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

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

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

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

Effect of the period on the sympathovagal balance (LF/HF) (mean ± SEM).

<p>*<i>P</i><0.05. (pairwise multiple comparison procedures were used to test the differences between the <i>control</i>, <i>prior</i> and <i>during</i> periods. Data were adjusted for multiple testing with the Tukey-Kramer test).</p

Effect of the period on normalized values (mean ± SEM) of the power spectra in the low- (LF_nu) and high-frequency (HF_nu) bands.

<p>*<i>P</i><0.05, **<i>P</i><0.01. (pairwise multiple comparison procedures were used to test the differences between the control, prior and during periods. Data were adjusted for multiple testing with the Tukey-Kramer test).</p

Multivariate associations between factors related to <i>in utero</i> exposure to pesticides and gestational age and prematurity (continued).

<p>*p = 0.05;</p><p>**p = 0.01;</p><p>***p = 0.001.</p><p>NA: an odds ratio was not available because too few cases were observed (n<3).</p

Multivariate associations between factors related to <i>in utero</i> exposure to pesticides and gestational age and prematurity.

<p>Multivariate associations between factors related to <i>in utero</i> exposure to pesticides and gestational age and prematurity.</p

Multivariate associations between (i) variables related to <i>in utero</i> exposure to pesticides, (ii) head circumference at birth (HCB, in cm) and (iii) small head circumference at birth (continued).

<p>HCB: head circumference at birth. SHCB: small head circumference at birth. NA: an odds ratio was not available because too few cases were observed (n<3).</p