BACKGROUND: Electrical stimulation therapy is effective for patients with dysphagia. However, because of the pain, strong stimulation cannot be applied. Although magnetic stimulation induces less pain, there are no reports on magnetic stimulation being synchronised with a swallowing reflex.
OBJECTIVE: This study aimed to determine whether it is possible to induce magnetic stimulation during a voluntary swallowing using electromyography (EMG)-triggered peripheral magnetic stimulation and to evaluate its effect on healthy individuals.
METHODS: A total of 20 healthy adults in seated position were instructed to swallow saliva and 10 ml of barium under videofluoroscopy. For concomitant use of magnetic stimulation, a magnetic stimulus for suprahyoid muscles at 30 Hz frequency was applied for 2 s when the EMG level in the sternohyoid muscle exceeded the threshold. During the voluntary swallowing, the movement of the hyoid bone and opening width of the upper oesophageal sphincter (UES) were measured. Furthermore, pressure topography was evaluated in 6 subjects using high-resolution manometry.
RESULTS: The magnetic stimulation significantly extended the movement time of the hyoid bone (p < 0.001). During liquid deglutition, significant increases were observed in the anterior maximum movement distance of the hyoid bone (p < 0.05), opening width of the UES (p < 0.001) and anterior movement distance of the hyoid bone at the maximum UES opening (p < 0.01). In the pressure topography, the maximum pressure immediately after UES closure significantly decreased with magnetic stimulation (p < 0.05).
CONCLUSIONS: EMG-triggered peripheral magnetic stimulation made it possible to apply magnetic stimulation during a voluntary 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.

OBJECTIVE: This study investigated the effects of bolus consistency on pharyngeal volume during swallowing using three-dimensional kinematic analysis.
METHODS: Eight subjects (2 males and 6 females, mean ± SD 44 ± 10 years old) underwent a 320-row area detector scan during swallows of 10 mL of honey-thick liquid and thin liquid. Critical event timing (hyoid, soft palate, UES) and volume of pharyngeal cavity and bolus were measured and compared between two swallows.
RESULTS: The pharynx is almost completely obliterated by pharyngeal constriction against the tongue base for both consistencies. There were no significant differences in maximum volume, minimum volume and pharyngeal volume constriction ratio values between thick and thin liquids. However, the pattern of pharyngeal volume change (decrease) was different. For thick liquids, the air volume started to decrease before the onset of hyoid anterosuperior movement and decreased rapidly after onset of hyoid anterosuperior movement. During thin liquid swallowing, air volume remained relatively large throughout the swallow and started to decrease later when compared to swallowing thick liquids. At onset of UES opening, the bolus volume was not significantly different between thin and thick liquids; however, air volume was significantly larger when swallowing thin liquids, which made the total volume of the pharyngeal cavity larger.
CONCLUSIONS: This difference between the two consistencies is associated with differences in tongue motion to propel the bolus and clear the pharynx from possible residue.

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.