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Biomechanics of milk extraction during breast-feeding.

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.

SUBMITTER: Elad D

PROVIDER: S-EPMC3986202 | biostudies-other | 2014 Apr

REPOSITORIES: biostudies-other

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Biomechanics of milk extraction during breast-feeding.

Elad David D Kozlovsky Pavel P Blum Omry O Laine Andrew F AF Po Ming Jack MJ Botzer Eyal E Dollberg Shaul S Zelicovich Mabel M Ben Sira Liat L

Proceedings of the National Academy of Sciences of the United States of America 20140324 14

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 t ...[more]

PMID: 24706845

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Project description:BackgroundIn spite of high rates of initiating breast milk feeding (BMF) among preterm infants, a significant rate of discontinuation occurs shortly after discharge.AimTo investigate the effect of mode (direct feeding at the breast vs. expressing) and exclusivity (breast milk combined with formula vs. breast milk only) as well as maternal perceptions on the duration of BMF among preterm infants.MethodsThe study included mothers whose infants were born before 32 weeks gestation, between January 2012 and August 2015 at Sheba Medical Center (SMC). Perinatal data were collected retrospectively from infants' computerized charts. Mothers were approached >12 months postpartum and were asked to complete a questionnaire. Those who agreed to participate were asked (during their visit to the follow-up clinic or by phone or mail) to complete a questionnaire regarding mode and duration of BMF as well as reasons for its discontinuation. Mothers were also asked about their pre-partum intentions to feed directly at the breast.ResultsOut of 162 eligible mothers, 131 (80.8%) initiated BMF during their intensive care unit (ICU) hospitalization. Of these, 66 (50.3%) discontinued BMF earlier than six months postpartum. BMF ? 6 months was significantly associated with direct feeding at the breast, duration of exclusive BMF, and singleton birth. Regression analysis revealed that direct feeding at the breast (any or only) and duration of BMF exclusivity were the only significant variables associated with BMF duration (Odds ratio (OR) 5.5 and 95% confidence interval (CI) 2.00-15.37; OR 1.5 and 95% CI 1.25-1.88, respectively). Milk supply (inadequate or nonexistent) was the most commonly reported cause for BMF discontinuation <6 months. Direct feeding at the breast was significantly associated with BMF duration and was more common among singletons.ConclusionsDirect feeding at the breast and duration of exclusive BMF are associated with duration of BMF among infants born <32 weeks of gestational age (GA). These findings suggest that targeting these two factors may play a key role in prolonging BMF duration among preterm infants.

Project description:The evolution of the modern human (Homo sapiens) cranium is characterized by a reduction in the size of the feeding system, including reductions in the size of the facial skeleton, postcanine teeth, and the muscles involved in biting and chewing. The conventional view hypothesizes that gracilization of the human feeding system is related to a shift toward eating foods that were less mechanically challenging to consume and/or foods that were processed using tools before being ingested. This hypothesis predicts that human feeding systems should not be well-configured to produce forceful bites and that the cranium should be structurally weak. An alternate hypothesis, based on the observation that humans have mechanically efficient jaw adductors, states that the modern human face is adapted to generate and withstand high biting forces. We used finite element analysis (FEA) to test two opposing mechanical hypotheses: that compared to our closest living relative, chimpanzees (Pan troglodytes), the modern human craniofacial skeleton is (1) less well configured, or (2) better configured to generate and withstand high magnitude bite forces. We considered intraspecific variation in our examination of human feeding biomechanics by examining a sample of geographically diverse crania that differed notably in shape. We found that our biomechanical models of human crania had broadly similar mechanical behavior despite their shape variation and were, on average, less structurally stiff than the crania of chimpanzees during unilateral biting when loaded with physiologically-scaled muscle loads. Our results also show that modern humans are efficient producers of bite force, consistent with previous analyses. However, highly tensile reaction forces were generated at the working (biting) side jaw joint during unilateral molar bites in which the chewing muscles were recruited with bilateral symmetry. In life, such a configuration would have increased the risk of joint dislocation and constrained the maximum recruitment levels of the masticatory muscles on the balancing (non-biting) side of the head. Our results do not necessarily conflict with the hypothesis that anterior tooth (incisors, canines, premolars) biting could have been selectively important in humans, although the reduced size of the premolars in humans has been shown to increase the risk of tooth crown fracture. We interpret our results to suggest that human craniofacial evolution was probably not driven by selection for high magnitude unilateral biting, and that increased masticatory muscle efficiency in humans is likely to be a secondary byproduct of selection for some function unrelated to forceful biting behaviors. These results are consistent with the hypothesis that a shift to softer foods and/or the innovation of pre-oral food processing techniques relaxed selective pressures maintaining craniofacial features that favor forceful biting and chewing behaviors, leading to the characteristically small and gracile faces of modern humans.

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Biomechanics of milk extraction during breast-feeding.

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Biomechanics of milk extraction during breast-feeding.

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