Can you tell the difference between normal and abnormal swallow features in a videofluoroscopic swallow study (VFSS)? Can your colleagues? Vose et al. (2018) found that 77% of surveyed SLPs identified at least 5 normal aspects of a swallow to be disordered. EEEEK!
It’s clear as a field that we need to be better able to distinguish disordered swallows from normal ones. So, what can we do? Well, let’s start by looking at some new data from Steele et al. (2019) on healthy swallows across the liquid International Dysphagia Diet Standardization Initiative (IDDSI)* levels. While most of the swallows were textbook normal—one swallow per sip, Penetration-Aspiration Scale (PAS) of 1, full laryngeal closure, no residue—there was more variation in young, healthy swallows than you might think. Here are some findings that you can use when interpreting your next VFSS:
Bolus location at swallow onset does not tell us anything about how “normal” a swallow is. For thin, slightly thick, and mildly thick boluses, the head of the bolus could be anywhere in the pharynx at swallow onset. In fact, the most common location (36% of the time) for a thin liquid bolus at the time of hyoid burst was in the pyriform sinuses. Note that all of the swallows in this study were non-cued.
There were also more second swallows than you might expect. While most natural sips were completed in one swallow, in 20% of trials the participants swallowed a second time. Again, normal variation. Also, these second swallows did not happen more frequently with thicker liquids.
Most young, healthy people scored a PAS of 1 on all their swallows. Not surprising. But a number of people in this sample scored a PAS of 2 on at least one trial, with one participant scoring PAS of 5 on two swallows. This might not be news to readers of The Informed SLP, but it is a good reminder to not overinterpret infrequent penetration. On the other hand, if you read this review and are surprised that there wasn’t more penetration and aspiration among young, healthy participants in this study, remember that most people who penetrated or aspirated in Butler et al. (2018) were over 60 and that Butler used endoscopy (FEES) not VFSS.
This paper is chock full of data on the sequence, timing, and movements during various swallowing events at each IDDSI level. Want to know the average swallow reaction time for mildly thick liquids? Hop over to Table 2 and go wild. Want to know if maximum hyoid excursion changes for different consistencies? Check out Table 6 (spoiler alert: the answer is no.) This paper offers a ton of data showing how increasing thickness of liquids affects swallow physiology.
One caveat of this study is that it was completed with 20% w/v barium mixtures that were thickened by xanthan gum. This is different from the 40% w/v barium in Varibar that is most commonly used in the United States. At the moment, we still don’t have the research to know whether barium brand or small differences in concentration matter. For more on this issue see this article or this article by the Steele Swallowing Lab.
Note: You may be wondering if this article has data you can use today to determine whether a feature like swallow onset timing is within normal limits or delayed. The answer is yes, but not without doing some calculations on your own. Dr. Steele addresses this question more in the comments section, below. The good news is that Dr. Steele and her team are putting together multiple resources, including a case-based ASHA presentation this November, to make these reference data as accessible and useful to clinicians as possible. We’ll update this review once those resources are available.
Also: To hear Dr. Steele discuss this study herself, click here.
* If you’re not yet familiar with the IDDSI framework, check it out here. For now, here’s a cheat sheet:
Slightly thick ≈ Between thin and nectar thick
Mildly thick ≈ Nectar thick
Moderately thick ≈ Honey thick
Extremely thick ≈ Puree
Steele, C. M., Peladeau-Pigeon, M., Barbon, C. A. E., Guida, B. T., Namasivayam-MacDonald, A. M., Nascimento, W. V., … Wolkin, T.S. (2019) Reference Values for Healthy Swallowing Across the Range From Thin to Extremely Thick Liquids. Journal of Speech, Language, and Hearing Research. doi: 10.1044/2019_JSLHR-S-18-0448.