Radiation therapy for head and neck cancer (HNC) is associated with the development of swallowing difficulties, or dysphagia. Dysphagia has profound negative effects on the health, nutritional status, and quality of life of HNC survivors. It also puts them at risk of developing life-threatening aspiration pneumonia. Radiation-associated dysphagia can be intractable and not responsive to conventional dysphagia therapy. HNC survivors with chronic severe dysphagia may be dependent on long-term tube feeding.

Expiratory Muscle Strength Training (EMST) is a low-cost, device-driven therapy. It has been studied as an approach to simultaneously improve cough and swallowing functions. During EMST, patients forcefully expire into a one-way spring-loaded valve to strengthen expiratory and submental musculature. The EMST-150 device is available for clinical use in Singapore. In other research studies, it has been shown to improve cough and swallowing in several populations of people with chronic dysphagia, most recently in people with chronic radiation-associated dysphagia.

The investigators propose to study the effect of EMST using the EMST-150 device on cough, airway protection, and swallowing functions of HNC survivors with radiation-associated dysphagia.

The investigators will recruit 40 participants to undergo an 8-week EMST programme, with weekly follow-up to calibrate their EMST device. It is hypothesised that EMST will improve participants' respiratory and swallowing functions. Respiratory function improvement will be shown by increased maximum expiratory pressure and improved cough airflow measures. Swallowing function improvement will be evidenced by reduced aspiration or improved ability to clear aspirated material during videofluoroscopic swallow studies. The investigators also hypothesize carryover effects on other aspects of swallowing, such as improved hyoid and laryngeal excursions, and improved laryngeal vestibule closure.

With the results of this study, the investigators aim to develop better evidence-based rehabilitation programmes for HNC survivors, and those living with chronic dysphagia.

Inclusion criteria

• Chronic dysphagia involving the pharyngeal phase of swallowing for at least 6 months
• Undergone radiation therapy for head and neck cancer
• Penetration and/or aspiration seen on previous clinical videofluoroscopy swallow study (Penetration-Aspiration Scale score of 2 to 8)
• Failure to respond to traditional dysphagia therapy, as indicated by no improvement or only an improvement of 1 point on the Functional Oral Intake Scale, over a period of at least 4 sessions of conventional dysphagia therapy.

Exclusion criteria

• Current pneumothorax
• Severe trismus impeding insertion of rubber mouthpiece into the mouth (as part of treatment protocol)

Patients who have "perforated tympanic membrane", "history of spontaneous pneumothorax" and "history of collapsed lung", will be considered on a case-by-case basis, depending on the stability of their condition. Permission from their primary team doctors, or ENT for tympanic membrane issues, will be sought prior to enrolment into the study. These participants will only be deemed suitable for the study if their primary team doctors, ENT or respiratory doctors agree that they are stable or fully recovered, and that doing EMST will not worsen these conditions. For these patient groups, permission from the patients' primary team doctors, ENT or Respiratory Doctors will be obtained via email. Participants will not be enrolled if there is no written consent indicating approval for subject to be enrolled.