Expiratory Muscle Strength Training for People With Parkinson's Disease

Participants will perform Expiratory Muscle Strength Training (EMST) using a CE-marked, calibrated handheld threshold device routinely used in clinical practice. The training protocol consists of 5 sets of 5 breaths per day, 5 days per week, for 5 weeks. Training resistance will be individually adjusted on a weekly basis according to participant performance and established EMST training recommendations.

Expiratory Muscle Strength Training (EMST) will be performed using a CE-marked, calibrated handheld threshold device that provides a fixed expiratory resistance. Participants will complete 5 sets of 5 forceful expiratory breaths per day, 5 days per week, for 5 weeks. The training load will be individually calibrated and adjusted weekly based on each participant's performance to maintain an appropriate training intensity. The intervention is designed to strengthen expiratory and submental muscles involved in respiration, phonation, speech, and swallowing.

Participants assigned to the passive control group will not receive the EMST intervention during the study period. No sham intervention will be provided. Following completion of all study assessments, including the 3-month follow-up, participants will be offered the opportunity to receive the EMST intervention.

Sound pressure level (SPL) will be assessed from audio recordings obtained in a sound-treated studio using calibrated recording equipment. Recordings will be made with a head-mounted omnidirectional microphone positioned at a fixed distance from the mouth. Speech samples will be collected using a Speech Range Profile (SRP), a two-dimensional graphical representation of vocal performance, with fundamental frequency (Hz) on the x-axis and vocal intensity (dB) on the y-axis. Participants will read a standardized text and produce spontaneous speech based on a standardized picture-sequence task. Data will be collected both at habitual speaking loudness and during exposure to white noise (70 dB) presented via headphones. SPL will be quantified in decibels [dB] and analyzed on an interval scale (minimum, maximum, and equivalent continuous sound level [Leq SPL]). Higher SPL values indicate greater vocal intensity.

Maximum phonation time (MPT) will be assessed from audio recordings obtained in a sound-treated studio using calibrated recording equipment and a head-mounted omnidirectional microphone positioned at a fixed distance from the mouth. Participants will sustain the vowel /a/ for as long as possible following a maximal inhalation. Three trials will be performed with approximately 15-second intervals between attempts. Data will be collected both at habitual speaking loudness and during exposure to white noise (70 dB) presented via headphones. MPT will be quantified in seconds [s] and analyzed on a ratio scale. The highest value obtained under each condition will be used for analysis. Higher MPT values indicate better phonatory performance, reflecting more efficient respiratory support and vocal fold function, whereas lower values may indicate reduced respiratory support and impaired vocal fold function.

Speech range (fundamental frequency, F0) will be assessed using a Speech Range Profile (SRP), a two-dimensional graphical representation of vocal performance, with fundamental frequency [Hz] on the x-axis and vocal intensity [dB] on the y-axis. Participants will read a standardized text and produce spontaneous speech based on a standardized picture-sequence task. Data will be collected both at habitual speaking loudness and during exposure to white noise (70 dB) presented via headphones. Speech range will be quantified in Hertz [Hz] and analyzed on a ratio scale (minimum, maximum, mean, modal frequency, and range in semitones). A reduced speech range indicates limited pitch variation and reduced prosodic variation during connected speech.

Phrase length will be assessed from audio recordings obtained in a sound-treated studio using calibrated recording equipment and a head-mounted omnidirectional microphone positioned at a fixed distance from the mouth. Participants will read a standardized text. Data will be collected both at habitual speaking loudness and during exposure to white noise (70 dB) presented via headphones. Phrase length will be quantified as the mean number of syllables per breath group and analyzed on a ratio scale (mean). Higher values indicate more efficient speech breathing, whereas lower values may indicate reduced speech breathing efficiency.

Maximal expiratory pressure (MEP) will be obtained using the MicroRPM respiratory pressure meter. Following a maximal inhalation, participants will exhale as forcefully as possible into the device mouthpiece. To ensure reliable measurements, the procedure will be repeated until three values within 10% of each other have been recorded. MEP will be quantified in cmH₂O and analyzed on a ratio scale. The highest value will be used for analysis. Lower MEP values indicate reduced expiratory muscle strength and impaired respiratory function, whereas higher MEP values indicate greater expiratory muscle strength and better respiratory function.

Swallowing capacity will be assessed using the Timed Water Swallow Test. Participants are instructed to drink a glass of still water as quickly and safely as possible without interruption. The time in seconds [s] from initial contact of the water with the lips to completion of the final swallow is recorded. To ensure accurate measurement, participants' mouth and neck regions are video-recorded during the assessment. Swallowing capacity is calculated by subtracting any residual volume from the initial volume and dividing the resulting volume by the recorded time. Swallowing capacity will be quantified in milliliters per second [mL/s] and analyzed on a ratio scale. Lower swallowing capacity values indicate reduced swallowing efficiency and poorer swallowing performance, whereas higher values indicate greater swallowing efficiency and better swallowing performance.

To assess participants' perceived respiratory functioning and breathing-related disability, the Dyspnea Index (DI) will be used. DI is a patient-reported outcome measure (PROM) designed to assess the severity of upper airway-related dyspnea. It consists of 10 items, each rated on a 5-point Likert scale (0-4), yielding a total score ranging from 0 to 40. Higher scores indicate more severe dyspnea symptoms and a greater impact on daily functioning and quality of life.

To assess participants' perceived voice functioning and the impact of voice problems on daily life, the Voice Handicap Index (VHI) will be administered. The VHI is a patient-reported outcome measure that evaluates the functional, physical, and emotional consequences of voice disorders. Higher scores indicate a greater perceived voice-related handicap and poorer voice functioning.

To assess participants' perceived speech functioning and communication-related difficulties, the Self-report Questionnaire on Acquired Speech Difficulties (SOFT) will be administered. The SOFT is a patient-reported outcome measure consisting of items rated on a 4-point Likert scale, yielding a mean score ranging from 0 to 3. Higher scores indicate a greater perceived impact of speech and communication difficulties on daily life.

To assess participants' perceived swallowing functioning and the impact of swallowing difficulties on daily life, the Sydney Swallow Questionnaire (SSQ) will be administered. The SSQ is a patient-reported outcome measure that assesses self-perceived swallowing difficulties using visual analogue scales, yielding a total score ranging from 0 to 1700. Higher scores indicate greater perceived swallowing impairment and swallowing-related disability.

The participant's level of functioning will be evaluated within the framework of the International Classification of Functioning, Disability and Health (ICF) using validated Therapy Outcome Measures (TOM). Likert scale, score range 0-5. Higher scores indicate better functioning, participation, and well-being, as well as reduced disability related to dysarthria.

The participant's level of functioning will be evaluated within the framework of the International Classification of Functioning, Disability and Health (ICF) using validated Therapy Outcome Measures (TOM). The participant's level of functioning will be evaluated within the framework of the International Classification of Functioning, Disability and Health (ICF) using validated Therapy Outcome Measures (TOM). Likert scale, score range 0-5. Higher scores indicate better functioning, participation, and well-being, as well as reduced disability related to dysphagia.

Measured using the International Dysphagia Diet Standardisation Initiative Functional Diet Scale (IDDSI-FDS). Ordinal scale, score range 0-7. Higher scores indicate better swallowing-related dietary function and fewer dietary restrictions.