To determine whether the sympathetic nervous system plays any role in the inter-individual variation of cardiovascular response to hypoxia in newborns, neonatal heart rate variability (HRV) analysis was used to assess autonomic response during hypoxia in piglets. Due to the nonstationary nature of HRV signals and the inaccuracy in pre-defined neonatal HRV frequency bands using standard spectral methods, we applied time-frequency distribution analysis to assess neonatal HRV. Although sympathetic activity was initially enhanced to stimulate the cardiac compensation, it did not account for the variation of cardiovascular response since the power of low frequency component in HRV neither showed corresponding changes with the heart rate nor had any correlation with the brain injury. This may be attributed to immaturity of the neural pathway.
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