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Dysphagia imposes a substantial economic burden on global healthcare systems due to its pervasive, high-cost nature. To comprehend this burden, we must first assess dysphagia's prevalence and incidence in the general population. Existing studies on dysphagia prevalence encompass minor symptoms, while it is the severe cases that drive significant healthcare costs. We address this knowledge gap by estimating dysphagia incidence and prevalence in the New Zealand population, projecting future demographics of affected individuals. Incidence and prevalence rates of dysphagia within specific underlying medical conditions are sourced from existing literature. Median projected population estimates from Statistics New Zealand, by age, sex, and ethnicity are used to calculate dysphagia projections. Where possible, projections by age and ethnicity are provided until 2038 and projections by age and sex until 2073. In 2020, 9300 New Zealanders are estimated to have newly developed dysphagia while 1.5% of the general New Zealand population are estimated to have been living with the effects of the condition. By 2073, the number of individuals newly diagnosed annually is projected to increase to 24,500 and the prevalence of dysphagia is projected to increase to 2.6%. These results indicate that a significant number of New Zealanders are impacted by dysphagia. This number is predicted to dramatically increase in the future, mostly due to population ageing, indicating an increased burden on society and healthcare systems. Our work provides a useful starting point for countries worldwide to assess future healthcare resource demands associated with dysphagia, assisting with healthcare provision planning., (© 2024. The Author(s).)

Over the past four decades, our understanding of swallowing neural control has expanded dramatically. However, until recently, advances in rehabilitation approaches for dysphagia have not kept pace, with a persistent focussing on strengthening peripheral muscle. This approach is no doubt very appropriate for some if not many of our patients. But what if the dysphagia is not due to muscles weakness? The purpose of this clinical manuscript is to reflect on where we have been, where we are now and perhaps where we need to go in terms of our understanding of swallowing motor control and rehabilitation of motor control impairments. This compilation is presented to clinicians in the hope that suggesting approaches "outside the box" will inspire clinicians to focus their attention "inside the box" to ultimately improve rehabilitation and long-term outcomes for patients with dysphagia., (© 2022. The Author(s).)

Supratentorial structures are known to be involved in the neural control of swallowing, thus the potential for volitional manipulation of pharyngeal swallowing is of rehabilitative interest. The extent of volitional control of the upper oesophageal sphincter (UOS) during swallowing remains unclear. Prior research has shown that the UOS opening duration can be volitionally prolonged during execution of the Mendelsohn manoeuvre, which does not change the UOS opening time in isolation but the swallowing response in its entirety. This study explored the capacity of healthy adults to increase the period of pressure drop in the region of the UOS (UOS-Pdrop) during swallowing, through volitional UOS pressure modulation in the absence of altered pharyngeal pressure. The period of UOS-Pdrop was used as a proxy of UOS opening duration that is associated with a pressure decrease at the region of the UOS. Six healthy adults were seen 45 min daily for 2 weeks and for one follow-up session. During training, high-resolution manometry contour plots were provided for visual biofeedback. Participants were asked to maximally prolong the blue period on the monitor (period of UOS-Pdrop) without altering swallowing biomechanics. Performance was assessed prior to training start and following training. There was evidence within the first session for task-specific volitional prolongation of the period of UOS-Pdrop during swallowing with biofeedback; however, performance was not enhanced with further training. This may suggest that the amount to which the period of UOS-Pdrop may be prolonged is restricted in healthy individuals. The findings of this study indicate a potential of healthy adults to volitionally prolong UOS opening duration as measured by the period of pressure drop at the region of the UOS. Further research is indicated to evaluate purposeful pressure modulation intra-swallow in patient populations with UOS dysfunction to clarify if the specificity of behavioural treatment may be increased., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The effortful swallowing technique aims to compensate for or rehabilitate impaired swallowing by using maximal volitional effort to behaviorally modify aspects of swallowing physiology. Given that swallowing is a submaximal task, swallowing at submaximal levels has recently been suggested as a more task-specific therapeutic technique. The aim of this study was to investigate differences in muscle activity during minimum, regular, and maximum effort swallowing of different boluses and across different ages, with the goal of characterizing the task specificity of minimum effort and maximum effort swallowing. Forty-three healthy adults (22 female) representing four age groups (20-39, 40-59, 60-79, and 80 + years) participated in the study. They were verbally cued to swallow saliva and 5 mL water boluses using participant-determined minimum, regular, and maximum levels of effort, in randomized order. sEMG peak amplitude and duration of each swallow were measured. Linear mixed effects analyses demonstrated that compared to regular effort swallowing, maximum effort swallowing resulted in increased sEMG amplitude (p < .001) and prolonged duration (p < .001), while minimum effort swallowing resulted in decreased amplitude (p < .001) but no significant difference in duration (p = .06). These effects occurred regardless of age or bolus type. Differences in sEMG activity were smaller between regular and minimum effort swallowing than regular and maximum effort swallowing. Both increasing and decreasing volitional efforts during swallowing translate to significant modulation of muscle activity. However, regular swallowing is more similar to minimal effort swallowing. Results reinforce the concept of swallowing as a submaximal task, and provide insight into the development of sEMG biofeedback techniques for rehabilitation., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Adequate hyoid and laryngeal displacement facilitate safe and efficient swallowing. Although videofluoroscopy is commonly used for assessment of this biomechanical event, ultrasound provides benefits as a radiation-free modality for this purpose. This study investigated validity of a pocket-sized ultrasound system (Clarius™) in the assessment of hyoid and laryngeal excursion. Hyoid excursion and thyrohyoid approximation were concurrently assessed in 20 healthy adults using ultrasound and videofluoroscopy during saliva, liquid, and puree swallowing. Correlation analyses were performed to evaluate validity. There was a strong and moderate positive association between ultrasound and videofluoroscopic measurements of hyoid excursion during dry and liquid swallowing, respectively. No evidence for a significant association was found for ultrasound and videofluoroscopic measurements of hyoid excursion for puree swallowing and of thyrohyoid approximation for any bolus type. Further work towards improved validity is necessary prior to clinical transfer of the pocket-sized Clarius™ system in clinical swallowing assessment., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.)

Resting pressure at the upper oesophageal sphincter (UOS) has been reported to be susceptible to factors such as emotional stress or respiration. This exploratory study investigated the potential for behavioural modulation of UOS resting pressure in healthy adults to increase our understanding of volitional control of UOS pressure, and the potential development of rehabilitation approaches. Six healthy adults were seen one hour daily for two weeks (10 days) and for one post-training session after a training break of two weeks. Manipulation of UOS resting pressure was practised during a protocol of alternating increased and decreased pressure. A high-resolution manometry contour plot was used as a biofeedback modality. Participants were asked to explore how to achieve warmer and cooler colours (pressure increase and decrease, respectively) at the UOS resting pressure band, without changing head position or manipulating activity of other muscles. Performance was analysed prior to training start and following daily training. Participants were able to increase resting pressure following one week of practice; however, there was no evidence for purposeful pressure decrease. The increased resting pressure achieved by participants indicates a capacity for purposeful pressure modulation given intensive biofeedback training. The lack of volitional reduction in pressure may be explained by sustained pressure generation due to the intrinsic muscular characteristics of the UOS and a flooring effect in healthy subjects, in whom physiology mandates a minimum degree of resting pressure to fulfil the barrier function. Distention caused by the presence of the intraluminal catheter cannot be ruled out.

Sleep is associated with stages of relative cortical quiescence, enabling evaluation of swallowing under periods of reduced consciousness and, hence, absent volition. The aim of this study was to measure and characterize changes in the characteristics of pharyngeal swallows during sleep and wake using high-resolution manometry (HRM). Pharyngeal swallows were recorded with a ManoScan™ HRM in wake-upright, wake-supine, and sleep conditions in 20 healthy participants (mean 27 years; range 21-52). Velopharyngeal and hypopharyngeal segments were analysed separately. Contractile integral, mean peak pressure, inverse velocity of superior-to-inferior pharyngeal pressure, and time to first maximum pressure were analysed with custom-designed software. The supine-wake condition was compared to both upright-wake and sleep conditions using linear mixed effects models. No significant differences were found between supine-wake and upright-wake conditions on any measures. The mean peak pharyngeal pressure was lower during sleep than during the supine-wake condition for both the velopharynx (- 60 mmHg, standard error [SE] = 11, p < 0.001) and hypopharynx (- 59 mmHg, SE = 9, p = 0.001), as was the pharyngeal inverse velocity (- 12 ms/cm, SE = 4, p = 0.012) for the hypopharyngeal segment and the pharyngeal contractile integral (- 32 mmHg s cm, SE = 6, p < 0.001). No significant differences were found in time to the first pharyngeal maximum pressure. This study used HRM to characterize and compare pharyngeal pressures during swallowing in both wake and sleep conditions. No differences were found between upright and supine awake conditions, a finding important to pharyngeal manometric measures made during supine positioning, such as in fMRI. Higher pressures and longer time-related measures of volitional pharyngeal swallowing when awake indicate that cortical input plays an important role in modulation of pharyngeal swallowing.

Changes in morphometry of head and neck muscles have received little attention in research relative to limb muscles. While recent literature suggests that high-frequency ultrasound transducers can provide superior spatial resolution compared to that of magnetic resonance imaging (MRI), no studies have compared these imaging methods for investigating the submental muscle group. This preliminary study sought to compare ultrasound and MRI as a method of quantifying the cross-sectional area (CSA) of the submental muscle group. Measurements were taken from coronal ultrasound and MRI images in 11 healthy participants. Comparisons were limited to the anterior belly of the digastric muscle because of differences in imaging resolution. Ultrasound CSA measurements were smaller than MRI measurements (p = 0.01) by 10 % (95% CI = -18 to -2). Correlations were significant and relatively high (left: r = 0.909, p < 0.001; right: r = 0.776, p = 0.005). Ultrasound imaging has the advantages of natural participant positioning, superior clarity of muscle borders of the submental muscles, requires less acquisition time, and is a less expensive method of imaging compared to MRI. This preliminary study has shown that ultrasound is a viable imaging modality for quantitative measurements of the anterior belly of the digastric muscle and has advantages over MRI beyond cost and accessibility.

The risk of aspiration pneumonia in Parkinson's disease (PD) may be increased by sensory loss in the laryngopharynx and a reduced cough reflex. This study investigated changes in chemo- and mechanosensation with age and in PD and documented cough thresholds and cortical influences over cough. Single-breath citric acid inhalation cough challenge and flexible nasendoscopy were performed in 32 participants with idiopathic PD (mean age = 68.5 years, range = 45.8-82.5) and 16 healthy young adults (8 males, mean age = 25.1 years, range = 21.3-32.4), and 16 healthy elders (8 males, mean age = 72.8 years, range = 61.5-84.7) as controls. Individuals with PD had reduced sensation at the base of the tongue compared to age- and gender-matched counterparts (p < 0.005). All groups demonstrated lower natural cough thresholds than suppressed cough thresholds. No differences in natural cough thresholds were found across groups. Young adults demonstrated greater ability to suppress cough compared to healthy elders (p = 0.021). Tongue-base mechanosensory impairment in PD may account for vallecular residue and complaints of globus sensation. However, decreased cough response was not found to be a characteristic of PD. This study provided evidence for voluntary control of cough and the lack of decline of chemosensitivity with age or disease.

No studies have investigated within-subject variation in measures of pharyngeal pressures during swallowing across sessions. This study aimed to document the variation in pharyngeal pressures both within and across three sessions. Twenty healthy participants were recruited for three sessions. For each session, peak or nadir pressures were recorded from the upper pharynx (sensor 1), mid-pharynx (sensor 2), and upper esophageal sphincter (sensor 3) during saliva and 10-ml water bolus swallows. Variance was larger across sessions than within sessions for sensors 1 and 2 but comparable for sensor 3. For all sensors there was a high correlation between the variance across sessions and within session (r = 0.92, p < 0.0001). There were no significant order effects of session or of trial at any sensor with estimated order effects less than 2% and the estimated maximum possible change no larger than 5% for trial and no larger than 12% for session. These data offer direction for longitudinal treatment studies in which pharyngeal pressures are an outcome measurement by (1) providing a basis for power calculations, (2) estimating the likely values of any confounding order effects, and (3) providing suggestions for more reliable data analysis.

The aim of this study was to examine the effects of repeated volitional saliva swallowing on corticobulbar excitability recorded during two muscle preactivation conditions of the submental muscle group. Motor-evoked potentials (MEPs), elicited by transcranial magnetic stimulation (TMS), were assessed in ten healthy volunteers prior to and at 5, 30, 60, and 90 min after 60 volitional saliva swallows (Protocol A). To control for intrinsic fluctuations in corticobulbar excitability during this assessment period, MEPs were also recorded, on a different day, at 30-min intervals across a 2-h period (Protocol B). At each assessment, 15 MEPs were recorded during two submental muscle preactivation conditions: volitional contraction and contraction associated with the pharyngeal phase of volitional swallowing. There were no significant effects of repetitive volitional swallowing or time on MEP measures (p>0.05). We conclude that volitional saliva swallowing does not have immediate effects on the excitability of corticobulbar projections to the submental musculature during volitionally initiated swallowing motor tasks. These results provide no evidence for use-dependent potentiation of corticobulbar excitability through repetitive saliva swallowing. The lack of effects of time on mean MEP measures supports previous reports of good intrasession reliability of MEPs as a measure of corticobulbar excitability.

This prospective, cross-sectional study evaluated the impact of dysphagia on quality of life in healthy ageing and in subjects with Parkinson's disease (PD) using the Swallowing Quality of Life (SWAL-QOL) questionnaire. Sixteen healthy young adults (8 males, mean age = 25.1 years) and 16 healthy elders (8 males, mean age = 72.8 years) were recruited. Thirty-two subjects with idiopathic PD (mean age = 68.5 years) were recruited from a movement disorders clinic. The severity of PD was staged using the Hoehn and Yahr scale. Results revealed that elders experienced symptoms of dysphagia more frequently than young adults but the overall SWAL-QOL scores were not significantly different. Subjects with PD who experienced dysphagia reported greatly reduced QOL, and significant differences were found in all but one subsection of the SWAL-QOL. Disease progression detrimentally impacts QOL, with subjects in later-stage PD experiencing further reduction in the desire to eat, difficulty with food selection, and prolonged eating duration. These features, which increase with disease severity, are likely to impact negatively upon nutritional status, which is already under threat from PD-related dysphagia.

This cross-sectional study investigated the effect of bolus volume on contact pressure within the pharynx and upper esophageal sphincter (UES). Three solid-state manometric pressure sensors were placed transnasally into the pharynx and the proximal esophagus of 40 participants (gender equally represented and between the ages of 20 and 45 years). Participants completed five repetitions each of three swallowing conditions: 5-, 10-, and 20-ml water bolus swallows. Repeated-measures ANOVA revealed no significant differences in the amplitude of pharyngeal contact pressure between the three swallowing conditions (sensor 1: p = 0.627, sensor 2: p = 0.764). Similarly, for durational measures nonsignificant main effects were found at both sensor 1 (p = 0.436) and sensor 2 (p = 0.350). Significant differences were found in UES pressure between the three conditions of bolus swallows (p = 0.000), with negative pressure in the UES inversely proportionate to bolus volume. However, durational measures of UES relaxation pressure were not significantly different between all conditions (p = 0.473). This study demonstrates no significant pressure differences of amplitude and duration between swallowing conditions in the pharynx. At the level of the UES, smaller boluses generated greater negative pressure.

Parkinson's disease is associated with both swallowing and respiratory dysfunction, increasing the risk of aspiration and pneumonia. Previous studies have shown improvements in measurements of swallowing and respiration with levodopa; however, the studies are small and some studies show conflicting reports. The aim of this study was to further investigate the effect of levodopa on respiration. Ten patients with Parkinson's disease were tested "On" and "Off" levodopa. Assessments included Unified Parkinson's Disease Rating Scale (UPDRS), coordination of swallowing and respiration, timed-test of swallowing, lung function testing, and, qualitative assessment of swallowing. There was a nonsignificant trend to lower volume per swallow when "On" levodopa, significant reduction in lung function when "On" levodopa, but no difference in coordination of swallowing and respiration or qualitative assessment of swallowing. There was a significant increase in motor examination score of the UPDRS when "Off" levodopa compared to "On." There may be a reduction in efficiency of swallowing with levodopa medication without any apparent increase in risk of aspiration. These pilot data suggest that further evaluation with larger numbers of participants is justified.

This study explored the influence of two methods of effortful swallow execution on the timing of pharyngeal pressure events. Participants were asked to either emphasize or minimize tongue-to-palate contact during performance of the maneuver. Twenty healthy participants were evaluated using concurrent submental surface electromyography (sEMG), orolingual manometry, and pharyngeal manometry. Each subject performed three repetitions of three counterbalanced tasks (noneffortful dry swallows, effortful dry swallows with tongue-to-palate emphasis, and effortful dry swallows with tongue-to-palate de-emphasis). Four variables were measured: Onset Lag vs. sEMG Peak, Peak Lag vs. sEMG Peak, Total Duration, and Percent Rise Time to Peak. Compared to noneffortful swallows, the effortful swallow task elicited significantly earlier onsets and peaks of pharyngeal pressures relative to the submental sEMG peak. Total pressure event durations were greater and rise times were significantly shorter. When comparing the two methods of effortful swallow execution, a longer latency to peak proximal pharyngeal pressure was found in the tongue-to-palate emphasis condition. These results support the interpretation that the effortful swallow maneuver involves generation of higher velocity bolus driving forces that propel the bolus into and through the pharynx with greater efficiency and that pressure is then sustained to facilitate more complete bolus clearance.

This study provides the first documented report of the maturation of breathing-swallowing coordination during feeding in ten healthy term human infants through the first year of life. A total of 15,073 swallows were obtained across ten assessments between 48 h and 12 months of age. Midexpiratory swallows represented the dominant pattern of breathing-swallowing coordination within the first 48 h (mean = 45.4%), but the prevalence of this pattern declined rapidly in the first week to 29.1% (p = 0.012). Inspiratory-expiratory swallows increased with age (p < 0.001), particularly between 9 (37.0%) and 12 months (50.4%). Between 72.6% and 75.0% of swallows were followed by expiration in the latter 6 months, which is an adult-like characteristic. These data suggest that while postswallow expiration is a robust feature of breathing-swallowing coordination from birth, two major shifts in the precise patterns occur: the first after 1 week of postnatal feeding experience and the second between 6 and 12 months, most likely due to neural and anatomical maturation.

The effect of effortful swallow on pharyngeal pressure and UES relaxation onsets and durations was examined. Eighteen adults, nine males and nine females (mean age=27.9 yr), participated. Timing of pharyngeal pressure and onset and duration of UES relaxation were measured across ten trials of normal and ten trials of effortful swallows. Results revealed that manometric timing measurements are consistent across trials. The first and second statistical analyses investigated the pharyngeal pressure and UES relaxation onsets and durations, respectively. Both analyses identified a significant interaction of swallow type (i.e., effortful vs. normal) by manometric sensor location (p<0.05). Across normal and effortful swallows, UES relaxation preceded pharyngeal pressure onsets, yet the rate of change (or degree of delay) varied across the sensors. Furthermore, the effortful swallow elicited longer pharyngeal pressure and UES relaxation durations, yet the pressure duration measured in the upper pharynx was significantly longer than that measured lower in the pharynx. These findings offer insight as to the potential positive and negative influence of the effortful swallow on pharyngeal timing.