Kazuhiro Hori

Coordination of Tongue Pressure and Jaw Movement in Mastication

The tongue plays an important role in mastication and swallowing by its contact with the hard palate. Using an experimental palatal plate with 7 pressure sensors, and recording jaw movement using mandibular kinesiography, we assessed, in healthy subjects, the coordination of tongue and jaw movements during the entire masticatory sequence of solids, by measuring tongue pressure against the hard palate. Tongue pressure appeared during the occlusal phase, reached a peak near the start of opening, and disappeared during opening. Specific patterns in order, duration, and magnitude of tongue pressure were seen at the 7 pressure sensors in each chewing stroke. Magnitude and duration were significantly larger in the late stage of chewing (8 strokes before initial swallowing) than in the early stage (until 8 strokes after starting mastication). The normal pattern of tongue contact against the hard palate, control of tongue activity, and coordination with jaw movement during mastication is described.

Newly developed sensor sheet for measuring tongue pressure during swallowing

PURPOSE The aim of this study was to develop a sensor sheet for measuring tongue pressure during swallowing and to clarify its usefulness by comparing it with a conventional pressure sensor installed in the palatal plate. METHODS A tactile sensor system was used for the construction of the measuring system. Based on our preceding study, a T-shaped sensor sheet with 0.1mm thickness, five measuring points (three points on the median line, two points on the posterior-lateral part) and three sizes based on the morphological analysis of 60 maxillary casts was designed for application on the hard palate. To elucidate the sensing characteristics of the sensor sheet, the output level of the sensor sheet was compared with that of a conventional pressure sensor under the same load. The maximal magnitude of tongue pressure (MP) during the swallowing of 15 ml water was recorded by a sensor sheet attached to the palatal mucosa and was compared with that recorded by pressure sensors installed in the palatal plate. RESULTS The output level of the sensor sheet was smaller than that of the pressure sensor. There was a high correlation between the output levels of the two sensors (R=0.952, P<0.001). Although MP at each sensing point of the sensor sheet was also smaller than that recorded by the pressure sensors, MP collected by the regression equation obtained in our experiment was quite similar to that for the pressure sensors. CONCLUSIONS This system could be useful for evaluating tongue activity during oropharyngeal swallowing.

Age-related Changes in Tongue Pressure during Swallowing

Although swallowing movement is known to change with aging, age-related differences in the tongue pressure for propelling a bolus from the oral cavity into the pharynx have yet to be investigated in a physiological condition. We hypothesized that tongue pressure during swallowing changed with aging and, using a 0.1-mm-thick sensor sheet with 5 measuring points, measured it while a 15-mL quantity of water was swallowed by young and elderly dentate individuals. Both groups showed a similar order of tongue pressure production at each point. However, the elderly group showed longer duration at each point, lower maximal magnitude in the anterio-median part of the hard palate, and higher magnitude in the circumferential parts of the hard palate than the young group. These results provide the first quantitative evidence of the age-related changes in tongue movement during natural swallowing, which could be attributed to muscle weakening and morphological changes in the oropharynx.

Reduced Tongue Pressure Against the Hard Palate on the Paralyzed Side During Swallowing Predicts Dysphagia in Patients With Acute Stroke

Background and Purpose— Dysphagia is important for prognosis in patients with stroke because this condition can cause aspiration pneumonia or nutritional deficits. The present study investigated the relationship between tongue motor deficits and dysphagia in patients with acute stroke. Methods— Maximal tongue pressure on the hard palate when swallowing 5 mL of water was measured using a T-shaped sensor sheet with 5 measuring points in 33 dysphagic and 31 nondysphagic patients with acute stroke. Maximum tongue pressures at each measuring point were compared between dysphagic and nondysphagic groups and between paralyzed and nonparalyzed sides. Results— Tongue pressure at each measuring point was significantly smaller in dysphagic patients than in nondysphagic patients with the largest significant difference on the paralyzed side. The magnitude of tongue pressure to predict dysphagia was calculated as 4.6 kPa on the paralyzed side, offering 71.4% sensitivity and 72.3% specificity. Conclusions— Reduced tongue pressure on the paralyzed side may predict dysphagia in patients with acute stroke.

Influence of human jaw movement on cerebral blood flow.

Temporal changes in cerebral blood flow induced by jaw movement have yet to be investigated. To assess the influence of pattern and intensity of muscle contraction during jaw movement on task-induced change in cerebral blood flow, we performed bilateral transcranial Doppler ultrasound examination during clenching, gum chewing, and tooth tapping in healthy volunteers. A random-effects model analysis revealed a significant increase in middle cerebral artery blood flow velocity during clenching (high muscle activity) and gum chewing (moderate muscle activity), compared with the preceding rest period; however, such an increase was not detected during tooth tapping (low muscle activity). Cerebral blood flow was greater on the working side during the intensive isometric contraction of the masseter muscle in clenching. These results suggest that task-induced change in cerebral blood flow during jaw movement is influenced by the change in peripheral circulation evoked by muscle contraction.

Relationship between Tongue Pressure and Dysphagia in Stroke Patients

Background: Although poststroke dysphagia is an important issue for determining prognosis, the pathophysiology of oral-phase dysphagia has yet to be clarified due to a lack of adequate devices and protocols. The present study investigated the relationships between swallowing pressure production by the tongue and dysphagia in stroke patients using a newly developed method of tongue pressure measurement with a sensor sheet system. Methods: Subjects were 64 stroke patients, including 30 patients with dysphagia. A T-shaped sensor sheet with 5 measuring points was attached to the hard palate to record tongue pressure while swallowing 5 ml of water. The average maximal magnitude and incidence of abnormalities such as asynchronous and/or polyphasic patterns in tongue pressure waves in 5 locations were compared between patients with and without dysphagia. Results: The average maximal tongue pressure was significantly smaller in patients with dysphagia than in those without dysphagia. Asynchronous and polyphasic patterns showed a sensitivity of 63 and 87%, and a specificity of 91 and 71%, respectively, for identifying patients with dysphagia. Conclusion: Tongue pressure production during swallowing appears closely related to poststroke dysphagia. Tongue pressure measurement appears useful for evaluating the pathophysiology of oral-phase dysphagia in stroke patients.

Role of tongue pressure production in oropharyngeal swallow biomechanics

The tongue is important for orofacial movements, including swallowing. Although numerous studies have focused on tongue pressure against the palate, its physiological role has not been fully evaluated. The tongue pressure generation may have the temporal coordination with the swallowing relational organs. The aim of this study was to clarify the physiological mechanisms of tongue pressure and to investigate the temporal relationship among tongue pressure, supra‐hyoid muscle activity, and videofluorographic (VF) images during swallowing. Fifteen healthy young subjects participated. Tongue pressure measured using a sensor sheet with five channels, electromyographic EMG, and VF was recorded synchronously during 4‐ml barium swallowing. Swallowing behavior in VF images with and without the sensor sheet was compared. Furthermore, the temporal relationship between events measured from tongue pressure, EMG, and VF was evaluated. Swallowing behavior on VF images was not affected by placement of the sensor sheet. Tongue pressure at the posterio‐lateral point of the hard palate tended to have biphasic peaks. Tongue pressure production with a monophasic pattern appeared during the same period as the second peak in the biphasic pattern. The onset of tongue pressure was later than the start of hyoid movement and onset of EMG, and offset was observed between the hyoid at the up‐forward position and reposition. Onset of tongue pressure at the anterior area was correlated with the start of slight hyoid elevation. Offset of tongue pressure at the posterio‐lateral points was strongly time locked with the hyoid at the up‐forward position. The present results suggested the temporal coordination of tongue pressure generation with the swallowing‐related organs. That is, the tongue pressure was produced for bolus propulsion, and was closely related to hyoid movement temporally during swallowing. These results may contribute to clarify the clinical state with the disorder of tongue kinetics.

Circulatory response and autonomic nervous activity during gum chewing

Mastication has been proven to enhance the systemic circulation, with circulatory responses seeming to be largely regulated by autonomic nervous activity via a more complex regulatory system than those of other activities. However, few studies have examined the relationships between changes in autonomic nervous activity and the systemic circulation that are induced by masticatory movement. We investigated changes in the systemic circulation and autonomic nervous activity during gum chewing to clarify the influence of mastication. Electrocardiograms, arterial blood pressure, and masseter electromyograms were taken while chewing gum continuously as indicators of systemic circulation in 10 healthy subjects with normal dentition. Cardiac sympathetic activity and vagus nervous activity, as well as vasomotor sympathetic nervous activity, were evaluated by fluctuation analysis of heart rate and blood pressure. Repeated analysis of variance and multiple comparisons were performed to determine chronological changes in each indicator during gum chewing. Gum chewing increased the heart rate and the mean arterial pressure. Although cardiac sympathetic activity and vagus nervous activity showed significant changes, vasomotor sympathetic nervous activity did not. These results suggest that changes in the autonomic nervous activity of the heart are mainly involved in the enhancement of systemic circulation with gum chewing. This explains some characteristics of autonomic nervous regulation in masticatory movement.

Tongue pressure modulation for initial gel consistency in a different oral strategy.

Background In the recent hyper-aged societies of developed countries, the market for soft diets for patients with dysphagia has been growing and numerous jelly-type foods have become available. However, interrelationships between the biomechanics of oral strategies and jelly texture remain unclear. The present study investigated the influence of the initial consistency of jelly on tongue motor kinetics in different oral strategies by measuring tongue pressure against the hard palate. Methods Jellies created as a mixture of deacylated gellan gum and psyllium seed gum with different initial consistencies (hard, medium or soft) were prepared as test foods. Tongue pressure production while ingesting 5 ml of jelly using different oral strategies (Squeezing or Mastication) was recorded in eight healthy volunteers using an ultra-thin sensor sheet system. Maximal magnitude, duration and total integrated values (tongue work) of tongue pressure for size reduction and swallowing in each strategy were compared among initial consistencies of jelly, and between Squeezing and Mastication. Results In Squeezing, the tongue performed more work for size reduction with increasing initial consistency of jelly by modulating both the magnitude and duration of tongue pressure over a wide area of hard palate, but tongue work for swallowing increased at the posterior-median and circumferential parts by modulating only the magnitude of tongue pressure. Conversely, in Mastication, the tongue performed more work for size reduction with increasing initial consistency of jelly by modulating both magnitude and duration of tongue pressure mainly at the posterior part of the hard palate, but tongue work as well as other tongue pressure parameters for swallowing showed no differences by type of jelly. Conclusions These results reveal fine modulations in tongue-palate contact according to the initial consistency of jelly and oral strategies.

Task-induced activation and hemispheric dominance in cerebral circulation during gum chewing

In elderly persons, it is thought that maintenance of masticatory function may have a beneficial effect on maintenance of cerebral function. However, few studies on cerebral circulation during mastication exist. This study aimed to verify a possible increase in cerebral circulation and the presence of cerebral hemispheric dominance during gum chewing. Twelve healthy, young right-handed subjects with normal dentition were enrolled. Bilateral middle cerebral arterial blood flow velocities (MCAV), heart rate, and arterial carbon dioxide levels were measured during a handgrip exercise and gum chewing. During gum chewing, electromyography of the bilateral masseter muscle was recorded.MCAV and heart rate significantly increased during exercise compared to values at rest.During gum chewing, there were no differences in the rate of increase in MCAV between the working and non-working sides, but during the handgrip exercise, the rate of increase in MCAV was significantly greater for the non-working side than for the working side.During gum chewing,muscle activity on the working side was significantly greater than that on the non-working side. These results suggest that during gum chewing, cerebral circulation increases bilaterally and does not show contralateral dominance, as it does during the handgrip exercise.