Cardiopulmonary monitoring at home: the CHIME monitor.

A new physiologic monitor for use in the home has been developed and used for the Collaborative Home Infant Monitor Evaluation (CHIME). This monitor measures infant breathing by respiratory inductance plethysmography and transthoracic impedance; infant electrocardiogram, heart rate and R-R interval; haemoglobin O2 saturation of arterial blood at the periphery and sleep position. Monitor signals from a representative sample of 24 subjects from the CHIME database were of sufficient quality to be clinically interpreted 91.7% of the time for the respiratory inductance plethysmograph, 100% for the ECG, 99.7% for the heart rate and 87% for the 16 subjects of the 24 who used the pulse oximeter. The monitor detected breaths with a sensitivity of 96% and a specificity of 65% compared to human scorers. It detected all clinically significant bradycardias but identified an additional 737 events where a human scorer did not detect bradycardia. The monitor was considered to be superior to conventional monitors and, therefore, suitable for the successful conduct of the CHIME study.

The effect of epoch length and smoothing on infant sleep and waking state architecture for term infants at 42 to 46 weeks postconceptional age.

STUDY OBJECTIVES: Epoch lengths from 20 seconds to 1 minute, and smoothing strategies from zero to three minutes are encountered in the infant sleep and waking literature. The present study systematically examined the impact of various epoch lengths and smoothing strategies on infant sleep state architecture. DESIGN: Overnight polysomnographic recordings were visually assessed by epoch as wake or as each of four sleep state parameters: electroencephalographic patterns, respiration, body movement, and eye movement. From these findings, sleep and waking states were assigned for each of six combinations of epoch length (30-second or 1-minute) and smoothing window length (none, 3-epoch, or 5-epoch). SETTING: N/A. PARTICIPANTS: Subjects were 91 term infants, 42-46 weeks postconceptional age, from the Collaborative Home Infant Monitoring Evaluation (CHIME) study. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: A greater epoch length resulted in more active and less quiet sleep as a percentage of total study; however, the size of the smoothing window did not affect the percentage of sleep/waking states. In general, the greater the epoch length and the greater the smoothing window length, the fewer the number of, the greater the mean duration of, and the greater the longest continuous episode of sleep/waking states. Analysis of significant interactions indicated that a 1-minute epoch length relative to a 30-second epoch length resulted in increasingly longer episodes of quiet and especially active sleep with a greater smoothing window length. CONCLUSIONS: Smoothing strategy significantly altered sleep state architecture in infants and may explain part of the variability in infant sleep state findings between laboratories.

Infant polysomnography: reliability. Collaborative Home Infant Monitoring Evaluation (CHIME) Steering Committee.

Infant polysomnography (IPSG) is an increasingly important procedure for studying infants with sleep and breathing disorders. Since analyses of these IPSG data are subjective, an equally important issue is the reliability or strength of agreement among scorers (especially among experienced clinicians) of sleep parameters (SP) and sleep states (SS). One basic issue of this problem was examined by proposing and testing the hypothesis that infant SP and SS ratings can be reliably scored at substantial levels of agreement, that is, kappa (kappa) > or = 0.61. In light of the importance of IPSG reliability in the collaborative home infant monitoring evaluation (CHIME) study, a reliability training and evaluation process was developed and implemented. The bases for training on SP and SS scoring were CHIME criteria that were modifications and supplements to Anders, Emde, and Parmelee (10). The kappa statistic was adopted as the method for evaluating reliability between and among scorers. Scorers were three experienced investigators and four trainees. Inter- and intrarater reliabilities for SP codes and SSs were calculated for 408 randomly selected 30-second epochs of nocturnal IPSG recorded at five CHIME clinical sites from healthy full term (n = 5), preterm (n = 4), apnea of infancy (n = 2), and siblings of the sudden infant death syndrome (SIDS) (n = 4) enrolled subjects. Infant PSG data set 1 was scored by both experienced investigators and trained scorers and was used to assess initial interrater reliability. Infant PSG data set 2 was scored twice by the trained scorers and was used to reassess inter-rater reliability and to assess intrarater reliability. The kappa s for SS ranged from 0.45 to 0.58 for data set 1 and represented a moderate level of agreement. Therefore, rater disagreements were reviewed, and the scoring criteria were modified to clarify ambiguities. The kappa s and confidence intervals (CIs) computed for data set 2 yielded substantial inter-rater and intrarater agreements for the four trained scorers; for SS, the kappa = 0.68 and for SP the kappa s ranged from 0.62 to 0.76. Acceptance of the hypothesis supports the conclusion that the IPSG is a reliable source of clinical and research data when supported by significant kappa s and CIs. Reliability can be maximized with strictly detailed scoring guidelines and training.

Episodes of bradycardia during early infancy in the term-born and preterm infant.

OBJECTIVE: To document the incidence of transient episodes of bradycardia in a group of healthy term and preterm infants during the first 1 to 6 months of life. DESIGN: Longitudinal polysomnographic study. SETTING: Sleep laboratory in a university-affiliated urban medical center. PARTICIPANTS: Fourteen healthy term-born infants, nine preterm infants with apnea in the nursery, and 10 preterm infants without apnea. Infants with neonatal morbidity except apnea were excluded. MEASUREMENTS: Transient episodes of bradycardia (< or = 100 beats per minute) were identified in 2- to 4-hour early evening polysomnographic tracings. The relationship with apnea, transcutaneous oxygen levels, and sleep state was determined. RESULTS: Transient episodes of bradycardia to 60 to 70 beats per minute were common, but there were no drops below 50 beats per minute. The incidence of transient episodes of bradycardia was inversely related to heart rate. Results for apneic and nonapneic premature infants were similar. CONCLUSIONS: Transient episodes of bradycardia are considered normal reflex responses and are not related to risk for sudden infant death syndrome. These results have implications for the setting of monitor alarms.

Obstructive apnea, associated patterns of movement, heart rate, and oxygenation in infants at low and increased risk for SIDS.

Repetitive polysomnograms were recorded between 40 weeks post-conceptional age and 6 months in a total of 49 infants, 19 healthy preterm infants, 14 normal term infants, and 16 subsequent siblings of infants who died of sudden infant death syndrome (SIDS). These nighttime recordings lasted 2-4 hours, except at 3 months when an overnight 12-hour recording was performed. Obstructive apneas (OA) > 3 seconds were divided into 3 categories: 1) clear obstructive, 2) mixed and 3) unclear because of movement artifacts. More than half belonged in category 3 and were excluded from further analysis unless accompanied by a transient episode of bradycardia (TEB), defined as heart rate < or = 100 beats per minute. Each OA with TEB was also examined for changes in transcutaneous oxygen tension (PtcO2). Most pauses were brief (median, 4 seconds), the longest (27 seconds) seen only once in the youngest premature infant. The majority of OA were accompanied by heart rate accelerations. The number of clear obstructive and mixed apneas was similar. The scores were combined to calculate a density (number per 100 minutes of recording). OA were not common: Their density decreased from 2 in 100 minutes at 40 weeks in the preterm to once every 300 minutes (5 hours) in the 6-month-old term infant. Ten percent of the OA were accompanied by TEB. Of these, 10% were accompanied by a PtcO2 decrease of > 10 mm Hg. OA with TEB followed a nonmonotonic curve, the highest percentage of infants showing this pattern at the age of highest risk for SIDS. Minor differences among study groups were confined to less movements with OA in subsequent siblings and an earlier peak incidence of OA with TEB in prematures, compared to normal term infants. OA were seen in all study groups, were self-limited, and apparently were devoid of pathological consequences.

Polygraphy after discharge in preterm infants with and without apnea in the nursery.

Nine of nineteen infants in this study exhibited two or more central apnea greater than or equal to 20 seconds when they were older than one week and between 32-36 weeks postconceptional age (PCA). We focused on the sequelae of these apneas. Apnea was separated from other morbidity associated with immaturity by the selection of consistently healthy infants. Following discharge, polygraphic tracings were obtained at 40, 44 and 52 weeks PCA in these non-apneic and previously apneic infants. Sleep states, minute by minute values for heart and respiratory rate, skin temperature and transcutaneous O2 (PtcO2) and CO2 (PtcCO2), apnea and transient decreases in PtcO2 were determined. Polygraphic measurements did not differentiate preterm infants with late apnea in the nursery from non-apneic ones. However, the apneic group exhibited a transient decrease in awakenings at 44 weeks PCA.

Polysomnography in newborns and young infants: sleep architecture.

Sleep architecture derived from long-term polysomnographic recordings during the first year of life is characterized by clear developmental trends against a backdrop of variability. Variability is due to differences in state definitions and data collection and analysis strategies but probably also to an intrinsic characteristic of the maturing central nervous system (functional plasticity). Changes in sleep and wakefulness probably constitute nonspecific responses to a variety of stimuli. The variability has frustrated efforts to use specific features of sleep architecture for diagnostic or prognostic purposes. At present, polysomnographic studies of sleep architecture independent from EEG and cardiorespiratory studies are not indicated for diagnosing specific medical conditions or prognoses of good/adverse outcomes. For accurate interpretation for cardio-respiratory data, however, studies of sleep and wakefulness are indispensable. Furthermore, the study of neonatal seizures, in particular the coherence of state-defining variables or the evolution of sleep morphology, may benefit from attention to sleep architecture. Initial findings from some laboratories suggest that the very feature of excessive instability, which can be measured by repetitive long-term polysomnographic monitoring, signals a poor prognosis. In addition, fragmented sleep and the evolving interrelationship between ultradian and circadian rhythms may contain useful information that has yet to be mined. The advent of computer technologies can make the clinical laboratory into a setting where both research and clinical studies contribute to an elucidation of risk for sudden infant death syndrome and sequelae of neonatal seizures.

Transcutaneous oxygen and carbon dioxide during the first half year of life in premature and normal term infants.

Repetitive polysomnograms were recorded from a total of 33 infants, 19 healthy preterm infants, and 14 term controls between 40 wk postconceptional age and 6 mo of age. These nighttime recordings lasted 2-4 h, except at 52 wk in preterm infants and at 3 mo of age in term infants when an overnight 12-h recording was performed. Minute by minute values of transcutaneous PO2 (PtCO2) and transcutaneous PCO2 (PtcCO2) levels and variability during the awake state, active sleep, and quiet sleep were obtained through computer analyses of the polygraphic data. The results from preterm infants at corrected postconceptional age could not be differentiated from those of control infants. PtCO2 levels rose between 40 wk and 3 mo, and PtcCO2 levels declined. Sleep states modulated only the variability of PtcO2, not the level; in contrast, state modulation was seen in both variability and level of PtcCO2 throughout the age span studied. During sleep the number of transient declines in PtCO2 greater than 2.03 kPa (15 mm Hg) decreased with advancing age. Hypercapnic PtcCO2 values decreased with age as well, but their prevalence in healthy, young infants suggests the need for reevaluation of criteria for hypercapnia based on transcutaneous measurements. The data demonstrate that ventilatory regulation continues to undergo changes between 1 and 3 mo, the age of highest risk for sudden infant death syndrome.

Apnea, transient episodes of bradycardia, and periodic breathing in preterm infants.

The occurrence of central apnea of 15 seconds or longer, transient episodes of bradycardia (TEB), and periodic breathing were studied in 66 healthy premature infants when at least 1 week old and between 32 and 36 weeks postconceptual age. Eight-hour cardiorespiratory recordings were visually scanned for the presence of these patterns. Central apnea of 15 seconds or longer was seen in almost half of the infants. The TEB were numerous, and the majority were not associated with central apnea; however, all but five of the apneic episodes that lasted 15 seconds or longer were accompanied by a TEB. Infants spent as much as 40% of their time in periodic breathing. The frequency with which these patterns are seen in healthy premature infants strongly suggests that they are normal findings. Our results do not support the opinion that brief periods of apnea are abnormal when accompanied by a TEB.

Airways and air pollution in childhood: state of the art.

Correlations between ambient pollutants and health effects, such as observed in SIDS, may in reality be to a larger extent the result of indoor sources. These distinctions between indoor and outdoor sources, while important, do not detract from the overall conclusion that pollution affects the airway in children directly and indirectly. Much still needs to be learned about the permanence of these effects, the mechanism by which the effect is mediated, and the conditions under which some of these effects are maximal. Two approaches seem particularly suited to shed further light on these issues. First, identification of biological markers for exposure to pollutants will yield both more accurate measures of exposure to pollutants and information about health consequences. Second, newer modeling techniques promise to predict health outcomes under a variety of environmental conditions. Shumway et al., for instance, describe a promising model predicting an increase in mortality due to ambient pollutants in the Los Angeles Basin with higher levels under extremes of temperature, especially during cold spells. Time series and factor analyses may further our knowledge as well. In the near future, large cohort studies should begin to reveal the cumulative effects of air pollution on the respiratory system, especially in relation to active smoking. Finally, studies in Black children are virtually unavailable. Given their high risk for respiratory illnesses, such studies are sorely needed.

Cardiopulmonary and intracranial pressure changes related to endotracheal suctioning in preterm infants.

Although endotracheal (ET) suctioning is performed frequently in sick newborn infants, its effects on cardiorespiratory variables and intracranial pressure (ICP) have not been thoroughly documented in neonates greater than 24 h who were not paralyzed while receiving mechanical ventilation. This study evaluates these changes in preterm infants who required ventilatory assistance. We measured transcutaneous PO2 and PCO2 (PtcO2 and PtcCO2, respectively), intra-arterial BP, heart rate, ICP, and cerebral perfusion pressure (CPP) before, during, and for at least 5 min after ET suctioning in 15 low birth weight infants less than 1500 g and less than or equal to 30 days of age. One infant was studied twice. A suction adaptor was used to avoid disconnecting the patient from the ventilator and to attempt to minimize hypoxemia and hypercapnia during suctioning. The patients were studied in the supine position and muscle relaxants were not used. PtcO2 decreased 12.1% while PtcCO2 increased 4.7% 1 min after suctioning; however, greater increases in mean BP (33%) and ICP (117%) were observed during suctioning. CPP also increased during the procedure. ICP returned to baseline almost immediately, whereas BP remained slightly elevated 1 min after suctioning. Our findings demonstrate that ET suctioning significantly increases BP, ICP, and CPP in preterm infants on assisted ventilation in the first month of life. These changes appear to be independent of changes observed in oxygenation and ventilation.

Polysomnographic sleep and waking states are similar in subsequent siblings of SIDS and control infants during the first six months of life.

Twenty-five subsequent siblings of infants who died of Sudden Infant Death Syndrome (SIDS) underwent 12-h overnight polygraphic recordings during the first week of life and at 1, 2, 3, 4, and 6 months of age. The polygraphic tracings from these infants were compared with those from 25 infants without a family history of SIDS. One dozen sleep and waking parameters were examined including state transition probabilities, the ratio between quiet sleep (QS) and active sleep (AS), the incidence and duration of sustained states and the stability of an infant's sleep and waking during the first half year of life. Variability within and between infants was marked with a reduction of variability in measures of QS at 3 months and of AS at 4 months of age. The similarities between subsequent siblings of SIDS and control infants far outweighted the differences. However, subsequent siblings exhibited a tendency, once asleep, to remain asleep longer than controls. This finding was observed in a comparison of 20 infants in each group. When five infants were added to each group, infants in both groups tended to awaken equally from QS, but once in AS the subsequent siblings tended to proceed into QS instead of awaken as the controls did.

Sleep and waking states in infancy: normative studies.

Twelve-hour polygraphic recordings were obtained in 20 normal healthy term infants at 1 week of age, at monthly intervals up to 4 months, and at 6 months of age. Each minute of these recordings was coded into active sleep (AS), quiet sleep (QS), wakefulness (AW), or indeterminate (IN) based on polygraphic and behavioral variables. For each state, a dozen variables were computed with the help of a laboratory computer. Together these variables describe trends in the development of sleep and wakefulness in the laboratory: an increase in QS and a concomitant decrease in AS, an increase in sustained episodes of these states, and continuous sleep onset in AS throughout this time span. Considerable variability appears to characterize immature sleep patterns, but a reduction in variability was noted between 3 and 4 months of age. The number of sustained sleep-state episodes and the percentage of AS and IN proved to be stable characteristics of individual infants. The large variability among and within infants sheds doubt on the usefulness of polygraphic monitoring of sleep states for early detection of abnormalities.

Factors involved in the decline of the developmental quotient in the very low birth weight infant during the first two years.

The developmental status of 62 infants with birth weights less than 1,501 g was evaluated at nine or 12 months and at two years of age corrected for prematurity. The mean developmental scores were 99.8 at the first examination and 84.4 at the second, a significant drop (P less than 0.0001). Half of the infants (Group 1) dropped less than 16 points (mean score from 97.1 to 91.3) and half of the infants (Group 2) dropped less than 15 points (mean score from 102.8 to 76.9). The incidence of small for gestational age infants was overrepresented in Group 2. A multivariate analysis revealed that a group of factors including maternal hypertension and diabetes, gestational age, birth weight, and resuscitation at birth correctly classified 87 per cent of the infants into the two groups. The influence of this cluster of medical factors on developmental decline of the very low birth weight infant deserves further consideration.

Factors affecting nursery survival of very low birth weight infants.

398 infants with birthweight (BW) 500-1500 g born from January 2 1982 to December 1983 were studied to determine incidence and survival rate by BW and gestational age (GA) categories and to determine causes of death and factors influencing mortality. 58% of the group survived. Factors other than those in the perinatal and postnatal period did not significantly influence survival. Infants with BW below 1000 g delivered by elective C-section had better survival than those delivered vaginally. Survival increased progressively with increasing BW and GA categories with GA more than BW being the limiting factor. Eleven (6.6%) of the deaths in the very low birth weight infants occurred during the nursery period after 28 days of age. These deaths would not have been addressed in the neonatal mortality.

Ventilatory control and carbon dioxide response in preterm infants with idiopathic apnea.

Idiopathic apnea in preterm infants, more than 30 weeks of gestation, after the first week of life is uncommon and poorly understood. To study ventilatory control in these infants we measured minute ventilation, respiratory frequency, tidal volume, end-tidal oxygen pressure and carbon dioxide pressure, and transcutaneous oxygen pressure before and during the fifth minute of breathing 4% carbon dioxide in air. Nine healthy preterm infants and eight infants with three or more episodes of apnea (greater than or equal to 20 s) in 24 hours were studied during active sleep. We found that infants with apnea had a significantly increased alveolar carbon dioxide pressure while respiratory frequency, minute ventilation, and slope were significantly decreased. Alveolar-transcutaneous oxygen gradients were essentially unchanged. These preterm infants with apnea have a decreased carbon dioxide sensitivity. They have a decreased minute ventilation primarily as a result of decreased respiratory frequency and their alveolar-transcutaneous oxygen gradient is normal. Our findings suggest that the major deficit in these infants is a central disturbance in the regulation of breathing.

Development of sleep-waking temporal sequencing in infants at risk for the Sudden Infant Death Syndrome.

The periodic organization of waking, quiet sleep, and active sleep was studied in control infants and siblings of victims of the Sudden Infant Death Syndrome. Spectral estimates of all-night binary state time series recorded at 1 week and 1, 2, 3, 4, and 6 months of age revealed disturbed patterns of sleep states, especially in active sleep, from as early as the first week of life. These disruptions continued until at least 6 months of age. These data support the contention that the temporal patterning of sleep state can be used as an important neurologic marker for development.

Respiratory behavior in near-miss sudden infant death syndrome.

Seventeen infants with unexplained prolonged apnea that has been designated near-miss sudden infant death syndrome were monitored for sleep and cardiorespiratory variables during a 12-hour, all-night recording session. Infants were matched for gestational age, sex, and age at recording with control infants. Respiratory variables studied included respiratory rate, respiratory variability, apnea duration, apnea density, and periodic breathing. No statistically significant differences were found in sleep state or respiratory variables between near-miss and control infants. Eight infants (47%) had no recurrence of prolonged apnea, whereas three (17.6%) had recurrent apneic episodes for six weeks to eight months following the original episode. No clinical or polygraphic finding predicted which infant would exhibit recurrent apnea. None of the infants was monitored at home. All infants were developing normally when examined at 1 to 2 years of age.