Defining dysphagia—it sounds easy, doesn't it? That's what I thought until my close friend and colleague in neurology, Anne Foundas, asked me to determine the number of individuals with stroke who had acute dysphagia at one month. I knew dysphagia when I saw it; surely as a clinician who specialized in deglutitive disorders, I could easily and objectively determine dysphagia. Well...wrong. This discovery sent me into a great funk, and I went into analysis with my shrink, Jay Rosenbek.
I explained to Anne that determining dysphagia depended on what we were measuring—for example, transfer through the oral cavity and pharynx, distance or duration of structural movement, post-swallow residual, or airway invasion.
As individuals normally age, I told her, swallowing changes. For example, material moves more slowly in the oral cavity and pharynx (Tracy et al., 1989). In addition, the extent and duration of structural movement decrease (Logemann, Pauloski, Rademaker, Colangelo, Kahrilas, & Smith, 2000), and incidents of airway invasion increase (McCullough, Rosenbek, Wertz, Suiter, & McCoy, 2007). So we would need to consider these factors when distinguishing between individuals with stroke (most of whom were over 60 years old) who had and did not have dysphagia.
Why should determining dysphagia be so complex? Anne asked if we could determine dysphagia based simply on treatment recommendations. Certainly individuals with dysphagia would receive compensatory and/or rehabilitative treatment strategies; diet would be modified, especially for those with a "functional" impairment in swallowing. What sounds like a reliable way to determine dysphagia, however, is not. Some clinicians may be overly conservative and recommend diet changes with most individuals who have impaired swallowing; this situation may be particularly true with new clinicians. Other clinicians, especially those with more experience, may have a greater threshold with respect to recommending diet changes. The use of treatment as an indicator of determining dysphagia is again based on clinicians' biases, with some clinicians regularly placing patients in a rehabilitation program, some monitoring patients, and others completing the evaluation with no further follow-up. Hence, these two measures are not consistent or objective.
With our study as reported in the February issue of the American Journal of Speech-Language Pathology (Daniels et al., 2009), we chose to identify individuals with dysphagia based on the results of multiple objective measures compared to an evaluation of these same measures in healthy age-matched adults. We targeted bolus flow of various liquid volumes and measured timing (oral transit time, stage transit duration, pharyngeal response time), post-swallow residual in the valleculae and pyriform sinus, and airway invasion as measured by the Penetration-Aspiration Scale (Rosenbek, Robbins, Roecker, Coyle, & Wood, 1996). The metric of two standard deviations above the mean for each measure in the control group was used to determine dysfunction. Our findings suggest that abnormality on more than one measure across multiple volumes, especially larger volumes such as 10 and 20 ml of liquid, appears to be a robust way to distinguish between healthy adults and individuals with stroke with and without dysphagia. Of course, swallowing assessments should start with smaller volumes (e.g., 3–5 ml), and work up from there if no signs of aspiration are detected.
Does this mean that we have come up with the definitive standard for determining dysphagia? The answer is no. Other measures such as the extent and duration of structural measures were not included. Only liquid volumes were used to identify dysphagia in this study. The patient's complaints or concerns of dysphagia were not evaluated. We did not calculate dysphagia severity. Yet, our approach represents a shift in thinking. We have developed a method that integrates findings from multiple measures and volumes to determine dysphagia objectively. Equally important, we used findings from healthy adults to identify dysphagia in our individuals with stroke.
Given that changes in swallowing occur with increasing age and diseases that impact deglutition are associated with aging, whatever standard a clinician uses must account for normal age-related variations when determining dysphagia. Over-identification and under-identification of dysphagia have a tremendous impact on our health care system.
The more I learn, the less I really know. Isn't that true in almost everything, especially research? For clinicians interested in research, the first step is just asking a very simple question. A great place to start the process is at the Dysphagia Research Society's annual meeting. The meeting for 2010 will be held March 3–6 in San Diego.