Influence of the thermal environment on HRV parameters calculated from the Poincaré plot.

<p>Mean values (± s.d.) of (A) SD1 and SD2 and (B) the cardiac vagal index and cardiac sympathetic index in the cool condition (T_N-2°C), at thermoneutrality (T_N) and in the warm condition (T_N+2°C) during active sleep (empty bars) and quiet sleep (black bars). * <i>P</i><0.05; ** <i>P</i><0.01; *** <i>P</i><0.001.</p

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

<div><p>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.</p></div

Heart rate and time-domain HRV parameters in the cool condition (T_N-2°C), at thermoneutrality (T_N) and in the warm condition (T_N+2°C) during active sleep (AS) and quiet sleep (QS).

<p>Values are quoted as the mean ± standard deviation. NS: non-significant in an analysis of variance with repeated measures.</p

Sleep and ventilatory data in the cool condition (T_N-2°C), at thermoneutrality (T_N) and in the warm condition (T_N+2°C).

<p>Values are quoted as the mean ± standard deviation. NS: not significant.</p

Frequency-domain HRV parameters in the cool condition (T_N-2), at thermoneutrality (T_N) and in the warm condition (T_N+2) during active sleep (AS) and quiet sleep (QS).

<p>Values are quoted as the mean ± standard deviation. NS: non-significant in an analysis of variance with repeated measures.</p

Intrinsic Mode Functions resulting from empirical decomposition of photoplethysmography signals.

<p>This figure shows the decomposition of signals recorded in the left foot (A) and right hand (B) in elementary functions (IMF) characterized by selective time-scale. This allowed the identification of components relating to cardiac activity (c5 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098763#pone-0098763-g003" target="_blank">figure 3A</a> and c6 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098763#pone-0098763-g003" target="_blank">figure 3B</a>). In these graphs, IMFs are organized in ascending order from top to bottom.</p

Histogram of distribution of PPD values (deg/cm).

<p>(A) Infant with closed ductus: the histogram of PPD is narrow and concentrated to segment less than 1 degree/cm; (B) Infant with patent ductus arteriosus: the histogram of PPD is broad, with values above 1 degree/cm.</p

Photoplethysmography signals acquisition technique using infrared sensors.

<p>Acquired signals were used to compute pulse phases corresponding to preductal (right hand sensor) and postductal (foot sensor) regions and their difference, the PPD.</p

Clinical characteristics of the study population.

<p>GA, gestational age; PNA, Postnatal age; BW, Birth weight; CRIB II, clinical risk index for babies score; Hb, Hemoglobin; FiO₂, Fractional inspired concentration of oxygen; IQR, interquartile interval</p

Raw photoplethysmography signals.

<p>These photoplethysmography traces show a delay between the recordings from the right hand and left foot in an infant with PDA.</p