Partner Spotlight – Under Pressure: The Importance of Physics for Infant Feeding

June 4, 2024
Lisa Kleinz, MA, SLP/L, CNT, Director of Education, Dr. Brown's Medical

Infant feeding involves a series of “Pressures.” As neonatal therapists, understanding different pressures and how they can affect infant feeding is important for positive feeding outcomes. Let’s take a look at some of the most common pressures in the current infant feeding literature.

1. Intra-oral pressure:
Whether breast or bottle feeding, there are two pressures at work intraorally. Suction correlates to the negative intraoral pressure that draws milk into the mouth; Expression is the positive pressure that ejects milk into the oral cavity by compression or stripping of the nipple between the tongue and the hard palate.¹Lau has described these types of sucking in stages, with Stage 1 being the most immature and characterized by the absence of suction. It has been suggested that with bottle feeding, mature suction is not required and that infants can feed from a bottle with more expression patterns, but inefficiently. More recent studies on breastfeeding have shown that the application of a vacuum (suction) is critical to milk removal from the breast.²

As neonatal therapists, we know that premature infants can have reduced suction, in addition to those infants with special considerations (e.g., reduced tone, cleft lip/palate). On the other hand, a very strong suction/vacuum during breastfeeding can result in mothers experiencing pain.²

Takeaway: Both positive and negative pressures are involved intraorally in oral feeding and are important for efficient feeding.

2. Hydrostatic pressure
By definition, hydrostatic pressure is the “pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity” (Dictionary.com). In other words, it is the force of gravity on liquid. Recent research has found that hydrostatic pressure is lower, along with milk ow rate, when bottles are positioned in a more horizontal placement or when

less milk is placed in the bottle.³ McGrattan found that the flow rate was over 50% faster when a bottle was filled with 4 oz of milk compared to 1oz. This may have clinical implications for the future. If providing the slowest flow rate is not sufficient for a safe swallow, currently therapists may rely on thickening, which can have negative consequences. The method of

reducing the amount of liquid in the bottle (along with a reduced nipple flow rate) may be considered effective for safe feedings.

Takeaway: Bottle positioning and the amount of liquid affect hydrostatic pressure. Consider positioning and/or reducing the amount of liquid for improved safety. More research is necessary to evaluate these strategies. In addition, for fragile infants, bottle positioning may be an additional factor to consider with a vented bottle system.

3. Atmospheric pressure
Simply stated, air pressure. During bottle feeding, internal air pressure is formed in the portion of the bottle where no milk, and only air, is present. ³As milk is extracted from unvented bottles, it causes a buildup of sub atmospheric, or negative, pressure. The literature suggests that this pressure requires the infant to exert greater force to overcome the pressure

differential and express a bolus. ^3,4McGrattan suggests that the use of a vented bottle* preventing negative pressure buildup may improve infant feeding performance. She further explains the use of a vented bottle can reduce sub atmospheric (negative) pressure buildup, which may offer a more consistent ow without increased energy expenditure in milk expression. Although many commercial bottles have some type of venting mechanism, currently the Dr. Brown’s® Zero-Resistance® bottle system is the only known bottle system without any negative pressure.

With breastfeeding, the mother’s letdown or milk ejection reflex (MER) increases positive pressure in the milk within the breast while also causing the milk ducts to dilate. ^5,2 This positive pressure provides less resistance to the flow of milk to the nipple surface.

Takeaway: Subatmospheric/Negative pressure during bottle feeding may impede feeding performance. A Zero-Resistance® bottle system should be considered, especially with premature infants. Consider: Since breastfeeding results in positive pressure rather than negative, is a Zero-Resistance® bottle system more similar to the breast during breastfeeding?

4. And the final “pressure” – Peer Pressure

Peer pressure, is when someone in your circle in influences your choices, positively or negatively. This pressure can be exerted on neonatal caregivers to achieve infants’ feeding goals. The previous volume-driven culture left many experiencing a need to “get the infants to feed” reaction. Thankfully, as we learn more about the science of bottle feeding, more supportive feeding tools and support strategies allow infants to feed safer and with better quality, and therefore, remove the peer-pressure environment.

*Bottle tested during this study was the Dr. Brown’s® Zero-Resistance® bottle system assembled with a Level 1 nipple.

For more information about the Dr. Brown’s® Zero Resistance® Bottle System (with NO negative pressure) contact us at medinfo@drbrownsmedical.com

Please click here for References.

Partner Spotlight – Under Pressure: The Importance of Physics for Infant Feeding

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