The Impact of Inspiratory Muscle Strength Training on Vocal Loudness in Individuals With Parkinson's Disease: A Pilot...

People with Parkinson's disease (PD) typically develop hypokinetic dysarthria with associated hypophonia, which is among the most prevalent and bothersome dysarthric symptoms of patients and caregivers. Reduced respiratory support may be related to chest wall rigidity and/or reduced respiratory muscle strength, which can negatively impact vocal intensity. Therefore, respiratory muscle strength training has been the focus of multiple studies aiming to improve loudness in PD. Inspiratory muscle strength training (IMST) has been explored, with results suggesting modest increases in vocal loudness during sustained vowel and maximum phonation time. However, it is not known whether IMST improves loudness during functionally connected speech tasks. The purpose of this study was to evaluate the effects of IMST on vocal loudness in connected speech in people with PD and hypokinetic dysarthria.

Five participants with PD and hypokinetic dysarthria were recruited to complete a 5-week IMST training protocol. Maximal inspiratory and expiratory pressures, maximum phonation duration, words per breath, acoustic measures (ie, decibels [dB], fundamental frequency, jitter, shimmer, and cepstral peak prominence [CPP]), auditory-perceptual measures (consensus auditory-perceptual evaluation of voice), and patient-reported outcomes (ie, Voice Handicap Index [VHI-10], communicative effectiveness survey [CES]) were collected before and after training. Participants were given a log to keep track of adherence to repetitions and were monitored during weekly telehealth sessions.

Post-treatment changes across acoustic, aerodynamic, and patient-reported measures demonstrated mixed but generally favorable outcomes. The maximum phonation duration task increased in 4/5 participants, with improvements up to +13.4 seconds. In connected speech, the average vocal intensity (measured in dB) increased in 4/5 participants, ranging from +2.43 dB to +4.42 dB, with one participant showing a decrease following a COVID-related interruption. CPP improved in 3/5 participants during connected speech, and speaking rate increased in 4/5. Most participants showed decreased perceived vocal effort and improved respiratory support, reflected by reduced breath counts and gains in maximum expiratory pressures and maximum inspiratory pressures. VHI-10 scores improved in all participants, with reductions of up to 12 points, and the CES improved in 3/5 participants.

These preliminary data suggest that IMST has the potential to increase vocal loudness and improve perceived vocal quality in connected speech for those with PD and hypokinetic dysarthria. Improvements in acoustic measures suggest more consistent pitch and loudness, which may indicate less severe dysphonia. Importantly, patient-reported outcomes also reflect these objective improvements. Results of this study support our aims, yet further research is needed to determine the role IMST may have in improving loudness and dysphonia in PD in a larger cohort.