Milk ejection patterns: an intra- individual comparison of breastfeeding and pumping.

BACKGROUND: Milk ejection is a transient episode critical to milk removal and women typically have multiple milk ejections during breastfeeding and pumping. Recently it was found that milk ejection characteristics such as number of milk ejections and periodicity were consistent throughout 12 months of lactation in women who expressed their milk with an electric breast pump. It is not known whether the stimulation of an infant at the breast influences milk ejection patterns or whether this is a programmed event. The aim of this study was to compare milk ejection patterns during breastfeeding and expressing milk with an electric pump within mothers. METHODS: Twelve lactating mothers with normal milk production (502-1356 mL) had milk ejection recorded by measuring the diameter of a major milk duct with ultrasound imaging throughout an entire breastfeed and a 15-min pumping session. Scans were analysed for timing, duration of duct dilation and maximum duct diameter. RESULTS: The initial milk ejection defined as the first increase in duct diameter was observed earlier during breastfeeding than during two phase pumping sessions but was not statistically significant (p = .057). There were no significant differences between the duration of the first or second milk ejection for mothers when breastfeeding or pumping at their maximum comfortable vacuum (p = .18; p = .99). The times taken to reach the peak duct diameter, or the first half of the milk ejection were also not found to be significantly different between breastfeeding and pumping. CONCLUSION: This study suggests that milk ejection patterns remain consistent within individual mothers regardless of whether the mother is breastfeeding or expressing milk indicating a likelihood of the process either being programmed or innate to the individual.

Asynchronous milk ejection in human lactating breast: case series.

BACKGROUND: Milk production is under the influence of autocrine control such that the rate of milk synthesis decreases as the breast fills with milk. Effective elimination of milk from the alveoli via the milk ejection reflex will therefore result in increased milk synthesis. It has been assumed that milk ejection occurs in all alveoli simultaneously; however, animal studies have indicated that full alveoli eject milk sooner than less full alveoli, suggesting heterogeneous emptying of the mammary gland. OBJECTIVE: The aim of this study was to determine whether milk ejection occurs asynchronously in the human lactating breast. METHODS: Retrospective analysis of videos made of ultrasound monitoring of milk ducts during pumping. Six video clips (4 women) of ultrasound monitored milk ejections showed obvious differences in the timing of milk flow between different main milk ducts. Duct diameter was simultaneously measured every second in 2 different ducts that drained 2 separate lobes of the breast. RESULTS: For 5 of 6 ultrasound duct monitoring sessions, both duct dilation and visualization of milk flow in the 2 separate main milk ducts differed by 2 to 8 seconds. For the remaining woman, milk was observed to eject from 1 part of the lobe, and when not removed, it flowed in a retrograde fashion into a different part of the lobe. CONCLUSION: Asynchrony of milk ejection occurs in the human lactating breast, suggesting that the timing of myoepithelial cell response differs, resulting in heterogeneous emptying of the gland.

Blood flow characteristics of the human lactating breast.

BACKGROUND: Despite the increased metabolic activity of the lactating breast, no studies have been carried out to determine mammary blood flow (MBF) parameters or the relationship between MBF and milk production in women. The aim of this study was to measure the MBF in the internal mammary artery (IMA) and lateral thoracic artery (LTA) of lactating women and determine if these were related to milk production. METHODS: Blood flow in the IMA and LTA was measured with color Doppler ultrasound in 55 lactating women. Twenty-four-hour milk production was determined with the test-weigh method. RESULTS: IMA contributed the greater proportion of blood flow to the lactating breast (70%). MBF was highly variable between women but consistent between the left (126 L/24 h; interquartile range, 76-169) and right (110 L/24 h) breasts. No relationship between MBF and milk production was demonstrated. For 3 women, MBF was markedly reduced in 1 breast that was synthesizing almost no milk compared to the other that was producing a normal volume of milk. DISCUSSION: Although no relationship between MBF and milk production was found, the substantial reduction in blood flow in the breasts of lactating women producing almost no milk suggests a threshold below which milk production is compromised. CONCLUSION: Doppler ultrasound did not demonstrate a relationship between MBF and milk production in lactating women. Further investigation is required to fully understand the role of blood flow in milk synthesis.

Tongue movement and intra-oral vacuum of term infants during breastfeeding and feeding from an experimental teat that released milk under vacuum only.

BACKGROUND: Recent literature supports the theory that vacuum is integral to the removal of milk from the breast rather than peristaltic compression of the breast. AIM: We aimed to determine if breastfed infants could remove breast milk from an experimental teat designed to release milk only when a vacuum is applied. METHODS: Submental ultrasound images and intra-oral vacuum measurements were recorded simultaneously during both a breastfeed and a feed with the experimental teat. RESULTS: Infants placed the nipple and teat a similar distance from the nipple hard-soft palate junction when the tongue was lowered (4.7 mm vs 5.3 mm). As the tongue lowered the nipple and teat expanded evenly although the nipple expanded more than the teat (3.1mm vs 1.5 mm). Both baseline (-31 mm Hg vs -12 mm Hg) and peak vacuum (-122 mm Hg vs -67 mm Hg) applied to the breast were significantly higher than for the teat. CONCLUSION: Breastfed infants are able to remove milk from a teat using only vacuum with a similar tongue movement to that of breastfeeding. This evidence supports the theory that vacuum is a critical factor in the removal of milk from the breast.

Effects of uteroplacental insufficiency and reducing litter size on maternal mammary function and postnatal offspring growth.

Human intrauterine growth restriction is often associated with uteroplacental insufficiency and a decline in nutrient and oxygen supply to the fetus. This study investigated the effects of uteroplacental insufficiency and intrauterine growth restriction (Restricted) or reducing litter size for normally grown pups (Reduced Litter) on maternal mammary development and function, milk composition, offspring milk intake, and their resultant effects on postnatal growth. Uteroplacental insufficiency was surgically induced by bilateral uterine vessel ligation on day 18 of gestation in the Wistar Kyoto rat. At birth, a group of sham control rats had their litter size reduced to five (Reduced Litter) to match that of the Restricted group. Cohorts of rats were terminally anesthetized on day 20 of gestation or day 6 of lactation, and a third group was studied throughout lactation. Restricted pups had a lower birth weight (by 16%) and litter size (by 36%) compared with controls, as well as reduced mammary parathyroid hormone-related protein content and milk ionic calcium concentrations associated with reduced total pup calcium. Restricted dams with lower circulating progesterone experienced premature lactogenesis, producing less milk per pup with altered composition compared with controls, further slowing growth during lactation. Reducing litter size of pups born of normal birth weight (Reduced Litter) was associated with decreased pup growth, highlighting the importance of appropriate controls. The present study demonstrates that uteroplacental insufficiency impairs mammary function, compromises milk quality and quantity, and reduces calcium transport into milk, further restraining postnatal growth.

Milk flow rates can be used to identify and investigate milk ejection in women expressing breast milk using an electric breast pump.

Currently there is no simple method available to assess milk ejection and breast milk flow in lactating women in both the clinical and research setting. The authors hypothesize that changes in milk flow rate are associated with milk ejection and therefore may provide a method suitable for the assessment of milk ejection and removal. Mothers (n = 23) expressed milk from one breast for a 15-minute period using both weak and strong vacuums on two to four separate occasions using an experimental electric breast pump (Medela AG, Baar, Switzerland). Breast milk flow rates were recorded at 5-second intervals by connecting a tube from the breast shield to a bottle placed on a balance that was connected to a computer. Milk ejection was determined by an acute increase in milk duct diameter in the contralateral breast using ultrasound (Acuson XP10, Siemens, Mountain View, CA), and the change in duct diameter was compared with milk flow rates. Milk flow rates ranged from 0 to 4.6 g per 5-second period. Increases in flow rates were positively associated with increases in duct diameter (p < 0.05). Furthermore, within each milk ejection, higher maximum duct diameters were positively related to greater volumes expressed per 5-second periods (p < 0.001). Time to the first milk ejection and number of milk ejections were the same when determined by ultrasound or flow rates. This direct relationship between increases in duct diameter and acute increases in milk flow rates suggests that changes in flow rates can be used to identify milk ejection in the absence of ultrasound data.

The use of ultrasound to characterize milk ejection in women using an electric breast pump.

This study aimed to use ultrasound imaging to investigate the milk ejection characteristics of women during a 10-minute expression using an electric breast pump capable of applying 2 markedly different vacuum patterns. The classic pattern (47 cycles/min) and 3-phase pattern (pre-milk ejection: 120 cycles/min, post-milk ejection: 20 cycles/min for 2 minutes post-milk ejection then 55-78 cycles/min for 8 minutes) were tested, and the milk expressed was collected in 30-second intervals. Multiple milk ejections (96%) were detected (classic: 3.27+/-2.05; 3-phase: 3.72+/-1.19) and associated with increases in milk flow. Almost half of the total volume of milk expressed was removed during the first milk ejection (classic: 41.38+/-21.48%; 3-phase: 46.72+/-26.60%). There was no correlation between the number of milk ejections and both the total volume of milk and percentage of available milk for either pattern. In conclusion, milk ejection characteristics and efficiency of milk expression did not change in response to different expression patterns.

Ultrasound imaging of milk ejection in the breast of lactating women.

OBJECTIVE: Currently, the methods for assessing milk ejection in women include serial sampling of plasma oxytocin and measurement of intraductal pressure, both of which are invasive and may induce stress. We hypothesized that milk ejection would cause an increase in milk-duct diameter that could be observed noninvasively with ultrasound, and this could be used to investigate the physiology of milk ejection in women. METHODS: One milk duct was scanned in the unsuckled breast in 2 groups of mothers: group BB (n = 21) for the beginning of a breastfeed and group EB (n = 24) for the entire breastfeed. A duct also was monitored for a 5-minute period on 2 separate days in the absence of factors that may induce milk ejection in group EB to provide a baseline duct diameter. Milk intake at a breastfeed was measured by test weighing. RESULTS: A significant increase in milk-duct diameter was observed when milk ejection was sensed and/or the infant changed its swallowing pattern in both groups. Multiple increases and decreases (mean: 2.5 per breastfeed; standard deviation: 1.5; n = 62) in duct diameter occurred in group EB. Duct diameter remained relatively stable between breastfeeds (coefficient of variation: 1.4%-8.3%). Infant milk intake was positively related to the number of milk ejections (r2 =.365; n = 57). CONCLUSIONS: Ultrasound is an objective, noninvasive technique for detecting milk ejection by observing an increase in milk-duct diameter. However, this technique requires an experienced ultrasonographer, adequate imaging time, and surroundings conducive to breastfeeding. Multiple milk ejections were common during breastfeeding, although they were not sensed by mothers. The number of milk ejections influenced the amount of milk the infant consumed.