This study obtained approval from the relevant Human Research Ethics Committees. The trial was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR).
Thirty-four adults who attended an Australian hospital with a diagnosis of Parkinson’s and who self-reported a difficulty with drooling were screened to participate in the research study. Seven declined to participate due to the time commitment required.
Participants were eligible to participate if they had a confirmed a diagnosis of Parkinson’s according to the UK Parkinson’s Disease Society Brain Bank Diagnostic Criteria .
Exclusion criteria were an inability to understand written or spoken English, evidence of cognitive impairment as indicated by a score of 17 or below on the Mini-Mental State Examination , botulinum toxin injections for drooling within the previous 8 months, and/or co-existing diagnosis that was likely to impact on sialorrhea or swallowing. Medical clearance was obtained from the participants’ doctors in order to rule out likely contra-indications for EMST. These included a recent history of broken ribs, pregnancy, untreated hypertension, untreated gastro-oesophageal reflux, severe asthma and acute stroke. Six participants were excluded.
Twenty-one participants consented to take part in the study. Five participants did not complete the study (24%). Two passed away, one became too unwell and two decided they no longer wished to participate. The results presented are of the remaining 16 participants.
The participants were predominantly male (1 female) consistent with a higher prevalence of Parkinson’s in the male population . Participants ranged in age from 63 to 91 years. Time since diagnosis ranged from 2 to 15 years. The Levodopa Equivalent dose ranged from 188 to 1000 mg/day. Further demographic data are provided in Table 1.
This study comprised three components. The first component (A) involved four pre-training assessment sessions which were completed over 1 to 2 weeks. The second component (B) constituted the intervention period, during which participants completed 30 sessions of EMST over 6 to 8 weeks. Each week, training comprised two supervised sessions (face to face with a speech pathologist) and three sessions at home (unsupervised). The third component (C) involved two post-training assessment sessions which were completed over the first week immediately following completion of component B.
The primary experimental measure, the Sialorrhea Clinical Scale for Parkinson’s Disease (SCS-PD) , was used to measure the severity of sialorrhea. During component A, to obtain a double baseline for this measure, the SCS-PD was completed twice, 1 week apart. It was collected once following training. This questionnaire has been found to be valid and reliable . Higher scores on the SCS-PD represent worse drooling.
The Mann Assessment of Swallowing Ability (MASA)  was used to assess severity of swallowing function and the Swallowing Quality of Life Questionnaire (SWAL-QOL)  was used to assess health-related quality of life (HRQoL) associated with swallowing. During component A, to obtain a double baseline for this measure, the MASA was completed twice, 1 week apart. The SWAL-QOL was assessed once prior to training. The MASA and SWAL-QOL were collected once following training. These assessments are reliable, valid and responsive [23,24,25,26]. Lower scores on the MASA and the SWAL-QOL represent greater difficulty with swallowing and impact on HRQoL.
Lip strength measures were collected using the Iowa oral performance instrument (IOPI Medical LLC, Washington, USA). Peak expiratory flow was measured during a cough manoeuvre using a hand-held flow meter (EasyOne spirometer, NDD Medical Technologies, Massachusetts, USA). During component A, measures of lip strength and peak cough flow were collected during four sessions, each separated by ≥ 24 h. During each assessment session, participants were asked to perform 10 efforts for each measure. The best measure that was within 10% of at least two others was recorded as the result for that assessment session. Lip strength and peak cough flow were collected once following training.
On study completion, participants were asked to rate the level of satisfaction with the training. The rating was based on a 10-point scale ranging from completely unsatisfied (0) to completely satisfied (10). Adverse effects reported by participants were also recorded.
During each session, EMST was conducted using a threshold loading device (EMST 150 device, Aspire Respiratory Products, North Carolina, USA). Prescription of the initial load was based on the principles of resistance training for adults described in the position stand by the American College of Sports Medicine . Specifically, it is recommended that older adults (and otherwise sedentary people) commence resistance exercise at loads equivalent to 40 to 50% of maximum. Hence for the initial training session, we aimed to have participants reach a load equivalent to 50% of the peak pressure that could be generated (by their expiratory muscles). This approach has been shown to be feasible in an earlier randomised control trial of inspiratory muscle training in people with chronic obstructive pulmonary disease . Thereafter, training loads were titrated according to symptoms. Although it is possible that higher training loads could have been tolerated and produced greater gains, this may have compromised their satisfaction with the training programme.
Participants performed the EMST in a seated position. Only one participant required a nose clip for the first two face-to-face therapy sessions to prevent leakage of air through the nose. All participants were instructed to breathe at their usual rate and depth. An interval-based training approach was used to optimise the training load that could be tolerated . Specifically, participants were asked to breathe with a single forced expiration, followed by a 15-s rest. This was repeated 25 times with a one-minute rest every five breaths. At the end of each five breath work interval, participants were asked to rate their perceived exertion, using the 0 to 10 Borg category ratio scale . Training loads were progressed as quickly as possible with the goal of having the load during the final two-minute work interval perceived as ‘very hard’ (7/10 on the Borg scale) with participants unable to consistently maintain lip closure during their last few expiratory efforts.
For measures that were collected multiple times during component A, one-way repeated measures analysis of variances (ANOVAs) were used as has been used in similarly designed research studies (for example see ). If the assumption of sphericity was violated, the Huynh–Feldt Epsilon adjustment was applied. For outcomes that were assessed once during component A, paired t-tests were used to compare the pre- and post-training measures.