Cardiac vagal tone and sustained attention in school-age children.

Three hypotheses tested relationships between cardiac responses mediated via the vagus and sustained attention in a population of normal school-age children. These hypotheses addressed the theoretical relationships among resting cardiac vagal tone (using the Porges estimate of respiratory sinus arrhythmia, V), performance measures of sustained attention, and cardiac reactivity during sustained attention. Thirty-two fourth and fifth grade children performed a continuous performance task while their electrocardiograms were monitored. Children with higher resting levels of V performed better on the first 3-min block of the continuous performance task. Additionally, levels of V were significantly reduced across the blocks of the 9-min task for all children. No relationships were found between resting levels of V and change in either V or heart period during task performance. These findings support two of the three hypotheses proposed by Porges regarding individual differences in cardiac vagal tone and sustained attention.