R-E-S-P-E-C-T for LVC: Laryngeal Vestibule Closure in the Spotlight

Title: “Hidden in Plain Sight”: A Descriptive Review of Laryngeal Vestibule Closure

Author: Alicia Vose & Ianessa Humbert

Journal: Dysphagia

Year of Publication: 2018

Design Type: Descriptive Review

Purpose: “The purpose of this review is to promote a better understanding of the mechanism of laryngeal vestibule closure.”


 

Let’s hear it for laryngeal vestibule closure y’all!!! Do you know what it is? Do you want to know more about it? Then here’s your article folks to help you understand the whats, hows, and whys of this potentially fatal part of the swallowing mechanism that many might glance over like a stack of bills or junk mail (Tax Day was yesterday so my head is still spinning…).

Before you jump ship after reading the strange, multisyllabic, drawn-out term “laryngeal vestibule closure” (can’t we just agree on “closing voicebox” and call it a day?), this article is a descriptive review—meaning there’s NO methods, results, fancy-schmancy charts with numbers and weird symbols (okay there are tables and stuff but mostly from cool references). So you may actually be able to sit down and relaaaax while reading it……..(maybe).

Guys, I honestly had some internal debate if I should even write this article and not just type “Go read it NOW!” The article gives suuch an amazing review and overview of the laryngeal sequences, making me somewhat more ashamed of the ONE dysphagia course I had in grad school where I essentially heard “this flap thing moves over your voicebox to close so something doesn’t go down the wrong tube.” Yes, you’re gonna need a basic understanding and possibly read it line-by-line at some points (not gonna lie this was me and it really did help me put it all together), but it’s totally worth it to get that stroke of inspiration. 😉


Many of us have educated patients/families on what a “safe” swallow is (aka nothing going down your windpipe) and possible consequences from unsafe swallowing (aspiration, pneumonia, etc.). And during this “Dysphagia Revolution” (new term I’ve coined the past couple decades, just check out the crazy number of publications lately!), we’ve learned a lot about the different components of swallowing physiology like pharyngeal residue, anterior hyoid excursion, upper esophageal sphincter relaxation, etc.

What exactly is LVC?

“LVC is the first line of defense for preventing material from penetrating the airway during swallowing and is distinct from true and false vocal-fold closure, which serves as a secondary defense.”  p. 2

Hopefully, most of us got at least the gist of general airway protection (even if it did mimic those embarrassing past grad school learnings) and how it comprises of 4 levels during normal swallowing: true vocal folds–false vocal folds–epiglottic inversion–forward/inward movement of arytenoids (if not check out the full article for a review!!!).

“Despite considerable overlap in the timing of these events, in videofluoroscopic images, the closure of the laryngeal vestibule space has been described as occurring gogurtby a compression from ‘‘bottom to top.’’ This occurs first at the supraglottic followed by the subepiglottic space in a peri-staltic-like motion that can clear the vestibule or squeeze out bolus material that has penetrated the area to avoid aspiration below the vocal folds.”  p. 2

But why is LVC so special and not just lumped together as one thing? I’ll be honest and say that I was not nearly as aware as I thought of all the multiple parts that make it up…..

In order to do its job, LVC is basically at the mercy of the movements and timing of arytenoid adduction + approximation to the base of the epiglottis + epiglottic inversion (which happens only from tongue base retraction+hyolaryngeal excursion+pharyngeal constriction).

So what if one of those is impaired? Does it even make a difference or can LVC still keep calm

The answer to this is just what the article gets us thinking about:

“In order to fully understand this mechanism, it is necessary to understand which component(s) are critical for achieving complete closure. Currently, it is unclear if each component is equally valuable, or if one holds more importance for the function to happen.”  p. 2


If you’re like me and always craving to get a better grasp on this sticky-web-of-swallowing thing, then you’d feel happy as a clam learning more about each of these components.

Arytenoid Adduction+Anterior Movement

“Anterior tilting of the arytenoid cartilages has been suggested as one of the most important contributors to closure of the laryngeal vestibule… arytenoid movement is not a biomechanical effect of laryngeal elevation and is under separate, active neuro-muscular control”  p. 2

Basically, arytenoids don’t move just because of something else making them move (aka elevation), and is actually controlled by the brain, making muscles move to cause this action.

Don’t forget about the aryepiglottic folds! “These lateral folds act as ‘walls’ allowing for the bolus to pass between the aryepiglottic folds and the lateral pharyngeal wall” and gets their “stiffness” from the corniculate and cuneiform cartilages (think water slides that separate the wave pool/glottis from the lazy river/pyriforms).

Epiglottic Inversion

How does that leafy thing move? Magic? Nope. Think it only moves from a forceful bolus push? Not quite. (yes this weighted force may contribute to it but it can also happen with less heavy boluses).

“Inversion of the epiglottis is primarily a passive movement that has been described as a two-step procedure, [1] moving from an upright position to a horizontal plane, then [2] moving from the horizontal position to its fully inverted position.”  p. 3  

There’s no way I could come close to the awesome illustration the article provides for this movement (seriously, check out the article!), the closest I can come up with is this, and it still doesn’t portray all the different moving parts:

 

 

Guess what…..

but wait.PNG

Yeah yeah, the epiglottis moves across different planes (vertical/horizontal), we got that. But did you realize that there are multiple and specific movements for this? Do you know what their role is in LVC? To quote Tim Gunn from Project Runway, to “Make it work.”

Base of tongue retraction

“Tongue Base Retraction, or posterior propulsion of the tongue, contributes to closure of the laryngeal vestibule by facilitating posterior and downward movement of the epiglottis to a horizontal position.”  p.3

Hyoid anterior excursion

This one’s a doozy and another newly hot topic. Apparently, hyoid elevation does NOT have to happen in order to have LVC (you can thank the authors and others for that info from previous studies using surface e-stim on supra+infra hyoid musculature to cause decreased elevation). Others have also come out in declaration to help us get it out of our heads that we need to be bowing down to the almighty elevating hyoid:

“Although hyoid excursion might correlate with epiglottic movement, hyoid movement alone does not generate either stage of epiglottic inversion when laryngeal elevation or tongue base retraction is impaired.”  p.3

Pharyngeal shortening+contraction

“The final movement of the epiglottis includes movement from the horizontal position to its fully inverted position with the epiglottis tip contacting the arytenoid base, which is accomplished by pharyngeal constriction..Contraction of the pharyngeal constrictors provides compression on the tip of the epiglottis to further aid its inversion”  p.3

Okay, but what’s all this really saying?

LVC needs separate parts to help contribute to it. While we don’t necessarily know which component is most critical for it to fully do its job, we DO have a better understanding that hyoid excursion does NOT need to be a bolus hog and get all the credit—actually, it doesn’t need to even be on the court and can actually sit out while the other players be all-stars (I think I may have been unconsciously referencing basketball there…?).

mindblown

 


The next question the article tackles is how exactly do we observe this?

If you’re thinking FEES……

Sorry. While FEES can be a stupendous tool for many things, it’s a no-go due to the “white out” period where you really are unable to visualize the closure of the glottis and with it LVC as the epiglottis covers this image (at least that’s the idea…).

So we’re left with MBSS/VFSS where the authors explain 2 important aspects for LVC—this is actually where I had my “aha” moment after always seeing the terms “LVCd” and “LVCrt” in a bunch of other research articles (I had no clue and just had to keep chuggin along before):

  • range of motion – amount of closure by visualizing the amount of airspace obliterated within the vestibule at the height of the swallow
  • timing – duration of closure and the duration to closure

I (along with a bunch of researchers I bet) wish there was a quick-and-easy standardized way to judge these 2 factors, but sadly the article hints at why nothing worth having comes easy (or free):

“The PAS [Penetration Aspiration Scale] is not useful for evaluating LVC because the PAS does not determine the physiologic impairment that causes airway invasion.”  p.4

That’s where the MBSImP comes in to save the day by at least categorizing LVC into either “complete” “incomplete” or “no closure.” time

Sometimes, timing just gets the best of us…..

If you’re trying to advocate for better fluoro measures and images in Radiology, then this article should be put in your folder to bust out, so I’m just gonna leave these here…….

Duration of laryngeal vestibule closure is a measure of how long the laryngeal vestibule maintains complete closure.”  

Duration to laryngeal vestibule closure is a measure of how quickly the laryngeal vestibule closes once the swallow is initiated, and is measured by calculating the time between the first frame of hyoid burst and the first frame of laryngeal vestibule closure.”  p.4

“Timing analysis requires access to frame-by-frame review of video-fluoroscopic images and some clinicians may not have the ability to record videofluoroscopy for secondary review due to lack of equipment or limited access to archived materials…thus, poor access can be a significant barrier to best practice.”  p.5

“Underutilization of these techniques is a barrier to clinicians’ ability to accurately diagnose and treat LVC…proper evaluation of swallowing events during videofluoroscopy requires a minimum temporal resolution of 30 frames per second.”  p.5

[also checkout this quick awesome link for more info on frame rates by one of the greats ]

Now that we got that outta the way…

The authors do an awesome job explaining and providing a small super-useful chart to help all those Video-Fluoroscopic-Swallow-Studiers (maybe our new name?) get the current normative values and just how the research came to somewhat agree on this variability of “normal” when it comes to timing of LVC (see full article for the deets).


Is it Normal, or Not Normal? That is the question….

When it comes to this debate, we actually should give ourselves credit for coming so far in distinguishing all the factors that can change different responses like in pharyngoesophageal opening, transit time, etc. during the swallowing mechanism (and by credit I mean we should be using this info 😉 ). marsha

But what is normal LVC? Well, as Jan Brady understands, nobody really pays as much attention to it in the research world. We don’t know yet how things like temperature, age, consistency, etc. affect LVC.

Here’s what we DO know so far about normal LVC:

“Studies that have reported factors that influence LVC timing have shown that duration of LVC increases with increasing bolus volume and increases with the time the bolus remains in the pharynx, yet none of these studies reported a change in duration to LVC.”  p.6

“Normal variability in patterns of laryngeal closure also varies according to the mode of delivery. In healthy individuals using sequential straw swallows, some exhibit a pattern of maintaining LVC throughout sequential swallows, while others demonstrate hyolaryngeal descent and opening of the laryngeal vestibule between sequential swallows” p.6

If you’d like to help out the authors, next time you’re watching that bolus head down with “complete” LVC closure and notice that that puree or colder bolus helped close that airway, give ’em a holla so they can do what they do best for giving us clinicians more answers 😀 !

Don’t we have a SAY in this?!?

According to some studies (including the authors), you can alter LVC merely by either doing effortful swallows and volitional closure particularly enhanced by biofeedback from VFSS.

“These data are significant because by instructing participants to prolong the
duration of LVC, they were able to demonstrate volitional control over a predominantly brainstem-mediated swallowing event given the control mechanisms of LVC are considered reflexive in nature when it occurs in the context of airway protection during swallowing. However, by implementing direct volitional control, manipulating this event has enormous rehabilitation potential.”  p.6

While the article continues to remind us that lack of airway protection is a major cause of aspiration and pretty darn prevalent in populations like post-CVA, neurologically older patients compared to healthy, and head&neck cancer patients with specific radiation treatments, we do still need to learn more about this phenomenon.

Lucky for us, they also point out that the studies looking at the above populations did NOT look at what the WHOLE POINT of this article is talking about which is:

“which component of LVC is delayed, absent, or impaired (i.e. epiglottic inversion due to impaired tongue, pharynx, or laryngeal elevation? Arytenoid movement?) ?”

While we can look forward to a bunch of research in the future hopefully touching on distrupting (aka perturbing) laryngeal motor control in order to help us gain understanding on which components are the most important, for now we will have to keep giving LVC the respect it clearly deserves.

And if you’re sitting there, wine glass empty, stressing or with the disappointed thought of “why does it matter if I don’t know the specific reason LVC is incomplete?” “I know the airway isn’t protected so I can just fix that,” :

“This is important because therapy targets for tongue base retraction might
differ greatly than those that target laryngeal elevation or pharyngeal constriction. Identifying the specific impaired component of LVC could lead to more effective treatment to improve swallowing airway protection.”  p.7

Hopefully, if anything at all in your car or house or any item has ever broken or failed to do its job, you didn’t simply just pay the mechanic or plumber and not ask WHAT specifically caused that leak, smoke, or tear? (I’ll also bet the professional likely offered you the explanation to this as well?).

mechanic

How can you use this article?!?

Maybe you’re desperately trying to advocate for improved radiology imaging/access?

Or you are wanting to up your VFSS game and comparing what you’re seeing in patients with the very variable norms?

What are your experiences with looking at LVC, understanding LVC, or even hearing about LVC for the first time?!?

**************************************************************************

Takeaways:

  • “While many studies report the influence of various therapies, maneuvers,
    stimuli, and patient factors swallowing physiology, many omit laryngeal vestibule closure as a primary outcome measure, thus limiting our understanding of how external factors influence this primary airway protection mechanism.”
  • “Epiglottic elevation, tongue base retraction, and pharyngeal constriction primarily facilitate epiglottic inversion in order to achieve LVC.”
  • “During normal swallowing, epiglottic inversion contributes to LVC by contacting the arytenoids, covering the laryngeal inlet, and diverting the bolus laterally away from the laryngeal vestibule toward the upper esophageal sphincter (bolus typically splits into two pieces to flow down and around the airway)”
  • “Contraction of the pharyngeal constrictors provides compression on the tip of the epiglottis to further aid its inversion.”
  • “Impairments in laryngeal closure are recognized as one of the major causes of aspiration. If the duration of laryngeal closure is absent, too short, or if closure is delayed, this can lead to the unwanted entrance of food or liquid into the airway.”

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Article Referenced:

Vose, A. & Humbert, I. Dysphagia (2018). https://doi.org/10.1007/s00455-018-9928-1

https://www.ncbi.nlm.nih.gov/pubmed/30062547

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