Associations between respiratory arrhythmia and fundamental frequency of spontaneous crying in preterm and term infants at term‐equivalent age

This study investigated whether lower vagal function in preterm infants is associated with increased fundamental frequency (F (0); frequency of vocal fold vibration) of their spontaneous cries. We assessed respiratory sinus arrhythmia (RSA) during quiet sleep as a measure of vagal function, and its relationship with the F (0) of spontaneous cries in healthy preterm and term infants at term‐equivalent age. The results showed that preterm infants have significantly lower RSA, and higher overall F (0) than term infants. Moreover, lower RSA was associated with higher overall F (0) in preterm infants, whereas higher RSA was positively associated with mean and maximum F (0), and a larger F (0) range in term infants. These results suggest that individual differences in vagal function may be associated with the F (0) of spontaneous cries via modulation of vocal fold tension in infants at an early developmental stage. © 2016 The Authors. Developmental Psychobiology Published by Wiley Periodicals, Inc. Dev Psychobiol 58:724–733, 2016.