Use of suction electrodes for measurement of intrinsic tongue muscular endurance during lingual pressure generation.

BACKGROUND: Lingual pressure (LP) generation is cooperatively controlled not only by the intrinsic tongue (I-ton) muscles but also by hyoid muscle activation. However, the measurement of endurance and fatigue properties of I-ton muscles is difficult due to the instability of electrodes. OBJECTIVE: The purpose of this study was to apply suction electrodes to measure electromyograms (EMGs) of I-ton muscle and to evaluate integrated EMG amplitude (iEMG) and mean power frequency (MPF) of EMG in the I-ton and hyoid muscles performing continuous LP. METHODS: Twenty healthy adult volunteers (10 males, 10 females, mean age 28.8 years) were instructed to perform 10-s LP generation tasks at 25%, 50%, 75% and 100% of maximum LP in randomised order with visual feedback. During each task, EMGs of the I-ton, suprahyoid (S-hyo), infrahyoid (I-hyo) and masseter (Mass) muscles were simultaneously recorded. The iEMG and MPF of EMG burst during 10-s LP tasks were compared. The recording period was divided into three substages to analyse temporal changes with the Friedman test. RESULTS: During the 10-s task, the iEMG significantly increased as the LP strength increased (p < .001). There was no time-dependent change in the I-ton iEMG; however, the MPF of the I-ton EMG burst decreased in all tasks (p < .05). The S-hyo and I-hyo iEMGs gradually increased, especially with strong LP (p < .01). CONCLUSION: While I-ton muscles may easily fatigue during 10-s LP generation, S-hyo and I-hyo muscles may help compensate for the weakened I-ton muscle activity by increasing their activity to maintain LP.

Effect of carbonation and thickening on voluntary swallow in healthy humans.

BACKGROUND: Liquid modification is a widely established strategy of treatment for patients with dysphagia. The modification of liquid particularly by thickening or carbonation is a common approach to promote safe swallowing. OBJECTIVE: This study sought to investigate how carbonated and/or thickened water modulates swallowing behaviours during swallowing in healthy young individuals. METHODS: Thirty-one healthy volunteers (9 men, 22 women; mean age ± standard deviation [SD], 25.7 ± 6.2 years) were instructed to swallow 20 mL of water, carbonated water and carbonated juice with and without added thickening agent. Electromyograms (EMGs) of the suprahyoid (S-hyo) muscles were recorded to evaluate swallowing behaviours. Obtained S-hyo EMG bursts was analysed using the following outcome parameters: onset latency, the time between swallowing que to onset of EMG burst; rising time and falling time, defined as the time between onset and peak, and between peak and offset, respectively; duration, defined as the time between onset and offset of EMG burst; and area integral value under the waveform. RESULTS: Effects of thickening demonstrated the extended onset latency, EMG burst duration including falling time and the larger area of EMG in thickened liquid compared to thin liquid, but there was not much difference between thin and thickened carbonated liquids. Carbonation significantly decreased the duration including falling time for thickened but not for thin liquids. CONCLUSION: Patients with dysphagia can benefit from use of carbonated or thickened water while the effects on swallowing physiology may differ between carbonation and thickening.

Effect of bolus property on swallowing dynamics in patients with dysphagia.

BACKGROUND: Modification of foods or liquids is commonly administered as part of dysphagia treatment. However, no consensus exists on the parameters for defining texture-modified food for patients with dysphagia. OBJECTIVES: The aim of this study was to evaluate the effect of food/liquid material on swallowing physiology in patients with dysphagia and to discuss the optimal food choice for direct swallowing therapy. MATERIALS AND METHODS: A total of 140 patients underwent a videofluoroscopic swallowing study using three test foods/liquids: 3 mL of mildly thick liquid (Thick liquid), jelly made of agar and polysaccharide (Jelly) and jelly made of pectin (Reset gel). Outcome measures of videofluoroscopic images, bolus transit time and hyoid movements were compared. RESULTS: The frequency of chewing movements was highest for Jelly, followed by Reset gel and Thick liquid. While the probability of oral residue was the highest for Reset gel, pharyngeal residue after swallowing was high for Thick liquid as compared to Jelly and Reset gel. Oral transit time and pharyngeal transit time for Thick liquid were significantly smaller than that for Jelly and Reset gel. Pharyngeal delay time was significantly smaller for Thick liquid than that for Jelly and Reset gel. There was no difference in hyoid elevation time and hyoid movement time among the conditions. CONCLUSION: Mildly thick liquid material may be optimal for patients with primarily oral motor function impairment and jelly, such as Reset gel, may be more suitable for patients with primarily pharyngeal motor function impairment or oral and pharyngeal coordinative motor function decline.

Impact of salivary flow inhibition on masticatory behaviours in healthy individuals.

BACKGROUND: It remains unclear how the salivary flow and the fat content of food affect bolus formation during mastication. OBJECTIVES: We aimed to clarify: (1) how hyposalivation affects jaw-closing and hyoid-elevating muscle activities in bolus formation, and (2) if the effect of hyposalivation on muscle activity depends on the fat content of food. METHODS: Eighteen healthy male volunteers were instructed to freely ingest four test foods: Plain, Fat without seasoning, Fat with seasoning, and Soft rice crackers. Masseter and suprahyoid electromyographic activities were recorded before and 30 min after the administration of atropine sulfate, a muscarinic receptor antagonist that induces hyposalivation. RESULTS: Hyposalivation extended the masticatory duration significantly in all the test foods except Fat with seasoning. Masticatory cycle time was significantly longer with vs without hyposalivation for the Soft (p = .011). Suprahyoid activity/cycle was significantly greater with vs without hyposalivation (p = .013). Masticatory cycle time was significantly longer at the late stage with vs without hyposalivation for the Soft (p < .001). Suprahyoid activity/cycle was significantly greater at the middle (p = .045) and late stages (p = .002) with vs without hyposalivation for the Soft and greater at the late stage with vs without hyposalivation for the Plain (p = .043). Changes in masticatory cycle time and suprahyoid activity/cycle for these foods had significantly positive relationship (p < .001). CONCLUSION: Hyposalivation-induced changes in masticatory behaviours resulted from the middle and late stage suprahyoid activity. Fat content and seasoning compensate for salivary flow inhibition.

Evaluating the effect of management on patients with oral hypofunction: A longitudinal study.

INTRODUCTION: Declining oral function may affect subsequent physical frailty in the older population. The aim of this longitudinal study was to summarise data on patients who underwent functional oral examination and evaluate the impact of management on patients with oral hypofunction (OHF). METHODS: Dental outpatients aged over 65 years at their initial visit to the Niigata University Hospital received detailed assessment of seven oral function items to diagnose oral hypofunction using diagnostic criteria defined by the Japanese Society of Gerodontology. Patients with OHF at the first assessment received management including oral health guidance for low function and dental treatment. They were re-evaluated approximately 6 months later and the two assessments were compared. According to the results of the second assessment, the patients were divided into two groups: OHF improved and OHF re-diagnosed. RESULTS: Of the 273 patients who underwent the first assessment, 86 (31.5%) were diagnosed with OHF and received management. Of those, 42 (48.8%) completed the second assessment. Comparing the first and second assessment, significant improvement was observed in oral hygiene, occlusal force, tongue-lip motor function of /pa/, mastication and swallowing. The change in values from the first assessment demonstrated a significant difference between the OHF improved and re-diagnosed groups only in occlusal force. CONCLUSION: Management for patients with OHF can contribute to the improvement of poor oral function, and an increase in occlusal force was notable in the recovery from OHF.

Functional evaluation of jaw and suprahyoid muscle activities during chewing.

BACKGROUND: It has not yet been clarified how the type of the chewing task affects related muscle activity and how the suprahyoid muscles contribute to masticatory function in humans. OBJECTIVES: This study aimed to investigate the difference in the suprahyoid muscle activity between the freely and unilaterally chewing tasks and between the working and non-working sides during chewing. MATERIALS AND METHODS: Twenty healthy volunteers were instructed to chew peanuts and two different types of rice crackers in two ways: freely and unilaterally while surface electromyograms of the masseter and suprahyoid muscles were recorded. The chewing duration, number of chewing cycles and chewing rate were compared between the tasks. Furthermore, the masseter and suprahyoid muscle activities per chewing cycle were compared between the sides. RESULTS: The chewing duration was significantly longer, and the chewing rate was significantly higher during unilaterally chewing than freely chewing. The chewing duration differed significantly among the different foods; the harder the food, the longer the duration. Chewing rate and suprahyoid activity were significantly higher during soft rice cracker chewing. Masseter activity was higher on the chewing side than on the non-chewing side while there was no difference in suprahyoid activity between the sides. CONCLUSION: The current results demonstrate a difference in the masticatory efficacy between the chewing tasks and a functional role of the suprahyoid muscles during chewing, which does not differ between the chewing and non-chewing sides.

Chewing modulates the human cortical swallowing motor pathways.

When eating, mastication is always followed by swallowing. The present study assessed the effect of mastication on swallowing-related neural pathways in humans. Twenty healthy volunteers participated and underwent baseline transcranial magnetic stimulation to evaluate cortico-pharyngeal and cortico-hand motor-evoked potentials (MEPs). Next, they performed a chewing task and a swallowing task. Repeated-measures ANOVA revealed that pharyngeal MEPs were significantly higher after the swallowing task than after the chewing task, even though the number of swallows across tasks was matched. This implies that chewing movements suppress swallowing-related activity in the pharyngeal motor circuit.

Functional Role of Suprahyoid Muscles in Bolus Formation During Mastication.

It still remains unclear how the suprahyoid muscles function in bolus formation during mastication. This study aimed to investigate the contributory role of the suprahyoid muscles during mastication. A total of 20 healthy young volunteers were asked to perform tongue pressure generation tasks and unilateral mastication tasks using peanuts and two different types of rice crackers. Surface electromyographic (EMG) activity of the masseter and suprahyoid muscles and mandibular kinematics were recorded. Suprahyoid activity increased with increasing tongue pressure. Masticatory duration until the first deglutition differed significantly among the different foods; the harder the food, the longer the duration. This was also the case in masseter activity per masticatory cycle. Masticatory rate and suprahyoid activity per masticatory cycle were significantly higher during soft rice cracker mastication. Masseter activity was higher on the masticatory side than on the non-masticatory side, however, there was no difference in suprahyoid activity between the sides. Suprahyoid activity and jaw gape showed significant positive correlation in the early stage on both the masticatory and non-masticatory sides. The suprahyoid muscles functioned dominantly for jaw-opening during peanut mastication, and for bolus formation, especially in the late stage during soft rice cracker mastication. Bolus formation was performed dominantly on the masticatory side during rice cracker mastication. These findings clearly demonstrate a functional role of the suprahyoid muscles during mastication of solid foods from assessments using both EMG activity and mandibular kinematic recordings.