Biomechanical and Neurophysiological Changes Associated with Modified Head-lift and Effortful-Swallowing Rehabilitation Techniques
Thesis DisciplineSpeech and Language Sciences
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Dysphagia can result from congenital disorders, structural damage, or neurological insult, therefore affecting individuals across the lifespan. Stroke is the leading cause of acquired dysphagia, with approximately half of stroke patients experiencing some level of swallowing impairment. Dysphagia negatively impacts survival and quality of life, highlighting a need for development of innovative and effective rehabilitative techniques. Management techniques have been developed to address disorders of swallowing but these techniques typically address symptoms of dysphagia rather than physiologic deficits. These techniques are often prescribed after neurological insult with little knowledge of their cumulative effect on swallowing biomechanics and neurophysiology. Effective treatment of dysphagia can only occur with knowledge of how commonly prescribed treatments influence all sensory and motor control aspects of swallowing. Without this detailed information, researchers are at risk of disregarding effective treatments, or employing treatments that are detrimental to unexamined swallowing processes. There are many tools available for measuring change in swallowing biomechanics and neurophysiology. Many of these tools require further assessment of reliability, validity, precision, and responsiveness to assist researchers with selecting appropriate measures and adequately powering studies to detect treatment effects. A series of four methodological studies and a treatment study were undertaken as part of this research. The methodological studies aimed to contribute insights into aspects of reliability, validity, and precision assessment for the measures utilized in the treatment study. These elements together are crucial for formulating research studies aimed at providing empirical evidence for dysphagia treatment techniques. The reliability of a novel method of calculating hyoid displacement with ultrasound relative to an anatomical reference point was investigated. This pilot study assessed intra- and inter-rater reliability across three raters for data analysis of five swallows from each of five healthy participants. The results suggest that the use of an anatomical reference point can alleviate the need for complex data calibration and transformation when utilizing ultrasound to quantify anterior hyoid displacement. The utility of ultrasound to quantify the morphometry of the submental muscles was also assessed. Within-participant comparisons were made between coronal images taken with magnetic resonance imaging (MRI) and ultrasound in each of 11 healthy participants. These results suggest advantages of ultrasound over MRI, thereby endorsing the use of this less expensive and more accessible method. Reliability and precision of longitudinal measures obtained with pharyngeal manometry were evaluated across three sessions in 20 healthy participants. This is the first study to have documented within-participant order effects and variance estimates for pharyngeal pressures. The results revealed no significant order effects but relatively large within-participant variance across sessions. These findings offer considerations for the use of manometry to document treatment outcomes, as considerable effect sizes, or substantial participant samples, are needed to supersede this variance. Studies utilizing motor evoked potential (MEPs) to document effects of swallowing treatments rarely report details of data extraction or analysis. Therefore, an investigation was completed to compare various methods for quantifying MEPs from the submental muscles. This study used a pre-existing data set including five blocks of 15 MEPs from each of six healthy participants. Methods of analysis included quantification utilizing the mean of 15 individual trials, the median of 15 individual trials, the ensemble-average waveform, the ensemble-median waveform, and the rectified and averaged waveform. The most reliable onset latency measures across the five recording blocks were obtained when analysis was performed on the ensemble-median waveform. The most reliable amplitude/area values were obtained from the mean of the 15 trials and from the rectified and averaged waveform. Additionally, this study provided variance estimates across- and within-participants, providing a prompt for researchers and clinicians utilizing MEPs to consider this variance when determining desired effect sizes and sample sizes required to document evidence of treatment efficacy. Part III of this thesis reports two treatment studies which independently assessed the cumulative effects (across six weeks) of effortful-swallowing and a modified head-lift manoeuvre on swallowing biomechanics and corticobulbar excitability utilizing the measures investigated in the methodological studies. Despite the common use of these two neuromuscular exercises in the management of dysphagia, discrepancies exist regarding the long-term effects of the head-lift manoeuvre on swallowing biomechanics, with no studies addressing long-term modifications associated with effortful-swallowing. Furthermore, no studies have previously documented adaptations of corticobulbar excitability following either technique. The current study recruited 41 healthy older participants (mean age = 69 years, 20 males) who were alternately assigned to complete six weeks of either effortful-swallowing or modified head-lift exercise. Prior to initiation of the exercise protocol, baseline measures were taken using the following measurements: submental muscle MEPs induced by transcranial magnetic stimulation (TMS); oropharyngeal, hypopharyngeal, and upper esophageal sphincter (UES) pressures measured with pharyngeal manometry; submental muscle cross-sectional area (CSA) measured with ultrasonography; hyoid displacement quantified with ultrasonography; and submental muscle activation measured using surface electromyography (sEMG). For the effortful-swallowing group, the six-week exercise programme involved 33 effortful swallows, three times daily, five days a week. The number of repetitions was chosen to correspond to the head-lift manoeuvre protocol typically reported in the literature. The three daily sessions for the modified head-lift exercise involved 30 isokinetic head-lifts, and three head-lifts sustained for 30 seconds each. The isometric component was modified from the protocol recommended in previous literature, which proposes three sustained lifts for 60 seconds each. Participants completed the exercise at home and recorded their compliance on a weekly log sheet. Home visits occurred weekly to check the exercise execution and to monitor exercise maintenance. Within 2 days of concluding the exercise programme, participants returned for an outcome session consisting of the same measures as the baseline session. The results revealed no adaptations in swallowing biomechanics or corticobulbar excitability following six weeks of either exercise. This research programme provokes consideration of the limitations of many measures used in swallowing research. Many of the measures used in swallowing studies have had very little research investigating their reliability, validity, precision, and responsiveness to treatment effects. Additionally, there is inadequate documentation of the magnitude of cumulative effects of rehabilitation techniques on swallowing biomechanics and neurophysiology. As these fundamental issues regarding measures utilized in swallowing research are addressed, researchers can be more confident in selecting appropriate measures, and adequately powering studies to detect treatment effects. This process will make treatment efficacy research less exploratory, and more reliant on logical consideration of the sensitivity of measures, and the magnitude of clinically relevant or desired treatment effects. This methodical approach to research is vital to justify the prescription of dysphagia rehabilitation techniques with the aim of promoting long-term change in swallowing biomechanics and neurophysiology and, hence, functional swallowing.