The influence of sleep state (i.e., active and
quiet) on heart period, heart period variability, respiratory
sinus arrhythmia (RSA), and the coupling between RSA and
heart period was evaluated in 24 healthy full-term newborns.
Electrocardiogram (ECG) data were collected, and sleep
state was coded 1 hr after feeding until at least 10 min
of data were collected in states of active and quiet sleep.
ECG data were analyzed for the first five continuous minutes
of each sleep state. Relative to active sleep, quiet sleep
was associated with significantly higher amplitude RSA,
lower heart period variability, and longer heart periods.
Because RSA amplitude reflects the functional output of
vagal pathways originating in the nucleus ambiguus, it
was hypothesized that sleep state would influence how these
vagal pathways regulate instantaneous changes in heart
period. A new method, evaluating the instantaneous coupling
of RSA and heart period, demonstrated that coupling was
significantly greater during active sleep. The neurophysiological
explanation extends the polyvagal theory to include potential
cortical–brain stem connections.