Feeding responses to free-flow formula in term and preterm infants.

OBJECTIVES: Although introducing freely flowing formula into the infant's mouth is a common feeding practice, its effect on feeding behavior is largely unknown. We evaluated the effects of free flow of formula from the nipple on infant feeding activity (sucking, swallowing, ingestion rate) and documented potential adverse behaviors such as cough, restless behavior, drooling, apnea, and bradycardia. METHODS: We studied 13 preterm and 7 term infants. During a feeding, bottle pressure was adjusted every 2 to 3 minutes to increase or decrease free flow from the nipple. RESULTS: Increase in free flow of formula from the nipple caused rapid increases in suck and swallow frequency in term and preterm infants and increased ingestion rate. The response was reversed by decreasing flow and was repeatable throughout the feeding. Peak suck and swallow rates were highest in term infants. Although drooling increased with increased milk flow, no effect of flow on coughing, restless behavior, or apnea was observed. CONCLUSIONS: Free-flow formula is a potent stimulus for feeding activity in both preterm and term infants and is not associated with increased apnea or other adverse behaviors. The ability of the infant to divert excess formula flow by drooling is an efficient airway protective behavior. Reduced maximum suck and swallow frequency may be a primary basis for slow feeding in preterm infants.

Ventilatory sparing strategies and swallowing pattern during bottle feeding in human infants.

During feeding, infants have been found to decrease ventilation in proportion to increasing swallowing frequency, presumably as a consequence of neural inhibition of breathing and airway closure during swallowing. To what extent infants decrease ventilatory compromise during feeding by modifying feeding behavior is unknown. We increased swallowing frequency in infants by facilitating formula flow to study potential ventilatory sparing mechanisms. We studied seven full-term healthy infants 5-12 days of age. Nasal air flow and tidal volume were recorded with a nasal flowmeter. Soft fluid-filled catheters in the oropharynx and bottle recorded swallowing and sucking activity, and volume changes in the bottle were continuously measured. Bottle pressure was increased to facilitate formula flow. Low- and high-pressure trials were then compared. With the change from low to high pressure, consumption rate increased, as did sucking and swallowing frequencies. This change reversed on return to low pressure. Under high-pressure conditions, we saw a decrease in minute ventilation as expected. With onset of high pressure, sucking and swallowing volumes increased, whereas duration of airway closure during swallows remained constant. Therefore, increased formula consumption was associated with reduced ventilation, a predictable consequence of increased swallowing frequency. However, when consumption rate was high, the infant also increased swallowing volume, a tactic that is potentially ventilatory sparing as a lower swallowing frequency is required to achieve the increased consumption rate. As well, when consumption rate is low, the sucking-to-swallowing ratio increases, again potentially conserving ventilation by decreasing swallowing frequency much more than if the sucking-to-swallowing ratio was constant.