Emerging and entraining patterns of the sleep-wake rhythm in preterm and term infants

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Preterm toddlers have low nighttime sleep quality and high daytime activity

A number of studies have been made on the sleep characteristics of children born preterm in an attempt to develop methods to address the sleep problems commonly observed among such children. However, the reported sleep characteristics from these studies vary depending on the observation methods used, i.e., actigraphy, polysomnography and questionnaire. In the current study, to obtain reliable data on the sleep characteristics of preterm-born children, we investigated the difference in sleep properties between 97 preterm and 97 term toddlers of approximately 1.5 years of age using actigraphy. Actigraphy units were attached to the toddlers' waists with an adjustable elastic belt for 7 consecutive days, and a child sleep diary was completed by their parents. In the study, we found that preterm toddlers had more nocturnal awakenings and more daytime activity, suggesting that preterm-born children may have a different process of sleep development in their early development.

Maturation of Arousals during Day and Night in Preterm Infants

The objective of this study was to compare the maturation of spontaneous arousals during day and night sleep in preterm and term infants. From the Autonomic Baby Evaluation study, the sleep and arousal characteristics of 12 preterm (35.1 ± 2.1 weeks’ gestational age, GA) and 21 term (39.8 ± 0.8 weeks GA) newborns were compared between diurnal and nocturnal sleep periods at birth (M0) and 6 months (M6) of age. Models were adjusted for time (night/day), maturation (M0/M6), prematurity (yes/no). We found that preterm infants had less active sleep (AS)% than term infants with maturation during both day and night sleep, which may reflect accelerated brain maturation secondary to stress or environmental exposure after birth. Moreover, there was a difference in arousal maturation during day and night sleep in the preterm infants, as shown previously for term infants, which suggests the emergence of a circadian rhythm during the earliest postnatal period. We also showed that compared to term infants, these moderate preterm infants had fewer total arousals and, more specifically, fewer arousals in AS during day and night sleep, exposing them to a higher risk of sudden infant death syndrome.

Nonrapid eye movement sleep characteristics and relations with motor, memory, and cognitive ability from infancy to preadolescence

Sleep plays a critical role in neural neurodevelopment. Hallmarks of sleep reflected in the electroencephalogram during nonrapid eye movement (NREM) sleep are associated with learning processes, cognitive ability, memory, and motor functioning. Research in adults is well-established; however, the role of NREM sleep in childhood is less clear. Growing evidence suggests the importance of two NREM sleep features: slow-wave activity and sleep spindles. These features may be critical for understanding maturational change and the functional role of sleep during development. Here, we review the literature on NREM sleep from infancy to preadolescence to provide insight into the network dynamics of the developing brain. The reviewed findings show distinct relations between topographical and maturational aspects of slow waves and sleep spindles; however, the direction and consistency of these relationships vary, and associations with cognitive ability remain unclear. Future research investigating the role of NREM sleep and development would benefit from longitudinal approaches, increased control for circadian and homeostatic influences, and in early childhood, studies recording daytime naps and overnight sleep to yield increased precision for detecting age-related change. Such evidence could help explicate the role of NREM sleep and provide putative physiological markers of neurodevelopment.

Sleep-wake patterns in newborns are associated with infant rapid weight gain and incident adiposity in toddlerhood

BACKGROUND

Rapid weight gain (RWG) by 6 months of life is a significant risk factor of childhood overweight (OW)/obesity. Infant sleep patterns are associated with incident OW in childhood, but few have examined its relationship with RWG.

OBJECTIVE

Examine associations between newborn sleep-wake patterns and incident RWG at 6 months of life and OW at 36 months.

METHODS

Low-income Mexican/Mexican-American women with OW/obesity and their infants (n = 126) enrolled in a 1-year randomized controlled trial designed to prevent incident, infant RWG and toddlerhood OW/obesity. Sleep pattern metrics at 1 month were extracted from the Brief Infant Sleep Questionnaire-Revised. Outcome measures included RWG (>0.67 positive change in weight-for-age Z-score) from birth to 6 months and incident OW (body mass index percentile ≥85) at 36 months.

RESULTS

By 6 months, 35.7% (n = 45) of infants experienced RWG, and by 36 months 42.3% (n = 41) of toddlers were OW. Napping ≥5x/day at 1-month was significantly associated with decreased odds for RWG compared to napping <5x (OR = 0.11, 95%CI:0.02, 0.63). Each 1-hour increase in nocturnal vs diurnal sleep was associated with greater odds of incident OW at 36 mos (OR = 1.51, 95%CI:1.13, 2.03).

CONCLUSIONS

Early-life sleep patterns related to infant nap frequency and nocturnal vs diurnal sleep distribution were associated with obesity outcomes and may be important intervention targets to prevent lasting consequences on infant growth.

Behavioral-state development and sleep-state differentiation during early ontogenesis

Sleep is a key process in neurodevelopment and essential for the maturation of fundamental brain functions. Premature birth can disturb the initial steps of sleep maturation, which may contribute to the impairment of neurodevelopment. It is thus fundamental to understand the maturation of the various sleep states and the quality of cerebral function in each vigilance state, as well as the development of sleep cyclicity, in at-risk neonatal infants, particularly those born premature. The objective of this review is to provide a precise description of sleep states and cycles and their rhythmic organization in premature and term newborns according to their gestational age. Technical aspects of polysomnography, which requires a high level of expertise in neonates, are also described. Principles of the visual interpretation of polysomnography, including the simultaneous analysis of behavioral (spontaneous motricity and eye movements), polysomnographic parameters (electro-oculogram, electrocardiogram, respiration), and electroencephalography patterns are presented. The neurophysiology of sleep ontogenesis and its interaction with brain maturation are discussed, highlighting the crucial role of sleep states and their duration in premature newborns. In particular, the involvement of myoclonic twitches in functional connectivity in sensorimotor development is discussed. Indeed, sleep quality, determined by combined polysomnographic parameters, reflects either normal or pathological developmental processes during the neonatal period. The fundamental place of neurophysiological explorations in the early detection of sleep disorders is discussed, as well as their potential consequences on neurodevelopmental care to improve the prevention of neurodevelopmental impairment.

The influence of feeding method on a mother's circadian rhythm and on the development of her infant's circadian rest-activity rhythm

An infant's circadian sleep-wake rhythm is established during the first three months after birth. It is crucial to identify how entrainment factors, such as maternal behavioural influences, feeding conditions, and others, contribute to the infant's obtaining circadian rhythm. This study examined the influence of feeding method on the mother's rhythm and on the development of her infant's circadian rest-activity rhythm. The subjects were 24 healthy primiparas (mean age, 29.8) and their full-term infants. We retrospectively divided the subjects into two groups based on feeding method (breastfeeding, 17; mixed-feeding, 7). Actographic recordings for the infants and their mothers were made over 3-5 consecutive days during the 2nd-3rd week, the 6th week, and the 12th week. First, we calculated the mean values of the autocorrelograms from the autocorrelation coefficients and calculated their statistical significance to see their rhythmicity for all the mothers and their infants at each of the periods. Second, we evaluated the mean values of the autocorrelograms to see statistical differences between the feeding methods. For the breastfed infants, the mean values of the autocorrelograms at 24-h for the 6th week were significant. However, the mean values for the mixed-fed infants were unclear. At the 12th week, the mean values of the autocorrelograms at 24-h for both groups of infants were significant. The mean value for the breastfeeding mothers at 24-h was significantly larger than that for the mixed-feeding mothers. In conclusion, the breastfeeding mothers contributed more to their infants achieving circadian rhythm than did the mixed-feeding mothers.

The Combined Impact of Sleep and Diet on Adiposity in Infants, Toddlers, and Young Children: A Systematic Review

OBJECTIVE

Short sleep duration and poor dietary habits may contribute to increased adiposity; however, the impact of the interaction between these variables on adiposity is less understood. To evaluate research investigating the combined effects of sleep and diet on adiposity in infants, toddlers, and young children.

METHODS

Systematic searches of electronic databases (PubMed, CINAHL, and Web of Science) from inception through April 2017 were conducted. All studies published in English that had at least 1 sleep (e.g., sleep duration and night awakenings), diet (e.g., 24-hour diet recall and breastfeeding duration), and adiposity (e.g., body mass index z-score and weight-for-length) measure were eligible for inclusion. Abstract and full-text article reviews were conducted by 2 independent reviewers. Data were extracted into a standardized spreadsheet.

RESULTS

Of the 17 full-text articles reviewed, 14 studies were included. Mediation (n = 2) and moderation (n = 2) were seldom used. Investigation of the combined effects of sleep and diet on adiposity demonstrated a substantial lack of evidence. Synthesis of articles suggests that the relationship between sleep and diet may be interactive and their effects additive in their impact when targeted simultaneously within interventions.

CONCLUSION

Without consideration of interaction effects among variables of interest, a substantial gap in the literature persists. Both diet and sleep need to be assessed simultaneously and repetitively in future longitudinal research.

Control of Rest:Activity by a Dopaminergic Ultradian Oscillator and the Circadian Clock

There is long-standing evidence for rhythms in locomotor activity, as well as various other aspects of physiology, with periods substantially shorter than 24 h in organisms ranging from fruit flies to humans. These ultradian oscillations, whose periods frequently fall between 2 and 6 h, are normally well integrated with circadian rhythms; however, they often lack the period stability and expression robustness of the latter. An adaptive advantage of ultradian rhythms has been clearly demonstrated for the common vole, suggesting that they may have evolved to confer social synchrony. The cellular substrate and mechanism of ultradian rhythm generation have remained elusive so far, however recent findings—the subject of this review—now indicate that ultradian locomotor rhythms rely on an oscillator based on dopamine, dubbed the dopaminergic ultradian oscillator (DUO). These findings also reveal that the DUO period can be lengthened from <4 to >48 h by methamphetamine treatment, suggesting that the previously described methamphetamine-sensitive (circadian) oscillator represents a long-period manifestation of the DUO.

Relationship between perfusion index and patent ductus arteriosus in preterm infants

BACKGROUND

Perfusion index (PI) is a noninvasive measure of perfusion. ΔPI (difference between pre- and postductal PI) may identify hemodynamically significant PDA. However, studies are limited to brief and intermittent ΔPI sampling. Our objective is to assess the value of continuous high resolution ΔPI monitoring in the diagnosis of PDA.

METHODS

Continuous ΔPI monitoring in preterm infants was prospectively performed using two high-resolution pulse oximeters. Perfusion Index measures (ΔPI mean and variability, pre- and postductal PI) were analyzed over a 4-h period prior to echocardiography. A cardiologist blinded to the results evaluated for PDA on echocardiography. Linear mixed regression models were utilized for analyses.

RESULTS

We obtained 31 echocardiography observations. Mean ΔPI (-0.23 vs. 0.16; P < 0.05), mean pre-PI (0.86 vs. 1.26; P < 0.05), and ΔPI variability (0.39 vs. 0.61; P = 0.05) were lower in infants with PDA compared to infants without PDA at the time of echocardiography.

CONCLUSION

Mean ΔPI, ΔPI variability, and mean pre-PI measured 4 h prior to echocardiography detect PDA in preterm infants. PI is dynamic and should be assessed continuously. Perfusion index is a promising bedside measurement to identify PDA in preterm infants.

The effects of flexed (fetal tucking) and extended (free body) postures on the daily sleep quantity of hospitalized premature infants: A randomized clinical trial

BACKGROUND

Proper sleep is essential for the development of premature infants. Infants, during hospitalization, might suffer from inappropriate postures and insufficient sleep hours. To compare the daily sleep quantities of premature infants in flexed (facilitated fetal tucking) posture and extended (free body) posture. This study is a randomized clinical trial which was conducted in neonatal ward of Al-Zahra Teaching Hospital of Tabriz, Iran, 2015. Thirty-two premature infants with the age range of 33-36 weeks were selected for the study.

MATERIALS AND METHODS

Every infant was studied for 4 days in a sequential format. Every infant was studied for 4 days and in a 12-h period every day (8 a.m-8 p.m). Each day, an infant was randomly put in one of the four statuses, namely, free body posture in the supine position, free body posture in the lateral position, facilitated fetal tucking in the supine position and facilitated fetal tucking in the lateral position. Films were recorded in the 12-h period (8 a.m-8 p.m). SPSS Software (version 13) was used for data analysis.

RESULTS

The results showed that about the main effect of posture on sleep variable, there was a statistically significant difference (P = 0.003). In addition, about the main effect of position on sleep variable; there was a statistically significant difference (P = 0.002). Meanwhile, there was no significant interaction effect between the posture and position for the daily sleep duration (P = 0.746). Daily sleep duration of the infants in flexed (facilitated fetal tucking) posture and lateral position is longer than that of the infants in extended (free body) posture and supine position.

CONCLUSION

Daily sleep duration in the infants experiencing flexed posture and lateral position at rest is longer. Moreover, it decreases wakefulness time of the premature infants.

Development of sleep/wake, activity and temperature rhythms in newborns maintained in a neonatal intensive care unit and the impact of feeding schedules

Biological rhythms in infants are described as evolving from an ultradian to a circadian pattern along the first months of life. Recently, the use of actigraphy and thermistors with memory has contributed to the understanding of temporal relations of different variables along development. The aim of this study was to describe and compare the development of the rhythmic pattern of wrist temperature, activity/rest cycle, sleep/wake and feeding behavior in term and preterm newborns maintained in a neonatal intensive care unit (NICU).

METHODS

Nineteen healthy preterm and seven fullterm newborns had the following variables monitored continuously while they were in the NICU: activity recorded by actigraphy, wrist temperature recorded with a thermistor and observed sleep and feeding behavior recorded by the NICU staff with diaries. Subjects were divided in 3 groups according to their gestational age at birth and rhythmic parameters were compared.

RESULTS

A dominant daily rhythm was observed for wrist temperature since the first two weeks of life and no age relation was demonstrated. Otherwise, a daily pattern in activity/rest cycle was observed for most preterm newborns since 35 weeks of postconceptional age and was more robust in term babies. Feeding and sleep/wake data showed an almost exclusive 3h rhythm, probably related to a masking effect of feeding schedules.

CONCLUSIONS

We found that wrist temperature develops a daily pattern as soon as previously reported for rectal temperature, and with acrophase profile similar to adults. Moreover, we were able to find a daily rhythm in activity/rest cycle earlier than previously reported in literature. We also suggest that sleep/wake rhythm and feeding behavior follow independent developmental courses, being more suitable to masking effects.

Regulatory Problems in Very Preterm and Full-Term Infants Over the First 18 Months

OBJECTIVE

This study is an investigation of differences in regulatory problems (RPs; crying, sleeping, feeding) expressed by infants born very preterm (VP; <32 wk gestation) or with very low birth weight (VLBW; <1500 g) and infants born at full term (FT) during the first 18 months of life. It investigates the prevalence of single and multiple RPs, their persistence and how early in infancy RPs still found at 18 months of age can be predicted.

METHOD

This prospective longitudinal study of 73 VP/VLBW and 105 FT infants utilized a standard interview of mothers to assess regulatory problems among the infants at term, 3, 6, and 18 months of age.

RESULTS

Few differences were found between VP/VLBW and FT infants in the first 6 months. At 18 months, VP/VLBW infants had more single sleeping (RR = 2.2, CI = 1.3-3.7), feeding (RR = 1.4, CI = 1.03-1.8), and multiple RPs (RR = 1.7, CI = 1.02-2.8) than FT infants. In VP/VLBW infants, RPs as early as 3 months and in FT infants RPs as early as 6 months predicted RPs at 18 months. Those infants who had persistent RPs in the first 6 months of life were more likely to still have RPs at 18 months.

CONCLUSION

VP/VLBW children are at slightly increased risk for RPs at term and in the second year of life. Clinicians should be aware that RPs that persist across the first 6 months point to increased risk of continuing RPs into toddlerhood in both VP/VLBW and FT infants.

Developmental changes in sleep and breathing across infancy and childhood

Sleep and breathing are physiological processes that begin in utero and undergo progressive change. While the major period of change for both sleep and breathing occurs during the months after birth, considered a period of vulnerability, more subtle changes continue to occur throughout childhood. The systems that control sleep and breathing develop separately, but sleep represents an activity state during which breathing and breathing control is significantly altered. Infants and young children may spend up to 12 hours a day sleeping; therefore, the effects of sleep on breathing are fundamental to understanding both processes in childhood. This review summarizes the current literature relevant to understanding the normal development of sleep and breathing across infancy and childhood.

Influence of light exposure during early life on the age of onset of bipolar disorder

BACKGROUND

Environmental conditions early in life may imprint the circadian system and influence response to environmental signals later in life. We previously determined that a large springtime increase in solar insolation at the onset location was associated with a younger age of onset of bipolar disorder, especially with a family history of mood disorders. This study investigated whether the hours of daylight at the birth location affected this association.

METHODS

Data collected previously at 36 collection sites from 23 countries were available for 3896 patients with bipolar I disorder, born between latitudes of 1.4 N and 70.7 N, and 1.2 S and 41.3 S. Hours of daylight variables for the birth location were added to a base model to assess the relation between the age of onset and solar insolation.

RESULTS

More hours of daylight at the birth location during early life was associated with an older age of onset, suggesting reduced vulnerability to the future circadian challenge of the springtime increase in solar insolation at the onset location. Addition of the minimum of the average monthly hours of daylight during the first 3 months of life improved the base model, with a significant positive relationship to age of onset. Coefficients for all other variables remained stable, significant and consistent with the base model.

CONCLUSIONS

Light exposure during early life may have important consequences for those who are susceptible to bipolar disorder, especially at latitudes with little natural light in winter. This study indirectly supports the concept that early life exposure to light may affect the long term adaptability to respond to a circadian challenge later in life.

Very preterm infants show earlier emergence of 24-hour sleep-wake rhythms compared to term infants

BACKGROUND

Previous studies show contradictory results about the emergence of 24-h rhythms and the influence of external time cues on sleep-wake behavior in preterm compared to term infants.

AIMS

To examine whether very preterm infants (<32 weeks of gestational age) differ in their emergence of the 24-h sleep-wake rhythm at 5, 11 and 25 weeks corrected age compared to term infants and whether cycled light conditions during neonatal intermediate care affects postnatal 24-h sleep-wake rhythms in preterm infants.

STUDY DESIGN

Prospective cohort study with nested interventional trial.

SUBJECTS

34 preterm and 14 control term infants were studied. During neonatal hospitalization, preterm infants were randomly assigned to cycled light [7 am-7 pm lights on, 7 pm-7 am lights off, n=17] or dim light condition [lights off whenever the child is asleep, n=17].

OUTCOME MEASURES

Sleep and activity behavior recorded by parental diary and actigraphy at 5, 11 and 25 weeks corrected age.

RESULTS

Sleep at nighttime and the longest consolidated sleep period between 12 pm-6 am was longer (mixed model analysis, factor group: p=0.02, resp. p=0.01) and activity at nighttime was lower (p=0.005) at all ages in preterm compared to term infants. Cycled light exposed preterm infants showed the longest nighttime sleep duration. Dim light exposed preterm infants were the least active.

CONCLUSIONS

Preterm infants show an earlier emergence of the 24-h sleep-wake rhythm compared to term infants. Thus, the length of exposure to external time cues such as light may be important for the maturation of infant sleep-wake rhythms. Trial registry number: This trial has been registered at www.clinicaltrials.gov (identifier NCT01513226).

Biological and psychological rhythms: an integrative approach to rhythm disturbances in autistic disorder

Biological rhythms are crucial phenomena that are perfect examples of the adaptation of organisms to their environment. A considerable amount of work has described different types of biological rhythms (from circadian to ultradian), individual differences in their patterns and the complexity of their regulation. In particular, the regulation and maturation of the sleep-wake cycle have been thoroughly studied. Its desynchronization, both endogenous and exogenous, is now well understood, as are its consequences for cognitive impairments and health problems. From a completely different perspective, psychoanalysts have shown a growing interest in the rhythms of psychic life. This interest extends beyond the original focus of psychoanalysis on dreams and the sleep-wake cycle, incorporating central theoretical and practical psychoanalytic issues related to the core functioning of the psychic life: the rhythmic structures of drive dynamics, intersubjective developmental processes and psychic containment functions. Psychopathological and biological approaches to the study of infantile autism reveal the importance of specific biological and psychological rhythmic disturbances in this disorder. Considering data and hypotheses from both perspectives, this paper proposes an integrative approach to the study of these rhythmic disturbances and offers an etiopathogenic hypothesis based on this integrative approach.

Relationship between infant and mother circadian rest-activity rhythm pre- and postpartum, in comparison to an infant with free-running rhythm

Some infants show a free-running rhythm in their rest-activity. We do not know why, nor do we know exactly what the entrainment factors are for the development of the normal 24-h rest-activity rhythm. Actigraphic recordings on 10 primiparae during late pregnancy and these mothers and their infants during the 2nd, 6th, and 12th wks after birth were made over 3-5 continuous days to investigate maternal and infant entrainment. One infant showed a free-running rest-activity circadian rhythm. In late pregnancy, the period in the autocorrelogram of the mother with the free-running infant was longer than the significant period of the mean autocorrelogram of the mothers with non-free-running infants. The finding of this study indicates the free-running rhythm of infant is not reset by maternal entrainment factors.

The development of the circadian heart rate rhythm (CHR) in Asian infants

OBJECTIVE

To test the hypothesis that term-born Asian infants, at reduced risk to die of Sudden Infant Death Syndrome (SIDS) exhibit a circadian heart rate rhythm (CHR) at a later age than non-Asian term infants.

METHOD

Repeated overnight heart rate (HR) traces obtained with a battery-operated Polar S810i heart-rate monitor at home in 17 Asian Torajan infants in Indonesia, were compared with those of 52 non-Asian infants monitored as part of the Collaborative Home Infant Monitoring Evaluation (CHIME). HR was determined using a moving window averaging technique. A comparison of median HR during quiet sleep (QS) episodes (identified by minimum HR variability), established the presence of CHR.

RESULTS

Seventy three percent of non-Asian CHIME infants ≤7 weeks exhibited CHR compared to 45% of Asian Torajan infants. Between 8 and 12 weeks, 94% of non-Asian CHIME infants exhibited CHR, compared to 33% of Asian Torajan infants (p<0.001). Forty seven and 56% of Asian Torajan infants exhibited the CHR at the age intervals of 16-20 weeks and 21-25 weeks respectively. Active wakefulness percentages as a function of the entire recording and median QS HR were not significantly different in the two groups.

CONCLUSION

Despite the fact that Asian Torajan infants were on average a week older than non-Asian CHIME babies, between two and three months of age only one in three exhibited the CHR, compared to virtually all non-Asian CHIME infants. We speculate that the cause of this difference rests in the infants' environment rather than their genetic origin.

Daily rhythms of the sleep-wake cycle

The amount and timing of sleep and sleep architecture (sleep stages) are determined by several factors, important among which are the environment, circadian rhythms and time awake. Separating the roles played by these factors requires specific protocols, including the constant routine and altered sleep-wake schedules. Results from such protocols have led to the discovery of the factors that determine the amounts and distribution of slow wave and rapid eye movement sleep as well as to the development of models to determine the amount and timing of sleep. One successful model postulates two processes. The first is process S, which is due to sleep pressure (and increases with time awake) and is attributed to a 'sleep homeostat'. Process S reverses during slow wave sleep (when it is called process S'). The second is process C, which shows a daily rhythm that is parallel to the rhythm of core temperature. Processes S and C combine approximately additively to determine the times of sleep onset and waking. The model has proved useful in describing normal sleep in adults. Current work aims to identify the detailed nature of processes S and C. The model can also be applied to circumstances when the sleep-wake cycle is different from the norm in some way. These circumstances include: those who are poor sleepers or short sleepers; the role an individual's chronotype (a measure of how the timing of the individual's preferred sleep-wake cycle compares with the average for a population); and changes in the sleep-wake cycle with age, particularly in adolescence and aging, since individuals tend to prefer to go to sleep later during adolescence and earlier in old age. In all circumstances, the evidence that sleep times and architecture are altered and the possible causes of these changes (including altered S, S' and C processes) are examined.

Comparing sleep measures of infants derived from parental reports in sleep diaries and acceleration sensors

AIM

Comparing sleep measures of infants derived from two data collection methods, acceleration sensors and sleep diaries, and identify the clinical application for each data collection method.

METHODS

The participants were 52 pairs of infants and mothers. Infant sleep measures were obtained through the actigraphs (Micro-mini RC, Ambulatory Monitoring Inc., Ardsley, NY, USA) and sleep diaries for over a period of 7 days.

RESULTS

The results showed that the concordance in sleep measures derived from two methods showed decreases in the following order: sleep offset time [r=0.91 (p=0.00)], sleep onset time r=0.89 (p=0.00), nocturnal sleep duration [r=0.75 (p=0.00)], the number of night wakings [r=0.46 (p<0.01)] and WASO [r=0.34 (p<0.05)]. It was revealed that the accuracy of sleep diary records was affected by the sleeping place and varied throughout the study period.

CONCLUSION

It was confirmed that the sleep measures indicating sleep schedule reported from the sleep diaries had high concordances compared with the data from the actigraphs. Using the sleep diary was recommended to understand behaviours when focusing on infant's daily rhythms. In terms of accuracy and stability of recording throughout the study period, understanding sleep quality and independence of sleeping places, the choice of actigraph was recommended.

Relationship between circadian salivary melatonin levels and sleep-wake behavior in infants

BACKGROUND

There have been calls for more aggressive intervention for infants with failure in development of a sleep-wake rhythm. If development of the 'biological clock' in infants can be assessed by measuring melatonin, this may provide a useful indicator of the sleep-wake rhythm development. Thus, we investigated relationship between circadian salivary melatonin concentrations and sleep-wake behavioral parameters in infants.

METHODS

Sixty-seven mothers who had infants aged 3-15 months were requested to record sleep-wake behavior of their baby for 2 days, and to collect their baby's saliva four times daily in the morning (06:00-09:00 h), noon (11:00-13:00 h), evening (16:00-18:00 h), and night (19:00-22:00 h) for measurement of melatonin concentrations by ELISA.

RESULTS

The mean melatonin concentrations of the saliva were: morning 40 ± 4 pg/mL, noon 14 ± 3 pg/mL, evening 15 ± 3 pg/mL, and night 23 ± 4 pg/mL. The melatonin concentrations, at each measurement point, were highest in infants aged 3-5 months, and decreased as age increased. Morning melatonin concentrations showed a negative correlation with nocturnal sleep duration (P<0.05). Increased morning concentrations were related to early waking time (P<0.05). In infants with open air baths on most days, evening and night melatonin concentrations were significantly lower (P<0.05).

CONCLUSION

Salivary melatonin concentrations in infants between 06:00 and 22:00 decreased by age, and elevation of morning values may indicate an immature sleep-wake rhythm. Frequent open air baths may contribute to decreased melatonin levels.

Mother-Infant Activity Synchrony as a Correlate of the Emergence of Circadian Rhythm

Objective: Entrainment to the day—night cycle is critical for infant sleep and social development. Synchronization of infant circadian systems with the social 24-hr day may require maternal activity signals as an entraining cue. This descriptive and exploratory research examines the activity level and circadian pattern in mothers and infants. Method: Twenty-two healthy mothers and their infants (postnatal age 49.8 ± 17.1 days) wore actigraph monitors for seven days. Daytime (06:00—21:59) and nighttime (22:00—05:59) activity levels and circadian parameters of rest—activity patterns (i.e., mesor, amplitude, acrophase, and 24-hr cosinor fit) were calculated. Results: Mothers and infants were significantly more active during the day than at night. The goodness-of-fit index for the model (R2) indicates that circadian rhythm accounted for a mean of 29 ± 10% and 12 ± 8% of the variability in maternal and infant activity, respectively. Acrophase of activity occurred at 15:46 ± 1:07 for the mothers and 15:20 ± 1:21 for the infants. The mean within-dyad correlation of activity counts was r = .46 ± .11, and the within-dyad correlation was associated with the amplitude (r = .66, p < .01) and 24-hr cosinor fit of infant activity (r = .67, p < .01). Conclusions: Our findings suggest maternal rhythms as a possible exogenous influence on shaping an infant’s emerging rhythms and synchronizing them with the external light—dark cycle. Strong pattern synchrony between maternal and infant activity may support infant circadian entrainment and enhance a regular 24-hr sleep—wake schedule during the early postnatal weeks.

Activity-based assessment of the sleep behaviors of VLBW preterm infants and full-term infants at around 12 months of age

PURPOSE

The aim of this study is to identify the characteristics of sleep behaviors assessed from activity data among very low-birth weight (VLBW) preterm infants in comparison to full-term infants at the age of around 12 corrected months, due to the possibility that sleep behaviors of preterm infants may be different from those of full-term infants.

METHOD

Cross-sectional study. Infant sleep measures were obtained through actigraphs (Micro-mini RC, Ambulatory Monitoring Inc., Ardsley, NY), which were attached to the infants' ankles during a week-long period. The subjects were 14 preterm infants and 14 full-term infants in which the mean ages were 13.3+/-2.1 corrected months and 12.3+/-2.4 month, respectively.

RESULTS

Preterm infants showed significantly less sleep duration during nighttime than full-term infants. The mean activity score and ACTX (Activity Index: percentage minutes with more than 0 activity score) of preterm infants during nighttime were significantly higher than those of full-term infants. No significant differences in total sleep duration, daytime sleep duration, the number of night-wakings, and sleep efficiency were found between the two groups.

CONCLUSION

Preterm infants slept less and had a larger percentage of less restful sleep during nighttime. The results indicated that prematurity at the time of birth remained throughout the developmental course of sleep behaviors among preterm infants at around the age of 12 corrected months.

[Ontogenesis of circadian rhythm in the human]

Ontogenesis of circadian rhythms in human beings, the history of the development of synchronisation of the daily rhythm describes the deployment of an adaptive capacity providing vital biological linkage to the environment. Methods for dating the stages in this temporal organisation have advanced and the genetics approach to the circadian cycle is dominated by studies of the maturation of the awake-asleep cycle. Disease involves the functional regression to one of the different stages of genesis or alternatively will involve a pathological lesion. Circadian dysfunction is characterised by loss of amplitude and multi-day fragmentation, correction of which requires control of multi-day pressure and within-day stabilisation.

Actigraphic Recordings of Activity-Rest Rhythms of Neonates Born by Different Delivery Modes

Activity-rest behavior of 20 neonates born vaginally, 18 neonates born by medically planned Cesarean section (C-section), and 19 neonates born by medically required C-section after labor onset (all born in the thirty-seventh to forty-second week of gestation) was monitored for six successive days starting in the first week of life. Actigraphy was used to record and show time patterns of activity and rest in neonates by using small wristwatch-like Actiwatch actometers. Nursing/feeding times were recorded by using the actometers' integrated event marker button. Recordings in both C-section groups were performed in the hospital; for neonates born vaginally and for some born by C-section, recordings were carried out in the hospital and in their homes. In addition to the actigraphic recordings, a standardized diary was kept regularly. To assess periodic characteristics, frequency components of activity-rest behavior were analyzed using fast Fourier transformation. Amount of sleep time during daytime, nighttime, and 24 h, as well as sleep bouts during the daytime and nighttime, were compared. The majority of vaginally born neonates showed a distinct circadian frequency in their spectra. In contrast, both groups of neonates born by C-section showed significantly less distinct circadian frequencies in their spectra. All three groups showed a significant difference in amount of nighttime sleep vs. daytime sleep, with more sleep at nighttime. There were no differences in the amount of nighttime sleep, daytime sleep, and sleep time during 24 h between the groups born by different delivery modes.

Development of the 24-h rest-activity pattern in human infants

The development of the 24-h rest-activity pattern was investigated in human infants under naturalistic conditions as assessed by continuous actigraphy. Seven infants and their mothers were recorded for 4 (n=1), 6 (n=5) and 12 months (n=1) after birth. Periodogram analysis of rest-activity data was performed over consecutive 10-day intervals. A weak 24-h rest-activity pattern was already present in some infants during the newborn period. The magnitude of the 24-h component in individual periodograms increased across the first months following a saturating function. The time constants of fitted saturating exponential functions--reflecting the rate of development of the 24-h pattern--ranged from 49 to 110 days (n=6) indicating a large interindividual variability. Furthermore, intraindividual variation was observed; the magnitude of the 24-h rest-activity component showed fluctuations around the trend. Miniaturized actigraphs are ideal tools for long-term longitudinal monitoring of rest-activity behavior in infants.

Sleep of preterm neonates under developmental care or regular environmental conditions

Sleep is the main behavioral state of the premature infant. In adult intensive care units, sleep deprivation has been reported as one of the major stressors. Developmental care (DC) aims to decrease stressful events in neonatal intensive care unit and support well-being.

AIM

To assess whether DC is accompanied by changes in sleep in preterm neonates.

METHODS

A prospective cross-over study included 33 preterm neonates [mean (S.D.): gestational age: 29.3 (1.8) weeks; birth weight: 1245 (336) g]. Polysomnography was performed in two randomly ordered 3-h periods with and without DC. A blinded electrophysiologist analyzed sleep. The total sleep time (TST) was the primary outcome, duration of active (AS), quiet (QS) and indeterminate sleep, and latency before sleep were the secondary outcomes. Non-parametric Wilcoxon tests and ANOVA were used.

RESULTS

In DC condition vs. control: TST increased [in minutes, mean (S.E.M.): 156.2 (2.9) vs. 139.2 (4.6), p=0.002], with increase in AS [86.6 (3.7) vs. 77.0 (4.2), p=0.024] and in QS [47.1 (4.1) vs. 36.9 (4.2), p=0.015], and sleeping latency decreased (2.1 (0.7) vs. 10.5 (2.0), p=0.0005].

CONCLUSION

DC promoted sleep in our study. The impact of DC on the neuro-behavioral outcome needs futures studies.

Actigraphic monitoring of the activity-rest behavior of preterm and full-term infants at 20 months of age

Differences in the activity-rest behavior of preterm and full-term infants provide an important contribution to the analysis of the ontogeny of circadian rhythms. In this study, we recorded the activity-rest behavior of 17 preterm and 8 full-term infants at the approximate age of 20 months over an average of 10 days by means of actigraphic monitoring (Actiwatch, Cambridge Neurotechnology Ltd.). At the same time, the parents of the infants kept a daily diary. The activity-rest rhythm, the nighttime sleep duration, the daytime rest duration, as well as the sleep quality of the infants were analyzed. Preterm and full-term infants at the age of 20 months show a circadian rhythm with a period length between 23 h 32 min (23:32 h) and 24 h 23 min (24:23 h). It can be concluded that the preterm and full-term infants all reached a vital developmental step by showing the dominant circadian rhythm in the spectrum. The daytime rest duration of preterm infants is significantly shorter than that of full-term infants. The sleep quality of preterm infants is significantly lower than that of full-term infants, which means that the preterm infants have a larger percentage of less restful nighttime sleep. In other studies preterm infants show an over-proportional frequency of attention deficit hyperactivity disorder (ADHD). For this reason, future analyses should reveal whether or not actigraphic monitoring is a suitable means for an early identification of activity-rest behavior in children who may develop ADHD.

Development of fetal and neonatal sleep and circadian rhythms

The origin of sleep and circadian rhythms development is found during the fetal period. Both quiet (NREM) and active (REM) sleep are distinguishable during the last 10 weeks of gestation. Comparable to fetuses, low risk preterm infants recorded at 30-40 weeks postconceptional age, had a similar development of sleep i.e. an increase in quiet sleep and a decrease in indeterminate sleep. A further development in sleep organization characterized by increased slow wave and spindle activity during quiet sleep and coupling with circadian rhythm takes place during the first 6 months of life in both term and preterm infants.Circadian rhythm of fetal heart rate synchronized with maternal rest-activity, heart rate, cortisol, melatonin, and body temperature rhythms is present during the last 10 weeks of gestation. Although maternally influenced, circadian rhythm antenatally becomes ultradian at birth. Both preterm and term infants show a significant increase in circadian body temperature rhythm amplitude during the first 3 months of life.

Effects of phototherapy in neonates on circadian sleep-wake and saliva cortisol level rhythms

The influence of phototherapy treatment during the neonatal period on sleep-wake rhythm, and its long-term effects on biological rhythms, was evaluated in preterm and full-term infants. Forty-three infants treated with phototherapy during the neonatal period and 47 untreated infants were examined for entrainment of sleep-wake rhythms between 16 and 52 weeks and for sleep-wake and saliva cortisol rhythms at 2.5 years of age. The age of sleep-wake rhythm entrainment was not significantly different between the 2 groups. No correlations between duration of exposure to phototherapy and corrected age of entrainment of sleep-wake rhythm were observed. At follow-up, no significant differences in sleep-wake and saliva cortisol rhythms were observed between the 2 groups, indicating that circadian variations were similar to those in adults.

Circadian and sleep development in preterm infants occurs independently from the influences of environmental lighting

This study investigated the effect of intermediate nursery illumination on circadian rhythm and sleep development of preterm infants. Preterm infants were randomly assigned to one of two intermediate nursery rooms: a dimly lighted room, the dim (control) group, or a day-night lighted room, the cycled (intervention) group. Continuous rectal temperature and sleep were recorded at 36 wk postconceptional age (before discharge) and at 1 and 3 mo corrected age at home. Forty infants, 21 in the dim group and 19 in the cycled group, were recorded. The clinical demographic data and neonatal scores were similar between groups before the intervention. Circadian rhythms and sleep showed significant development with age, but there was no environmental lighting effect. Circadian and sleep organization seems to develop endogenously in preterm infants.

Massage therapy by mothers enhances the adjustment of circadian rhythms to the nocturnal period in full-term infants

The objective of this study was to investigate the effect of massage therapy on phase adjustment of rest-activity and melatonin secretion rhythms to the nocturnal period in full-term infants. Rest-activity cycles of infants (measurement 1, n = 16) were measured by actigraphy before and after 14 days of massage therapy (starting at age 10 [+/-4] d) and subsequently at 6 and 8 weeks of age. 6-Sulphatoxymelatonin excretion was assessed in urine samples at 6, 8, and 12 weeks of age (measurement 2, n = 21). At 8 weeks the controls revealed one peak of activity at approximately 12 midnight (11 p.m.-3 a.m.) and another one at approximately 12 noon (11 a.m.-3 p.m.), whereas in the treated group, a major peak was early in the morning (3 a.m.-7 a.m.) and a secondary peak in the late afternoon (3 p.m.-7 p.m.). At 12 weeks, nocturnal 6-sulphatoxymelatonin excretions were significantly higher in the treated infants (1346.38 +/- 209.40 microg/night vs 823.25 +/- 121.25 microg/night, respectively; <.05). It is concluded that massage therapy by mothers in the perinatal period serves as a strong time cue, enhancing coordination of the developing circadian system with environmental cues.

Preterm infant temperature circadian rhythm: possible effect of parental cosleeping

The purpose of this study was to describe the circadian rhythm of abdominal skin temperature and explore factors related to the timing of circadian rhythm acrophase. Thirty-four preterm infants (gestational age 26 to 33 weeks) were studied in the home environment at 44 to 46 weeks postconceptional age. Insulated abdominal skin was monitored continuously, and parents recorded sleep/wake activity over a 24-h period. Circadian rhythm was analyzed using cosinor analysis. Using MANCOVA, the effects of cosleeping, feeding method, night feeding, hospital stay, time home, and illness on acrophase were determined. Infants demonstrated evidence of developing circadian rhythm of temperature. Cosleeping and length of hospital stay were significantly related to acrophase. The mean acrophase for cosleeping infants was 07:44 (95% confidence interval = 05:12, 11:08), whereas that for non-cosleeping infants was 22.05 (95% confidence interval = 17:31, 01:42). Proximity with parents during nighttime hours may serve to entrain preterm infant circadian rhythm.

Influence of light in the NICU on the development of circadian rhythms in preterm infants

The fetal biological clock is an endogenous clock capable of generating circadian rhythms and responding to maternal entraining signals. By at least the third trimester of pregnancy fetal diurnal rhythms are entrainable by maternal day-night rhythms. Maternal illness during pregnancy and premature birth are obvious clinical factors that may adversely affect circadian rhythm development. Premature birth of the fetus has a most dramatic impact on maternal fetal interactions. The effect on biorhythms appears to be temporary and is greatest on the most immature infants. The results to date support the importance of fetal circadian rhythms and the relative lack of these rhythms in the preterm infant. It is well known that growth and development in the prematurely born infant are influenced by a multitude of factors; clearly, the neonatal intensive care unit is not a surrogate for the maternal placental unit. This article reviews what is known about circadian development in the human infant with an emphasis on the unique circumstances of the preterm infant. The research on the short- and long-term effects of environmental interventions on circadian, sleep, and neurologic development is discussed. Although an earlier onset of circadian development did not result with cycled lighting in the neonatal nursery, there may still be important biological effects that have not been studied. There are sufficient data to state that there is no reason for continuing a chaotic, noncircadian environmental approach for the care of the prematurely born infant.