Respiratory frequency during sleep in siblings of sudden infant death syndrome victims. A comparison with control, normal infants

The present study was carried out on 76 polygraphic recordings performed on 38 siblings of sudden infant death syndrome victims and on 38 control (2 days to 18 weeks old) infants. Each sibling corresponded to a control infant according to gender, gestational age at birth and postnatal age criteria. We found that in siblings as in controls, respiratory frequency (RF) was higher in active sleep (AS) compared to quiet sleep (QS) state (P less than 0.05 for 11-18 week siblings, p less than 0.01 for the other groups). During the transitional sleep (TS), RF was on an intermediate level (AS greater than TS greater than QS). There were no significant differences between RF of siblings compared to controls, except that RF during QS in 6-10 week control infants was higher than in siblings of the same age (P less than 0.05). We found a wide variability between RF of different individuals within all the age groups of siblings and of controls (P less than 0.001). However, a high correlation was usually noted between RF found in different sleep states: some infants (siblings or controls) breathed more rapidly and others more slowly in all states studied. In siblings, as previously described in other groups of normal infants, RF seems to be an individual characteristic. In addition, the present work shows that according to RF criterion, healthy siblings are similar to normal infants.     

Mechanism of the suddent infant death syndrome?

Abstract Polygraphic tracings of 13 normal infants were recorded in a morning sleep at 1 and 2 weeks of age and 1, 2, 3, 4, and 6 months of age. A vibrotactile stimulus graded at 25, 50 and 100 Hz (frequency) and amplitudes of 1, 2 and 3 mm (intensity) was used, each combination being applied twice at 30 s intervals to the hand of the sleeping infant during active sleep (AS) and quiet sleep (QS). The results were analysed as percentages of failure to arouse (FTA) in relation to the number of stimulus trials, the criteria for FTA being the absence of a response in heart or respiratory rate, electroencephalogram, or chin electromyogram. The percentages of FTA from QS did not change significantly from 1 week to 6 months of age, irrespective of frequency or intensity. The percentages of FTA from AS fell sharply and significantly from 1 week to 2 months of age ( P < 0.001). At 3 months of age there was a significant increase followed by a significant decrease at 4 months of age, both changes showing a significant difference at P < 0.05. Apart from the first week of age, the numbers of FTA from QS were greater than from AS for all stimulus trials. It is concluded that there is an arousal deficit in QS from 1 week to 6 months of age and the temporary deficit in AS at 3 months of age could explain the peak incidence of SIDS at this time.     

Variability of the initial phase of the ventilatory response to hypoxia in sleeping infants

Most of the available data on the hypoxic ventilatory response (HVR) in infants has been obtained in quiet sleep (QS), and only one study has made repeated tests in the same infant. We aimed to gain a more complete knowledge of the maturation and consistency of the initial phase of the HVR by performing multiple tests in both QS and active sleep (AS) over the first 6 mo of life in term infants. Fifteen healthy term infants were studied with daytime polysomnography longitudinally at 2-5 wk, 2-3 mo, and 5-6 mo after birth. Each infant received multiple hypoxic (15% O2, balance N2) challenges (three or more) in both AS and QS. In AS, infants consistently aroused to hypoxia; however, in QS, infants both aroused and failed to arouse. The initial phase of the HVR varied considerably between infants with the changes in ventilation/kg [SD of inspired minute ventilation per kilogram of body weight (V(I)/kg)] being more variable during AS than QS at all three ages and overall decreasing with postnatal age in both sleep states. The variability between replicate V(I)/kg measurements was also significantly greater in AS compared with QS at 2-5 wk postnatal age. There was no evidence of habituation to repeated hypoxic tests in either sleep state. Our study has demonstrated that the initial phase of the HVR is variable both between and within term infants in both AS and QS, with responses being markedly more variable during AS, and becoming more consistent with increasing postnatal age. By performing only one test or by failing to account for arousal responses, previous studies may not have detected the natural variation of the infant HVR.     

Breathing patterns, oxygen and carbon dioxide levels in sleeping healthy infants during the first nine months after birth

Data on arterial oxygen saturation (SaO2), transcutaneous PO2, pCO2 (tcpO2, tcpCO2) and breathing patterns in sleeping healthy term infants were obtained during the first 9 mo after birth. Forty-four healthy infants, mean GA at birth 40 +/- 1.0 wk, mean BW 3520 +/- 562 g were examined between 2 wk and 9 mo postnatally in a cross-sectional study. SaO2, tcpO2, tcpCO2, heart rate (HR), rib cage and abdominal respiratory movements were recorded during natural nocturnal sleep, stratified for sleep states (active sleep (AS), indeterminate sleep (IS), quiet sleep (QS)). The data on AS and IS were pooled as in previous studies. The variables were analysed with respect to age. SaO2 in AS + IS and QS was 96.1 +/- 1.3%, 96.6 +/- 1.4%, respectively. TcpO2 in AS + IS was 10.6 +/- 1.1 kPa and 10.7 +/- 1.3 kPa in QS, while tcpCO2 in AS + IS was 5.4 +/- 0.3 kPa and 5.4 +/- 0.4 kPa in QS. Neither SaO2 nor tcpO2 was influenced by age. TcpCO2 decreased significantly postnatally. Five infants (11.3%) experienced episodes of hypoxaemia with a mean decrease in SaO2 to 86 +/- 1.5%. In four infants these hypoxaemic episodes were linked to upper airway obstructions. Episodes of SaO2 < 90% in conjunction with a decrease in HR to < 100 bpm were detected in one infant only. Periodic breathing (PB) was observed in 38.6% of infants. Conclusion: Oxygenation and carbon dioxide levels in sleeping healthy term infants were comparable to those reported in older children. Hypoxaemic episodes, if present, are associated with upper airway obstruction. PB, often assumed to be a pathological feature, is a normal breathing pattern in this age group.     

Arousal deficit: mechanism of the sudden infant death syndrome?

Polygraphic tracings of 13 normal infants were recorded in a morning sleep at 1 and 2 weeks of age and 1, 2, 3, 4, and 6 months of age. A vibrotactile stimulus graded at 25, 50 and 100 Hz (frequency) and amplitudes of 1, 2 and 3 mm (intensity) was used, each combination being applied twice at 30 s intervals to the hand of the sleeping infant during active sleep (AS) and quiet sleep (QS). The results were analysed as percentages of failure to arouse (FTA) in relation to the number of stimulus trials, the criteria for FTA being the absence of a response in heart or respiratory rate, electroencephalogram, or chin electromyogram. The percentages of FTA from QS did not change significantly from 1 week to 6 months of age, irrespective of frequency or intensity. The percentages of FTA from AS fell sharply and significantly from 1 week to 2 months of age (P less than 0.001). At 3 months of age there was a significant increase followed by a significant decrease at 4 months of age, both changes showing a significant difference at P less than 0.05. Apart from the first week of age, the numbers of FTA from QS were greater than from AS for all stimulus trials. It is concluded that there is an arousal deficit in QS from 1 week to 6 months of age and the temporary deficit in AS at 3 months of age could explain the peak incidence of SIDS at this time.     

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.     

Physiologic brain dysmaturity in late preterm infants

Neonatal EEG sleep was used to determine whether differences are expressed between healthy late preterm and full-term (FT) groups. Twenty-seven 24-channel multihour studies were recorded at similar postmenstrual ages (PMA) and analyzed for eight asymptomatic late preterm infants (LPT) compared with 19 healthy FT infants as a preliminary analysis, followed by a comparison of a subset of eight FT infants, matched for gender, race, and PMA. Z scores were performed on data sets from each group pair comparing each of seven EEG/Sleep measures for entire recordings, active sleep (AS) and quiet sleep (QS) segments and artifact-free intervals. Six of seven measures showed differences between the eight LPT and eight matched FT cohort pair comparisons of >0.3; rapid eye movements, arousals during QS, spectral correlations between homologous centrotemporal regions during QS, spectral beta/alpha power ratios during AS and QS, a spectral measure of respiratory regularity during QS, and sleep cycle length. Quantitative neurophysiologic analyses define differences in brain maturation between LPT and FT infants at similar PMA. Altered EEG/Sleep behaviors in the LPT are biomarkers of developmental neuroplasticity involving interconnected neuronal networks adapting to conditions of prematurity for this largest segment of the preterm neonatal population.     

Music exposure and maturation of late preterm sleep–wake cycles: a randomised crossover trial

Aim

To determine the effect of music on sleep–wake cycle (SWC) patterns in late preterm neonates.

Methods

In a masked crossover study, infants between 32 and 36 6/7 weeks gestation were randomised to music exposure either during the first six or last six hours of a 12‐hour observation period. SWC characteristics were determined by continuous amplitude‐integrated electroencephalography (aEEG) read by two coders masked to exposure sequence. Analysis was performed in paired comparisons. ANOVA was used to assess the effects of music exposure, period and crossover on SWC outcomes: (i) Burdjalov Scores (BS) during active sleep (AS) (ii) per cent and duration of quiet sleep (QS).

Results

Thirty infants were studied. A total of 222 QS cycles (median seven per patient; range five to 12) were analysed. Music exposure was associated with higher BS (F = 10.60, p = 0.0019) in AS and decreased interruptions during QS. The advanced postconceptual age (PCA) SWC pattern during AS was equivalent to a one‐week mean. Number, duration and ratio of QS cycles did not change with music exposure.

Conclusion

Music exposure elicits an increasing PCA pattern in AS and fewer interruptions in QS. Music may benefit sleep in late preterm infants.     

Increased inspiratory effort in infants with a history of apparent life-threatening event

The objective of this study was to compare the results of polysomnography between infants with a history of apparent life-threatening event (ALTE) and controls. In this case-control study, 40 full-term ALTE infants, aged 2-36 wk at the time of the event, were compared with 40 age- and sex-matched randomly selected controls. SaO2, tcpO2, tcpCO2, heart rate (HR), vector of rib cage and abdominal respiratory movements (phase angle, as an index of inspiratory effort) were recorded during natural nocturnal active and quiet sleep (AS, QS). SaO2, tcpO2, tcpCO2 were similar in ALTE and controls in both sleep states. Phase angle was increased in ALTE infants in both AS (59+/-46 vs 26+/-17 degrees) and QS (53+/-46 vs 18+/-14, p < 0.001). Eleven ALTE infants (27.5%) experienced SaO2 < 90%, with a mean decrease in SaO2 to 86+/-1.6% (mean +/- SD), compared with 10% for controls (p=0.003). In eight ALTE infants, SaO2 values <90% were linked to thoracoabdominal asynchrony. SaO2 < 90% in conjunction with HR <100 bpm were detected in three ALTE infants and one control. Periodic breathing was observed in 45% of ALTE infants and 40% of controls. CONCLUSION: The mean values of oxygen saturation, tcpO2 and carbon dioxide levels in ALTE infants are comparable with those of healthy controls but the ALTE infants exhibit more hypoxaemic episodes and increased inspiratory effort during sleep.     

Thoracico-abdominal respiratory correlations in infants: constancy and variability in different sleep states.

28 polygraphic recordings were made in normal infants: 20 in full-term newborns and 8 in 2- to 10-wk-old babies. Data were analysed by 20-sec epochs. Relationships between thoracic (3rd-4th rib level) and abdominal respiratory movements were studied according to their maximum out-of-phase occurring (180 degrees maximum) in every 20-sec period. The thoracico-abdominal phase relationships according to sleep states do not change during the first trimester of life. In quiet sleep, while in-pase thoracico-abdominal respiration was the most frequent pattern, the out-of-phase one was also a possible pattern. In active sleep, out-of-phase respiration is characteristic, in-phase relation being a rare exception. In transitional sleep, respiratory relationships could be those appropriate for the preceding or the following sleep state. Nasal air flow always occurred in the phase with abdominal movements. Total flatteninf of thoracicorespiratory movements only were found in all sleep states; these thoracic flattenings must be differentiated from apnea. Transient fluctuations in the degree of phase relations are possible. There exists both interand intraindividual variability in normal infants. Variability of fusimotor system tonus is probably the neurological mechanism underling these phenomena.     

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.     

Responses to partial nasal obstruction in sleeping infants

Partial nasal obstruction was performed during a morning of quiet sleep (QS: non-REM) and active sleep (AS: REM) at ages 1 week, 2 weeks, 1, 2, 3, 4 and 6 months on 12 normal infants, 15 subsequent siblings of victims of the Sudden Infant Death Syndrome (SIDS) and 12 infants admitted for investigation of infant apnoea ('near-miss' SIDS). In all three groups the numbers failing to arouse after 240 s (FTA-240) in QS were significantly greater than those in AS. After 2 months of age all groups showed a decrease in the number FTA-240 in AS, whereas in QS the number did not change significantly. Subsequent siblings of SIDS had a significantly higher number FTA-240 in QS than controls. There was no significant difference in FTA-240 in QS between controls and infant apnoeas, although there was a trend for this to be higher in subsequent siblings of SIDS than infant apnoeas.
It was concluded that arousal from AS is more marked than from QS, that after 2 months of age the ability to arouse from AS increases, and that in relation to SIDS, QS is the sleep state in which the infant is less able to arouse. Furthermore, subsequent siblings of SIDS differ from normal infants in their ability to arouse from QS.     

Responses to partial nasal obstruction in sleeping infants

Partial nasal obstruction was performed during a morning of quiet sleep (QS: non-REM) and active sleep (AS: REM) at ages 1 week, 2 weeks, 1, 2, 3, 4 and 6 months on 12 normal infants, 15 subsequent siblings of victims of the Sudden Infant Death Syndrome (SIDS) and 12 infants admitted for investigation of infant apnoea ('near-miss' SIDS). In all three groups the numbers failing to arouse after 240 s (FTA-240) in QS were significantly greater than those in AS. After 2 months of age all groups showed a decrease in the number FTA-240 in AS, whereas in QS the number did not change significantly. Subsequent siblings of SIDS had a significantly higher number FTA-240 in QS than controls. There was no significant difference in FTA-240 in QS between controls and infant apnoeas, although there was a trend for this to be higher in subsequent siblings of SIDS than infant apnoeas. It was concluded that arousal from AS is more marked than from QS, that after 2 months of age the ability to arouse from AS increases, and that in relation to SIDS, QS is the sleep state in which the infant is less able to arouse. Furthermore, subsequent siblings of SIDS differ from normal infants in their ability to arouse from QS.     

Developmental changes in electroencephalogram for term and preterm infants using an autoregressive model

The purpose of the present study was to clarify the developmental changes of electroencephalogram (EEG) background activity in term and preterm infants that take place with increasing conceptional age (CA) through an autoregressive (AR) model. Polygraphical EEG recordings were obtained from 76 healthy term and preterm infants with a CA ranging between 31 and 40 weeks. Decreases in total power and component power of δ were noted with CA during burst activity (BA) in quiet sleep (QS) and during active sleep (AS). Increases in total power and component power of δ were noted with CA during interburst interval activity (IBIA) of QS. Regression analysis (RA) of the information amount (IA) indicated a negative correlation with increasing CA in AS and in the monopolar EEG tracings Fp1, C3, O1 and O2 in BA, and a positive correlation in O1 in IBIA. Regression analysis of the IA of δ indicated a negative correlation with increasing CA in AS and in Fp1, C3, O1 and O2 in BA, and a positive correlation in O1 in IBIA. Regression analysis of the IA of δ indicated a negative correlation with increasing CA in BA and AS. These results showed that the high voltage slow wave component changed to a low voltage slow one with development in AS and that BA was longer in duration and lower in power with increasing CA, while IBIA was shorter in duration and higher in power. In conclusion, significant developmental changes occur in all derivatives of AS. Even though the EEG of BA and IBIA change separately, they are followed by EEG of QS in a continuous pattern.     

Apnoea of prematurity and arousal from sleep

The incidence of sudden infant death syndrome (SIDS) has been found to be consistently higher in preterm and low birth weight infants than in infants born at term and this increase is inversely related to gestational age. The incidence and severity of apnoea of prematurity, are also inversely related to gestational age. The aim of this study was to investigate whether a neonatal history of apnoea/bradycardia affected the maturation of arousal responses. Twenty-five premature infants were studied. A perinatal risk score was determined for each infant and infants were divided into those with a neonatal history of apnoea/bradycardia (n=16) and those without (n=9). All infants were studied using daytime polysomnography on three occasions: (a) a preterm study around 36 weeks gestation, (b) within 3 weeks of term, and (c) 2-3 months post-term. Multiple measurements of arousal threshold (cm H2O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). Arousal thresholds were elevated in apnoeic infants compared to control infants in both AS (P<0.05) and QS (P<0.001) at the term study and in QS at 2-3 months post-term (P<0.01). In addition, arousal thresholds were positively correlated with perinatal risk score in both sleep states, in all studies, with the exception of AS at 2-3 months when all infants were readily arouseable. We conclude that a history of prematurity with neonatal apnoea has a persisting effect on decreasing arousabilty from sleep and these infants may be at increased risk for SIDS.     

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.     

Behavior and EEG concordance of active and quiet sleep in preterm very low birth weight and full-term neonates at matched conceptional age

BackgroundSleep organization in neonates is an established predictor of neurological outcome and can be evaluated through the concordance between EEG and behavioral parameters.AimsTo evaluate the correlation between sleep stages and behavioral states in neonates.Study designLongitudinal study performed in a birth-cohort of preterm low birth weight neonates.SubjectsTwenty five neonates, 15 preterm (gestational age between 27 and 33 weeks) and low birth weight (800–1500 g) and 10 full-term neonates that served as controls.MeasuresAll neonates were submitted to video-electroencephalography of, at least, 60 minute duration. The preterm during the first 15 days of life and, subsequently, at 38–42 weeks of conceptional age. The full-term between the 1st and 2nd days of life. The characterization of sleep stages by EEG parameters and behavioral states (based on Prechtl scale) was performed independently by previously trained researchers.ResultsActive sleep (AS) was the predominant sleep stage in the three groups. Preterm neonates had an increase in concordance between state 1 and quiet sleep (QS) from the 1st to the 2nd EEG (p < 0.001), however in both observations it remained inferior when compared to state 2 and AS (p < 0.001). Concordance between AS and state 2 was similar (p = 0.567).ConclusionsConcordance between EEG and behavior is lower in QS in preterm and full-term neonates when compared to AS. Extra-uterine development of preterm neonates seems to accelerate concordance in QS. Prechtl behavior scale proved to be useful in preterm as percentage of concordance was similar in AS in the groups studied.     

Quality of diet,body position,and time after feeding influence behavioral states in low birth weight infants

The effects of variations in carbohydrate and fat intake and body position on behavioral activity states were evaluated in 64 healthy, growing low birth weight infants (birth weight, 750-1600 g). The infants, enrolled in a prospective, randomized, double-blind, controlled study of effects of quality of dietary energy, were fed one of the five formulas. These formulas contained fixed intakes of protein (4 g/kg per day) but different intakes of carbohydrate (9.1 to 20.4 g/kg per day) and fat (4.3 to 9.5 g/kg per day). Six-hour daytime sleep studies were performed at 2-wk intervals from time of full enteral intake until discharge (mean postconceptional age at first study, 33.2 +/- 1.8 wk). Infants were randomly assigned to the prone or supine position for the first 3-h postprandial period; the position was reversed during the second 3 h. Behavioral activity state, i.e. quiet sleep (QS), active sleep, indeterminate sleep, awake, or crying was coded each minute throughout the postprandial period. The overall incidence of QS was almost double in the prone position versus the supine (p < 0.0001). In contrast, the probability of being in either of the two wakeful states (awake and crying) was increased when infants were placed in supine position (p < 0.0001). Increased likelihood of being in QS while prone was found only during the 30 min after and before feeding in a 150-min prandial cycle. In contrast, increased amounts of awake and crying in supine position were observed throughout the feeding interval. As carbohydrate intake increased, time spent in QS in supine position increased (from 8.6% to 12.5%, p < 0.02), and a trend in the same direction was noted for the prone position (p = 0.06). However, during postprandial minutes 10-100, when QS is likely to be entrained by the nutrient intake, enhancement of QS was found in the prone position only (p < 0.02). Carbohydrate intake influences the total time spent and the distribution of behavioral activity states within the postprandial period in low birth weight infants. The effect of nutrient intake on sleep profile is dependent on body position and time after feed. Mechanistic hypotheses relating sudden infant death syndrome to sleeping position may need to take these observations into account.     

Effect of sleep position on transcutaneous oxygen tension in SIDS siblings

To assess the influence of sleep position in sudden infant death syndrome siblings (SIDSS), we have studied 60 healthy SIDSS between the 1st and 3 + 4th month of life polygraphically. Infants were grouped according to postnatal age (1st, 2nd and 3 + 4th month) and sleep position (supine and prone). Transcutaneous oxygen tension (tcPO2) was continuously recorded and studied in each sleep state (active (AS) and quiet sleep (QS)) during the 1st and 2nd sleep cycle. No statistical difference could be found in tcPO2 levels as regards different sleep positions, postnatal ages (except for AS during the 2nd sleep cycle in prone and supine positions: 3 + 4th month greater than 2nd month, P less than 0.05), sleep states (except for the 1st month in supine: QS greater than AS, P less than 0.05; and 3 + 4th month in prone: AS greater than QS, P less than 0.05) or sleep cycles. tcPO2 variability was found to be significantly higher in AS as compared to QS (P less than 0.05). These results suggest that sleep position does not influence tcPO2 levels in SIDSS.     

Relationship between functional residual capacity and oxygen desaturation during short central apneic events during sleep in "late preterm" infants

Apneic episodes are frequent in the preterm neonate and particularly in active sleep (AS), when functional residual capacity (FRC) can be decreased. Furthermore, FRC may be inversely correlated with the speed of blood-O(2)-desaturation. We evaluated the potential involvement of FRC in the mechanisms responsible for blood-O(2)-desaturation during short central apneic events (>3 s) in "late-preterm" infants and analyzed the specific influence of sleep state. Apneic events were scored in 29 neonates (postmenstrual age: 36.1 +/- 1.2 wk) during AS and quiet sleep (QS). FRC was measured during well-established periods of regular breathing. Apneas with blood-O(2)-desaturation (drop in SpO(2) >5% from the baseline, lowest SpO(2) during apnea: 91.4 +/- 1.8%) were more frequent in AS than in QS, whereas no difference was seen for apneas without desaturation. The magnitude of the FRC did not depend on the sleep state. In AS only, there was a negative relationship between FRC and the proportion of apneas with desaturation. Even in late preterm infants who do not experience long-lasting apnea, blood-O(2)-desaturation during short apneic events is related (in AS but not QS) to a low baseline FRC. Sleep stage differences argue for a major role of AS-related mechanisms in the occurrence of these apneas.