Potential for Behavioural Pressure Modulation at the Upper Oesophageal Sphincter in Healthy Swallowing.

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.

Effect of Volitional Effort on Submental Surface Electromyographic Activity During Healthy Swallowing.

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.

Ultrasound: Validity of a Pocket-Sized System in the Assessment of Swallowing.

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.

Potential for Volitional Control of Resting Pressure at the Upper Oesophageal Sphincter in Healthy Individuals.

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.

Quantifying test-retest variability of natural and suppressed citric acid cough thresholds and urge to cough ratings.

INTRODUCTION: The citric acid cough reflex test (CRT) is used to quantify cough sensitivity and evaluate the effects of cough therapies and antitussive medications. This study quantifies the test-retest variability of natural and suppressed citric acid cough thresholds and urge to cough ratings in healthy individuals. METHODS: Healthy adults (n = 16) inhaled increasing concentrations of citric acid (0.01-3.2 mol/L) on three alternate days (1, 3, 5) until C2 cough thresholds (i.e. two consecutive coughs within 3 s) or the highest concentrations of citric acid was reached. Participants were instructed to "cough if you need to" in the natural cough condition, and "try not to cough" in the suppressed cough condition. Following each inhalation, participants were asked to rate their urge to cough (UTC) using a modified Borg Scale. RESULTS: Natural cough thresholds (NCTs) increased across days 1-3 (0.87 doubling concentrations, 95% CI, 0.28, 1.44, p = 0.004) and 1-5 (0.87 doubling concentrations, 95% CI, 0.33, 1.41, p = 0.004). Suppressed cough thresholds (SCTs) increased across days 1-5 (0.64 doubling concentrations per day, 95% CI, 0.03, 1.22, p = 0.04). After taking the effect of day into account, NCTs and SCTs varied within-participants by 0.75 (95% CI, 0.53, 0.93) and 0.78 (95% CI, 0.55,0.98) doubling concentrations respectively. UTC ratings at NCT, or SCT did not significantly increase across days 1-3 or 1-5. Sub-threshold (0.05 mol/L) UTC ratings increased across days 1-3 (-1.43 ratings per day, 95% CI, -2.31, -0.5, p = 0.005) and 1-5 (-1.71 ratings per day, 95% CI, -2.59, -0.79, p = 0.001). UTC ratings at NCT, SCT, and sub-threshold varied within-participants after taking into account the effect of day by 1.34 (95% CI, 1.03, 1.71), 1.47 (95% CI, 1.10, 1.91) and 1.20 (95% CI, 0.91, 1.50) ratings. CONCLUSIONS: Natural and suppressed cough thresholds and UTC ratings are subject to test-retest variability. These data are important for the use of citric acid CRT as an outcome measure in longitudinal cough research, as they facilitate interpretation of whether changes in citric acid cough thresholds across days reflect true changes in cough sensitivity, rather than an artefact of repeating the test.

A systematic review of methods of citric acid cough reflex testing.

INTRODUCTION: This systematic review summarises and appraises methods of citric acid cough reflex testing (CRT) documented in published literature. METHODS: Electronic databases, MEDLINE, EMBASE, CINAHL, PsychINFO, Scopus were searched up to and including 11th February 2018. Studies reporting a method of citric acid CRT, published in peer-reviewed journals in English or Spanish, were assessed for the inclusion criteria. Of the selected studies, information on the instrumentation and CRT protocol was extracted. RESULTS: A total of 129 studies were included. Instrumentation and protocols differed widely across studies. Reporting of methods of citric acid CRT was sub-standard, with many crucial methodological components omitted from published manuscripts, preventing their full replication. CONCLUSIONS: Considerable methodological variability exists for citric acid CRT in published literature. The findings suggest that caution is warranted in comparing citric acid cough thresholds across studies. Full replication of previously published methods of citric acid CRT is limited due to crucial elements of the citric acid CRT protocol being omitted from published manuscripts. These findings have implications on the use of citric acid CRT in clinical and pharmaceutical studies to evaluate the effects of antitussive medications and cough therapies.

Pharyngeal Swallowing During Wake and Sleep.

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.

A systematic review of current methodology of high resolution pharyngeal manometry with and without impedance.

PURPOSE: This systematic review appraises and summaries methodology documented in studies using high resolution pharyngeal manometry (HRM) with and without impedance technology (HRIM) in adult populations. METHODS: Four electronic databases CINAHL, EMBASE, MEDLINE, and Cochrane Library were searched up to, and including March 2017. Studies reporting pharyngeal HRM/HRIM for swallowing and/or phonatory assessment, published in peer-reviewed journals in English, German, or Spanish were assessed for the inclusion criteria. Of the selected studies, methodological aspects of data acquisition and analysis were extracted. Publications were graded based on their level of evidence and quality of methodological aspects was assessed. RESULTS: Sixty-two articles were identified eligible, from which 50 studies reported the use of HRM and 12 studies used HRIM. Of all included manuscripts, the majority utilized the ManoScan™ system (64.5%), a catheter diameter of 4.2 mm was most prevalently documented (30.6%). Most publications reported the application of topical anesthesia (53.2%). For data analysis in studies using HRM, software intrinsic to the recording system was reported most frequently (56%). A minority of the studies using HRM provided data about measurement reliability (10%). This is higher for studies using HRIM (50%). CONCLUSIONS: Considerable methodological variability exists regarding data acquisition and analysis in published studies using HRM/HRIM. Lacking reports of methodology make study replications difficult and reduce the comparability across studies. More data regarding the impact of individual methodological aspects on study outcomes are further required for the development of methodological recommendations.

Quantitative assessment of oral phase efficiency: validation of the Test of Masticating and Swallowing Solids (TOMASS).

BACKGROUND: The Test of Masticating and Swallowing Solids (TOMASS) has been developed to provide clinicians with objective data regarding the efficiency of oral phase function and solid bolus ingestion. AIMS: To determine if the TOMASS will detect changes in the oral phase of swallowing imposed by topical anaesthesia, thus providing validation of its clinical utility. METHODS & PROCEDURES: Per the standard protocol, 10 healthy participants ate one-quarter of an Arnotts SaladaTM biscuit. The number of bites per cracker, number of masticatory cycles, number of swallows and total time taken were recorded at baseline, following application of topical oral anaesthetic; this was additionally compared with a post-anaesthetic condition. Median and interquartile range (IQR) were calculated. Wilcoxon signed-rank tests were conducted to evaluate trial effect, and Friedman's tests were used to detect differences in the number of bites, number of swallows, number of chews and time taken to eat the crackers. OUTCOMES & RESULTS: Results indicated that the number of both bites and swallows did not significantly change across conditions (χ²(2) = 0.105, p = 0.949, χ²(2) = 1.357, p = 0.507); however, the number of chews for the anaesthetic condition was significantly higher when compared with the baseline (p = 0.02) and post-anaesthesia conditions (p = 0.02). Further, the durations of ingestion in the anaesthetic condition were significantly longer than the baseline (p = 0.01) and post-anaesthesia (p = 0.01) conditions. Across all measures, there were no differences between baseline and post-anaesthesia conditions. CONCLUSIONS & IMPLICATIONS: Although further exploration is required, these early data suggest the TOMASS is a sensitive measure in the evaluation of the oral-phase preparation of solid textures.

Comparison of unidirectional and circumferential manometric measures within the pharyngoesophageal segment: an exploratory study.

BACKGROUND: Notable differences have been identified between low-resolution manometry (LRM) and high-resolution manometry (HRM) in normative data. OBJECTIVE: This study aimed to investigate within-subject differences between unidirectional LRM and circumferential HRM solid-state measurement sensors in the pharyngoesophageal segment during swallowing. METHODS: Ten healthy subjects (mean 26.9 years) were evaluated with both a 2.10 mm unidirectional catheter and a 2.75 mm circumferential catheter, with randomized order of catheter placement. Unidirectional measurements were made in four directions (posterior, anterior, right-lateral, left-lateral). Pressures and durations were analyzed to compare (1) posterior to anterior and lateral recordings and (2) posterior and average-LRM measures (C-LRM) to HRM measures at same anatomical location. RESULTS: No significant differences were found in any of the measures across the four radial directions. A lower amplitude was measured in C-LRM compared to HRM for pharyngeal sensors (LRM Sensor 1: - 39.7 mmHg; Sensor 2: - 61.4 mmHg). Compared with posterior-LRM, HRM recorded higher UES pressures (- 12.8 mmHg) and longer UES relaxation durations (- 0.31 s). CONCLUSION: This exploratory study is the first to compare within-subject pressures between unidirectional LRM and circumferential HRM. Substantial differences in pharyngeal manometric measures were found, particularly with regard to UES function. This is clinically important as manometry is uniquely able to evaluate UES function and clarify differential diagnoses in patients with dysphagia.

Transcutaneous auricular vagus nerve stimulation alters cough sensitivity depending on stimulation parameters: potential implications for aspiration risk.

Background: Transcutaneous auricular vagus nerve stimulation (taVNS) is considered a safe and promising tool for limb rehabilitation after stroke, but its effect on cough has never been studied. It is known that the ear and larynx share vagal afferent pathways, suggesting that stimulating the ear with taVNS might have effects on cough sensitivity. The specific stimulation parameters used can influence outcomes. Objective: To investigate the effect of various stimulation parameters on change in cough sensitivity, compared to the reference parameter of 25 Hz stimulation at the left concha (most commonly-used parameter for stroke rehabilitation). Design, setting, and participants: Randomized, single-blind, active-controlled, eight-period cross-over design conducted March to August 2022 at a New Zealand research laboratory with 16 healthy participants. Interventions: All participants underwent eight stimulation conditions which varied by stimulation side (right ear, left ear), zone (ear canal, concha), and frequency (25 Hz, 80 Hz). Main outcome measures: Change in natural and suppressed cough threshold (from baseline to after 10 min of stimulation) assessed using a citric acid cough reflex test. Results: When compared to the reference parameter of 25 Hz stimulation at the left concha, there was a reduction in natural cough threshold of -0.16 mol/L for 80 Hz stimulation at the left canal (p = 0.004), indicating increased sensitivity. For the outcome measure of suppressed cough threshold, there was no significant effect of any of the stimulation conditions compared to the active reference. Conclusion: Since stroke patients often have cough hyposensitivity with resulting high risk of silent aspiration, using 80 Hz taVNS at the left canal may be a better choice for future stroke rehabilitation studies than the commonly used 25 Hz taVNS at the left concha. Treatment parameters should be manipulated in future sham-controlled trials to maximize any potential treatment effect of taVNS in modulating cough sensitivity. Clinical trial registration: ACTRN12623000128695.

Effects of cerebellar transcranial direct current stimulation (tDCS) on motor skill learning in swallowing.

OBJECTIVE: This study evaluated the effects of cerebellar tDCS on motor learning for swallowing. METHODS: In a double-blind RCT, 39 healthy adults received either sham, anodal tDCS, or cathodal tDCS in two sessions on two consecutive days. Following 20 min cerebellar tDCS (2 mA) or sham, they underwent swallowing skill training that targeted control of timing and magnitude of submental muscle activation during swallowing. Linear mixed models were used to identify the effects of stimulation on timing and magnitude accuracy as measured by the change in task performance for each training session, and for skill retention on days 3 and 10 post-intervention. RESULTS: Only the sham group had a reduced temporal error from baseline to all following timepoints. When compared to error changes in the sham group, changes from baseline in temporal errors were higher at all timepoints post-intervention for the anodal group, and higher at both retention assessments for the cathodal group. Amplitude errors were smaller for all conditions at all timepoints post-intervention compared to baseline. CONCLUSIONS: Cerebellar tDCS was found to inhibit temporal aspects of motor skill learning in swallowing. For the tDCS parameters used in this study, there is no support for use of tDCS to facilitate swallowing rehabilitation. Trial Registry Number (https://www.anzctr.org.au/): ACTRN12615000451505.IMPLICATIONS FOR REHABILITATIONCerebellar tDCS, in combination with motor skill training, has been demonstrated to increase motor skill learning in healthy individuals and neurologically impaired patients.In this study, cerebellar tDCS applied prior to swallowing skill training adversely affected timing measures of submental muscle activation during swallowing.In contrast to published outcomes in the corticospinal literature, both anodal and cathodal tDCS resulted in a relative inhibitory effect on motor skill learning in swallowing when compared to the sham condition.Swallowing skill training without tDCS produced increased accuracy in outcomes.

A Sensory Stimulation Protocol to Modulate Cough Sensitivity: A Randomized Controlled Trial Safety Study.

Purpose This study evaluated the safety and efficacy of a sensory stimulation protocol that was designed to modulate citric acid cough thresholds as a potential treatment for silent aspiration. Method Healthy adults (n = 24) were randomly assigned to one of three sensory stimulation groups: (a) high-intensity ultrasonically nebulized distilled water (UNDW) inhalations (1.6 ml/min); (b) low-intensity UNDW inhalations (0.5 ml/min); and (3) control, 0.9% saline inhalations (1.6 ml/min). Sensory stimulation was delivered once a day, for 4 consecutive days. Citric acid cough thresholds were determined at baseline, Day 3, and Day 5 to evaluate changes in cough sensitivity. Spirometry was undertaken before, during, and after each sensory stimulation session to monitor for bronchoconstriction. Results No participant showed evidence of bronchoconstriction during the sensory stimulation protocol. There was an interaction effect between day and group on suppressed cough thresholds, χ2(4) = 11.32, p = .02. When compared to the control group, there was a decrease in citric acid cough thresholds across Days 1-5 in the high-intensity (-1.8 doubling concentrations, 95% confidence interval [-2.88, -0.72], p = .01) and low-intensity (-1.3 doubling concentrations, 95% confidence interval [-2.4, -0.2], p = .03) UNDW inhalation groups, representing a sensitization effect of UNDW inhalations on cough sensitivity. Conclusions The UNDW sensory stimulation protocol was safe in healthy adults. The findings provide preliminary evidence that UNDW inhalations sensitize laryngeal afferents related to citric acid-induced cough induction. The therapeutic potential of the UNDW sensory stimulation protocol will be explored in patients with reduced cough sensitivity who are at risk of silent aspiration and aspiration pneumonia. Plain Language Summary This study explored the safety and efficacy of a sensory stimulation protocol that was designed to modulate cough sensitivity as a potential treatment for silent aspiration. The study revealed that inhalations of nebulized distilled water were safe and increased cough sensitivity, when compared to control saline inhalations.

Effect of topical nasal anesthetic on swallowing in healthy adults: A double-blind, high-resolution manometry study.

OBJECTIVE: Topical nasal anesthetic (TNA) is used when evaluating pharyngeal swallowing with high-resolution manometry (HRM). It is unclear if desensitizing the nasal mucosa improves procedure tolerability or affects pharyngeal pressure. This study evaluated the effects of TNA on comfort and pharyngeal pressure using HRM. METHODS: A double-blinded study was conducted with 20 healthy participants ( x¯ = 27 years). Participants performed five saliva and five 10-mL swallows during two exams with ManoScan HRM ESO catheter (Medtronic, Minneapolis, MN) randomized under placebo (nonanesthetic lubricant) and anesthetized (0.4 mL of 2% viscous lidocaine hydrochloride) conditions. Comfort was rated using a 100-mm visual analog scale (VAS). Pharyngeal HRM amplitude and timing were analyzed. RESULTS: VAS ratings were similar under placebo (mean = 38.4, standard deviation [SD] = 19.92) and TNA conditions (mean = 33.78, SD = 18.9), with no significant differences between placebo and anesthetized conditions (t[19] = 1.23, P = 0.23) or tolerability at first and second procedure (t[19] = 1.38, P = 0.18). Lower maximum and mean pharyngeal pressure were found for the TNA condition when compared to placebo (dry: maximum [-15.45 mmHg, standard error (SE) = 5.06 mmHg, P = 0.021]; mean [-5.22 mmHg, SE = 1.58 mmHg, P = 0.005]), and (liquid: maximum [-14.79 mmHg, SE = 5.01 mmHg, P = 0.010]; mean [-2.79 mmHg, SE = 1.99 mmHg, P = 0.008]). CONCLUSION: This double-blind, randomized study is the first to investigate effects of TNA on tolerability and pharyngeal pressure using HRM. Results indicate TNA offered no significant difference in procedure comfort while affecting the magnitude of pharyngeal swallowing. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:1335-1339, 2018.