Podcast link + transcription part 3. Dr Nikki Mills and Dr Pamela Douglas discuss the functional anatomy of sucking and swallowing in breastfed babies
Part 3
Dr Nikki Mills is a New Zealand based paediatric ENT surgeon, who has a special clinical and research interest in breastfeeding and is also an International Board Certified Lactation Consultant. Nikki worked for many years at the Starship Children’s Hospital in Auckland, moving in 2020 to Nelson Hospital in Nelson, New Zealand.
In this third and final episode of an in-depth conversation, Pam and Nikki continue their deep dive into our biomechanical understandings of infant suck during breastfeeding. This episode considers ultrasound studies of infant suck, and the implications for the clinical support of breastfeeding mother-baby pairs.
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Pam
So Nikki, are you right now if we move into a more detailed conversation about this whole fascinating thing. I'm fascinated by the biomechanics of the suck. I started a little riff there on the use of ultrasound to begin to elucidate suck biomechanics in breastfed babies. And we talked a little bit about Elad's study. That's the 2014 study, I think. And then what I think is world-leading research in this particular area coming out of the Geddes Hartmann Human Lactation Research Group. Although of course your work sits alongside world-leading work in terms of suck and swallow in breastfeeding.
One thing I'd like to talk to you about is the different way of analyzing, of measuring and then analyzing that was used by Elad, versus the measures used in the human lactation research group. Because they're actually quite different, aren't they?
Nikki
Yes.
Pam
That one study by Elad used quite a different approach to the measures that are used and have been validated actually in the whole body of work around sucking breastfeeding from the human lactation research groups. So do you mind just addressing that?
Nikki
I mean, obviously this is me just I guess reading and trying to understand the work they're doing, rather than anything that I've done myself specifically in this area. But obviously like you I've visited Donna and have in fact visited the group in Columbia as well, at Columbia University. So the interesting thing and again, most of the research in this area was done with bottle feeding because that was easier to view with videofluoroscopy. Looking at tongue movement and certainly the concept of how babies breastfeed was believed to be a peristaltic movement. Which is like a wave-like ripple that moves anteriorly to posteriorly on the dorsal surface of the tongue...
Pam
We could call that the stripping model couldn't we?
Nikki
Yeah so...
Pam
Which then... can I break in because that then naturally leads to a kind of structural model of suck dysfunction. If you're having this concept of the peristaltic movement that strips compresses the breast and strips out milk. Then that leads to, okay, there's a structural problem that's interfering with suck. Something's wrong with the way that tongues moving. Wrong with for instance, the frenulum.
Nikki
Yeah, I'm not sure. I think I'm not sure if that relates specifically to it being structural. Because I would have thought from that, that it could be just a coordination or a functional or coordination issue. But anyway, certainly. And certainly some of the earliest ultrasound work was thought to support that as a concept. That, and I'm sure you...
Pam
I might just break in there again to say that the reason why I make that sort of link between a stripping model and then structural assumptions around tongue movement is just that in the early work around ankyloglossia. That was using posterior tongue tie as a diagnosis. The whole biomechanics of suck that were being used to support for frenotomy for posterior tongue tie developed out of a stripping model, at least at the outset. And then that model began to sort of change and blur. But that was why I mentioned it, Nikki.
Nikki
So David Elad's work used ultrasound and they used computer generated analysis, using a form of surface tracking. So what they did is they looked at the outline of the hard palate. And they looked at the outline of the dorsal surface of the tongue and they were able to mark fixed points. So they numbered them along each of those surfaces and the midline. And then they did a quite complex computerized analysis of how those contours moved relative to each other during the sucking process. And what they identified was that in fact, the anterior tongue did not have any periostitis. That it moved on block. So that moved all together and it moved synchronously with the mandible. So as the mandible lowered, the dorsal surface of the tongue also moved away from the hard palate.
Pam
This had already been shown in the human lactation research groups, ultrasound studies too. So it confirmed that?
Nikki
Yeah. So I think this was the first time that it had been looked at from a very bioengineering perspective where they were able to analyze it with numbers and give statistics and a quite quantitative assessment of that.
Pam
Can I jump in too. Because when you say anterior tongue, can we just clarify the terms that you're using now? So I notice in your papers and in our discussion today, we're talking about the tongue base that would previously have been referred to as the posterior tongue?
Nikki
Yes. So I think ...
Pam
And probably just to clarify, can I jump in a little bit more there. Because there was also a time in the human lactation research groups work with ultrasound, that what we now call the mid tongue was being labeled as the posterior tongue. So it's just to get out terms straight, isn't it. So when you're talking tongue base, you're talking about what has more recently at the human lactation research group been identified as the posterior tongue. And can I clarify with you because you can't really see that posterior tongue, clinically?
Nikki
So just to clarify. I think tongue base and posterior tongue are used synonymously. So they're not referring to different things. I think the tongue base extends right down to the base of the epiglottis, so the vallecula. So it includes the pharyngeal surface of the tongue. So it extends quite significantly down into the hypo pharynx.
Pam
So if I do a neuro motor assessment, how much of the posterior tongue or the tongue base can I actually see, can actually visualize?
Nikki
I would say none.
Pam
Okay, that's really important to clarify things for our listeners.
Nikki
So I think if everyone remembers back to their anatomy days. So the foramen caecum is in the circumvallate papillae. You know, the little V at the back of the tongue. Everything beyond this are the lingual tonsils and down into the surface of the tongue that faces the back of the pharynx is the tongue base. And I guess you might, if the lingual tonsils are quite bulky and if they gag, you might be able to see the back of the posterior tongue. But generally we're looking at the anterior tongue, which is the free tongue from where it attaches to the floor of mouth to the tip of the tongue. And the mid tongue, which is everything between that and the tongue base. And they're not, the anterior tongue is not clearly demarcated or anything like that. I think it's a little bit artificial to separate them really.
Pam
Yes, but I think the important finding that you also saw in your real time MRI. But which both this single David Elad study and also Donna's team have shown. Is that the anterior and mid tongue move on block really with the mandible tracking the excursion of the mandible. Would you agree?
Nikki
Yes. So to create and I think it's really kind of putting together what David's group and Donna's group have done to get their understanding. So I think what the work that they've done is quite complimentary. If you put together the components that they've looked at, so Donna's...
Pam
Well, can I jump in again? Sorry, Nikki. But I just muse on whether that's true. Because I heard one member of the team interpreting the Elad study in a way that did seem quite different to my mind, to what I would say has emerged out of Donna and her team's work. So this person was saying that there's a kind of wave like movement between the anterior tongue and the posterior tongue. And she was using almost a seesaw analogy and was talking about the tongue coming up and compressing if you like. And at the same time as the posterior tongue moved downwards. And I just was interested to hear your thoughts about that.
Nikki
I don't believe that that's a correct interpretation. It's hard without, I mean obviously I haven't heard what they've said specifically. But I think my understanding of those two bodies of work is that I think they are quite complimentary. So I think that...
Pam
And that your MRI work fits quite nicely with it all as well.
Nikki
Yeah I think that, I mean it doesn't... I don't believe ...
Pam
Which is hopeful, isn't it? It gives us that sense of really starting to develop a nice picture of what's going on.
Nikki
And I think too remembering that the ultrasound is really just looking in the midline and not understanding the three-dimensional nature of the... so the tongue is a muscular hydrostat, so it's essentially a, like a bean bag if you like, that has no skeletal structure. And the intrinsic muscles of the tongue attached to the connective tissue on the outer surface of the tongue. So when they contract, they alter the contour of the tongue by pulling or relaxing to allow the surface of the tongue to change and contour.
Pam
But the volume doesn't change?
Nikki
The volume doesn't change. So the tongue, essentially to be like a bean bag that can change and contour and shape very responsively to what's required of it. And if you imagine that the oral cavity is a room or a space, and every individual, the dimensions of that space at different, right. So everyone has a little bit different, the shape of and contour of the hard palate and the angle down to the alveola ridge. And the tongue in an infant actually fills a lot of the oral cavity. So at rest, if you look at [inaudible 02:02:56] pictures, the tongue fills and that's considered a age developmental difference between infants and adults. Is that the tongue is relatively large in the oral cavity, in an infant.
Nikki
And the reason for that is breastfeeding because the tongue has to be able to fill all of the space around the nipple and bring the nipple to the roof of the mouth and close all of that space to create the vacuum. Which is what Donna's team has shown is that the latch is baseline vacuum. And to create that vacuum, you have to have no air in the oral cavity. And so the tongue has to be this magic bean bag that can fill all of that space and cup around the sides of the tongue and create that, fill all of that space.
Pam
And so then the contouring of the tongue, and this is something that I'm really interested to continue to talk with you about. Because I know we've had these discussions in the past. But the contour of the tongue then actually conforms to, almost suppley wraps around the intra-oral breast tissue that's available. And given that the amount of intraoral breast tissue is dynamic, dependent on how that little baby's bodies is fitted into the mother's body.
Nikki
Absolutely.
Pam
Then in fact, we've got tongue contour, that's changing dynamically in response to intraoral breast tissue volume, and often in the interpretation of this research around the biomechanics of infant suck, we're measuring changes in the contour of the tongue. And talking about that as tongue movement, that's driving the breastfeeding. Whereas in the Gestalt interpretation of the biomechanics, I've been arguing that actually the tongue as much as anything is conforming to available intraoral breast tissue. Which is dependent on vectors of force that might be contradicting the vacuum that's been created.
Pam
And while I'm on this little riff, Nikki, this paper's under review. But since you and I last spoke Donna and Sharon and I have written up that small case series that I'd mentioned to you previously. And it's clear that a brief Gestalt intervention was, I say clear in the context of a small case series, which is very preliminary. But a brief Gestalt intervention really did alter those parameters of tongue movement. I would argue alter the contour of the tongue because of its impact on vectors of force operating within the baby's mouth. And this change in tongue contour that's often previously referred to as change in tongue movement, is consistent with parameters that have been measured post-frenotomy.
Nikki
That makes sense to me completely. There's nothing at all that surprises me in that and I guess from a biomechanical perspective. Just in my mind, trying to understand and kind of think about general principles that you then apply to an individual. Is there are things that can't be changed in the short term, for example, the contour and height of the arch of the hard palate or the size and position of the mandible. So those things are fixed as such. They do change with huge growth of the mandible in the first three to six months.
Nikki
And obviously the amount that the tongue has to elevate to create that vacuum around the nipple, is hugely dependent on the volume of breast tissue inside the mouth. So if the infant is let's just say, the mother has large nipples. The tongue and the infant's palate is not high arch. Then the tongue essentially doesn't have to elevate at all in the midline because the tongue... The nipple fills that space and the sides of the tongue, just cup around to close that space. But if we have an infant with a mother who has a small nipple and the infant has a high arch hard palate, the potential space that the tongue has to fill is greater.
Nikki
But if in that same infant you get a deeper latch...
Pam
That's it, that's it.
Nikki
So that's a variable that has the biggest impact on how high the tongue has to elevate. There's a lot of rationalization around frenotomy that the lingual frenulum is stopping elevation of the tongue and stopping creating the vacuum. But actually the first thing that you want to try, obviously you can't change the actual anatomy and elasticity of the mother's breast tissue. But you can alter how high that infant's tongue has to elevate by altering the fit and hold.
Pam
That's exactly it.
Nikki
And that's the biggest... and I do wonder...
Pam
The biggest variable did you say? Sorry, it just cut out there and I want it to capture that. Yes, I completely concur.
Nikki
Yes and I think perhaps just, you know musing. That perhaps some of these mothers that are having significant pain with breastfeeding, that they have a poor fit and hold, they don't have a lot of breast tissue in the baby's mouth. The baby is creating trauma because of those biomechanical issues and is having trouble getting a vacuum. And they're getting a frenotomy to allow the tongue to elevate more when in fact what they should be doing is trying to get a deeper latch and a better fit and hold that would affect fix those problems rather than having to cut their babies.
Pam
And I wonder if that's a place for us to close Nikki? Because in fact, I completely agree with you.
Pam
I want to thank you for giving so generously of your time for this conversation today, between New Zealand, Nelson, New Zealand and Brisbane Queensland, because I've found it absolutely fascinating. So I want to thank you for that.
But even more so, Nikki, I want to thank you on behalf of women who are wanting to breastfeed their babies. For the years of work that you've put in to this series of papers around the functional anatomy of suck and swallow in breastfeeding babies. It's such an important contribution to our understanding of how to help women have that experience, That so many are really craving. Pain-free enjoyable. Workable, but enjoyable breastfeeding of their baby. So for that, I thank you.
Nikki
Thanks Pamela.