Sweet until sour?? Taking a bite out of taste manipulation

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Title: Taste Manipulation and Swallowing Mechanics in Trauma-Related Sensory-Based Dysphagia
Authors: Dietsch, Dorris, Pearson, Dietrich-Burns, & Solomon
Journal: 2019
Year of Publication: Journal of Speech, Language, and Hearing Research
Design Type: prospective experimental
Purpose: “This study explored the effects of high-concentration taste manipulation trials on swallow function in persons with sensory-based dysphagia.”
Population: polytraumatic-related injured U.S. military service members at Walter Reed National Military Medical Center (WRNMMC)
Inclusion criteria: stable service members referred to speech pathology clinic at (WRNMMC) for evaluation of swallowing functioning during hospitalization for management of service-related traumatic injuries
Exclusion criteria: injured service members admitted for reasons other than traumatic injuries or facility discharged prior to SLP swallow evaluation

  • Only got a sec?
    • Highly concentrated sour or sweet-sour bolus presentations may demonstrate immediate physiological changes in those with sensory dysphagia (but not entirely generalizeable)
  • Only got a minute?
    • Intense sour is different from most other tastes in that it stimulates additional chemoreceptors associated with pain, touch, and thermal perception in a process called chemesthesis. Thus, strong sour tastants may amplify the trigeminal nerve signal and further influence swallowing physiology through feedforward and feedback mechanisms that function to “prime” the associated swallowing network
    • CASM results confirmed that sour elicited increased hyolaryngeal excursion and also identified increased pharyngeal shortening and tongue base retraction for sour versus unflavored trials in this small sample. These biomechanical changes have been shown to contribute to laryngeal vestibular closure and may also help explain the lower PAS scores 
    • Penetration-aspiration scores were significantly lower for sour trials compared to unflavored trials. The significant difference in pharyngoesophageal opening scores was primarily influenced by lower scores for sweet–sour trials compared to unflavored and sour trials
  • Got more time? Keep Reading!!

While I could pop 20 in my mouth, chew a few times, and let my sensory nerves run wild with these lil treats, I’ve never really thought about how the sweet/sour taste sensation actually impacts how my body manages what I just placed in my mouth…🤔🤔. Why do I enjoy it? How do my tongue and body react to it and why? What makes us make that funny sour face? These are just some random questions I might ask, so could you imagine what clinical and research experts are asking to learn more about sensory experiences for our patients?!

I don’t know if it’s because I’m biased given I’m hooked on these lil guys or the fact that I am always fascinated when it comes to sensory dysphagia, either way, this article definitely hit MY sweet spot!😊

Just like when watching your favorite TV show series, it’s always a good idea to get a nice recap to bring you up to speed in case you might’ve forgotten any details. Right outta the gate the authors easily provide this to us in a very simple way, explaining first the comparisons for normal and sensory dysphagia.

“In an intact swallowing system, motor patterns are known to vary based on sensory response to bolus properties (Lazarus, 2017). A range of bolus properties—including temperature, volume, texture, carbonation, and taste—has been explored relative to certain temporal and kinematic swallowing features in neurotypical adults.”

“Taste stimulation, particularly strong sour, elicited increases in tongue-to-palate pressures and submental muscle activity in healthy persons.” p.1

Ahhh, refreshing, right?😊

They then move on to also review in more detail just how this plays a role in swallowing (way better than I ever could)…

“These responses to taste stimulation may be explained by the sensorimotor networks underlying oral sensation and swallowing.”

“Pure taste information is relayed via branches of the facial and glossopharyngeal nerves from the taste buds in the oral cavity to the nucleus tractus solitarius in the brainstem and other subcortical and cortical regions involved in taste perception.”

“In addition to this taste network, somatosensory information about temperature, texture, and touch is conducted to the brainstem through the trigeminal nerve. Inputs from the trigeminal pathway are theorized to have stronger, more preferentially attenuated input to the nucleus tractus solitarius as compared to those from the facial and glossopharyngeal nerves.” p.1-2


It’s hard for me to stop there because they just give you a lot of awesome info that really ties into the background for why they are even studying this area. A final nugget-of-knowledge I learned was that different studies involving neuroimaging have led to the conclusion that cerebral blood flow in swallow-specific regions is actually increased for not just certain tastes, but even more heightened for extremely sour tastes! Guess I should’ve just done my own study with all those lip-puckering sour candies!!!😂🤤

Many of us (*hopefully*) know that dysphagia can inhibit many sensory responses in the swallowing system thanks to the hard work of many researchers (too many to name, but just take a look at the article’s nice reference list to know who to thank!!).

“For example, a very sour liquid elicits more rapid oral and pharyngeal onset times (Logemann et al., 1995), reduced pharyngeal transit time (Pauloski et al., 2013), and lower Penetration-Aspiration Scale than other stimuli.” p.2

But outside of my sweet & sour chicken takeout orders, I’ve never thought about this pairing when it comes to improving SWALLOWING (improving my delicious dinner experience is another story🤤).

The authors wanted to bounce off some previous work done but this time with more detailed and improved metrics to actually know the effects of sour vs sweet-sour vs bland tastes.

So what’d they do you ask?

It’s really up to you where you want to start because a lot of the tools they used in my opinion are pretty cool..

By looking at a specific sample – U.S. military service members all at Walter Reed National Military Medical Center – that were actually already part of a larger study that was being conducted, the authors could easily get quick access and pick those participants who met their criteria. However, there is a caveat to this fastrack to keep in mind later on🧐…

So by reviewing medical charts for info, applying the inclusion/exclusion criteria, while the authors began with 45 inpatients, they ended up with 32 who were eligible and agreeable.

not so fast2

After reviewing everyone, and after the clinicians in the study (which consisted of clinicians & researcher-scientists) decided when+who were appropriate for VFSS (18 total😲), the clinicians immediately determined if further assessment for sensory-dysphagia appropriate.

But how did they decide that?🤔

Actually, how do we even decide that??😓

Along with their facility’s implementation of MBSImP bolus administration protocol, commercially-mixed barium products, and Penetration-Aspiration Scale (PAS), the authors do a great job giving the details for this so YOU can even think about replicating it😉:

“Indications of sensory impairment used by cSLPs to inform their clinical judgments included (a) delayed onset of the pharyngeal swallow response and/ or (b) reduced awareness of pharyngeal residue, laryngeal penetration, and/or aspiration. The onset of the pharyngeal response was considered delayed if the leading edge of the (liquid) bolus had advanced beyond the valleculae at the initiation of hyoid movement.”

“Factors marking reduced awareness included the absence of a cough or throat clear when the bolus pooled on or passed below the vocal folds, lack of spontaneous repeated swallow to clear marked pharyngeal residue, and/or verbal acknowledgment that the bolus had cleared despite visual presence of residue on fluoroscopy.” p.3

**quick note about the leading edge of the bolus at the valleculae….see some related studies provided with all the references for more about age, viscosity, temperature boluses, and the RANGE OF NORMAL before automatically labeling a “delay” or impairment😉**


Ok, but what did they really do?

A deeper look into the madness of their methods shows there was much more to all the sensory stuff after you’re a candidate for VFSS:

The additional taste-stimulus trials procedures looked like this:

  • Three 5 ml trials via syringe (3 each)
    • Unflavored barium mix
    • Sour-lemon juice-like mix (citric acid)
    • Sweet-sour-like mix (citric acid+sucrose)
  • Multiple oral tap water rinses (usually 2-3) until no residual taste was reported (completed before each trial)
  • Instructions to “swallow normal whenever ready
  • 16/18 participants took at least 1 of the 3 different taste-stimulus trials
    • (this was because of accumulated radiation exposure time and medical disposition)
  • All presentations were counterbalanced (aka evened out) across participants to avoid order effects

“The fluoroscopic swallowing images included in this study were captured in the lateral view at pulse rates consistent with clinical standards at that time (typically 7.5 or 15 pulses/s) and digitally recorded at 30 frames/s for further analysis.” p.3


Given what we have learned in the field regarding videofluoroscopic frame rates and pulse rates (as well as just the effect of cued coughing/swallowing and how materials are presented), this is clearly not ideal. . . (Check out more info on this at Dr. Steele’s lab and these influential articles by Mulheren & colleagues and Bonilha & colleagues !)

But, when that’s what you’ve got then that’s what you’ve got, and that is a great place to start for improvement.😕🤷‍♀️

A little more on what they did. . .

So, anyone who knows me easily understands that I.AM.NOT.GOOD.WITH.TECHNOLOGY.🤖

So, when I – ME – actually get hyped-up about something involving a computer and say it’s really cool, you know it’s the real deal!

Enter: CASM, or Computational analysis of swallowing mechanics(a quick Google search gives even more studies and info!)

“CASM considers the interaction of various component movements within oropharyngeal swallows by relationally tracking the displacement of anatomical landmarks.”

“Whereas MBSImP categorizes ratings of specific movement trajectories and tissue approximations using ordinal scales, CASM tracks landmarks’ movements in any direction using interval measures. This may enable detection of subtle changes in oropharyngeal swallowing physiology that could be unappreciated using clinical ratings or more traditional distance measurements of isolated swallowing movement trajectories.” p.2

🤓Anyone else? Just me??👩‍🔬😅

Now, CASM only looked at participants who took all 3 of the different stimulus trials (bland, sour, sour+sweet), but that’s because it needed this info to compute and do all of its robotic-brain-power analyses, along with only participants who on VFSS visually/radiographically showed all the anatomical structures needed to do the above fancy analyses.

What are those structures you ask?🤔🤔

“Ten key anatomical landmarks representing muscle groups underlying pharyngeal swallowing mechanics were tracked frame by frame from the beginning of oral transport through the pharyngeal phase of swallowing using a MATLAB-based semiautomated software tool.” p.4

I will literally buy someone a jumbo size pizza to anyone who can guess what specific structures were used?!!😅🤓 

Anyhoo, the researchers scrutinized over this (blinded) data in order to make sure it was comparable to an expert rater (with “excellent intra- and interrater reliability levels)….Can you just imagine how freaking extraordinary these people have to be able to pinpoint ALL of these points, even if it was frame-by-frame??

Who’s up for a VFSS CASM-off !!?!?!?       

Looking forward to what they found!

“Of note, more than half of the participants were not receiving an oral diet prior to the VFSS due to swallowing safety concerns, and PAS scores during the clinical VFSS trials generally reflected airway compromise to or below the level of the vocal folds, confirming the cSLPs’ impressions regarding the existence of dysphagia…seven also demonstrated concomitant motor deficits.” p.3

Now that we got that outta the way, after 85 total ‘taste trials,’ 68 trials from the 18 participants were “good enough” for clinical analysis, and 3 participants were ‘good enough’ for CASM  and were receiving ‘nothing through the mouth” prior to the studies thus avoiding outliers .talk about your valedictorians!!🥇🥈🥉

I won’t bore you with all of the terms like “Morphometric canonical variate analysis” and “Eigenvectors” (literally not even making these up!) because I have absolutely no clue what they are or mean, but if you’re ever so inclined please feel free to get back to me with what you find😅!

“tastant type was a primary predictor of swallowing physiology” p.6

(Canonical Variates 1 and 2 represent these shape changes). “Color coding by taste stimulus type reflects complete separation in the pharyngeal swallow shape features across the three taste stimuli”

They actually give you a pretty basic, easy-to-interpret color-coded chart where you can see just how different these 3 stimuli are when it comes to pharyngeal swallowing (they all have a different pattern it seems!). After using a test that compares differences between groups like ANOVA, but for ordered scales like “pain 1-10” versus using categories like “male/female, the researchers found 2 sets of statistically significant results involving the PAS and pharyngoesophageal opening. Further results across all methods indicated:


“Penetration-aspiration scores were significantly lower for sour trials compared to unflavored trials. The significant difference in pharyngoesophageal opening scores was primarily influenced by lower scores for sweet–sour trials compared to unflavored and sour trials.” p.5


“Sweet–sour and sour stimuli elicited increases in hyolaryngeal displacement, pharyngeal shortening, and tongue base retraction during the pharyngeal phase compared to the unflavored trials”

“The magnitude of increase in hyolaryngeal displacement and tongue base retraction was greater for the sweet–sour stimulus compared to sour tastants.” p.6

To try to put all that in a simple sentence at least how my brain interprets it: sweet-sour > sour > bland for changes in swallow physiology. Even further, the super-specialized CASM also detected differences in swallowing physiology that were not captured by the ordinal ratings and associated analysis. That was so interesting to me because obviously this isn’t something we’re not gonna have clinically and readily available today, but it could be helpful to at least validate clinical observations when analyzing and determining swallow pathophysiology in the #realworld!!! Ahh, one can dream…😊

If you know me, or anyone who, dare-I-say-it, *likes* reading research and trying to get as many questions answered as possible, we can’t just stop there!! It’s always important to know why something happened, or at least make sure that ‘why’ rationale makes sense to you! Otherwise, we’d be believing every single one of those infomercial advertisement salespeople!! (no judgment here-I’ve been so close to ordering those turkey cookers😂, but sometimes thinking twice is best😉)

While the authors provide a legit and encouraging rationale as to why they think these changes occur,

“CASM results confirmed that sour elicited increased hyolaryngeal excursion and also identified increased pharyngeal shortening and tongue base retraction for sour versus unflavored trials in this small sample. These biomechanical changes have been shown to contribute to laryngeal vestibular closure and may also help explain the lower PAS scores.” p.7

“Certain stimuli, such as intense sour, stimulate multiple cranial nerve pathways to a greater extent than do tastants without chemesthetic properties.”

“Thus, stimuli that take advantage of the multisensory integration within the gustatory/swallowing network, including strong sour and possibly intense sweet–sour, may be more able to overcome or bypass any “breaks” in the circuitry of the polytrauma population studied here, as well as in other clinical populations with peripheral and/or central nervous system damage” p.8

Before we all start handing out sweet-sour boluses to everyone….

There’s also a LOT we can’t say here and limitations….

I know, I know. I’m sorry to be the fun police😩, but before getting too ahead of ourselves as super eager clinicians, here are some things that were running through my mind and some which the authors actually acknowledge:

1. non-significant changes in PES, hyolaryngeal excursion/elevation, etc.

2. small sample size

3. Remember how nice it was that they were able to pick from an already selected group? Well, we can’t really generalize to larger populations outside of polytraumatic military servicemen just yet (the majority of subjects were young, fit men)

Some other quick thoughts that popped up. . .

  1. Can’t necessarily generalize to any other impairment (although they do give theoretical rationale that does align)
  2. I’m curious if there was any kind of ‘priming’ of the swallow prior to the Specific-Sensory trials????
  3. Again, the issues with the image quality from VFSS, therefore making the sample for CASM and MBSImP even smaller, which means there’s less info to analyze😕
  4. While there were functional changes in the swallowing physiology enough to impact PAS scores for swallow safety, these were only for immediate effects, so much more research would be needed to even try to answer “Will this change the swallow long-term for a therapeutic impact?” (similar to all those cold-sour swabs that were used for thermal-tactile stim)

Do we stay sour?

Should we try to make things sweeter?

As I mentioned, the article #IMO really does do a good job laying out a lot of information to replicate or further investigate (Interested? Be sure to reach out to the authors!!!). But for now, at the very least, it not only gives us a good review how sensory experiences directly affect the motor changes in swallow physiology, but also makes us think deeper into what we are seeing, why we are seeing it, and using our clinical knowledge, experience, and evidence to come up with our own clinical hypothesis for, “I wonder if this will work/help” or wanting to try something based on the theories and principles we know (aka neuroplasticity, motor learning, etc.).

Article Referenced: [FREE ASHA ACCESS]

Dietsch, A., Dorris, H., Pearson, W., Dietrich-Burns, K., & Solomon, N. (2019). Taste Manipulation and Swallowing Mechanics in Trauma-Related Sensory-Based Dysphagia. Journal Of Speech, Language, And Hearing Research62(8), 2703-2712. doi: 10.1044/2019_jslhr-s-18-0381

References for “Normal:”

Nishikubo, K., Mise, K., Ameya, M., Hirose, K., Kobayashi, T., & Hyodo, M. (2015). Quantitative evaluation of age-related alteration of swallowing function: Videofluoroscopic and manometric studies. Auris Nasus Larynx42(2), 134-138. doi: 10.1016/j.anl.2014.07.002

Molfenter, S., Leigh, C., & Steele, C. (2014). Event Sequence Variability in Healthy Swallowing: Building on Previous Findings. Dysphagia29(2), 234-242. doi: 10.1007/s00455-013-9501-x

Plowman, E., & Humbert, I. (2018). Elucidating inconsistencies in dysphagia diagnostics: Redefining normal. International Journal Of Speech-Language Pathology20(3), 310-317. doi: 10.1080/17549507.2018.1461931

Humbert, I., Sunday, K., Karagiorgos, E., Vose, A., Gould, F., & Greene, L. et al. (2018). Swallowing Kinematic Differences Across Frozen, Mixed, and Ultrathin Liquid Boluses in Healthy Adults: Age, Sex, and Normal Variability. Journal Of Speech, Language, And Hearing Research61(7), 1544-1559. doi: 10.1044/2018_jslhr-s-17-0417

And a nice review for Sensory Dysphagia related articles (ALL FREE ACCESS!):

  • Steele, C., & Miller, A. (2010). Sensory Input Pathways and Mechanisms in Swallowing: A Review. Dysphagia25(4), 323-333. doi: 10.1007/s00455-010-9301-5
  • Loret, C. (2014). Using Sensory Properties of Food to Trigger Swallowing: A Review. Critical Reviews In Food Science And Nutrition55(1), 140-145. doi: 10.1080/10408398.2011.649810
  • Dietsch, A., Solomon, N., Steele, C., & Pelletier, C. (2013). The Effect of Barium on Perceptions of Taste Intensity and Palatability. Dysphagia29(1), 96-108. doi: 10.1007/s00455-013-9487-4

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