Validation of actigraphy for determining sleep and wake in preterm infants.

BACKGROUND: Actigraphy has been widely used in adults and children for the determination of sleep and wake. However, there have been limited studies in infants and to date there have been no studies to validate the reliability of actigraphy in preterm infants. AIM: To evaluate the usefulness of actigraphy in preterm infants in a neonatal unit setting for determining sleep-wake by comparing results with those recorded from behavioural observations. METHODS: Thirty-eight studies were carried out in 10 preterm infants (8M/2F) born at 29-34 weeks gestational age. Sleep-wake patterns were assessed over 24 h with behavioural observations and compared to actigraphy (Actiwatch AW64, Mini Mitter Company Inc., Sunriver, OR, USA). The studies were grouped into gestational ages 30-33 weeks (n = 8), 34-36 weeks (n = 20) and 37-40 weeks (n = 10). RESULTS: Overall, on the low-activity threshold we found agreement rates of 84.5-88.9% between actigraphy and behavioural scoring with the predictive value for determining sleep (PVS) being between 91.3% and 95.6% and sensitivity between 88.2% and 96.8%. However, the actiwatch was not reliable for determining wakefulness with low values for predictive value of wake (PVW,31.1-53.7%) and specificity (31.5-33.6%). CONCLUSION: Actigraphy can be used as a reliable indicator of sleep patterns in preterm infants in the neonatal unit setting.

Relationship between sleep/wake patterns, temperament and overall development in term infants over the first year of life.

BACKGROUND: This study sought to assess the relationship between the development of infant sleep/wake patterns, temperament and overall mental, motor and behavioural development over the first year of life. We hypothesised that infants with more regular sleep/wake patterns and longer sleep durations would have an easier temperament and higher developmental scores. STUDY DESIGN: Sleep/wake characteristics were recorded with the use of both parental sleep diary and actigraphy (Actiwatch AW64, Mini Mitter Company Inc, Sunriver, OR, USA) in 20 healthy term infants at monthly intervals over the first year of life. Temperament was assessed using the Early Infant Temperament Questionnaire (EITQ) at 3 months and the Revised Infant Temperament Questionnaire (RITQ) at 6 and 11 months and mental, motor and behavioural development at 12 months using the Bayley Scales of Infant Development II (BSID-II). RESULTS: At all 3 ages studied increased nocturnal sleep was correlated with increased approachability. In addition, at 11 months increased diurnal sleep duration was also correlated with increased rhythmicity and adaptability. At 12 months of age decreased daytime sleep duration was correlated with emotional regulation. CONCLUSIONS: Our findings highlight the importance of considering maturational and regulatory aspects of sleep when evaluating infant daytime behaviour. We suggest that concerns regarding sleep characteristics should become a significant aspect of clinical assessment and diagnosis of developmental delay or behaviour problems, particularly in the first year of life.

The use of actigraphy for assessment of the development of sleep/wake patterns in infants during the first 12 months of life.

Maturation of sleep/wake patterns is one of the most important physiological developments during the first year of life. In this study, we aimed to compare the use of actigraphy and parental sleep diaries (SD) for recording the development of sleep/wake patterns longitudinally in term infants in their own home environments over the first 12 months of life. Twenty healthy term infants (7F/13M) were studied for 3 days each month in their own homes over the first 12 months of life. Sleep/wake patterns were recorded using both SD and actigraphy (AW) (AW64, Mini Mitter Co. Inc., Sunriver, OR, USA). The development of sleep and wake was analysed over 24 h, during the day (08:00-20:00 hours) and during the night (20:00-08:00 hours). A total of 186 studies had complete data sets for both analysis methods. Overall, there was no difference between methods of measurement for determination of the total percentage of sleep or wake over 24 h, or for the total percentage of sleep or wake during the day. However, at night, AW scored less time asleep (73.3 +/- 0.9%) and more time awake (26.7 +/- 0.9%) compared with the SD (80.7 +/- 1.04% and 19 +/- 1.0%, respectively, P < 0.001). Mean percentage sleep during the day decreased from 51% at 1 month to 28% at 12 months with the 1-month values being significantly higher than all other ages, while mean percentage sleep at night was only different between 1 month and 11 and 12 months. In conclusion actigraphy provides a useful tool for assessing the development infant sleep.

Actigraphy correctly predicts sleep behavior in infants who are younger than six months, when compared with polysomnography.

Actigraphy has been widely used in adults and children. In infants, validation of actigraphy has typically used a comparison with behaviorally determined sleep state classification rather than polysomnography (PSG). This study validated actigraphy against PSG for determining sleep and waking states in infants who were younger than 6 mo. Twenty-two healthy infants, 13 term and 9 preterm, were studied at three different matched postconceptional ages. Actigraph data were compared with PSG recordings in 1-min epochs. Agreement rate (AR), predictive value for sleep, predictive value for wake, sensitivity. and specificity were calculated and compared between activity thresholds and across ages with two-way ANOVA for repeated measures. Thirty-two validation studies were analyzed. Overall AR with PSG of 93.7 +/- 1.3 and 91.6 +/- 1.8 were obtained at 2-4 wk and 5-6 mo, respectively, at the low activity threshold setting, whereas the auto activity threshold gave the best agreement with PSG at 2-4 mo (AR 89.3 +/- 1.3%). Sensitivity values of 96.2 +/- 1.1% at 2-4 wk, 91.2 +/- 1.5% at 2-4 mo, and 94.0 +/- 1.9% were obtained at these same settings. There was no difference across ages in AR or sensitivity. PVW and specificity values were low in this study. We conclude that actigraphy is a valid method for monitoring sleep in infants who are younger than 6 mo.

Heart rate responses to non-arousing trigeminal stimulation in infants: effects of sleep position, sleep state and postnatal age.

AIMS: The aim of this study was to examine the effects of maternal smoking, sleeping position, sleep state and postnatal age on heart rate changes following non-arousing trigeminal stimulation in infants. SUBJECTS: We studied healthy term infants, 13 of whom were born to mothers who did not smoke and 11 to mothers who smoked during pregnancy. Each infant was studied using daytime polysomnography on 3 occasions: (a) 2-3 weeks, (b) 2-3 months and (c) 5-6 months after birth. Nasal air-jet stimulation was presented in both active sleep (AS) and quiet sleep (QS) when infants slept both prone and supine. RESULTS: We found no difference between infants of smoking and non-smoking mothers in any of the parameters measured. Minimum HR (MinHR) following non-arousing trigeminal stimulation was significantly lower in the supine compared to the prone sleeping position at 2-3 weeks and 2-3 months of age (p<0.05) in AS, and at all 3 ages in QS (p<0.01). MinHR was significantly lower in QS compared to AS at 2-3 months when infants slept prone and at 5-6 months when sleeping supine (p<0.01). In QS, MinHR became lower with increasing postnatal age in both sleep positions (p<0.01). In AS, there was no maturational effect. The normalized bradycardia (DeltaHR%) was significantly greater in AS than in QS at 2-3 weeks of age (p<0.05) when infants slept supine. CONCLUSION: Our study has shown that there was a decrease in heart rate (MinHR) following trigeminal stimulation in infants up to 6 months of age and this was affected by sleep position and sleep state, being larger in the supine sleeping position and the QS state.

Influences of maternal cigarette smoking on infant arousability.

Since the reduction in the incidence of the prone sleeping position, maternal cigarette smoking has become the strongest modifiable risk factor for Sudden Infant Death Syndrome (SIDS). This risk is dose dependent. Various mechanisms have been postulated to explain the increased risk of SIDS associated with maternal smoking, among these, impairment of arousal from sleep. This paper reviews the effects of maternal smoking on infant arousability from sleep, cardiorespiratory controls and sleep architecture. Infants exposed to maternal smoking have been shown to have both decreased spontaneous and evoked arousability from sleep. Such impairment of arousal has been demonstrated to be associated with changes in control of autonomic cardiac function. Sleep architecture appears not to be altered by smoking. During arousal, heart rate, blood pressure and breathing movements increase, while gross body movements occur to avoid the stimulus. Any impairment in arousability from sleep could occur when infants are exposed to maternal cigarette smoking, and could possibly contribute to the final pathway to SIDS.

Arousal and ventilatory responses to hypoxia in sleeping infants: effects of maternal smoking.

Our aim was to determine whether maternal cigarette smoking affects arousal and ventilatory responses to hypoxia in infants. Infants born to non-smoking (NS, n = 15) and smoking mothers (SM, n= 9) were studied at 2-5 weeks, 2-3 and 5-6 months. Ventilatory responses to 15% O(2) were determined preceding arousal. At each age and in both groups, infants aroused more frequently and earlier to hypoxia in active sleep (AS) than quiet sleep (QS). Arousal latency was longer in SM infants (in QS) at 5-6 months (P < 0.05). Baseline respiratory parameters were not different between groups, except that, at 2-3 months, SM infants had higher SP(O2) during AS than NS infants. Maternal smoking did not affect ventilatory responses preceding hypoxia-induced arousal in either sleep-state at any age. We conclude that mild hypoxia stimulates ventilation and arousal in infants up to 6 months and that arousability is depressed in SM infants at 5-6 months; however, ventilatory responses preceding arousal are not adversely affected by smoking.

Of sleep state and postnatal age on arousal responses induced by mild hypoxia in infants.

STUDY OBJECTIVES: It has been suggested that mild hypoxia may not be a potent stimulus for arousal during sleep in infants because infants frequently fail to arouse from quiet sleep (QS). Our aim was to characterize arousal responses of sleeping infants in both active sleep (AS) and QS under normoxic and mildly hypoxic (15% O2) conditions over the first 6 months of life. PARTICIPANTS: Five healthy term and 6 healthy preterm infants were each studied at 2 to 5 weeks, 2 to 3 months, and 5 to 6 months postterm. All infants underwent daytime polysomnography during which nasal airflow was monitored using a purpose-built pneumotachograph. All infants were studied under both normoxic (21% O2) and hypoxic (15% O2, balance N2) conditions (presentation order randomized) in each sleep state at each study age. Tests were terminated at arousal, O2 saturation falling below 85%, or 5 minutes (failure to arouse). MEASUREMENTS: Probability of failure to arouse and mean arousal latency were compared between each experimental condition, with each infant serving as its own control. RESULTS: Infants aroused more frequently under hypoxic conditions than under normoxic conditions. Overall, arousal latencies were shorter during hypoxia compared to normoxia in both sleep states at each age. Arousal latencies were longer in QS compared to AS in both hypoxic and normoxic conditions. CONCLUSION: In sleeping infants, mild hypoxia serves as a stimulus for arousal in both AS and QS. Of particular significance is our finding that arousal from AS is readily elicited by mild hypoxia.

Arousal responses to somatosensory and mild hypoxic stimuli are depressed during quiet sleep in healthy term infants.

STUDY OBJECTIVES: To compare arousal responses to somatosensory and hypoxic stimuli in sleeping human infants and to determine whether sleep state and postnatal age exerted similar changes in these arousal responses. DESIGN: We delivered somatosensory (nasal air-jet) stimulation and mild hypoxia (15% oxygen) to 10 healthy term infants aged 2 to 4 weeks, 2 to 3 months, and 5 to 6 months during identified sleep states. Hypoxic challenges were terminated at arousal, when the oxygen saturation fell below 85%, or at 5 minutes (failure to arouse). RESULTS: Infants failed to arouse to a greater percentage of hypoxia tests during quiet sleep (QS) than during active sleep (AS) at 2 to 3 months and 5 to 6 months of age (P < 0.01). Infants failed to arouse to a greater percentage of hypoxic challenges during QS at 2 to 3 months and 5 to 6 months than at 2 to 4 weeks of age. Arousal latency to hypoxia was significantly longer in QS than in AS at each study age; however, arousal latency was not affected by postnatal age. Arousal thresholds to somatosensory stimulation were significantly greater in QS than in AS, except at 2 to 4 weeks of age. In AS, arousability to the air-jet was greater at 2 to 3 months compared to 2 to 4 weeks of age (P < 0.05); in QS it was lower at 5 to 6 months compared to 2 to 4 weeks of age (P < 0.05). Arousal latency to hypoxia and arousal thresholds to air-jet stimulation were not correlated within infants. CONCLUSION: We conclude that arousal responses of infants to somatosensory and respiratory stimuli are similarly affected by sleep state and postnatal age. Infants are less arousable to both stimulus modalities in QS than in AS, and less arousable at 5 to 6 months of age than at 2 to 4 weeks in QS.

Ventilatory responses preceding hypoxia-induced arousal in infants: effects of sleep-state.

Augmented ventilation and/or arousal in response to hypoxia are important protective mechanisms during sleep. We aimed to quantify ventilatory responses preceding hypoxia-induced arousal in infants and determine the effects of sleep-state. Fifteen term infants were studied at 2-4 weeks, 2-3 and 5-6 months of age. Ventilatory responses to 15% oxygen inhalation were expressed as breath-by-breath changes from normoxic levels and averaged over 5, 10 and 15 breaths preceding arousal. Minute ventilation preceding arousal significantly increased above normoxic levels only in AS at 5-6 months. There were no sleep-state related differences in minute ventilation, oxygen saturation or carbon dioxide levels (expressed as changes from normoxic values) at 5, 10 or 15 breaths preceding arousal. However, the rate of oxygen desaturation during hypoxia in AS was two to four times faster than in QS at each age. We conclude that the ventilatory responses preceding hypoxia-induced arousal do not differ between sleep-states and that arousal occurs at similar levels of desaturation in both states.

Effects of sleep position, sleep state and age on heart rate responses following provoked arousal in term infants.

Previous studies have suggested that autonomic dysfunction may be involved in Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS are the prone sleeping position and maternal smoking. Our aim was to examine the effects of sleeping position and maternal smoking on the postnatal maturation of autonomic function by examining heart rate responses following arousal in healthy term infants. Twenty-four infants (11 born to mothers who smoked during pregnancy and 13 to mother who did not smoke) were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). We demonstrated no difference between smoking and non-smoking groups of infants in any of our measurements, and thus combined data from the groups. Baseline (BHR) was elevated in the prone compared to the supine position in quiet sleep (QS) at 2-3 weeks (p<0.001) and 5-6 months (p<0.001), and in active sleep (AS) at 2-3 and 5-6 months (p<0.05). BHR was significantly elevated in AS compared to QS in the supine position at all ages (p<0.01) and in the prone position at 2-3 (p<0.001) and 5-6 months (p<0.05). Increases in heart rate (deltaHR%) following arousal were significantly greater in the supine compared to the prone position in QS at 2-3 weeks (p<0.05) and in AS at both 2-3 (p<0.01) and 5-6 months (p<0.05). DeltaHR% was significantly greater in AS compared to QS in both supine (p<0.05) and prone (p<0.001) positions at 2-3 weeks and in the supine position at 2-3 months (p<0.001). We conclude that sleep state, sleep position and postnatal age affect the cardiac responses following arousal from sleep in healthy term infants. Impairment of heart rate control in the prone position may be important in understanding the increased risk for SIDS in this position.

Effect of infant sleeping position on sleep spindles.

Sleep spindles play an active role in inducing and maintaining sleep and may affect arousal by blocking the transmission of external stimuli through the thalamus to the cortex. Previously we have demonstrated that sleeping in the prone position impairs arousal in infants at 2-3 months of age, but not at 5-6 months. We aimed to examine if sleeping position and postnatal age affected duration and/or density of sleep spindles. Twenty-one healthy term infants were studied using daytime polysomnography at 2-3 months and 16 were again studied at 5-6 months. Infants slept both prone and supine at each study. The mean duration of non-rapid eye movement (NREM) sleep was not different between the two studies in either position. At 2-3 months both spindle density (P < 0.001) and proportion of NREM sleep (P < 0.025) with spindles were significantly greater in the supine than in the prone position. At 5-6 months spindle duration was longer in the supine than in the prone position (P < 0.03). Spindle density in the supine position was not different between the two studies, however, when infants slept prone, it was significantly increased at 5-6 months compared with 2-3 months (P < 0.001). Arousal threshold was not correlated with either spindle density or percentage of NREM sleep with spindles in either position at either study. In this study spindle density and the percentage time spent with spindles were not well correlated with infant arousability, and hence may not be able to be used as markers of depressed arousal responses in infants.

Temperament ratings do not predict arousability in normal infants and infants at increased risk of sudden infant death syndrome.

This study sought to determine whether temperament was an indicator of arousability from sleep in infants. We hypothesized that the "threshold" dimension would be the most predictive characteristic because it measures the stimulus intensity required to evoke a discernible response. Healthy term, healthy preterm, and preterm infants with a neonatal history of apnea underwent polysomnography at 2 to 3 months. Arousal was induced using air-jet stimulation of the nostrils in active (AS) and quiet sleep (QS). Temperament was assessed using the Early Infancy Temperament Questionnaire. Arousal thresholds were elevated in QS compared with AS in each group ( <.001), and preterm infants with a neonatal history of apnea were less arousable than healthy preterm infants ( <.05). Temperament was not a predictor of arousability in AS. "Adaptability" was the only significant predictor of arousability in QS. This study demonstrates that temperament characteristics as measured by questionnaire may not be reliable indicators of arousability from sleep.

Effects of age and sleeping position on arousal from sleep in preterm infants.

STUDY OBJECTIVES: Preterm infants are at increased risk of sudden infant death syndrome (SIDS). We investigated whether the prone sleeping position impaired arousal from sleep in healthy preterm infants and whether this impairment was related to cardiorespiratory variables, temperature or postnatal age. DESIGN: Longitudinal SETTING/PARTICIPANTS: 14 healthy preterm infants (mean 32 +/- 0.4 weeks) were studied using daytime polysomnography on 4 occasions: 36-38 weeks postconception age, 2 to 3 weeks postterm, 2 to 3 months postterm, and 5 to 6 months postterm. INTERVENTIONS: N/A. MEASUREMENTS: Multiple measurements of arousal threshold (cm H2O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. RESULTS: Arousal thresholds were significantly higher in both AS and QS when infants slept prone at 36 to 38 weeks postconception age and 2 to 3 months postterm but not at 2 to 3 weeks or 5 to 6 months postterm. These increases were independent of any sleep position-related changes in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation or heart rate. CONCLUSIONS: At the age when the risk of SIDS is highest, the prone position significantly impairs arousal from both active sleep and quiet sleep in healthy infants born prematurely. This impairment in arousability occurred with no clinically significant changes in cardiorespiratory parameters or body temperature. Decreased arousability from sleep in the prone position may explain its role as a risk factor for SIDS.

Effects of body position on sleep and arousal characteristics in infants.

The prone sleeping position has been identified in world-wide epidemiological studies as a major risk factor for sudden infant death syndrome (SIDS). Public awareness campaigns throughout the western world have led to an over 50% reduction in postneonatal mortality and frequency of SIDS. This reduction in mortality has been mainly attributed to the avoidance of the prone sleep position. Various mechanisms have been postulated to explain the increased risk of SIDS associated with prone sleeping, among these, impairment of arousal from sleep. This paper reviews the effects of prone sleeping on infant sleep architecture, arousability from sleep and cardiorespiratory controls. Sleeping in the prone position has been shown to increase the amount of time spent sleeping, particularly time spent in quiet sleep (QS). Sleeping prone has also been demonstrated to be associated with a reduced responsiveness to a variety of arousal stimuli. Such impairment of arousal has been demonstrated to be associated with changes in control of autonomic cardiac function. During arousal, heart rate, blood pressure and breathing movements increase, while gross body movements occur to avoid the stimulus. Any impairment in arousability from sleep such as could occur when infants sleep in the prone position, could possibly contribute to the final pathway to SIDS.

Arousal from sleep in infants is impaired following an infection.

Numerous studies have postulated a link between recent infection and Sudden Infant Death Syndrome (SIDS). In this study we contrasted arousal responses from sleep in infants on the day of discharge from hospital following an infection with those when fully recovered and also with well age-matched control infants. Thirteen term infants comprised the infection group and nine well infants acted as age-matched controls. All infants were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). All infants were studied on two occasions: firstly, immediately before discharge from the Paediatric ward, and secondly, 10-15 days later when they were completely well in the case of the infection group.Arousal thresholds in QS in the infection group were significantly elevated on the day of discharge (262 +/- 48 cm H(2)O) compared with 10-15 days later (205 +/- 31 cm H(2)O, p<0.05). Thresholds in the control group were not different between studies. This study provides evidence that arousability from QS is impaired following an infection and we postulate that this may explain the increased risk for SIDS following infection observed in previous studies.

Arousal responses and risk factors for sudden infant death syndrome.

BACKGROUND: Failure to arouse from sleep has been postulated as a mechanism to explain the final pathway of sudden infant death syndrome (SIDS). METHODS: We have reviewed the effects of the major risk factors for SIDS, prone sleep position, maternal smoking, prematurity and recent infection on arousability from sleep. In human infants it has been consistently demonstrated that arousal from sleep in response to a variety of stimuli is more difficult to induce from quiet sleep (QS) compared to active sleep (AS) over the first 6 months of life. RESULTS: In the prone position both stimulus-induced and spontaneous arousability from both QS and AS were impaired at 2-3 weeks and 2-3 months, but not at 5-6 months of age in both term and preterm infants. In term infants exposed to maternal smoking during pregnancy both stimulus-induced and spontaneous arousability were impaired when infants slept supine in QS at 2-3 months of age. Healthy preterm infants showed no impairment in arousability compared with term infants at matched postconceptional ages. However, preterm infants with a history of apnoea and bradycardia of prematurity showed decreased arousal responses in both QS and AS and this impairment was positively correlated to their 'perinatal risk score'. Infants who had recently suffered an infection requiring hospitalization showed decreased arousability in QS on the day of discharge when compared to 2 weeks later when they were completely well. CONCLUSIONS: In summary it has been found that the major risk factors for SIDS identified from epidemiological studies also decrease arousability from sleep in infants. We propose that this decreased arousability from sleep may be involved in the final pathway of SIDS.