Physiological markers in early infancy: Stability of 1-to 6-month vagal tone

Twenty-six full-term infants were evaluated at 1-, 3-, and 6-months postpartum to explore the stability of Porges' (1985a) cardiac vagal tone index. One-month vagal tone (V) was not found to be associated with either 3- or 6-month measures of cardiac vagal tone, however, 3-month cardiac vagal tone was found to be predictive of 6-month cardiac vagal tone. Interestingly, 1-month heart period range was predictive of 6-month heart period range. These findings both replicate and extend previous research examining early patterns of development in cardiac indices.