When we SLPs hear a cough in a restaurant, at the dinner table, or at bedside, our brains automatically go into assessment mode ping-ponging an array of questions and assumptions: “Why did they cough?” “Oof, that sounded bad” “They probably aspirated“
But what does a “bad” cough sound like?🤔
How do we know?🧐 Is a more experienced clinician’s ears better at detecting this??🤨
Surely there’s got to be a better way!
After browsing through some articles that look at this topic, I’ll give ya the short ‘n sweet version.😇
While we know clinical bedside swallow evaluations differ clinician to clinician, setting to setting, and patient to patient, they still remain a sacred value in beginning our swallowing assessment journey.
But what is actually happening when you hear a cough? On the flip side, what be if you don’t hear one😱??
First, let’s get on the same page for what a cough actually is.
Watts et al. (2016) bring us back to the 3 distinct phases researchers over time have concluded:
“Inspiratory phase: composed of contraction of the external intercostal muscles elevating the anterior rib cage and drawing down the diaphragm as it contracts, while laryngeal muscle activation allows for passage of air through the glottis resulting in a negative pressure drawing air into the lungs.
Compression phase: during which adduction of the vocal folds builds and maintains subglottic pressure generation.
Expiratory phase: composed of a forceful and rapid abduction of the vocal folds.” p.6
While we aren’t simply going to start using the gold standard of pneumotachograph to measure the airflow signals across all these phases for physiological cough testing, other studies have looked at different means of cough testing.
Next, we should know why we might want to look into assessing a cough (and no, it’s not just because we were told “they coughed, that’s your job”). As some may say, sometimes a cough can just be a cough. But–it can also sometimes be something more that the mere eyes or ears can’t detect. The same authors gave a simple overview of how coughs are manufactured in the central nervous system and how they relate to another critical system for swallowing with both efferently (motor outputs) and afferently (sensory inputs): (seriously though, checkout the full *FREE ACCESS* article for an even better detailed overview)
“The CPGs are inherently flexible in their connectivity to allow for rapid, on-line modification between the behaviors of cough, breathing, and swallowing, such as increasing apnea duration due to a larger swallowed bolus or the execution of a rapid and protective cough in response to aspirated material during swallowing. Changes in respiratory muscle activation occur as the swallow CPG is informed about characteristics of the swallow (i.e., safe vs. unsafe, sequential vs. single sip).”
“Thus, these two sensorimotor acts have highly co-ordinated and reciprocal functions with shared anatomical and neurologic underpinnings that provide a mechanistic, anatomical, and neurologic foundation for considering the role of cough during a clinical swallow examination.” p.4
So since both these critically important networks seem to be like 2 CPGs in the brainstem pod🧠, why aren’t we assessing both?
The above article lists 11 commonly validated CSE tools at the time yet finding only 4 included some type of cough assessment. All 4 only used perceptual cough judgment, but all the instructions and rating measures varied across each, with some simply grouping as “safe” or “unsafe” and others using different subjective ratings like strength, duration, quality, quantity, and “effectiveness” from audio recordings of cough.
But there’s even more to consider because are also different types of cough: reflexive vs voluntary (induced). Where volitional cough (i.e. asking someone to cough) can depend on the instructions and cognitive preparation thus ultimately changing different airflow patterns, reflexive cough is a protective response to some kind of stimulus sensed in the airway.
Even though some researchers have looked at voluntary cough in different populations like stroke, Parkinson’s, and ALS, the general consensus seems to be that there is a relationship between cough and airway safety for swallowing (aspirators vs non-aspirators), but many suggest that more objective ways of measuring cough is best.
As far as causing a reflexive cough, the same authors describe the intricate process:
“Using this method, an individual inhales an aerosolized irritant such as capsaicin, citric acid aerosols, fog, tartaric acid, acetic acid, or hypertonic solutions that can be delivered at different concentrations through a nebulizer or face mask.”
“Cough output is affected by irritant type, concentration, volume and duration of exposure, order of presentation, placebo trials, nasal afferent stimulation, and lung volume at the start of cough initiation. These variables impact cough flow rates, number of coughs produced, urge to cough (self-report), amplitude and duration of expiratory muscle activation, and time to initiation of a cough response.” p.9
While there have been many studies that use this type of method across a variety of the same populations again–from “nonspecific complaints of dysphagia” to progressive neurological diseases and even and extubated ICU patients–because there are just so many different balls up in the air as far as how each study looks at different measures, the authors make a great but unsurprising conclusion yet again :-/ .
“Cough reflex testing methodology may be more practical as part of a screening assessment as the methodology is inexpensive, quick to administer, and objective outcomes relatively are simple to interpret.”
“However, the lack of consensus for testing protocols and scarce data in multiple patient populations highlight an important gap in the literature. This leads to the inability to provide cohesive practice recommendations in regards to the optimal irritant type and strength of solution, length of delivery, and outcome measures.” p.11
But before we turn our heads from looking forward and lose hope–recent research is starting to look at innovative, clinically-relevant ways on how to include this in our toolbox while also thinking even more broadly about how to work from the bottom up to lay the groundwork in education and training levels.
In a recent 2020 publication, Curtis & Troche looked at using a handheld cough testing tool with the Parkinson’s population using FEES, cough airflow (aka peak expiratory flow rate), reflex cough threshold, and “urge-to-cough” measures. Interestingly, instead of a very fancy machine or expensive equipment, they creatively used a facemask, handheld nebulizer, and an analog peak flow meter across randomized 6 reflexive cough tasks and 1 voluntary cough task (using randomized amounts of capsaicin).
While some limitations included being underpowered, the use of FEES thereby possibly missing transient airway invasion events, and lack of reliability as well as needing simultaneous lung volume and respiratory measures in future studies, the authors concluded:
“While voluntary cough testing can be easily and expeditiously administered in the clinical setting (e.g., cueing someone to cough on command), this research supports the notion that reflex cough assessments should also be included in clinical evaluations when assessing airway protection and cough in PD. Evaluating only voluntary coughs without the inclusion of reflex coughs may overestimate cough effectiveness and airway protective function in this patient population.”
“An optimal capsaicin intensity and PEFR cut-off value for dysphagia screening was identified, which exhibited a sensitivity of 90.9% and specificity of 80.0% for predicting the presence of airway invasion. Identifying that 50 µM of capsaicin was the single-most effective concentration for dysphagia screening is an important observation because it improves the clinical ease and feasibility of HCT by reducing the need to prepare, transport, and administer multiple capsaicin intensities.“
“Using portable, affordable, and commercially available equipment, the HCT is a clinically feasible tool valid for cough assessment, dysphagia screening, and potentially identifying people at risk of aspiration pneumonia.” p.7
Because authors Mir & Hegland also understand you and me live in the real world full of productivity requirements, lack of time, materials, funding, and support at times, they used a recent 2021 survey aimed at SLPs, students, & doctorates across the world to see what can be done to reduce the gap and help this idea of cough testing become a reality across clinical settings.
- While 85% participants reported they ‘clinically evaluate cough,’ the remaining stating a “lack of time, training, or others completed it“
- Most common method of cough assessment was qualitative
- perceptual judgements for voluntary cough (28%)
- during clinical swallow evaluation with PO (29%)
- during instrumentation with PO (27.6%)
- Of 655 respondents, only 11% reported use of quantitative tools, such as peak flow meteres and urge-to-cough ratings
- only 14% reported competence with interpretation of quantitative mreasures compared to 43% with qualitative measures
- 50% of clinicians reported that they received training about cough evaluation outside of their academic training, from either workshops or continuing education courses
- Almost 80% of participants reported they did not receive education/training to understand and evaluate cough mechanism during their academic experiences
- Almost 98% of respondents indicated interest in a formal cough assessment training program
- Acute care made 23% of respondents’ clinical practice setting
So what can we do with all this info?
While we don’t have a definitive way to clinically measure cough yet, at least we know what’s been studied so far, what we know is never gonna be feasible, and what just might be on the horizon. We also know that a lot of us are in the same boat just facing some different waves.
In the meantime, we can continue working together near or far, across departments, and thinking of the possibilities to continue to forge our field ahead still remains our noble and never-ending fight!
What do you currently use for assessing cough? (seriously, I wanna know!!)
Have you worked with other colleagues or departments to improve or initiate changes in this area??
Are there certain patient populations you might be assessing cough more in???
Watts, Tabor, & Plowman, (2016). To Cough or Not to Cough? Examining the Potential Utility of Cough Testing in the Clinical Evaluation of Swallowing. Current Physical Medicine And Rehabilitation Reports, 4(4), 262-276. doi: 10.1007/s40141-016-0134-5 [FREE ACCESS]
Curtis, & Troche (2020). Handheld Cough Testing: A Novel Tool for Cough Assessment and Dysphagia Screening. Dysphagia, 35(6), 993-1000. doi: 10.1007/s00455-020-10097-z
Mir & Hegland. (2021). A Survey of Speech-Language Pathologists’ Experience With Clinical Cough Assessment. Retrieved 9 June 2022, from https://pubs.asha.org/doi/10.1044/2021_PERSP-21-00144 [FREE ACCESS]