Behavioural changes and bioelectric brain maturation of preterm and fullterm newborn infants: a polygraphic study

Randomized controlled trial to compare sleep and wake in preterm infants less than 32weeks of gestation receiving two different modes of non-invasive respiratory support

AIM

To determine whether respiratory support via heated humidified high flow nasal cannulae (HHHFNC) results in infants <32weeks gestation spending a greater proportion of time in sleep compared to those receiving nasal continuous positive airway pressure (NCPAP).

METHODS

A subgroup of infants enrolled in a randomized controlled trial to compare HHHFNC or NCPAP post-extubation had sleep and wake activity measured by actigraphy for 72hours post-extubation. Activity diaries were completed contemporaneously to record episodes of infant handling. Actigraphy data were downloaded with known periods of handling excluded from the analysis.

RESULTS

28 infants with mean gestation of 28.3weeks (SD 2) and birth weight 1074g (SD 371) were studied. Infants receiving HHHFNC spent a lesser proportion of time in sleep 59.8% (SD 18.5) than those on NCPAP 82.2% (SD 23.8) p=0.004. Infants receiving HHHFNC had a lower sleep efficiency and higher mean activity score than those on NCPAP (p=0.003, p=0.002, respectively).

CONCLUSION

Infants receiving HHHFNC had a higher mean activity score and spent less time in sleep than those allocated NCPAP. Further study of sleep wake activity in preterm infants receiving respiratory support is required as this may impact on neurodevelopmental outcomes.

Ontogeny of sleep and awake states in relation to breathing in preterm infants

This review will focus on the development of behavioural states and breathing during early developmental stages prior to term gestation. Although these behavioural states are immature during early development, their cyclicity is clearly seen. Preterm infants characteristically have a large proportion of indeterminate sleep and small amount of wakefulness. Whereas oxygenation is relatively stable during active and quiet sleep in ventilated preterm infants, indeterminate sleep and arousals are associated with hypoxaemic episodes. Arousals have also been linked to apnoea in spontaneously breathing infants. Since well-defined sleep cycles are beneficial for the oxygenation of preterm infants, we should explore ways to promote their natural sleep while they are exposed to neonatal intensive care. Care practices such as clustering procedures, kangaroo care and optimal positioning have been shown to improve the integrity of sleep. Optimizing the sleep cycling might improve the long-term outcome of preterm infants. More studies in this area are clearly needed.

Effects of prone and supine positions on sleep state and stress responses in mechanically ventilated preterm infants during the first postnatal week

BACKGROUND/RATIONALE

Preterm infants in mechanical ventilation are vulnerable and may manifest physiological instability and a disorganized behavioural state when responding to external stimuli. Adequate positioning strategies may play an important role in protecting infants from environmental stressor and assisting quality of sleep. However, no study has examined effects of prone and supine positions on behavioural state and stress signs including startle, tremor, and twitch responses for ventilated preterm infants during the critical first week postbirth.

AIM OF THE STUDY

The purpose of this study was to compare effects of prone and supine positions on behavioural state and stress responses in mechanically ventilated preterm infants.

DESIGN/METHODS

The infants were aged 25-36 weeks of gestation, < or = 7 days of age, and without sedation or congenital abnormalities. Using a crossover design, 28 infants were randomly assigned to supine/prone or prone/supine position sequence. Infants were placed in each position for 2 hours. A stabilization period of 10 minutes before observation of each position was allowed. During the protocol, care procedures were kept minimal and ventilator settings remained unchanged. Behavioural state and frequencies of stress signs including startle, tremor, and twitch were systemically recorded and analysed with repeated measures analysis of variance.

FINDINGS

Infants when prone compared with supine had (a) less crying, less active sleep, and more quiet sleep states, and (b) fewer stress responses of startle, tremor, and twitch.

CONCLUSION

Results indicate that prone positioning improves the quality of sleep and decreases stress for ventilated preterm infants during the first week postbirth. These may conserve energy and assist infants' extrauterine adaptation.

Preterm infant behavioral and heart rate responses to antenatal phenobarbital

The effects of antenatal phenobarbital on behavioral state and heart rate (HR) were examined in a randomized sample of 49 preterm infants > 24 and < 34 weeks postconceptional age. Behavioral state and HR observations were made during a routine care giving procedure on Days 1, 2, and 3 of life. There were no differences in behavioral state and HR responses between control and experimental subjects, suggesting that antenatal phenobarbital did not have a sedative effect on experimental subjects. Infants in both study groups responded to caregiving with changes to fussy/cry behavior and increases in HR. Older infants and nonventilated infants were more often in fussy/cry states during care giving than younger infants and ventilated infants. The HR increases were not clinically important, but the behavioral changes were, suggesting that behavioral response may be a more sensitive sign of distress than HR in very young preterm infants.

More awakenings and heart rate variability during supine sleep in preterm infants

OBJECTIVE

The Task Force of The American Academy of Pediatrics (1996) recommends the nonprone sleeping position for asymptomatic preterm infants to prevent sudden infant death syndrome. The mechanism by which the nonprone sleeping position reduces the rate of sudden infant death syndrome is unclear for full-term infants and the precise effect of sleeping position on sleep and cardiorespiratory characteristics has never been addressed in preterm infants. The purpose of the present study was to clarify the effect of sleeping position on sleep and cardiorespiratory characteristics in preterm infants at an age when they are ready for discharge.

STUDY DESIGN

Sixteen asymptomatic preterm infants were studied in both supine and prone sleeping positions at 36.5 +/- 0.6 weeks' postconceptional age using videosomnography. Sleep, respiratory, and heart rate characteristics were compared between the two positions using each infant as his/her own control.

RESULTS

More awakenings (ie, arousals >/=60 seconds) were seen during all sleep states in the supine sleeping position but overall the total sleep and percent sleep state were not affected by sleeping position. After each feeding, the first quiet sleep was significantly shorter, with more heart rate variability and awakenings in the supine position. There were no significant differences in the occurrence of arousals (<60 seconds) or the incidence or severity of apnea and periodic breathing. No clinically significant apnea (>/=15 seconds), bradycardia, or oxygen desaturations were seen.

CONCLUSION

In 36-week-postconceptional age preterm infants, the supine sleeping position had less quiet sleep and was associated with greater heart rate variability during the first sleep cycle after the feeding. More awakenings were seen during all sleep states in the supine position. These data support the American Academy of Pediatrics recommendation for "Back to Sleep" for asymptomatic preterm infants because more awakenings and lower threshold for arousal may provide some benefit for the infant responding to a life-threatening event. However, further studies are needed to address positional effect on the physiologic measures in preterm infants at older ages (later stages of development). Precisely what constitutes the most healthy or advantageous sleep for newborn infants remains an important question.

Sporadic apnea: paradoxical transformation to eupnea by perturbations that inhibit inspiration

We speculate that sporadic apneas may be initiated and terminated by stochastic neural perturbations arising within or impinging upon the respiratory oscillator. A curious situation can then arise in which tiny perturbations that inhibit inspiration, paradoxically stimulate breathing. The plausibility of the hypothesis is supported by numerical analysis of a noisy attractor-cycle oscillator, and in studies of a preterm sleeping infant with sporadic apnea; low-level vibratory stimulation transformed the irregular apneic rhythm to eupnea.

Neurophysiological assessment of brain function and maturation: I. A measure of brain adaptation in high risk infants

Neurophysiologic assessments using EEG/polysomnographic studies permit the clinician to recognize expected patterns of brain maturation in the healthy neonate. By comparison, one can detect encephalopathic behaviors of newborns who are medically at risk. Severe physiologic expressions of encephalopathy are associated with neuropathologic lesions on postmortem examinations, brain lesions documented on neuroimaging studies, and major neurodevelopmental sequelae of survivors. However, such patterns are observed for only a minority of high risk neonates; less severe encephalopathies occur more frequently in neonates without evidence of brain lesions on imaging studies who either recover from medical illness or who manifest no findings of neurological dysfunction. These subtle and persistent brain disorders are obviously more difficult to detect and grade. This is specifically relevant for preterm infants in whom various degrees of encephalopathy may exist, but whose physiologic behaviors must be distinguished form expected behavioral and neurophysiologic patterns of prematurity. Neonates may express brain dysfunction as altered rates of brain maturation, as compared with expected patterns for a given conceptional age. Neurophysiologic expressions of brain dysmaturity, either from prenatal and/or postnatal stresses, may actually occur in a substantially larger segment of the high risk neonatal population than has been anticipated. EEG-sleep studies can serve as a noninvasive neurophysiologic probe of brain organization and maturation to extend clinical observations to assess the severity and persistence of brain dysfunction in a neonate who may be at risk for later neurodevelopmental compromise.

[Actimetry: simplified analysis of wake-sleep rhythms in the newborn. Preliminary results]

Actimetry in newborns is relevant if two actimeters are placed, one on each ankle. This study has been conducted on nine normal three days old newborns. It has shown an indisputable link between the lack of activity and the observed sleep during the night that was missing during the day. The longest period of wake was recorded during the day and the longest period of sleep or inactivity was during the night. This study has confirmed the existence of an ultradian rhythm of quiet sleep and wake. It is also possible that a beginning of a circadian rest-activity rhythm exists already in the neonatal period, that is still discussed in the literature.

Maturational trends of EEG-sleep measures in the healthy preterm neonate

Five physiologic groupings of 45 EEG-sleep measures were acquired from serial 24-channel EEG-sleep recordings (i.e., sleep architecture, continuity, EEG spectral, phasic, and autonomic measures), utilizing 129 studies on 56 healthy preterm infants from 28 to 43 weeks postconceptional age (PCA) who were neurodevelopmentally normal on follow-up. Regression analyses chose the least number of measures that best reflected maturation. Four of 45 variables (i.e., spectral alpha energy during quiet sleep, total spectral EEG energy, arousal number during active sleep, and percentage of EEG discontinuity) most significantly explained brain maturation in neonates < 36 weeks PCA. Three of 45 variables (i.e., spectral theta and beta energies during active sleep and spectral alpha energy during quiet sleep) were most representative after 36 weeks PCA. Spectral EEG energies were the strongest indicators of maturation compared with other measures, particularly in near-term neonates.

Functional analysis of spontaneous movements in preterm infants

Spontaneous movements of premature infants between 25 and 34 weeks conceptional age were observed for 1 hr on two or three occasions. Subjects had low-risk prognoses and were clinically stable at the time of testing. Behavioral acts were scored using a 0/1 time sampling technique in 60 continuous, 1-min time blocks. Temporal associations between individual movements were found using chi-square analyses. Some associated behaviors contained combinations consistent with neonatal action patterns, for example, single and bilateral leg kicking, head turning, and mouthing. Features of state organization were also evident in that general motor activity (GM), which has been used as a marker of active sleep (AS) in neonates, was found to cluster temporally with startle, facial, and head movements but not eye movements. Behavioral quiescence (> or = 5 s) was dissociated from AS-related behaviors (GM, facial, head, and eye movements). Combinations of state-segregated behaviors were more likely to exhibit co-occurrence within 1-min intervals in infants 30 weeks conceptional age and older.

Spontaneous motility in premature infants: features of behavioral activity and rhythmic organization

The spontaneous motor activity of clinically stable premature infants, 26-36 weeks gestational age, was investigated. Movements were recorded using a pressure-sensitive transducer positioned below the infant's head and torso. Behavior samples were digitized every 0.5 s during 2 and 3-hr continuous recording sessions. Time-series analyses revealed prominent motility cycles of circa 80 min and circa 30 min. These results are consistent with periodicities in motility and REM activation observed in full-term neonates. The longer rhythms of 70-100 min of motility found in this study establish that these periods are present at this stage of development independent of maternal zeitgebers. Developmental changes in motility rhythms and movement burst durations were also observed. Bout durations became somewhat longer in older (> 30 weeks) infants, but the relative time devoted to movement per session was comparable in older and younger (< or = 30 weeks) infants.

Evoked potentials in full-term and premature infants: a comparative study

In this study the maturation of the central nervous system of full-term and premature infants were investigated electrophysiologically. The subjects were 16 full-term and 15 premature infants. Neurologic examination, psychometric tests, and measurement of evoked potentials were carried out periodically in babies who had no birth trauma, metabolic disorder, or intrauterine infection. Neurophysiologic comparison of the results was evaluated. As the babies grew older, I-V interpeak latency became shorter according to the results of brainstem auditory evoked potentials; N1-P1 amplitude became higher and P1 latency shorter according to the results of visual evoked potentials. Central nervous system maturation of full-term babies and prematures appear to be alike at 6 months of age.

Physiological correlates of sleep development in premature and full-term neonates

Differentiation of motor and automatic function control during different sleep states appears early in human ontogeny. Time of first appearance, magnitude of between-state differences and modifications with age depend on which particular parameters are considered. For some parameters, significant between-state differences appear at 31 weeks conceptional age (wk CA). For nearly all parameters, this difference is clear from 35 wk CA onwards. The analysis presented herein is based on studies of body movements, spontaneous skin potential responses, respiratory characteristics, heart rate and heart rate variability, and correlations between different functions. It examines clinically and neurologically normal premature and full-term neonates of 28-41 wk CA.

A developmental marker of central nervous system maturation: Part II

Computer technology facilitates simultaneous comparison of changes among various neurophysiologic measures. Evaluating relationships among various sleep events provides information concerning normal central nervous system development, as well as perturbations in the electroencephalographic rhythms that accompany pathologic conditions in the neonate. Prognostic information may be derived from the "recovery" pattern of the abnormal electroencephalogram after acute neonatal illness.

A developmental marker of central nervous system maturation: Part I

Sleep is the predominant behavioral state of the neonate and the neurophysiologic expression of cerebral function during rapid brain growth and maturation that characterizes the neonatal period. The ontogeny of electroencephalographic (EEG) sleep in the neonate can be monitored by serial EEG/polygraphic recordings. A variety of physiologic markers accompany neonatal sleep, such as specific EEG patterns, rapid eye movements, arousals, autonomic signs, and body movements. These parameters vary in occurrence and abundance during different segments of the neonatal sleep cycle. Time-dependent interrelationships among these different physiologic components can be assessed by visual inspection of EEG recordings to monitor specific patterns that appear during one or more sleep cycles. Mathematical modeling and computer technologies permit the study of interactions among neurophysiologic signals which are not apparent by visual inspection. An understanding of biological rhythm relationships among different sleep events offers insights into the effects of extrauterine environment on the development of the central nervous system in the healthy preterm neonate and the disturbances in the sleep EEG rhythm in abnormal neonates. Sleep EEG analysis may be useful prognostically because "normalization" of abnormal EEG patterns often occurs following the initial acute illness. Suitable, normative data from very premature neonates are needed before pediatric neurologists can rely on neonatal EEG as an indicator of brain maturation in this low-birth weight group. An understanding of the biologic significance of the ontogeny of neonatal sleep, as well as the clinical significance of perturbations in this sleep cycle with disease, will lead to more reliable analyses of sleep physiology for research and clinical purposes.

Development of sleep states in normal premature and full-term newborns

THE AIMS OF OUR STUDY WERE

1) to answer the question "Do sleep states exist in normal premature infants;" 2) to analyze the development of sleep cycle and sleep state characteristics in premature and full-term newborns. Polygraph recordings were done on 38 normal, appropriate for gestational age newborns, born at 30 to 41 weeks (w) of gestation. All infants fell asleep in active sleep (AS). Postwaking AS was significantly shorter than the next AS. Mean sleep cycle duration increased from approximately 46 min at 31-34 w of conceptional age (CA) to 70 min. at 35-36 w CA. In all infants we observed stable, greater than 5 min AS and quiet sleep (QS) periods, as defined by EEG and REM criteria. Indeterminate sleep was about 30% of the total sleep cycle at 31-34 w; it decreased to 12% at 35-36 w. Both duration and percentage of AS and QS significantly increased at 35-36 w and remained stable up to 39-41 w CA. Values of QS were significantly reduced when defined by additional criteria (respiratory rate, tonic chin EMG or motility). Concordance of QS criteria was not significantly better in older versus younger groups of infants. At all ages, AS values were insensitive to changes in the criteria chosen to define them. The contrast, starting from 31-34 w CA, between AS and QS as defined by EEG and REM criteria could account for state differences in the control of many physiological variables in prematures.