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.     

Sleep position alters arousal processes maximally at the high‐risk age for sudden infant death syndrome

An impaired ability to arouse from sleep may play an important role in the pathogenesis of sudden infant death syndrome (SIDS). This study aimed to investigate the effects of prone sleeping on the nature of both induced and spontaneous arousal responses in infants. Thirteen healthy term infants were studied longitudinally at 2–4 weeks, 2–3 months and 5–6 months postnatal age. A pulsatile jet of air to the nostrils was used to induce arousal from both active sleep and quiet sleep in both prone and supine positions. For each stimulus, arousals were classified as sub‐cortical activations and cortical arousals, scored using physiological and electroencephalogram changes and expressed as a percentage of the total number of arousals. Spontaneous arousals were similarly analysed. Increased proportions of cortical arousals, hence decreased proportions of sub‐cortical activations, were observed in the prone position at 2–3 months. This distinct peak in the proportion of cortical arousals occurred regardless of sleep state and regardless of whether the arousal occurred spontaneously or was induced by air‐jet stimulation. The nature of arousal responses in healthy term infants is altered in the prone sleeping position at 2–3 months after birth, the age where SIDS incidence is highest. We postulate that a greater propensity for cortical arousal may be a protective mechanism to promote complete arousal in a vulnerable sleeping position and/or a vulnerable period of maturation. Inadequate or incomplete cortical arousals may explain the increased risk of SIDS associated with the prone position at this age.     

Prone sleeping impairs circulatory control during sleep in healthy term infants: implications for SIDS

STUDY OBJECTIVES: To determine the effects of sleeping position on development of circulatory control in infants over the first 6 months of postnatal age (PNA). DESIGN: Effects of sleeping position, sleep state and PNA on beat-beat heart rate (HR) and mean arterial pressure (MAP) responses to a head-up tilt (HUT) were assessed during sleep in infants at 2-4 wks, 2-3 mo and 5-6 mo PNA. MEASUREMENTS: Daytime polysomnography was performed on 20 full-term infants (12 F/8 M) and MAP was recorded continuously and noninvasively (Finometer). HUTs of 15 degrees were performed during active sleep (AS) and quiet sleep (QS) in both the prone and supine sleeping positions. MAP and HR data were expressed as the percentage change from baseline, and responses were divided into initial, middle and late phases. RESULTS: In the supine position HUT usually resulted in an initial increase (P < 0.05) in HR and MAP, followed by decreases (P < 0.05) in HR and MAP in the middle phase; subsequently HR and MAP returned to baseline in the late phase. By contrast, in the prone position the initial HUT-induced rises in HR and MAP were usually absent, and at 2-3 mo MAP actually decreased (P < 0.05); subsequently HR but not MAP returned to baseline. At 2-3 mo, MAP was lower (P < 0.05) in prone than supine sleeping throughout the HUT. CONCLUSIONS: Prone sleeping alters MAP responses to a HUT during QS at 2-3 mo PNA. Decreased autonomic responsiveness may contribute to the increased risk for SIDS of infants sleeping in the prone position.     

Cardiac autonomic characteristics in infants sleeping with their head covered by bedclothes

The risk of Sudden Infant Death Syndrome is increased in infants sleeping with their head covered by bedding items. This study was designed to evaluate cardiac autonomic nervous controls in infants sleeping with the head covered by bedclothes. Sixteen healthy infants with a median age of 12 weeks (range 9-13 weeks) were recorded polygraphically for one night. While they slept in their usual supine position, a bedsheet was placed over their head for about 45 min. All infants were challenged with the head covered and with the head free during both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. Sleep, breathing and heart rate (HR) characteristics were recorded simultaneously, together with rectal and pericephalic temperatures. In both head-free and head-covered conditions, autoregressive spectral analysis of HR was evaluated as a function of sleep stages. During the head-covered periods, parasympathetic tonus decreased and sympathetic activity increased in both REM and NREM sleep. Compared with the head-free periods, the head-covered sleep periods were characterized by greater rectal (P = 0.012) and pericephalic temperatures (P = 0.002). Covering the infant's head with a bedsheet was associated with significant changes in autonomic balance. The finding could be related to an elevation in temperatures within the infant's microenvironment.     

Spontaneous arousability in prone and supine position in healthy infants

STUDY OBJECTIVE: Compared with control infants, those who will be future victims of sudden infant death syndrome (SIDS) show a decreased arousability during sleep, with fewer cortical arousals and more-frequent subcortical activations. These findings suggest an incomplete arousal process in victims of SIDS. Prone sleep position, a major risk factor for SIDS, has been reported to reduce arousal responses during sleep. The present study was undertaken to evaluate whether the prone sleep position impairs the arousal process in healthy infants. METHODS: Twenty-four healthy infants were studied polygraphically during 1 night; 12 infants regularly slept supine and 12 infants regularly slept prone. Infants were matched for sex, gestational age, and age at recording. Arousals were differentiated into subcortical activations or cortical arousals, according to the presence of autonomic and/or electroencephalographic changes. Frequencies of subcortical activations and cortical arousals were compared in the prone- and the supine-sleeping infants. RESULTS: Compared with supine sleepers, prone sleepers had significantly fewer cortical arousals during rapid eye movement (REM) sleep (p = .043). There were no significant differences in cortical arousals between the 2 groups during non-REM sleep. No significant differences were seen in the frequencies of subcortical activations during both REM and non-REM sleep between supine and prone sleepers. The ratio of cortical arousal to subcortical activation showed no significant differences between the prone and the supine sleepers. CONCLUSIONS: Prone sleep position decreased the frequency of cortical arousals but did not change the frequency of subcortical activations, as has been previously found in SIDS victims. These results suggest specific pathways for impairment of the arousal process in SIDS victims.     

Increased cardiac autonomic responses to auditory challenges in swaddled infants

STUDY OBJECTIVES: When infants have been swaddled and sleep supine, their risk of dying from sudden infant death syndrome (SIDS) is reduced with an odds ratio of 0.64 to 0.69. Alternatively, the risk for SIDS in swaddled infants shows a 3-fold increase in the prone position. The protective role of swaddling during supine sleep has remained unexplained. This study was designed to evaluate the effects of swaddling on cardiac reactivity to auditory stimuli during sleep in both the prone and the supine position. DESIGN: Thirty healthy infants with a median age of 11 weeks (range 8 to 15 weeks) were studied polygraphically for 1 night while sleeping successively prone and supine, or vice versa. The infants were studied while swaddled and nonswaddled in both positions. Heart rates were studied during rapid eye movement sleep, before and after exposure to 90 dB(A) of white-noise. RESULTS: Ten infants were excluded from the study because they woke up during the position change or the auditory challenge. Before the administration of the noise stimulus, swaddling decreased values of basal heart rates in the supine position only (P = .049). Following swaddling, the values of basal heart rate were significantly lower in the supine than in the prone position (P = .003). Auditory challenges were followed by a greater increase in heart rate when the supine sleeping infants were swaddled than when not swaddled (P = .018). When swaddled, beat-to-beat heart-rate variability increased following auditory stimulation in the supine position only (P = .012). CONCLUSION: When sleeping supine, swaddled infants had greater cardiac autonomic changes in response to noise challenges than when they were not swaddled.     

Maturation of spontaneous arousals in healthy infants

OBJECTIVE: The propensity to arouse from sleep is an integrative part of the sleep structure and can have direct implications in various clinical conditions. This study was conducted to evaluate the maturation of spontaneous arousals during the first year of life in healthy infants. DESIGN: Nineteen infants were studied with nighttime polysomnography on 3 occasions: aged 2 to 3 months, 5 to 6 months, and 8 to 9 months. Ten infants with a median age of 3 weeks were added to the main study to assess the maturation of arousals from birth. The infants were born full-term, were healthy at the time of study, and had no history of apnea. Sleep-state and cardiorespiratory parameters were scored according to recommended criteria. Arousals were differentiated into subcortical activations or cortical arousals, according to the presence of autonomic and/or electroencephalographic changes. Frequencies of subcortical activations and cortical arousals were studied at different ages in both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. RESULTS: During sleep time, the frequency of total arousals, cortical arousals, and subcortical activations decreased with age. The maturation of the arousal events differed according to sleep states and types of arousals. With age, cortical arousals increased in REM sleep (P = 0.006) and decreased in NREM sleep (P = 0.01). Subcortical activations decreased with age in REM (P < 0.001) and NREM sleep (P < 0.001). CONCLUSIONS: During total sleep time, the frequency of cortical arousals and subcortical activations decreased with maturation. However, the maturation process was different between cortical arousals and subcortical activations. This finding suggests a difference in the maturational sequence of the different brain centers regulating arousals.     

Maturation of the initial ventilatory response to hypoxia in sleeping infants

In infants most previous studies of the hypoxic ventilatory response (HVR) have been conducted only during quiet sleep (QS) and arousal responses have not been considered. Our aim was to quantify the maturation of the HVR in term infants during both active sleep (AS) and QS over the first 6 months of life. Daytime polysomnography was performed on 15 healthy term infants at 2-5 weeks, 2-3 and 5-6 months after birth and infants were challenged with hypoxia (15% O2, balance N2). Tests in AS always resulted in arousal; in QS tests infants either aroused or did not arouse. A biphasic HVR was observed in non arousing tests at all three ages studied. The fall in SpO2 was more rapid in arousal tests at all three ages. At 2-5 weeks, in non-arousing QS tests, there was a greater fall in respiratory frequency (f) despite a smaller fall in SpO2 compared with 2-3 and 5-6 months. When infants aroused there was no difference in the HVR between sleep states or with postnatal age. However, when infants failed to arouse from QS, arterial desaturation was less in the younger infants despite a poorer HVR. We suggest that arousal in response to hypoxia, particularly in AS, is a vital survival mechanism throughout the first 6 months of life.     

Development of NREM Sleep Instability-Continuity (Cyclic Alternating Pattern) in Healthy Term Infants Aged 1 to 4 months

Study Objectives:

To evaluate non-rapid eye movement (NREM) sleep instability, as measured by the cyclic alternating pattern (CAP), in the first months of life in a group of normal healthy infants, in order to obtain more information on the maturation of arousal mechanisms during NREM sleep and to set normative data of CAP parameters in this age range (from 1 to 4 months of life).

Design:

Retrospective study.

Setting:

Sleep unit of an academic centre.

Participants:

Twenty-three healthy newborns and infants with a mean conceptional age (gestational age plus postnatal age) of 47.6 ± 3.8 weeks, age range 42 to 55 weeks, 10 boys (43.47%), were studied while they slept in the morning between feedings, by means of a 3-hour video-electroencephalographic (EEG)-polygraphic recording. Sleep was visually scored for sleep architecture and CAP in a blinded fashion, using standard criteria.

Measurements and results:

We found 3 different sleep EEG patterns in our infants, according to their age, and we subdivided the entire group into 3 subgroups. Group 1—Tracé alternant mixed with high-voltage slow activity included 9 subjects (3 boys), with a mean conceptional age of 43.9 ± 1.3 weeks; Group 2 (high-voltage slow activity and rudimentary spindles) included 6 subjects (4 boys), with a mean conceptional age of 49.4 ± 3.1 weeks; and Group 3 (slow-wave activity and spindles, scored as NREM sleep) included 8 subjects (3 boys), with a mean conceptional age of 50.4 ± 2.9 weeks. CAP rate was 6.83 ± 3.58 in infants belonging to Group 2 and increased to 12.91 ± 2.21 in Group 3. We found a statistically significant higher A1 index in only Group 3. The relative percentages of the A1, A2, and A3 subtypes showed non significant changes with age. The duration of CAP events and the cortical and subcortical arousal indexes were not statistically different between Groups 2 and 3.

Conclusions:

With this study, we provide the first data on CAP analysis in infants from 1 to 4 months of life, and we found that there is a transitory period when tracè alternant disappears and CAP events begin to occur. Furthermore, we suggest that the more appropriate time of life when CAP analysis can be first performed is related to the appearance of mature stage 2 NREM with spindles and slow delta waves mixed with theta waves, at approximately 3 months of life.

Citation:

Miano S; PiaVilla M; Blanco D; Zamora E; Rodriguez R; Ferri R; Bruni O; Peraita-Adrados R. Development of NREM sleep instability-continuity (cyclic alternating pattern) in healthy term infants aged 1 to 4 months. SLEEP 2009;32(1):83-90.     

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.     

Magnesium deficiency promotes muscle weakness, contributing to the risk of sudden infant death (SIDS) in infants sleeping prone.

A review was published (1991) of 19 retrospective case-control studies that had investigated the relationship between prone sleeping position (on the stomach) and the sudden infant death syndrome (SIDS). These studies, which had been conducted between 1965 and 1990 in New Zealand, Australia, England, France and the Netherlands, showed an overall higher rate of SIDS in infants who usually slept prone. In those countries, vigorous community intervention to change babies' sleep position away from the prone has resulted in marked declines of 50 per cent or more in the rate of SIDS. Such encouraging reports from many countries prompted the American Academy of Pediatrics to recommend that infants be placed to sleep on their backs to reduce the risk of SIDS. This was followed by a successful campaign in the United States between mid-1994 and 1998. Despite the decreased incidence, SIDS remains the leading cause of death in infants 1 month to 1 year of age of industrialized nations of the world. Studies have been conducted in human infants, mechanical models and animal models to learn the role of risk factors in prone sleeping infants. Soft bedding, thermal stress and biologic risk factors such as impaired ventilatory and arousal responsiveness are among many factors that have been investigated. Hunt states that there is not a single unifying factor that explains increased SIDS in prone sleeping infants. Two major studies conducted in the 1970s showed: (1) muscle weakness in the upper half of the body in infants who subsequently died of SIDS, and (2) shoulder hypotonia in near-miss for SIDS infants. An infant sleeping face-down in the prone position could be jeopardized if he lacked the muscle strength to shift his position or turn his head to rescue himself from a life-threatening situation. In contrast, recent studies in neonates sleeping in the prone position report that normal infants can spontaneously arouse and turn their heads. Some data support the hypothesis that magnesium deficiency contributes to SIDS. Muscle strength is seriously impaired in the young magnesium deficient subject, while magnesium rapidly reverses muscle weakness. In rats, marginal deprivation in dietary magnesium reduces exercise capacity, an early effect of magnesium deficiency which is preventable by consuming magnesium-enriched mineral water. It is concluded that magnesium deficiency is at least one major unifying factor that explains increased SIDS in prone sleeping infants.     

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.     

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.     

Bladder voiding in sleeping infants is consistently accompanied by a cortical arousal

The aim of the study was to find out whether bladder voiding in healthy sleeping infants was accompanied by any arousal reaction. Polygraphic recordings were performed in 21 healthy infants (11 female) born at term. The infants' age at study entry was 42 +/- 4 days and actual body weight was 4852 +/- 689 g (mean +/- SD). Bladder voiding was recorded by an adapted enuresis detector which was connected to the polygraphic computer unit. Arousals were defined as suggested by the 'International Paediatric Work Group on Arousals'. Awakenings were excluded from the study. Bladder voiding was recorded at a mean time of 68 +/- 7 min after the infant had fallen asleep and occurred during quiet sleep (QS). Electroencephalogram frequency (P < 0.01) and heart rate (P < 0.05) were higher during the 5-s period before and after bladder voiding when compared with a 30-s interval before voiding. Furthermore, bladder voiding was accompanied by body movements in all infants. Respiratory frequency did not change significantly. We could demonstrate for the first time in sleeping infants, that bladder voiding during QS was accompanied by a cortical arousal.     

Spindle frequencies in sleep EEG show U-shape within first four NREM sleep episodes

It has been shown in previous studies on sleep electroencephalogram (EEG) that spindles are slower in the beginning of the night fastening towards the end of the night. Corresponding findings have been obtained by spectral analysis. The present study was based on our preliminary observation that slower spindles are found in the middle of the non-rapid eye movement (NREM) sleep episodes as compared with the beginning or the end of the episodes. Eight healthy female and six male subjects were studied. Sleep spindles were visually selected and spindle frequencies calculated for 11 analysis points in each NREM sleep episode. The median spindle frequencies formed a clear U-shape within NREM sleep episodes with an initial decrease and final increase. The decrease was statistically significant within the first four NREM sleep episodes. It is possible that the spindle frequency pattern could be used to reveal variations in sleep depth within sleep stage 2. In animal studies the spindle frequency has been found to be associated to the duration of the hyperpolarization-rebound sequences of the thalamocortical cells. If it is assumed that the same cellular mechanisms are responsible for spindle frequencies in humans then the study of variations in spindle frequency could be used to examine the NREM sleep process in humans.     

Effect of sleep deprivation on NREM sleep ERPs and related activity at sleep onset.

This research assessed the impact of one night of sleep deprivation on the amplitudes of NREM-sleep event-related potentials (NREM ERPs) and on the frequency of occurrence of related electroencephalogram activity including sleep spindles, arousals, K-complexes, and vertex sharp waves (VSWs). The NREM ERPs identified included P220, N350, P450, N550 and P900. During a pre-deprivation night, ten subjects took two 20-min naps separated by a 20-min break at their normal bedtime. Brief tones were presented at three intensity levels (60, 75 and 90 dB) with a 5-s interstimulus interval. Following these naps, subjects were kept awake until their normal bedtime the following day. At that time, they repeated the two-nap procedure. The ERPs obtained for each tone and wake/sleep state for pre- and post-deprivation conditions were analyzed using repeated measures statistical procedures. As anticipated, NREM ERP amplitudes recorded both pre- and post-deprivation increased with tone intensity and with approaching sleep. Also, sleep deprivation was associated with more rapid sleep onset, reduced arousability, and greater spindle production. While sleep deprivation had no effect on the amplitude of P220. Post-deprivation amplitudes of N350, N550 and P900 were greater, especially following the 90-dB tone. There was a corresponding increase in VSWs and K-complexes. These findings are inconsistent with the view that NREM ERPs reflect arousal. The underlying mechanism(s) may facilitate initiation and maintenance of sleep.     

Sleep spindle dynamics during NREM and REM sleep following distinct general anaesthesia in control rats and in a rat model of Parkinson’s disease cholinopathy

On the basis of our previous studies and the important role of the thalamo‐cortical network in states of unconsciousness, such as anaesthesia and sleep, and in sleep spindles generation, we investigated sleep spindles (SS) and high‐voltage sleep spindle (HVS) dynamics during non‐rapid eye movement (NREM) and rapid eye movement (REM) sleep following different types of general anaesthesia in both physiological controls and in a rat model of Parkinson's disease (PD) cholinopathy, to follow the impact of anaesthesia on post‐anaesthesia sleep at the thalamo‐cortical level through an altered sleep spindle dynamics. We recorded 6 hr of spontaneous sleep in all rats, both before and 48 hr after ketamine/diazepam or pentobarbital anaesthesia, and we used 1 hr of NREM or REM sleep from each to validate visually the automatically detected SS or HVS for their extraction and analysis. In the controls, SS occurred mainly during NREM, whereas HVS occurred only during REM sleep. Ketamine/diazepam anaesthesia promoted HVS, prolonged SS during NREM, induced HVS of increased frequency during REM, and increased SS/HVS densities during REM versus NREM sleep. Pentobarbital anaesthesia decreased the frequency of SS during NREM and the HVS density during REM sleep. Although the pedunculopontine tegmental nucleus lesion prolonged SS only during NREM sleep, in these rats, ketamine/diazepam anaesthesia suppressed HVS during both sleep states, whereas pentobarbital anaesthesia promoted HVS during REM sleep. The different impacts of two anaesthetic regimens on the thalamo‐cortical regulatory network are expressed through their distinct sleep spindle generation and dynamics that are dependent on the NREM and REM state regulatory neuronal substrate.     

Arousal and ventilatory responses to mild hypoxia in sleeping preterm infants

A failure to adequately respond to hypoxia has been implicated in the Sudden Infant Death Syndrome (SIDS). Preterm infants are at increased risk for SIDS, thus we compared ventilatory and arousal responses to mild hypoxia [15% oxygen (O₂)] in preterm and term infants. Eight preterm and 15 term infants were serially studied with daytime polysomnography during which nasal airflow was monitored by pneumotachograph at 2–5 weeks, 2–3 and 5–6 months. At each age, in both groups, hypoxia induced a significant decrease in oxygen saturation (SpO₂) during both active sleep (AS) and quiet sleep (QS). Infants invariably aroused in AS; and in QS either aroused or failed to arouse. In preterm infants arousal latency in AS was longer than in term infants ( P  < 0.05) at 2–5 weeks. Compared with term infants, preterm infants reached significantly lower SpO₂ levels at 2–5 weeks in both AS and QS non-arousing tests and at 2–3 months in QS. A biphasic hypoxic ventilatory response was observed in QS non-arousing tests in both groups of infants at all three ages. We conclude that the greater desaturation during a hypoxic challenge combined with the longer arousal latency in preterm infants could contribute to greater risk for SIDS.     

Ambient temperature is associated with changes in infants' arousability from sleep

STUDY OBJECTIVE: To evaluate the influence of ambient temperature on infants' arousability from sleep. DESIGN: Two groups of healthy infants with a median age of 11 weeks were recorded polygraphically during one night: 31 infants were studied at 24 degreesC and 31 infants at 28 degreesC. To determine their arousal thresholds, the infants were exposed to white noises of increasing intensities during REM and NREM sleep. Arousal thresholds were defined by the auditory stimuli needed to induce arousals. SETTING: N/A. PATIENTS or PARTICIPANTS: N/A. INTERVENTIONS: N/A. MEASUREMENTS and RESULTS: The arousal thresholds decreased across the night in the infants sleeping at 24 degreesC (p=.017). The finding was not found for the infants sleeping at 28 degreesC. When analyzing the arousal responses according to time of the night, it was found that the auditory thresholds were significantly higher at 28 degreesC than at 24 degreesC between 03:00 hr and 06:00 hr (p=.003). These findings were only seen in REM sleep. CONCLUSION: High ambient temperature could add to the difficulty to arouse from REM sleep in the late hours of the night.