Rhythmic organization of heart rate in breast‐fed and bottle‐fed newborn infants

Abstract

AbstractHeart rates and behavioural states of 14 breast‐fed and 14 bottlefed newborn infants were assessed every 30 seconds for 2 continuous hours. The 240 observations of heart rate were treated as time‐series data and spectrum‐analysed for behavioural rhythmicities. Of the 28 infants, 25 showed reliable cycles in heart rate; 22 of the 25 infants showed a dominant frequency with a 30–60 min periodicity, one that approximates the basic‐rest activity cycle (BRAC). In addition to this basic cycle, additional higher frequency cycles in long‐term heart rate variability were evident in the spectra of many infants. Breast‐fed newborns had greater numbers of reliable cycles in heart rate than bottle‐fed newborns. Further, breast‐fed newborns had lower overall mean heart rates and lower mean heart rates in Quiet and Active Sleep states than bottle‐fed newborns. Bottle‐fed newborns were observed more often in Quiet Sleep than breast‐fed newborns. Without knowledge of the specific mechanisms causing these behavioural differences, the results of this study suggest that the context in which breast‐feeding occurs results in a more complex and energy‐efficient pattern of behavioural organization than the context of bottle‐feeding.