Our understanding of the neural control of breathing-swallowing coordination (BSC) is largely unclear. Although brainstem control is undoubtedly predominant, this research investigated the hypothesis that the cortex becomes increasingly influential in BSC between birth and adulthood. The main paradigm used to test this primary hypothesis was a comparison of BSC in conditions along a continuum of volitional through non-volitional swallowing on the basis of a decreasing level of cortical activation along this continuum. Voluntarily-initiated swallows during wakefulness were at one end of the continuum and reflexively-initiated swallows during sleep were at the other extreme. Non-volitional wakeful swallows were considered between these two conditions. The BSC of ten infants between birth and 1 year of age and twenty adults between the ages of 20 and 75 years was recorded using non-invasive time-locked recording methods. In order to apply the 'continuum-of-volition' paradigm to swallowing conditions in infants, BSC was monitored during nutritive (breast- or bottle-feeding), non-nutritive wake, and sleep swallows. Infants were monitored longitudinally to determine whether maturation of the cortex and corticobulbar tracts during the first year of life influenced the patterns of BSC. In adults, BSC was monitored during three non-nutritive conditions: volitional, spontaneous wake, and sleep conditions. Post-swallow expiration was found to be predominant in all conditions for all participants at all ages. In addition, the infant results revealed that nutritive BSC matured during the first year of life and differed to non-nutritive wakeful BSC, particularly in the first 2 months of life. Non-nutritive wakeful and sleep BSC did not differ from one another. In summary, the infant results support increasing cortical input into volitional nutritive BSC, an early impact of feeding on BSC, and no difference between BSC when asleep and non-volitional non-nutritive swallows when awake. The results obtained from adults revealed that irrespective of the level of arousal, volitional BSC is different to non-volitional BSC. These results imply that cortical influence on BSC is limited to conditions in which swallowing is voluntarily initiated. The combined interpretation of infant and adult results suggest that cortical influence over BSC, although increasing with maturation, is limited to the volitional swallowing conditions of feeding in infants and during non-nutritive but volitional swallows in adults. From this, it can be deduced that the most likely cortical sites involved in BSC are those involved in the voluntary initiation or planning of swallowing. Infant and adult swallowing apnoea duration (SAD) was also compared across all of the above conditions. SAD was influenced by feeding throughout the first year of life but was not influenced by level of arousal at any stage in the first year or in adulthood. Also, SAD did not change with age in any swallowing condition during infancy. However, comparison of non-nutritive wake SAD across the lifespan revealed that SAD of newborns and young adults is shorter than that of elderly adults, with no difference between consecutive age-groups: newborns, one-year-olds, and young adults. These results suggest SAD is largely mature at birth and impervious to descending suprabulbar influence. Finally, the effects of volitional swallowing and level of arousal on peak submental surface electromyography (SEMG) was investigated in adults. Like BSC, submental muscle activity was influenced only by volitional swallowing, being longer for volitional than non-volitional swallows without being influenced by level of arousal. Since peak submental SEMG activity represents a measure of relative hyolaryngeal excursion, these results suggest that the cortex has some degree of influence over this particular feature of pharyngeal-stage swallowing.

Safe and efficient swallowing requires integrity of both motor and sensory systems. Prior studies have established that motor impairment in individuals with PD frequently manifests as abnormalities in swallowing biomechanics. In contrast, very few studies have investigated the contribution of sensory impairment towards pharyngeal biomechanics and airway protection in this patient cohort. This area should be addressed in light of evidence that the severity of limb motor dysfunction in PD does not reliably predict severity of dysphagia. Emerging data suggests that dysphagia in PD cannot be solely attributed to motor impairment, but may also be influenced by deficits in sensory aspects of airway protection. As an example, silent aspiration in up to 100% has been reported in individuals with PD due to laryngopharyngeal sensory deficits have. Even so, current research lacks information on the integration of both motor and sensory components that make up the swallowing process. The aim of this study was to document changes in airway protection with age, in PD and across severity levels of PD. The project was comprised of two parts. In part one, three parallel studies were conducted to assess a series of both motor and sensory airway mechanism (Chapters 4 to 9). In the first study, 16 young (8 males, age range 21.3 - 32.4) and 16 elder adults (8 males, age range 61.5 - 84.7), were assessed to investigate changes in airway protection that accompany ageing. In the second study, data from individuals diagnosed with PD across severity levels (Hoehn-Yahr 1 - 4, age range 64.2 - 84.5) were age and gender-matched to 16 healthy elders in order to examine the effects of PD on airway protection. In the third, the impact of disease severity was studied with data from 16 individuals in the earlier stages (Hoehn-Yahr ≤ 2, 13 males, age range 51.3 - 82.5, ) compared to 16 individuals in the later stages (Hoehn-Yahr ≥ 2.5, 10 males, age range 61.5 - 78.9). In part two of this project, two smaller, pilot studies were completed to probe the influence of pharmacologic and behavioural treatments on airway protection mechanisms. In the first pilot study, the effect of pharmacotherapy on airway protection was investigated in 10 patients 'on' and 'off' levodopa (Chapter 10). In the second study, 5 patients were assessed before and after completing the Lee Silverman Voice Treatment (LSVT) to document effects of speech rehabilitation on airway protection (Chapter 11). Multimodality assessment elicited data from all participants on both motor and sensory components of airway protection (Chapter 3). Specifically, breathing-swallowing coordination (BSC) and swallowing apnoea (SA) were captured using simultaneous directional nasal airflow and surface electromyography (sEMG). Standard, closed-loop spirometry was used to assess pulmonary function. Swallowing biomechanics were screened using a validated timed test of swallowing efficiency and further evaluated using fibreoptic endoscopic evaluation of swallowing (FEES). Finally, chemo-sensation of the laryngopharynx was determined with the administration of the inhalation cough challenge while mechanosensation was examined using FEES. Results suggest that motor control for airway protection is reasonably robust in PD, although sensory response is impaired. The predominant pattern for swallowing respiratory coordination was mid-expiration for all participants regardless of age and disease severity (Chapter 4). Individuals with PD demonstrated a reduction in average time and volume per swallow, leading to an overall decrease in swallowing capacity (Chapter 5). No difference was found for swallowing efficiency between those in early and later stages of PD. Pulmonary function measures were not significantly different as a function of age, PD or PD severity (Chapter 6). In summary, results from motor assessments contributing to airway protection support the robustness of breathing-swallowing coordination (BSC) and pulmonary function across research groups, but identify a reduction in overall swallowing efficiency in PD. Results from sensory assessments contributing to airway protection revealed that chemosensation was not different between age groups but base of tongue mechano-sensation was diminished in individuals with PD. Natural cough thresholds did not differ between young adults and elders but when asked to stifle coughing, elders were less able to do so compared to young adults (Chapter 7). For the first time, a reduction in mechano-reception at the base of tongue was recorded in individuals with PD (Chapter 8). These patients also demonstrated increased post swallow residual (Chapter 5), which offers an explanation for the complaint of globus in this population. These assessments highlight some compromise to sensory aspects of airway protection in PD. Overall, dysphagia had a negative impact on the quality of life of individuals with PD and even more as disease severity progresses (Chapter 9). Results from part two of the study looking at the effects of therapeutic interventions on airway protection revealed some unexpected findings. In chapter 10, results showed a reduction in pulmonary function when 'on' levodopa, but no differences in swallowing efficiency, BSC, or laryngopharyngeal chemo- and mechano-reception were observed. These results suggested a reduction in pulmonary function with levodopa without any increase in risk of airway protection compromise1. Unexpectedly and documented for the first time, the percentage of post swallow inspiration increased after LSVT (Chapter 11) but as with the levodopa study, this was also not accompanied by any apparent increase in aspiration risk. An increase in submental surface electromyography (sEMG) amplitude across all 5 participants may serve as a proxy measure of improvement in hyolaryngeal excursion. Finally, participants reported an overall improvement in social functioning and communication after LSVT. In conclusion, this study provided evidence that mechano-sensory aspect of airway protection is diminished in individuals with PD, possibly compromising airway protection. Patients not only demonstrated increased residue but the lack of sensation may prevent clearing or spontaneous multiple swallows. Overall, airway protection is maintained in ageing but swallowing efficiency declines in the presence of PD. This study contributes significantly to current research efforts in PD by expanding on existing reports regarding motor aspects of airway protection. Specifically, BSC, swallowing efficiency and evaluation of biomechanics using FEES research have never before been investigated exclusively in the PD population. Finally, the chemo- and mechano-sensation evaluated in this study are an important addition to the limited evidence that sensory impairment in individuals with PD potentially compromises airway protection. Results of the present study will serve as a platform upon which future studies may compare and expand.

No description available.

Masters of Science in Medicine / The relationship between COPD and laryngopharyngeal sensitivity has not been previously determined. Limited research into the relationship between COPD and swallow function suggests that patients with COPD are at increased risk of aspiration. One possible mechanism for this is a reduction in laryngopharyngeal sensitivity (LPS). Reduced laryngopharyngeal sensitivity (LPS) has been associated with an increased risk of aspiration in pathologies such as stroke, however impaired LPS has not been examined with respect to aspiration risk in COPD. The Aims of this study were to investigate the effect of COPD on laryngopharyngeal sensation using Laryngopharyngeal Sensory Discrimination Testing (LPSDT) and to determine whether a relationship between LPS and swallow function in patients with proven COPD exists. Method: 20 patients with proven COPD and 11 control subjects underwent LPSDT utilising an air-pulse stimulator (Pentax AP4000) via a nasendoscope (Pentax FNL10AP). The threshold of laryngopharyngeal sensation was measured by the air pressure required to elicit the laryngeal adductor reflex (LAR). A number of further examinations were also completed for COPD subjects. These included respiratory function testing, self-reporting questionnaire on swallowing ability (SSQ), bedside clinical examination of swallowing (MASA) and endoscopic assessment of swallowing (EAS). Results: subjects with COPD had a significantly higher LAR threshold when compared to their normal healthy counterparts (p<0.001). Positive correlations were identified for the relationships between MASA score and EAS results for presence of laryngeal penetration / aspiration (p<0.04), vallecular residue (p<0.01) and piriform residue (p<0.01). Conclusion: Patients with COPD have significantly reduced mechanosensitivity in the laryngopharynx. Patients with COPD also have impaired swallow function characterised primarily by pharyngeal stasis. These changes may place patients with COPD at increased risk of aspiration.

Swallowing accelerometry may provide a portable and cost-effective bedside alternative to currently available instrumentation. In this study, dual-axis accelerometry signals were collected simultaneous to videofluoroscopic records from 29 pediatric participants (age 6.8 $\pm$ 4.8 years; 20 males) previously diagnosed with neurogenic dysphagia. Videofluoroscopic records were reviewed by a clinical expert to extract swallow timings and ratings. The dual-axis accelerometry signals corresponding to each identified swallow were pre-processed, segmented and trimmed prior to feature extraction from time, frequency, time-frequency and information theoretic domains. Feature space dimensionality was reduced via principal components. Using 8-fold cross-validation, 16-18 dimensions and a support vector machine classifier with an RBF kernel, an adjusted accuracy of 89.6\% $\pm$ 0.9 was achieved for the discrimination between swallows with and without airway entry. Our results suggest that dual-axis accelerometry has merit in the non-invasive detection of unsafe swallows in children and deserves further consideration as a pediatric medical device.

Swallowing accelerometry may provide a portable and cost-effective bedside alternative to currently available instrumentation. In this study, dual-axis accelerometry signals were collected simultaneous to videofluoroscopic records from 29 pediatric participants (age 6.8 $\pm$ 4.8 years; 20 males) previously diagnosed with neurogenic dysphagia. Videofluoroscopic records were reviewed by a clinical expert to extract swallow timings and ratings. The dual-axis accelerometry signals corresponding to each identified swallow were pre-processed, segmented and trimmed prior to feature extraction from time, frequency, time-frequency and information theoretic domains. Feature space dimensionality was reduced via principal components. Using 8-fold cross-validation, 16-18 dimensions and a support vector machine classifier with an RBF kernel, an adjusted accuracy of 89.6\% $\pm$ 0.9 was achieved for the discrimination between swallows with and without airway entry. Our results suggest that dual-axis accelerometry has merit in the non-invasive detection of unsafe swallows in children and deserves further consideration as a pediatric medical device.

Electrical stimulation has been a controversial treatment option for acquired dysphagia since the initial study by Freed, Freed, Chatburn, and Christian (2001). This report investigates the efficacy of electrical stimulation by addressing three issues related to the use of this technique: 1) the movement of the hyolaryngeal complex during stimulation, 2) the population(s) for which electrical stimulation is efficacious, and 3) the necessity of combining electrical stimulation with traditional treatments for the treatment to be effective. Twenty-two studies were evaluated and revealed overall positive findings for the use of electrical stimulation as a treatment technique. To further analyze the strength of these findings, the studies were evaluated for methodological limitations with regards to participant selection, treatment design, and outcome measure selection. This analysis revealed two main methodological limitations: 1) a lack of established treatment protocol which led to differences in how and with what other techniques electrical stimulation was used and 2) an absence of follow-up measures. While these factors do not appear to affect the applicability of the study findings, future research should focus developing a treatment protocol and investigating the long-term benefits of electrical stimulation treatment. / text

The works contained in this dissertation were motivated by a desire to better understand the variability of patient performance on videofluoroscopic assessments of swallowing. Specifically, the variation present in kinematic and temporal measures of swallowing was investigated in three main phases: narrative literature review, healthy swallowing, and disordered swallowing. The primary goals were to identify which factors explain (or do not explain) variation, to develop methods to control for variation and to investigate the association between swallowing physiology and swallowing impairment. The literature reviews revealed wide ranges of variation for kinematic (Chapter 2) and temporal (Chapter 3) measures of swallowing in the existing literature on healthy deglutition. The kinematics (Chapter 4) and timing (Chapter 5) of swallowing were investigated in a prospectively collected sample of young healthy participants stratified by height. One main objective was to investigate the impact of participant size on physiological parameters of swallowing. Finally, kinematic and temporal measures of swallowing were investigated in a sample of patients referred for swallowing assessment (Chapter 6) to explore associations between swallowing physiology and impairment. The findings of this dissertation make several unique contributions to the dysphagia literature. It has demonstrated that inherent variation appears to exist in physiological measures of both healthy and disordered swallowing. Further, when certain sources of variation are controlled (such as participant size), men and women do not demonstrate significant differences for any of the parameters tested. Importantly, this work has demonstrated that participant size impacts the expected extent of hyoid excursion and that this variation can be controlled through normalization of hyoid movement to internal anatomical scalars. Two temporal variables trended toward detecting functional swallowing impairment. Finally, this dissertation provides the first set of normative reference values for parameters of swallowing with an ultra-thin liquid barium. Limitations are acknowledged and future work is suggested.

The works contained in this dissertation were motivated by a desire to better understand the variability of patient performance on videofluoroscopic assessments of swallowing. Specifically, the variation present in kinematic and temporal measures of swallowing was investigated in three main phases: narrative literature review, healthy swallowing, and disordered swallowing. The primary goals were to identify which factors explain (or do not explain) variation, to develop methods to control for variation and to investigate the association between swallowing physiology and swallowing impairment. The literature reviews revealed wide ranges of variation for kinematic (Chapter 2) and temporal (Chapter 3) measures of swallowing in the existing literature on healthy deglutition. The kinematics (Chapter 4) and timing (Chapter 5) of swallowing were investigated in a prospectively collected sample of young healthy participants stratified by height. One main objective was to investigate the impact of participant size on physiological parameters of swallowing. Finally, kinematic and temporal measures of swallowing were investigated in a sample of patients referred for swallowing assessment (Chapter 6) to explore associations between swallowing physiology and impairment. The findings of this dissertation make several unique contributions to the dysphagia literature. It has demonstrated that inherent variation appears to exist in physiological measures of both healthy and disordered swallowing. Further, when certain sources of variation are controlled (such as participant size), men and women do not demonstrate significant differences for any of the parameters tested. Importantly, this work has demonstrated that participant size impacts the expected extent of hyoid excursion and that this variation can be controlled through normalization of hyoid movement to internal anatomical scalars. Two temporal variables trended toward detecting functional swallowing impairment. Finally, this dissertation provides the first set of normative reference values for parameters of swallowing with an ultra-thin liquid barium. Limitations are acknowledged and future work is suggested.

Objective: Traditionally, swallowing rehabilitation has involved the use of muscle strengthening exercises, such as the head-lift manoeuvre (Shaker et al., 1997), to strengthen the floor of mouth muscles. Clinical reasoning suggests that this particular exercise may be problematic for patients with cervical spine injuries or increased frailty. Recently, Bauer and Huckabee (2010) attempted to determine the efficacy of an alternative exercise for the floor of mouth muscles in healthy adults. The present study aims to expand on this work in a larger population of healthy adults. Study design: Controlled trial; participants matched for age and sex. Participants: 23 healthy adults with no history of neurological or muscular impairment. Method: Participants were assigned into one of two groups: jaw opening exercise (JOE; n = 12) and sham exercise (SE; n = 11). Groups were matched for age and gender. Participants performed their respective exercises three times per day, five days per week, over a six week period. At three times during this period, measures of submental 2-D cross-sectional area and anterior hyoid movement were taken via ultrasound. Additionally, measures of submental muscle myoelectrical activity were taken via surface electromyography. Pre- and post-treatment comparisons, as well as inter-group comparisons, were undertaken. Results: No significant differences were observed between groups on measures of muscle size, anterior hyoid movement, or myoelectrical activity over time. However, this study has contributed to the future development of an alternative exercise to target the submental muscle group.