preparation and cDNA synt
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In total three methods were trialle
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2.11 Statistical methods For compar
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test that each infant‟s height an
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Power calculation Sample size: Fift
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3 Results 3.1 Recruited subjects an
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predominantly affluent areas of the
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Birth history and past medical hist
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3.1.3 Socioeconomic demographics of
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her best friend losing her battle w
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Sleep environment of infants All mo
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Summary 1. This study had higher ra
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4 Results 4.1 Core body temperature
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Degrees Celsius 36.70 36.60 36.50 3
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11-13 weeks There is no significant
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Core body temperature (degrees Cels
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Number of infants 10 8 6 4 2 0 7 8
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Mean minimum rectal temperature in
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Mean minimum rectal temperature in
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Figure 4.7 shows the changes in the
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Chapter 5 Result
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4 or 6 hourly samples. Circadian rh
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Figure 5.1 - Distribution of mean n
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5.1.2 Emergence of diurnal rhythm f
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Figure 5.3 - Histogram showing dist
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Figure 5.4 - Changes in night time
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Night-day difference in melatonin s
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Summary 1. There is an increase in
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6 Results DESCRIPTION OF THE URINAR
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6.1.2 Emergence of diurnal rhythm f
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Figure 6.3 - Histogram showing dist
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Cortisol values were corrected to a
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6.1.4 Relationship between night an
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Chapter 7 Results
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Mean Length of Sleep/ Wake Bouts Th
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Sleep parameters were recorded as m
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7.3 Development of infant sleep rel
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Figure 7.2 - Changes in infant slee
Page 165 and 166: Figure 7.4 - Changes in percentage
Page 167 and 168: Figure 7.5 - Changes in infant frag
Page 169 and 170: Figure 7.7 - Changes in number of m
Page 171 and 172: Figure 7.9 - Changes in the percent
Page 173 and 174: Sleep efficiency (%) 100.0 90.0 80.
Page 175 and 176: Chapter 8 Results
Page 177 and 178: Considering only those weeks of mea
Page 179 and 180: 8.2 Description of peripheral gene
Page 181 and 182: 18:30 hours 0.9927; 01:00 ours 1.01
Page 183 and 184: The weeks after temperature maturat
Page 185 and 186: Further peripheral gene graphical r
Page 187 and 188: Raw data points are represented by
Page 189 and 190: H3f3b/Gap H3f3b/Gap H3f3b/Gap H3f3b
Page 191 and 192: 8.3 Detailed gene expression analys
Page 193 and 194: Summary 1. H3f3b was selected as ge
Page 195 and 196: 9 Results FACTORS AFFECTING SLEEP A
Page 197 and 198: Care and infant related factors �
Page 199 and 200: Table 9.3 - Effect of family occupa
Page 201 and 202: * Class 7 used as reference group
Page 203 and 204: Table 9.6 - Effect of measured infa
Page 205 and 206: Summary: 1. A mature physiological
Page 207 and 208: 10 Results 10.1 Circadian rhythms -
Page 209 and 210: value of above 0.5 for R squared wa
Page 211 and 212: Table 10.1 - Temporal relationship
Page 213 and 214: Chapter 11 Discussion
Page 215: � What if any are the factors whi
Page 219 and 220: There are other proven factors whic
Page 221 and 222: drawbacks of the spread of data - a
Page 223 and 224: presented in table 6.1 do not have
Page 225 and 226: separate methods were applied to th
Page 227 and 228: significant. Sleep latency was cons
Page 229 and 230: The function of sleep in developmen
Page 231 and 232: Melatonin secretion was higher on n
Page 233 and 234: In this study sleeping in the same
Page 235 and 236: Timing of sleep maturation was diff
Page 237 and 238: systematic, ordered developmental p
Page 239 and 240: individual gene plots that provide
Page 241 and 242: temperature recording devices adapt
Page 243 and 244: Both melatonin and cortisol rhythms
Page 245 and 246: Extension of this period of monitor
Page 247 and 248: Second, we demonstrated the gene of
Page 249 and 250: Cortisol and melatonin Slope based
Page 251 and 252: Summary and Future work This study
Page 253 and 254: � Maximise technique for measurin
Page 255 and 256: “There is a science of infant car
Page 257 and 258: References
Page 259 and 260: Bajanowski, T., Vege, Å., Byard, R
Page 261 and 262: Chamley, C.A., Carson P, Randall D,
Page 263 and 264: Frank, M.G., Heller, H.C., 2003. Th
Page 265 and 266: intrahypothalamic administration of
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Mirmiran, M. & Ariagno, R.L., 2000.
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Rawson, D., Petersen, S.A., Wailoo,
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Stokkan, K.A., Yamazaki, S., Tei, H
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Winter, J.S.D., 1985. The adrenal c
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