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.

Cardiorespiratory events recorded on home monitors: Comparison of healthy infants with those at increased risk for SIDS.

CONTEXT: Home monitors designed to identify cardiorespiratory events are frequently used in infants at increased risk for sudden infant death syndrome (SIDS), but the efficacy of such devices for this use is unproven. OBJECTIVE: To test the hypothesis that preterm infants, siblings of infants who died of SIDS, and infants who have experienced an idiopathic, apparent life-threatening event have a greater risk of cardiorespiratory events than healthy term infants. DESIGN: Longitudinal cohort study conducted from May 1994 through February 1998. SETTING: Five metropolitan medical centers in the United States. PARTICIPANTS: A total of 1079 infants (classified as healthy term infants and 6 groups of those at risk for SIDS) who, during the first 6 months after birth, were observed with home cardiorespiratory monitors using respiratory inductance plethysmography to detect apnea and obstructed breathing. MAIN OUTCOME MEASURES: Occurrence of cardiorespiratory events that exceeded predefined conventional and extreme thresholds as recorded by the monitors. RESULTS: During 718 358 hours of home monitoring, 6993 events exceeding conventional alarm thresholds occurred in 445 infants (41%). Of these, 653 were extreme events in 116 infants (10%), and of those events with apnea, 70% included at least 3 obstructed breaths. The frequency of at least 1 extreme event was similar in term infants in all groups, but preterm infants were at increased risk of extreme events until 43 weeks' postconceptional age. CONCLUSIONS: In this study, conventional events are quite common, even in healthy term infants. Extreme events were common only in preterm infants, and their timing suggests that they are not likely to be immediate precursors to SIDS. The high frequency of obstructed breathing in study participants would likely preclude detection of many events by conventional techniques. These data should be important for designing future monitors and determining if an infant is likely to be at risk for a cardiorespiratory event.

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.

Agreement among raters in assessment of physiologic waveforms recorded by a cardiorespiratory monitor for home use. Collaborative Home Infant Monitoring Evaluation (CHIME) Study Group.

There are numerous reports of cardiorespiratory patterns in infants on home monitors, but no data to determine whether "experts" agree on the description of these patterns. Therefore, we evaluated agreement among four experienced investigators and five trained technicians who assessed independently the same sample of physiologic waveforms recorded from infants enrolled in a multicenter study. The monitor used respiratory inductance plethysmography and recorded waveforms for apnea > or = 16 s or a heart rate < 80 beats/min for > or = 5 s. The investigators and technicians initially assessed 88 waveforms. After additional training, the technicians assessed another 113 additional waveforms. In categorizing waveforms as apnea present or absent, agreement among technicians improved considerably with additional training (kappa 0.65 to 0.85). For categorizing waveforms as having bradycardia present versus absent, the trends were the same. Agreement in measurement of apnea duration also improved considerably with additional training (intraclass correlation 0.33-0.83). Agreement in measurement of bradycardia duration was consistently excellent (intraclass correlation 0.86-0.99). Total agreement was achieved among technicians with additional training for measurement of the lowest heart rate during a bradycardia. When classifying apnea as including > or = 1, > or = 2, > or = 3, or > or = 4 out-of-phase breaths, agreement was initially low, but after additional training it improved, especially in categorization of apneas with > or = 3 or > or = 4 out-of-phase breaths (kappa 0.67 and 0.94, respectively). Although researchers and clinicians commonly describe events based on cardiorespiratory recordings, agreement amongst experienced individuals may be poor, which can confound interpretation. With clear guidelines and sufficient training raters can attain a high level of agreement in describing cardiorespiratory events.

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.

Endogenous event-related potentials in term and preterm infants.

Event-related brain potentials generated in an auditory oddball paradigm were recorded in term and preterm infants. The amplitudes of these brain potentials were significantly larger when generated by a rare improbable stimulus compared to a common frequently presented stimulus. While the magnitude of this novelty detection effect depended on the gestational status (full term and preterm) of the infant, these findings suggest the developmental continuity of cognitive processes such as selective attention and recognition memory ordinarily observed in adults. The significant relationship between the amplitudes of these brain potentials and states conducive for sustained attention in infants further supports the endogenous nature of these potentials.

Race, ethnicity and birth-weight: Hawaii 1983 to 1986.

A study of racial/ethnic-specific mean infant birth-weights reported on 1968 to 1972 live birth-weight certificates for Oahu, Hawaii is reviewed here. The 1983 to 1986 data confirm those earlier results: (a) The Hawaiian group is significantly heavier in mean birth-weights than other cohorts during the preterm period (33 to 36 weeks gestational age); (b) statistically significant differences also were present in mean birth-weights for the term and post-term periods (37 to 45 weeks gestational age); and (c) the ranking of cohorts from heaviest to lightest in mean birth-weights is Caucasian, Hawaiian, Japanese and Filipino respectively. The data raises 2 questions: (1) Which birth-weight standards are most applicable for Asian and Pacific Islanders; and (2) what are the implications of the race/ethnic-specific mean birth-weight differences relative to mortality, morbidity and developmental outcome?

Childhood developmental changes in the auditory P300.

In this study we investigated developmental changes in the auditory P3 latency from childhood to adolescence. Event-related potentials evoked by improbable auditory stimuli were recorded from 35 normal children between the ages of 5 and 13 years. Regression analyses showed significant age trends in the auditory P3 latency. Latencies decreased at a rapid rate (Cz: 20.34 msec/yr; Pz: 19.27 msec/yr) from childhood to adolescence, suggesting an increased efficiency in processing information as children mature. This rate was linear or constant in nature as evidenced by the failure of the quadratic and cubic components to significantly increase predictability of the regression equation. The slope of the P3 latency/age regression line was also shown to be influenced by the interactive effects of task difficulty and maturation. It was hypothesized that neuro-developmental processes (increased myelination and dendritic arborization) may underlie the maturational changes observed in the P3 latency during childhood.

Identifying sleep apnea from self-reports.

An apnea score (AS) was developed as a potential screening tool for sleep apnea. This was based on self-report questionnaire responses of 76 sleep disorder center patients and 20 sleep survey volunteers. Twenty volunteers and 23 patients (group I) comprised the initial AS development group. Their questionnaire responses were compared to polysomnographic apnea indexes (AI) and apnea plus hypopnea indexes (AHI). Stepwise multivariate discriminant analysis was used to test whether or not selected group I questionnaire responses could be used to correctly classify respondents into apnea (AI or AHI greater than 5) or nonapnea (AI, AHI less than or equal to 5) groups. Self-reports of "stops breathing during sleep," "loud snoring," and history of adenoidectomy best discriminated normal (AI less than or equal to 5) from apnea (AI greater than 5) cases. The AS derived from group I responses to these three variables was then computed for group II (n = 53). After examination of the AS results, the AS was modified to include just "stops breathing" and "loud snoring" and the AI criterion was raised to 10 per hour. This revised AS correctly identified 100% of the cases with moderate-severe sleep apnea (AI or AHI greater than 40) and 70-76% of all sleep apnea cases with AI or AHI greater than 5. Predictive accuracy was 88% for AI greater than 10. The two questions that comprise the AS should be incorporated into risk appraisal instruments or interviews to screen for sleep apnea.

Auditory responsivity and intrauterine growth retardation in small for gestational age human newborns.

Auditory responsivity in term small for gestational age (SGA) compared to term appropriate for gestational age (AGA) human newborns reflects functional differences which may be attributable to intrauterine growth retardation (IUGR). Between-group comparisons of percent of responses of averaged late component auditory evoked events (AEEs) to pure tone stimuli (500, 1000, 2000, 4000, 6000 and 8000 Hz) at 63 and 80 dB SPL revealed significantly greater AGA responsivity at 80 dB SPL. Conversely, the AEE mean latencies were significantly shorter for SGA infants at both intensity levels. Between-group responsivity differences suggest developmental retardation in term (38-42 weeks) SGA newborns, but the faster SGA latencies may reflect 'induced' acceleration in auditory neurophysiologic function.

Daytime sleep stage organization in three-month-old infants.

Sleep monitoring at 3 months post term of clinically normal term infants, pre-term infants with no demonstrable pathologic clinical signs, and pre-term and term infants with a history of metabolic disorders show that these infants have EEG sleep stages resembling those seen in adults, as well as the adult pattern of sleep stage organization. The presence of NREM stage organization and stage sequencing suggest that sleep regulatory mechanisms are approaching a level of functional maturity in the human infant at 3 months post term. There is a significant relationship between sleep staging at 3 months post term and mental and motor performance at 12 months post term. In light of this, it is hypothesized that early bioelectric maturation may reflect the development of neural mechanisms which are also the substrate for later cognitive and behavioral functioning. Sleep stage organization at 3 months post term may be utilized as a benchmark of CNS development and for research on the pathophysiology of sleep disorders.

Multiple carboxylase deficiency: clinical and biochemical improvement following neonatal biotin treatment.

Multiple carboxylase deficiency is characterized by deficient activities of three biotin-dependent enzymes, propionyl coenzyme A carboxylase, pyruvate carboxylase, and beta-methylcrotonyl coenzyme A carboxylase. A newborn infant was seen with metabolic ketoacidosis, hyperammonemia, organic aciduria, seizures, and coma. Multiple carboxylase deficiency was subsequently confirmed by enzyme activity determinations in his peripheral blood leukocytes and cultured skin fibroblasts. The infant's neurologic and metabolic status improved markedly within a few days of administration of pharmacologic doses of oral biotin. His EEG, which was distinctly abnormal, became normal; his extensive computed tomography scan changes resolved, with the exception of ventricular dilation, over the next two months. After two weeks of biotin treatment the excretion of abnormal organic acid metabolites was reduced and his carboxylase activities increased to the normal range. However, the activities of these enzymes increased only to 30% to 55% of normal in fibroblasts incubated in supplemental biotin. This partial correction of enzyme activity differs from that observed in other individuals with multiple carboxylase deficiency and suggests biochemical heterogeneity in this disorder. Prompt diagnosis and intervention can avert some of the pathologic complications of this biotin-responsive condition.

Autoregressive analysis: a method for detecting electroencephalic changes in newborns to tones.

This report presents an autoregressive technique for detectiong statistically significant changes in brain activity to tones. The change detectin model is applied to stationary time series electroencephalogram samples from sleeping newborn infants. The electroencephalic responses of neonates to tones are quantified and analyzed in terms of t-statistics. Confidence limits applied to averaged t-statistics objectively and reliably defined statistically significant late components in newborns.

Effects of induction of labor on the neurophysiologic functioning of newborn infants.

Neurophysiologic responses of newborn infants delivered after normal onset of labor are compared with those of newborn infants whose mothers had labor induced with oxytocin or prostaglandin F2 alpha. No differences in brain activity or heart rate were detected between groups in terms of frequency of response to auditory, visual, tactile, or olfactory stimulation. Significant differences were found for resting brain activity defined in terms of autoregressive spectral estimates or coefficients. The largest differences were between the groups with normal onset of labor and prostaglandin F2 alpha.

A comparison of clinical behavioral audiometry and autoregression analysis of EEG and heart rate in hearing-impaired children.

Autoregressive analysis, a statistical technique for detecting changes in electroencephalic (EEG) and heart rate (HR) data was compared with clinical behavioral audiometric results on 10 hearing-impaired children in schools for the hard of hearing and deaf. EEG and HR data were collected in a screening paradigm involving tones of .5, 1, and 4 kc/s at 80 db SPL in a free field. An index of reliability, or acceptable level of agreement, was set at 70%. This criterion was met 5 out of 6 times. For the EEG, agreements exceeded 70% at 1 and at 4 kc/s, and for HR at all 3 frequencies. Results suggest that the autoregressive approach yields data very similar to behavioral audiometry in this population. Continued exploration of autoregressive analysis of electrophysiologic indices in determining reactivity to tones is warranted, particularly since the statistical method can be used with younger infants.

Neonatal electroencephalographic patterns as affected by maternal drugs administered during labor and delivery.

Effects of drugs used during labor and delivery on spontaneous (resting) and evoked brain electrical activity were studied in 45 normal human newborns 48 hours after delivery. Mothers received either anesthesia (general plus local) alone (group 1), anesthesia plus meperidine (group 2), anesthesia plus meperidine and promethazine (group 3), or anesthesia plus meperidine and diazepam (group 4). Autoregressive spectral analyses and subsequent stepwise discriminant analyses showed no differences in spontaneous brain electrical activity in the infants related to the type of drugs given to the mother. However, when auditory stimuli were reduced in intensity from 80 dB to 63 dB, a significant effect was found in newborn brain electrical activity between the anesthetic-only drug pattern (group 1) and the drug patterns of anesthetics with meperidine (group 2) and anesthetics with meperidine plus diazepam (group 4). The data suggest that this effect diminishes in the presence of promethazine (group 3). Evoked responses to visual, tactile, and olfactory stimuli remained unaffected.