Short ‘n Sweet – Pharyngeal Swallow Initiation Factors

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It’s somehow 2023, and long are the days when anytime a dark contrasted bolus passes the ramus of the mandible equals an automatic “fail” or impairment. With an all-star cast, this is another article to highlight and keep to better understand this ever-changing pharyngeal phenomenon.🤓

Title: Factors Influencing Initiation of Pharyngeal Swallow in Healthy Adults
Authors: Bhutada, Dey, Martin-Harris, & Garand
Journal: American Journal of Speech-Language Pathology
Year of Publication: 2020
Design Type: “Study data were extracted from a large normative MBSS data set”
Purpose: “The purpose of this study was to investigate factors influencing the initiation of pharyngeal swallow (IPS) in healthy, non-dysphagic adults”
Population: 195 healthy adult participants (21-89 y/o)
Inclusion criteria: >21 years old, adequate cognitive functioning to follow study procedures, consumption of regular diet with thin liquids for daily oral intake (tonsillectomy/adenoidectomy/tooth removal were included)
Exclusion criteria: current diagnosis or history of upper aerodigestive tract surgery/anterior neck surgery, hiatal hernia (>2 cm), pulmonary disease, HNC, or neurological condition (e.g. Parkinson’s disease, stroke, etc.); current or suspected to be pregnant

The authors start with a great history of how long we’ve been trying to solve this complex swallow task, from way back in Logemann’s ’90s to Humbert, and more of Martin-Harris’ work along with some of Steele’s insights, it’s a great way to really appreciate how new our field is and how much more we still have to discover.🧐

Besides the obvious MBSImP standardized protocol with Varibar in lateral projection only, here’s what the MBSs that they extracted from their data pool looked like:

  • Thin liquid
    • 5 ml, cup sip, and sequential swallows
  • Nectar (Mildly thick) liquid
    • 5 ml, cup sip, and sequential swallows
  • 5 ml Honey (Moderately thick) liquid
    • (“thin honey” per Varibar)
  • 5 ml Pudding (Extremely thick)
  • 1/2 cookie w/3ml barium pudding
  • All 5ml tasks+cookie = teaspoon
  • Cued: All single liquid tasks, instructions to “take a normal-sized sip and hold bolus in the oral cavity until a command to swallow was provided by clinician
  • Uncued: Sequential swallows had instructions to “drink in their normal manner until told to stop (after 2 consecutive swallows)” and 5 ml pudding+cookie
  • 30 frames per second

Since the authors were only interested in initiation of pharyngeal swallow (IPS) for the study, only Component 6 (Initial Pharyngeal Swallow) from MBSImP Guidelines was scored across all 9 swallow tasks by 2 expert and blinded* SLPs (*no demographic info was known). Another important note is that while each swallow task was scored separately, the “highest” score across all swallow tasks was used for the Overall Impression Score (ratings 0-4), with higher scores correlating to bolus head at deeper areas of the pharynx at the time of “first brisk movement of the hyoid.”

As far as just what specific factors they were looking at:

Therefore, the current study investigated influences of viscosity, volume, age, sex, and race on IPS in a large data set of healthy, non-dysphagic adults.” p.2

Viscosity (thinner=deeper)

“higher IPS scores occurring during thin liquid swallow tasks. Our results corroborate findings by Steele et al. (2019), which reported that thinner consistencies (thin, “slightly” thickened) had higher frequencies of IPS within the pyriform sinuses compared to “moderately” and “extremely” thickened liquids.” p.4

This means that when we see thinner liquids reach those pyriforms, we don’t HAVE to panic anymore as this can be totally normal compared to thicker textures. When you think about it, it just makes sense even from a physics-logic since regular ‘ole thin liquid moves way faster and is more fluid than something closer to molasses. Don’t believe this? Let’s start having rheologyo races in the back lots😜

When it came to solids, their results were #samesies as a previous 2007 study that IPS frequently occurred at the level of the valleculae when ingesting a solid, which was attributed to mastication, lingual-palatal contact, and vertical palatal movements.

Volume (larger= deeper)

“Overall, a significant difference was observed in IPS scores across volumes (p< .001), with higher IPS scores observed for larger volumes. Specifically, significantly higher IPS scores were observed during the thin liquid sequential swallow task compared to 5-ml thin liquid task, with a large effect size observed.”

“A significant and moderate effect was also noted between the thin liquid cup sip and sequential swallow tasks (p< .001), with higher IPS scores again observed during the sequential swallow task.” p.3

This same eye-mesmerizing phenomenon was also consistent for the same comparisons with Nectar/Mildly Thick Liquids: “A significant and large effect was also observed between nectar-thickened liquid 5-ml and cup sip tasks compared with the sequential swallowing task; that is, higher scores were observed during the sequential swallow tasks.”

While this can be a possible age-old myth that I’ll admit is even hard for me to break from sometimes, the authors give some nice rationale to start sharing with colleagues and you-name-it why we might not have to be so afraid of larger boluses ending up in the deep end of the throat (at least if it doesn’t impact safety😉**):

“They attributed the differences between discrete (single) swallow and sequential swallow tasks to the motor control of the lingual, hyolaryngeal, and velopharyngeal subsystems. Thus, motor control for sequential swallows employs task-induced adjustments of these subsystems when compared to the discrete tasks, allowing for greater motor adaptation, flexibility, and overlapping gestures of the subsystems.” p.5

Age (inconclusive?)

“Age category was not found to be a significant factor influencing IPS scores, which is consistent with results reported by Humbert et al. (2018).” p.6

Hold the phone though guys!! A *huge* caveat is explained that this also is different from some other big studies, with variables like sample size, swallow tasks, methodology, and how age groups were determined as well as how many subjects were in each group.

So, probably take this with the hugest grain of salt that your dietician will allow for now🧂. . . (FYI there are many more studies that do look specifically at age and swallow components with a bunch of evidence in the meantime🤓)

Sex (female= deeper?)

While “none of the swallow tasks separately were found to be significantly affect by sex,” the authors did find that:

“we found sex to be a significant predictor for IPS OI scores. Our findings support that women were more likely to initiate the pharyngeal swallow beyond the ramus of the mandible compared to men.” p.6

While some other studies have opposite findings, again differences in methodology, sample sizes, and swallow tasks are likely factors that play a art in the discrepancy. (FYI the authors share more info on plausible explanations for all types of findings if you’re interested in learning more into this difference🚺🚹)

Race (African American = deeper?)

The authors admit that they couldn’t find any studies that looked at all the factors they did while also including the racial category, so this is one for the books but hopefully will not be the last!👍

“Surprisingly, the present investigation found a significant difference in IPS OI scores between racial categories. Higher IPS OI scores were more likely to be observed among non-Caucasians over Caucasians. Additionally, race was determined to be a significant factor across majority of swallowing tasks except for thin liquid cup sip, thin and nectar-thickened liquid sequential swallow, and pudding tasks.” p.7

After finding this statistically significant result, the authors chose to run with it and go even further since the majority of their participants who were non-Caucasian were African American racial identify (86%) and after excluding any other racial category (e.g. Asian, Native American, Hawaiian, more than 1 race) even finding “similar results as our previous analysis, with two additional tasks becoming significant (thin liquid sequential swallow and pudding).”

The authors try to shed light on the possible interpretations relating to anthropometric differences.

Beghini et al. (2017) revealed lingual differences between African Americans compared to Caucasians. Because the tongue has a crucial role in influencing pharyngeal swallow onset, differences in lingual dimensions may help to explain variations in typical swallowing behaviors. Future studies should investigate the influence of race to determine if the racial difference observed in the current study is supported.” p.7


While there’s lots to unpack, as always there’s also lots of things to keep in mind and balance everything out:

  • Unequal number of participants in age, racial, and sex groups
  • Only 1 trial for each swallow task (“consistency of IPS scores across trials of the same bolus volume and consistency remains unclear”)
  • Only 5 ml swallow tasks were explicitly measured (assuming all cup sips were likely larger)
  • Overall Impression (OI) Score for MBSImP = highest/worst score (“For example, significant differences were found in IPS OI scores between sexes, al- though no significant differences were observed at the task level”)

With that being said, the authors are comfortable enough concluding:

“Bolus location at pharyngeal swallow onset past the ramus of the mandible may not be an indicator of a swallow impairment per se, and clinicians should take caution restricting or modifying diets based on this observation alone, particularly if safety is not compromised (i.e., aspiration of material).” p.7

What does that mean for us clinicians sprinting into that fluoro suite? Hopefully a big, bright, blinking ⚠️Caution⚠️ sign before making quick judgments about what is “ok” vs what is “bad” or even impaired.

We also need to keep in mind that these findings are based on NORMAL, HEALTHY ADULT SUBJECTS! So we cannot yet jump to thinking of our disordered, unhealthy, sick patients as anything but. However, if we do see any of the above revelations (especially if they are NOT impacting the swallow safety of other adverse risks), we can now think twice before jumping on the Fix-It bandwagon and calling something impaired that may just be, totally fine.🤠

Article Referenced: 💥FREE ASHA ACCESS💥

Bhutada, A., Dey, R., Martin-Harris, B., & (Focht) Garand, K. (2020). Factors Influencing Initiation of Pharyngeal Swallow in Healthy Adults. American Journal Of Speech-Language Pathology29(4), 1956-1964. doi: 10.1044/2020_ajslp-20-00027

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