Early on in my career, I was drawn to the wondrous world of swallowology. I have always been amazed with the intricacy of the neural muscular underpinnings of deglutition and the power of neural plasticity through rehabilitation. Evidence of improved swallow function with application of exercise physiology and neural plasticity principles has been shown in several therapies. Expiratory muscle strength training (EMST) is one of only a few swallow exercises incorporating these important principles.
EMST is categorized as respiratory muscle strength training (RMST), which also includes inspiratory muscle strength training (IMST). As the name implies, the purpose of IMST is to strengthen the muscles of inhalation with improvement in function such as weaning from mechanical ventilation1 and slowing the progression of respiratory deterioration in individuals with ALS2. For the purpose of this article, EMST will be discussed along with its utility in cough function and swallow rehabilitation.
Overview of EMST
The effects of EMST have been shown to increase the strength of respiratory muscles for improving cough, voice and swallow functions. EMST is implemented by hand-held devices, which are categorized as either resistance or pressure-threshold types. Resistance-based devices rely on exhalation through adjusting the size of an internal diameter. Decreasing the size of the diameter imposes resistance requiring increased respiratory muscle force. However, there is no threshold within the device for the user to overcome and can be used with inadequate airflow thus making it ineffective for strength-training. Furthermore, these devices are limited due to its lack of standardization3.
EMST is one of only a few dysphagia therapies incorporating principles of exercise and neural plasticity which are essential for successful rehabilitation.
Pressure-threshold devices rely on pressure exerted during expiration. The premise of this type of device for strength training is based on an imposed physiological load set by the amount of pressure 4. This calibrated device is comprised of an internal spring-loaded valve with an adjustable external dial (see picture). The pressure-threshold device allows the amount of pressure to be adjusted, ranging from 0-150 cmH205. Determination of the pressure-threshold load is based on a person’s maximum expiratory pressure (MEP), which is obtained through a pressure manometer. The threshold-load is then set to 75% of the MEP in which the load will increase with training progression.
Sufficient pressure from expiratory force must surpass the spring-loaded valve and when achieved, the valve will open and air will flow through the device. The pressure-released valve requires a consistent flow of air for the valve to remain open5. However, if there is inadequate force during expiration, the valve will stay closed and no air will flow through the device. Of note, these mechanics may serve as biofeedback to aid in accuracy during use. There are several EMST trainers available; however, the only device with proven evidence to improve swallow function is the EMST 150 (www.emst150.com), which will be discussed in further detail.
EMST and principles of exercise and neural plasticity
The goal of swallow rehabilitation is to facilitate neuromuscular plasticity for achieving long-term improvement in function by integrating exercise and neural plasticity principles. As previously mentioned, EMST is one of only a few swallow rehabilitative exercises following these principles. While there are numerous components of plasticity, EMST particularly incorporates intensity, repetition, overload, specificity, saliency and transference. These principles apply both to peripheral (muscle) and central (neural) plasticity.
As with most exercises, muscles must be challenged beyond their usual activity to promote the desired neuromuscular adaptations for improving function. The research-based EMST protocol for improving swallow and/or cough functions incorporates the intensity and repetition principles with a training duration of 4 or 5 weeks, 25 reps a day, 5 days a week. The pressure-threshold load can be increased progressively throughout the training, accounting for the overload principle. With regards to improving the cough function, the excessive force and continued airflow during exhalation into the device is salient and specific to a cough. Although EMST is a “non-swallow” exercise, evidence of transference has been shown in which respiratory strength training facilitated improvements in deglutition.
How does a respiratory exercise improve swallow function?
The utility of EMST for improving the biomechanics of deglutition was initially studied through use of surface electromyography (sEMG) and videoflouroscopy in healthy subjects. In 2007, Dr. Wheeler Hegland and her co-investigators found an increase in the duration and amplitude of the submental muscles when subjects used the EMST device compared to a swallow5. In this study, the authors reported, “expiratory pressures associated with completing an EMST task coupled with maintaining a tight lip seal around the device mouthpiece require recruitment of the submental muscle group to transfer the expiratory pressure though the upper airway and into the device5.”
In a subsequent study, hyoid displacement increased using the device compared to the swallow as shown during videoflouroscopy6. These findings led to research of EMST for swallow rehabilitation in several different etiologies.
Effects of EMST in Parkinson Disease
Pneumonia is a leading cause of mortality in people diagnosed with Parkinson Disease (PD)7 in part, due to dysphagia and inadequate cough function or dystussia8. Inadequate cough function poses a threat to the pulmonary system, decreasing the effectiveness of clearing the airway of aspirated food, liquid or secretions. The use of EMST has been shown to improve voluntary cough function following a 4 week training of EMST4. Strengthening the respiratory muscles for cough function is vital in PD to minimize the risk of aspiration and associated sequelae.
Several studies have demonstrated improvements in swallow function with EMST4,9,10. Significant decrease in penetration aspiration scale (PAS) was shown, and in some subjects, aspiration was eliminated post-training 4,9. Additionally, an increase in hyoid displacement post- training was exhibited compared to a sham group, likely due to strengthening of the submental muscles9. The clinical significance of this finding indicates EMST may improve hyoid excursion to facilitate bolus passage and reduce aspiration from possible pharyngeal retention.
The effects of EMST following detraining in people with PD have also been studied. Detraining refers to a reduction or loss of the gains achieved once the training has ceased. Following a 3-month detraining phase, some subjects demonstrated a decline in swallow function compared to post-training (at the 4-week period)10. These findings are an important contribution to the field of swallow rehabilitation elucidating the need and importance for maintenance programs to maintain treatment effects.
Effects of EMST in Stroke Population
There are emerging studies examining the effects on deglutition and airway protection using EMST in the stroke population. In a randomized controlled trial by Park et al.11, participants diagnosed with stroke were randomized to EMST or placebo. The protocol consisted of 5 reps x 5 sets, 5 days/week for 4 weeks with the EMST 150 or sham device. Pre and post measures included surface electromyography (sEMG) for analyzing muscular activity of the suprahyoids, penetration aspiration scores (PAS) and functional oral intake scores (FOIS). Following the protocol, the experimental group showed statistically significant increase in suprahyoid muscle activity, a decrease in PAS for both liquids and semisolids and an increase in FOIS. In the study by Hegland et al.8, use of EMST resulted in a significant effect on expiratory muscle strength and reflexive cough function. Initiation of the swallow and laryngeal vestibule closure demonstrated improvement post training.
How to use EMST
In addition to the device, it comes with nose clips and instructions. To use the device, first the nose clips are placed on nose, then after a deep inhalation, the mouthpiece is positioned in oral cavity maintaining a tight lip seal around the device followed by a forceful exhalation.
In order to determine the pressure-threshold load, a pressure manometer is used however many SLPs do not have this equipment available. Fortunately there is a low-tech option for implementing the training protocol with using the external dial to gauge the desired setting. Starting at the lowest setting, the dial is rotated one 1/4 turn clockwise to increase the pressure load, followed by 1 forceful exhalation through the device. The dial is progressively turned ¼ until valve fails to release with exhalation (air will not flow through). This level is considered a person’s maximum threshold. Once this level has been found, the dial is rotated one 1/4 turn counter-clockwise to reduce the load, generally equating to 75% of the maximal threshold. The 75% threshold level will then be used for the training protocol. After each week of training, this process is repeated to determine new threshold load.
From my clinical experience, some of my patients required 2 weeks of training on the same threshold load due to more significant respiratory muscle weakness. Additionally, an instructional video can be viewed through the website to help with training.
Summary and considerations
Swallow rehabilitation with EMST has been demonstrated through multiple, high-quality controlled studies in both stroke and PD. The use of EMST as well as any other intervention requires application of evidence-based decision-making with incorporation of patient-centered goals. EMST for swallow rehabilitation or improving cough may not be suitable for all people with dysphagia or dystussia; thus instrumental swallow and/or pulmonary assessments should be conducted if possible. Patients must be educated and understand the exercise protocol to reach the desired outcomes of improving swallow and/or cough functions. The benefits of the EMST protocol include strong evidence-base, easy and quick to use and biofeedback to guide accuracy in performing the exercise. A possible obstacle with EMST is accessibility, cost and/or non-adherence with training protocol.
EMST is one of only a few dysphagia therapies incorporating principles of exercise and neural plasticity which are essential for successful rehabilitation. EMST provides SLPs with a tool for improving swallow function and airway protection. Combining EMST with other evidence-based exercises as part of a comprehensive rehabilitative regimen strengthens our arsenal to optimize safety and quality of life.
Links of Interest
- Martin AD, Smith BK, Davenport PD, Harman E, Gonzalez-Rothi RJ, Baz M, Layon AJ, Banner MJ, Caruso LJ, Deoghare H, Huang TT, Gabrielli A.(2011). Inspiratory muscle strength training improves weaning outcome in failure to wean patients: a randomized trial. Crit Care.15(2):R84.
- Cheah BC, Boland RA, Brodaty NE, Zoing MC, Jeffery SE, McKenzie DK, Kiernan MC.(2009). INSPIRATIonAL–INSPIRAtory muscle training in amyotrophic lateral sclerosis. Amyotroph Lateral Scler. 2009 Oct-Dec;10(5-6):384-92.
- Troche MS. (2015). Respiratory Muscle Strength Training for the Management of Airway Protective Deficits. Perspect Swal and Swal Dis(Dysph), 24 (2), 58-64.
- Pitts T, Bolser D, Rosenbek J, Troche M, Okun MS, Sapienza C.(2009). Impact of expiratory muscle strength training on voluntary cough and swallow function in Parkinson disease. Chest. May;135(5):1301-8.
- Wheeler KM, Chiara T, Sapienza CM.(2007). Surface electromyographic activity of the submental muscles during swallow and expiratory pressure threshold training tasks. Dysphagia. Apr;22(2):108-16.
- Wheeler-Hegland KM, Rosenbek JC, Sapienza CM.(2008). Submental sEMG and hyoid movement during Mendelsohn maneuver, effortful swallow, and expiratory muscle strength training. J Speech Lang Hear Res. Oct;51(5):1072-87.
- Wermuth L, Stenager EN, Stenager E, Boldsen J.(1995). Mortality in patients with Parkinson’s disease.Acta Neurol Scand. Jul;92(1):55-8.
- Hegland KW, Davenport PW, Brandimore AE, Singletary FF, Troche MS. (2016). Rehabilitation of Swallowing and Cough Functions FollowingStroke: AnExpiratory Muscle Strength Training Trial.Arch Phys Med Rehabil. Apr 26. pii: S0003-9993(16)30078-8.
- Troche MS, Okun MS, Rosenbek JC, Musson N, Fernandez HH, Rodriguez R, Romrell J, Pitts T, Wheeler-Hegland KM, Sapienza CM (2010). Aspiration and swallowing in Parkinson disease and rehabilitation with EMST: a randomized trial. Neurology. Nov 23;75(21):1912-9.
- Troche MS, Rosenbek JC, Okun MS, Sapienza CM.(2014) Detraining outcomes with expiratory muscle strength training in Parkinson disease. J Rehabil Res Dev. 51(2):305-10.
- Park JS, Oh DH, Chang MY, Kim KM. (2016). Effects of expiratory muscle strength training on oropharyngeal dysphagia in subacutestroke patients: a randomised controlled trial. J Oral Rehabil. May;43(5):364-72.