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

Background: The 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.

Aims: To investigate the parameters of the infant suck cycle in relation to the volume of milk removed from the breast.

Study Design: Cross-sectional study to elucidate the role of infant intra-oral vacuum in efficient milk removal from the breast.

Subjects: Nineteen fully breastfed term infants.

Methods: Intra-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 2min of NS from the first breast were analysed.

Results: The 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 2min of NS to the next 2min including significant reduction in peak vacuum and area under first half of the suck cycle.

Conclusion: These 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.