Biomechanics of milk extraction during breast-feeding

David Elad; Pavel Kozlovsky; Omry Blum; Andrew F. Laine; Ming Jack Po; Eyal Botzer; Shaul Dollberg; Mabel Zelicovich; Liat Ben Sira

doi:10.1073/pnas.1319798111

New Research In

Edited by Sheldon Weinbaum, The City College of New York, City University of New York, New York, NY, and approved February 25, 2014 (received for review October 24, 2013)

Significance

We have resolved a century-long scientific controversy and demonstrated with a 3D biophysical model that infants suck breast milk by subatmospheric pressures and not by mouthing the nipple–areola complex to induce a peristaltic-like extraction mechanism. Analysis of ultrasound (US) movies demonstrated that the anterior tongue, which is wedged between the nipple–areola complex and the lower lips, moves as a rigid body with the cycling motion of the mandible, while the posterior section of the tongue undulates like a peristaltic wave, which is essential for swallowing. The computational simulations of breast-feeding successfully mimicked the dynamic characteristics observed in US imaging and also predicted the subatmospheric pressure required to draw the nipple–areola complex into the infant mouth during latch-on.

Abstract

How do infants extract milk during breast-feeding? We have resolved a century-long scientific controversy, whether it is sucking of the milk by subatmospheric pressure or mouthing of the nipple–areola complex to induce a peristaltic-like extraction mechanism. Breast-feeding is a dynamic process, which requires coupling between periodic motions of the infant’s jaws, undulation of the tongue, and the breast milk ejection reflex. The physical mechanisms executed by the infant have been intriguing topics. We used an objective and dynamic analysis of ultrasound (US) movie clips acquired during breast-feeding to explore the tongue dynamic characteristics. Then, we developed a new 3D biophysical model of the breast and lactiferous tubes that enables the mimicking of dynamic characteristics observed in US imaging during breast-feeding, and thereby, exploration of the biomechanical aspects of breast-feeding. We have shown, for the first time to our knowledge, that latch-on to draw the nipple–areola complex into the infant mouth, as well as milk extraction during breast-feeding, require development of time-varying subatmospheric pressures within the infant’s oral cavity. Analysis of the US movies clearly demonstrated that tongue motility during breast-feeding was fairly periodic. The anterior tongue, which is wedged between the nipple–areola complex and the lower lips, moves as a rigid body with the cycling motion of the mandible, while the posterior section of the tongue undulates in a pattern similar to a propagating peristaltic wave, which is essential for swallowing.

Footnotes

↵¹To whom correspondence should be addressed. E-mail: elad{at}post.tau.ac.il.

Author contributions: D.E., S.D., and L.B.S. designed research; E.B., S.D., M.Z., and L.B.S. recruited subjects; D.E., P.K., O.B., M.Z., and L.B.S. performed research; D.E., A.F.L., and M.J.P. contributed new reagents/analytic tools; D.E., A.F.L., M.J.P., E.B., S.D., and L.B.S. analyzed data; and D.E., A.F.L., and S.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1319798111/-/DCSupplemental.