Developmental changes in respiratory sinus arrhythmia

Respiratory sinus arrhythmia (RSA) can be quantified with spectral analysis of the frequencies of variation and used as an index of vagal tone. This study was designed to determine if the quantification of RSA could detect developmental changes in the vagal tone. Three groups were studied, consisting of healthy preterm infants (group 1), term infants (group 2) and older children (group 3). No significant differences in RSA were detected between group 1 (16.5 ± 4.6%) and group 2 (15.4 ± 4.5%; p = 0.66); however, group 3 had significantly more RSA (29.1 ± 4.0%) than either group 1 (p < 0.001) or group 2 (p < 0.001). Potential confounding influences were significant differences in the mean heart and respiratory rates among the groups. Appropriate interpretation of changes in the vagal tone as determined by spectral analysis of RSA requires a better understanding of the role of the heart and respiratory rate in these age groups.