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      Heart Rate Variability in Sleeping Preterm Neonates Exposed to Cool and Warm Thermal Conditions

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          Abstract

          Sudden infant death syndrome (SIDS) remains the main cause of postneonatal infant death. Thermal stress is a major risk factor and makes infants more vulnerable to SIDS. Although it has been suggested that thermal stress could lead to SIDS by disrupting autonomic functions, clinical and physiopathological data on this hypothesis are scarce. We evaluated the influence of ambient temperature on autonomic nervous activity during sleep in thirty-four preterm neonates (mean ± SD gestational age: 31.4±1.5 weeks, postmenstrual age: 36.2±0.9 weeks). Heart rate variability was assessed as a function of the sleep stage at three different ambient temperatures (thermoneutrality and warm and cool thermal conditions). An elevated ambient temperature was associated with a higher basal heart rate and lower short- and long-term variability in all sleep stages, together with higher sympathetic activity and lower parasympathetic activity. Our study results showed that modification of the ambient temperature led to significant changes in autonomic nervous system control in sleeping preterm neonates. The latter changes are very similar to those observed in infants at risk of SIDS. Our findings may provide greater insight into the thermally-induced disease mechanisms related to SIDS and may help improve prevention strategies.

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          Most cited references38

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          Prolongation of the QT interval and the sudden infant death syndrome.

          The sudden infant death syndrome (SIDS) is multifactorial in origin, but its causes remain unknown. We previously proposed that prolongation of the QT interval on the electrocardiogram, possibly resulting from a developmental abnormality in cardiac sympathetic innervation, may increase the risk of life-threatening ventricular arrhythmias and contribute to this devastating disorder. We prospectively tested this hypothesis. Between 1976 and 1994, we recorded electrocardiograms on the third or fourth day of life in 34,442 newborns and followed them prospectively for one year. The QT interval was analyzed with and without correction for the heart rate. One-year follow-up data were available for 33,034 of the infants. There were 34 deaths, of which 24 were due to SIDS. The infants who died of SIDS had a longer corrected QT interval (QTc) than did the survivors (mean [+/-SD], 435+/-45 vs. 400+/-20 msec, P<0.01) and the infants who died from causes other than SIDS (393+/-24 msec, P<0.05). Moreover, 12 of the 24 SIDS victims but none of the other infants had a prolonged QTc (defined as a QTc greater than 440 msec). When the absolute QT interval was determined for similar cardiac-cycle lengths, it was found that 12 of the 24 infants who died of SIDS had a QT value exceeding the 97.5th percentile for the study group as a whole. The odds ratio for SIDS in infants with a prolonged QTc was 41.3 (95 percent confidence interval, 17.3 to 98.4). Prolongation of the QT interval in the first week of life is strongly associated with SIDS. Neonatal electrocardiographic screening may permit the early identification of a substantial percentage of infants at risk for SIDS, and the institution of preventive measures may therefore be possible.
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            An efficient algorithm for spectral analysis of heart rate variability.

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              The visual scoring of sleep and arousal in infants and children.

              Age is probably the single most crucial factor determining how humans sleep. Age and level of vigilance significantly influence the electroencephalogram (EEG) and the polysomnogram (PSG). The Pediatric Task Force provide an evidence-based review of the age-related development of the polysomnographic features of sleep in neonates, infants, and children, assessing the reliability and validity of these features, and assessing alternative methods of measurement. We used this annotated supporting text to develop rules for scoring sleep and arousals in infants and children. A pediatric EEG or PSG can only be determined to be normal by assessing whether the EEG patterns are appropriate for maturational age. Sleep in infants at term can be scored as NREM and REM sleep because all the polysomnographic and EEG features of REM sleep are present and quiet sleep, if not NREM sleep, is at least "not REM sleep." The dominant posterior rhythm (DPR) of relaxed wakefulness increases in frequency with age: (1) 3.5-4.5 Hz in 75% of normal infants by 3-4 months post-term; (2) 5-6 Hz in most infants 5-6 months post-term; 3) 6 Hz in 70% of normal children by 2 months of age; and 3) 8 Hz (range 7.5-9.5 Hz) in 82% of normal children age 3 years, 9 Hz in 65% of 9-year-olds, and 10 Hz in 65% of 15-year-old controls. Sleep spindles in children occur independently at two different frequencies and two different scalp locations: 11.0-12.75 Hz over the frontal and 13.0-14.75 Hz over the centroparietal electrodes; these findings are most prominent in children younger than 13 years. Centroparietal spikes are often maximal over the vertex (Cz), less often maximal over the left central (C3) or right central (C4) EEG derivation. About 50% of sleep spindles within a particular infant's PSG are asynchronous before 6 months of age, 30% at 1 year. Based on this, we recommend that: (1) sleep spindles be scored as a polysomnographic signature of NREM stage 2 sleep (N2) at whatever age they are first seen in a PSG, typically present by 2 to 3 months post-term; (2) identify and score sleep spindles from the frontal and centroparietal EEG derivations, especially in infants and children younger than 13 years. NREM sleep in an infant or child can be scored if the dominant posterior rhythm occupies 20% of the 30-second epoch contain 0.5 to 2 Hz >75 microV (usually 100-400 microV) activity as N3. The DPR should be scored in the EEG channel that is best observed, (typically occipital), but DPR reactive to eye opening can be seen in central electrodes. Because sleep spindles occur independently over the frontal and central regions in children, they should be scored whether they occur in the frontal or central regions. Because sleep spindles are asynchronous before age 2 years, simultaneous recording of left and right frontal and central activity may be warranted in children 1-2 years of age. Simultaneous recording of left, right, and midline central electrodes may be appropriate because of the asynchronous nature of sleep spindles before age 2 years, but reliability testing is needed. Evidence has shown that the PSG cannot reliably be used to identify neurological deficits or to predict behavior or outcome in infants because of significant diversity of results, even in normal infants. Normal sleep EEG patterns and architecture are present in the first year of life, even in infants with severe neurological compromise. Increasing evidence suggests that sleep and its disorders play critical roles in the development of healthy children and healthy adults thereafter. Reliability studies comparing head-to-head different scoring criteria, recording techniques, and derivations are needed so that future scoring recommendations can be based on evidence rather than consensus opinion. We need research comparing clinical outcomes with PSG measures to better inform clinicians and families exactly what meaning a PSG has in evaluating a child's suspected sleep disorder.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2013
                1 July 2013
                : 8
                : 7
                : e68211
                Affiliations
                [1 ]PériTox-INERIS Laboratory, Jules Verne University of Picardy, Amiens, France
                [2 ]Neonatal and Pediatric Intensive Care Unit, Amiens University Medical Center, Amiens, France
                University of Adelaide, Australia
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: ES-B AL VB FT. Performed the experiments: ES-B KC AL. Analyzed the data: ES-B SD. Contributed reagents/materials/analysis tools: ES-B SD. Wrote the paper: ES-B KC VB FT.

                Article
                PONE-D-13-06750
                10.1371/journal.pone.0068211
                3698119
                23840888
                bb872e39-e769-42ce-b3cb-6413abee9e03
                Copyright @ 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 29 January 2013
                : 27 May 2013
                Page count
                Pages: 7
                Funding
                This work was funded by grants from the French Ministry of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine
                Anatomy and Physiology
                Physiological Processes
                Homeostasis
                Sleep
                Cardiovascular
                Acute Cardiovascular Problems
                Pediatric Cardiology
                Epidemiology
                Pediatric Epidemiology
                Neurology
                Autonomic Nervous System
                Sleep Disorders
                Non-Clinical Medicine
                Health Care Policy
                Health Risk Analysis
                Pediatrics
                Neonatology
                Pediatric Cardiology
                Pediatric Critical Care
                Public Health
                Child Health

                Uncategorized
                Uncategorized

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