As a scientist working in dysphagia rehabilitation, I frequently receive inquiries both from clinicians and the public regarding surface EMG biofeedback (sEMG). These inquiries suggest that sEMG is confused with an emerging technology, electrical stimulation (E-stim). The ASHA Leader has reported about E-stim for dysphagia, and controversies surrounding its adoption in clinical settings prior to the availability of empirical research to support and guide its utilization (Humbert & Ludlow, 2004, March 16; Sullivan, 2004, April 13).
Biofeedback refers to the use of equipment to measure body functions that are not monitored consciously. These measurements are displayed as a signal that clients can learn to manipulate, allowing them to develop control over the corresponding body functions. Biofeedback has been widely used in physical therapy, psychiatry, and medical settings for management of functions such as hypertension, anxiety, pain, and incontinence. A familiar example to most speech-language pathologists is the use of a Visipitch to display vocal functions (e.g., pitch and intensity). Clients gain improved vocal control through vocal exercises guided by the Visipitch display.
Electromyography (EMG), which displays activity from the muscles involved in swallowing, has been proposed as a tool for swallowing rehabilitation. Previous studies demonstrate a linear relationship between the force of muscle contraction and the amplitude of an EMG signal. Bryant (1991) first reported the use of sEMG in treatment of a client with dysphagia secondary to head and neck cancer. Bryant measured the collective activity of a group of floor-of-mouth muscles (mylohyoid, anterior belly digastric, and stylohyoid) using electrodes placed under the chin. These muscles contract in a stereotypic sequence during swallowing and are involved in the biomechanics of hyolaryngeal excursion. Bryant proposed that visual monitoring of the sEMG signal could be used to guide performance of effortful swallows and the Mendelsohn maneuver.
After nine weeks and 27 sessions of treatment, the client's swallowing had improved and she was able to resume functional oral intake. Note that the biofeedback was used only to enhance learning and performance of exercises that are already accepted in our clinical inventory. Additional details on using sEMG biofeedback in dysphagia therapy can be found in a tutorial by Crary and Groher (2000).
Case Series Reports
Our literature contains three case series reports, in which sEMG biofeedback was used to treat severe pharyngeal phase dysphagia secondary to stroke, head, and neck cancer or brainstem injury (M.A. Crary, 1995, 1997; Huckabee & Cannito, 1999). These articles, originating from two independent laboratories, show remarkable agreement in reported results. In all cases, clients with long-standing dysphagia underwent a short course of 10-15 sessions of swallowing treatment, delivered on an intensive schedule (5-15 days). Swallowing maneuvers (e.g., effortful swallow and Mendelsohn maneuver) were taught and practiced repeatedly under sEMG guidance, either on dry swallows or with a bolus. Reported outcomes included a return to functional oral intake in the majority of clients.
These reports suggest that positive treatment outcomes result from the techniques used. Did these clients improve simply because swallowing maneuvers were practiced repeatedly in a concentrated block of treatment sessions? Was the schedule important for the observed outcomes? Or was the fact that these exercises were practiced under guidance of a biofeedback signal crucial to the results? These questions are the subject of continuing research.
Meanwhile, however, evidence appears adequate to suggest that clinicians should consider using biofeedback to assist their clients in learning and performing swallowing exercises. A few words of caution are necessary. First, note that the amplitude of submental sEMG is influenced by the amount of cutaneous tissue between the surface of the neck and the underlying muscles; this will dampen the sEMG signal to different degrees from person to person. Consequently, there are no norms for submental sEMG activity and variation in the signal can only be interpreted within the individual client. Second, because electrode placement may differ slightly from day to day, comparison of sEMG amplitudes across sessions is not advised. This means that the sEMG signal itself is not sensitive to the effectiveness of swallowing therapy.
The signal can be used within a session to provide the client with performance-contingent information regarding the quality of an attempted swallowing maneuver, but it does not measure swallowing function. To do this, other instrumental forms of swallowing assessment must be used. Finally, the sEMG signal does nothing to directly intervene with the function of the swallowing musculature, and there is no transmission of electrical current into the client's body as in E-Stim. Rather, familiar swallowing exercises are practiced under the guidance of a signal that provides information regarding their execution. It offers both the client and the clinician a means for online evaluation and shaping of those maneuvers.
At the University of Toronto, we are collaborating with Maggie-Lee Huckabee on a multi-site randomized study of swallowing treatment outcomes using sEMG biofeedback for clients with chronic dysphagia post-stroke. We also conduct controlled case studies in individual clients with dysphagia of other etiologies. In all cases, specific swallowing exercises are selected to target physiological deficits observed in a pre-treatment videofluoroscopy. Treatment outcomes are measured through comparison of pre- and post-treatment videofluoroscopies.
We continue to lack specific knowledge regarding the ideal duration and intensity of treatment, or the minimum number of sEMG biofeedback-guided sessions that are necessary for clients to acquire the necessary skills to execute swallowing maneuvers properly. However, our clients tell us that they find the signal beneficial for learning and helpful in motivating them to practice their swallowing exercises.