The use of electrical stimulation (ES) to aid dysphagia has gained increasing attention within clinical and research arenas of speech-language pathology. With recent advances in technology, the use of ES is becoming more widely available to speech-language pathologists and may be incorporated as a tool in dysphagia rehabilitation along with behavioral therapy in the future.

Electrical stimulation is most effective when applied to an intact system of nerves and muscles in patients who have lost the central nervous system control of movement due to brain injury. When ES is applied to the nerve endings in the muscle or to nerves innervating the muscles to produce muscle contractions, it is referred to as neuromuscular stimulation. When ES is applied to the skin (surface stimulation), it will activate sensory fibers in the skin and only those muscles immediately below the skin surface, if enough intensity is applied. Most applications use electrodes inserted into the muscles (intramuscular) and an indwelling controller like a pacemaker to provide the stimulation either under patient or automatic control. Neuromuscular stimulation is used in rehabilitation of patients with spinal cord injury to control hand movements and bladder function, and is now being developed for sleep apnea and dysphagia (Grill et al., 2001).

Dysphagia as a result of brain disorders may be alleviated by direct stimulation of the muscles that are no longer receiving the correct signals from the brain. When the patient can no longer produce the muscle activity necessary to elevate the larynx, for example, ES could control muscles to produce movements that the patient cannot control. Intramuscular stimulation using electrodes inserted into these muscles has been shown to produce laryngeal elevation similar to that which occurs during normal swallowing (Burnett et al., 2003). On the other hand, electrical stimulation over the surface of the skin will provide stimulation of the skin but has not been shown to elicit movement to control laryngeal elevation (Freed et al., 2001).

Research Underway

Researchers of the Laryngeal and Speech Section of the National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH) are conducting experimental studies of ES for swallowing disorders. The goal of this study is to determine the feasibility of using extrinsic laryngeal muscle stimulation to elevate the larynx in a manner that occurs during normal swallowing in patients with chronic dysphagia. This research also will determine whether laryngeal elevation will assist with opening the upper esophageal sphincter for entry of the bolus into the esophagus. The studies are comparing the physiological effects of both surface and intramuscular stimulation in both normal volunteers and patients with dysphagia.

This research, "Feasibility of Neuromuscular Stimulation for Laryngeal Elevation During Swallowing" (99-N-0178), includes studies in both normal volunteers and patients with chronic pharyngeal dysphagia (six months post onset) who are at risk of aspiration. The outcome of this study will be relevant to future use of ES for treatment of patients with pharyngeal dysphagia. Normal volunteers and patients are being evaluated using (intramuscular and surface) stimulation of extrinsic laryngeal muscles to determine if neuromuscular stimulation in dysphagic patients will reduce aspiration during swallowing in persons with delayed onset of laryngeal elevation, reduced extent of laryngeal elevation, and/or reduced opening of the upper esophageal sphincter for clearance of the bolus from the airway during swallowing. This study will lead to the overall goal of developing a laryngeal neuromuscular prosthesis, with implantable electrodes and a controller that can be triggered by a button press to deliver stimulation to the muscles to aid in laryngeal elevation during swallowing.

Previous laboratory studies have demonstrated that an implanted laryngeal neuromuscular prosthesis is stable, remains functional for at least 1.5 years, and causes limited tissue injury (Ludlow et al., 2000). In addition, CT scanning showed three-dimensional shaping of the airway with intramuscular stimulation (Ludlow et al., 1999).

Previous clinical studies conducted by the NINDS Laryngeal and Speech Section have demonstrated that intramuscular stimulation can be used for several applications: to open the airway to potentially improve breathing in patients with obstructive sleep apnea (Mann et al., 2002), to provide vocal fold closure and reduce voice breaks in patients with abductor spasmodic dysphonia (Bidus et al., 2000), and to elevate the larynx for swallowing. When intramuscular stimulation for mylohyoid, thyrohyoid, and geniohyoid muscle regions was used in normal volunteers, it was found that muscles stimulated in pairs resulted in approximately 50% of the elevation and approximately 80% of the velocity produced during a swallow (Burnett et al., 2003).

Currently, the NINDS Laryngeal and Speech Section is recruiting up to 50 patients between the ages of 18-80 with chronic pharyngeal dysphagia secondary to neurological deficit (i.e., stroke, traumatic brain injury, Parkinson's disease, multiple sclerosis). The screening procedure for patient recruitment will include records review of previous history. Examinations to be administered at the NIH include swallowing function studies, tests of laryngeal sensation, cognitive screening, and training on coordination of button press (for stimulation) with the onset of a swallow. Patients who qualify will undergo intramuscular and surface stimulation to evaluate reduced risk of aspiration during swallowing.

To refer patients or be considered as a normal volunteer, contact Ianessa Humbert at 301-402-1109, by e-mail at humberti@ninds.nih.gov, or by mail at 10 Center Drive MSC 1416, Bldg. 10, Rm 5D-38, Bethesda, MD 20892-1416. The NIH will pay all study-related expenses and travel for the patient and an accompanying person.