Vacuum characteristics of the sucking cycle and relationships with milk removal from the breast in term infants

• The strength of peak intra-oral vacuum is associated with greater volumes of milk removed from the breast by the breastfeeding infant.
• Infant sucking parameters changed from the first 2 min of nutritive sucking to the subsequent 2 min of nutritive sucking, which likely relates to changes in milk flow from the first to the second milk ejection and/or satiety.
• The sucking curve of a breastfed infant is typically asymmetrical with a more rapid application of vacuum as the infant lowers its tongue and a slower release of vacuum as the tongue is raised.

BackgroundThe importance of an infant's intra-oral vacuum in milk removal from the breast has been established. However, the relationship between the vacuum curve and milk transfer is not well understood.AimsTo investigate the parameters of the infant suck cycle in relation to the volume of milk removed from the breast.Study designCross-sectional study to elucidate the role of infant intra-oral vacuum in efficient milk removal from the breast.SubjectsNineteen fully breastfed term infants.MethodsIntra-oral vacuum was recorded during monitored breastfeeds using a pressure transducer. Ultrasound imaging (milk flow) and respiratory inductive plethysmography (swallowing) were used to determine the nutritive sucking (NS) portion of the feed. Milk intake was determined by weighing infants before and after feeds. Vacuum traces of the first and next 2 min of NS from the first breast were analysed.ResultsThe volumes of milk removed during both NS periods were negatively associated with peak vacuum (p < 0.001) and rate of vacuum application (p < 0.001), and positively related to area under first half of the suck cycle (p < 0.001). Most parameters changed significantly from the first 2 min of NS to the next 2 min including significant reduction in peak vacuum and area under first half of the suck cycle.ConclusionThese results further support the role of intra-oral vacuum, specifically optimal peak vacuum, in effective and efficient milk removal during breastfeeding. It also appears that infants modify their sucking dynamics to adapt to changes in milk flow during milk ejection as the breast empties.