Ichiro Ashida

Influence of food properties and body position on swallowing-related muscle activity amplitude

This study was designed to examine the effect of different food properties and body positions on electromyographic amplitudes of the anterior tongue (AT) and suprahyoid (SH) muscles during swallowing in normal subjects (six men and three women; 21-30 years old). Each subject was asked to swallow three foods (consisting of 2.0%, 5.7% or 9.1% of a thickening agent dissolved in water) with different textural properties in one of four body positions: upright, inclined at 60 degrees or 30 degrees , or supine. Surface electromyograms (EMG) were recorded from the anterior tongue and SH muscles, and the integrated and cumulated EMG were used to evaluate the amplitude changes. The increases in food hardness and adhesiveness elevated the integrated and cumulated EMGs of both the AT and SH muscles during swallowing in a stepwise manner (P < 0.0001, one-way anova) that was independent of the body position. There was a linear relationship between the concentrations of the thickening agent and the logarithmic values of the food hardness. There was also a parallel relationship between the logarithmic hardness values and the final logarithmic values of the cumulated muscle activity during swallowing. Unlike these simple amplitude responses of the AT and SH muscles to the different food properties, our previous studies have shown that the durational responses of these muscle activities to different food properties are more complicated. Possible neural mechanisms responsible for the amplitude responses observed are discussed.

Activity patterns of the suprahyoid muscles during swallowing of different fluid volumes

Influences of bolus volumes on activity patterns of the suprahyoid muscles during swallowing were examined using the T(P) technique (which quantitatively evaluates muscle activity patterns and indicates a negatively skewed pattern at lower T(P) values) in healthy young adults (eight men and four women). One of six volumes of tea ranging from 10 to 32 mL was delivered randomly to each subject while recording an electromyogram of the suprahyoid muscles and a laryngeal mechanogram with a piezoelectric sensor. Each subject was asked to swallow the full volume of liquid in a gulp if possible. T(P) values were calculated as deciles from T(0) to T(100) during intervals that were defined by the trajectory of the laryngeal mechanogram recorded during swallowing. Seven significant differences were detected in the average T(P) values from T(30) to T(60): between 16 mL (e.g., 0.448 in T(30)) and 25 mL (0.408 in T(30)) and between 20 mL (0.453 in T(30)) and 25 mL. There were significant differences among the 12 subjects for all of the nine average T(P) values (Ps < 0.001), suggesting a notable intersubject variation in the suprahyoid (SH) activity patterns. The average peak amplitudes of the integrated suprahyoid activity differed significantly among the six volumes (P < 0.001), while the average durations measured by the laryngeal mechanogram did not. The present results suggest that the swallowing volume mainly affects SH activity patterns, which were evaluated by the T(P) technique, during the early period of each swallow.

Analysis of head movements coupled with trunk drift in healthy subjects

Accelerometers were used to measure sequential head tilt and trunk drift in 14 healthy young subjects while they performed three kinds of head task. First, maximum inclination angles in anterior, posterior, right and left directions were measured to estimate cervical ranges of motion for flexion-extension and lateral bending. The inclination angles measured (61.2° on average for flexion, 51.7° for extension, 42.7° for right bending and 43.9° for left bending) were consistent with previous findings. Secondly, cross-correlation analysis was applied to evaluate the degree of functional coupling between the head and trunk during flexion-extension and lateral bending. Significantly higher correlation coefficients were found between head tilt and trunk drift when these movements were in the same (iso-) directional condition than in a different (allo-) directional condition. The coupled trunk drift in flexion-extension for the iso-directional condition (10.3° on average) was much larger than for the allodirectional condition (2.3°). Finally, head turning was recorded as oval traces in a biaxial plane. In both clockwise and counter-clockwise head turning conditions, the maximum inclination angles of the traces were larger in the anterior-posterior direction (59.8° anterior and 58.2° posterior, in the clockwise condition, and 47.4° and 47.4° in the counter-clockwise condition) than in the right-left direction (36.3° right and 39.0° left, in the clockwise condition, and 40.5° and 36.7° in the counter-clockwise condition), and the angles in the four directions were almost equal to flexion-extension and lateral bending. The characteristics of the traces recorded and a possible application of the present recording system are discussed.

Comparison of video-recorded laryngeal movements during swallowing by normal young men with piezoelectric sensor and electromyographic signals

The movement of the larynx in five young men during the swallowing of a liquid was examined by simultaneously recording a video-movie, the trajectory of a piezoelectric sensor, and the surface electromyogram of the suprahyoid muscles (SH). The movies revealed swallowing was associated with four characteristic spatial points of laryngeal movement: (1) a slight movement in the superoposterior direction (1.9 ± 1.2 s; mean ± SD of the time elapsed after the command to swallow was issued); (2) the initiation of anterosuperior elevation (2.3 ± 1.3 s); (3) the turn at the highest position (3.2 ± 1.2 s); and (4) the return to the initial position (4.1 ± 1.4 s). The piezoelectric sensor and the SH electromyogram also detected characteristic temporal points that closely corresponded to the characteristic temporal points captured by the video. The advantages of using movies in swallowing research are discussed.

Analysis of the pattern of suprahyoid muscle activity during pharyngeal swallowing of foods by healthy young subjects

We previously developed the TP technique to discriminate between the activity patterns of skeletal muscles. In this study we aim to identify the TP value(s) that can be used to sensitively evaluate the activity patterns of the suprahyoid (SH) muscles during swallowing. We also analyse the effect of food textural properties on the activity patterns of the SH muscle during oral and pharyngeal swallowing. Three test foods consisting of 3%, 6% and 9% of a thickening agent, Mousse-up (MU) were prepared. Their textural properties differed significantly. Swallowing of 9% MU involved a significantly longer average duration than 3% MU. The average T50 value for 6% MU was significantly larger than that for 3% MU. However, the average T20 and T80 values of the test foods did not differ. Thus, the T50 value is particularly suitable for evaluating SH muscle swallowing patterns. Moreover, test foods that vary in their textural properties elicit different durations and patterns of SH muscle activity.

Generalization of the Bolus Volume Effect on Piezoelectric Sensor Signals during Pharyngeal Swallowing in Normal Subjects

To generalise the effect of bolus (tea) volume on the piezoelectric sensor (PES) signals during pharyngeal swallowing by general linear models (GLMs), laryngeal movement PES data were recorded from eleven healthy adults while they swallowed one of a wide range of volumes. A PES was attached to the front of the neck to record a laryngeal mechanogram, and then each subject was asked to swallow one of six volumes (10 to 32 mL) of tea after a command. For each swallow, four characteristic points on each PES record were defined and four intervals that spanned these points were measured. GLM-ANOVA analysis revealed statistically significant linear regression coefficients for two ‘volume’ effects and four main ‘subject’ effects. The two linear coefficients of the ‘volume’ effect were 2.5 and 2.7, which suggests that a 10-mL increase in tea volume lengthens these intervals by 25 and 27 ms, respectively.

Sequential analysis of masseter activity patterns during chewing in healthy males

Abstract The present study examined sequential changes in masseter activity patterns observed during chewing of four different agar samples in eight healthy young males. Two parameters, T50 and D50, were specifically used for evaluation of the activity patterns of individual bursts. Statistical significances were detected in regression coefficients (21.9% of 32 trials) and Spearman’s rank correlation coefficients (28.1%) between the calculated T50 values and chewing cycles, whereas no significant differences among the four agar samples were found. Three (I–III) types of activity patterns of masseter bursts during chewing sequences were classified by the D50 values, which were derived from the T50 values. The three types physiologically corresponded to incrementing (Type I), decrementing (Type III) and mixed discharge patterns (Type II). The classification of activity patterns suggested the usefulness of D50 values in the sequential analysis of masseter activity patterns.

Differential sweetness of commercial sour liquids elicited by miracle fruit in healthy young adults

Miracle fruit (Synsepalum dulcificum) contains the glycoprotein miraculin which turns a sour taste into a sweet one. Chemical analyses and sensory evaluation experiments were conducted to examine the sweetening effect of miracle fruit with regard to five different commercial sour liquids which were diluted until they were subjectively equally sour. HPLC-based analyses revealed that (1) the predominating acids in two and three of the liquids were citric acid and acetic acid, respectively and (2) all five liquids contained fructose and glucose. Healthy young adults (eight males and 10 females) in the sensory evaluation experiments were asked to chew a miracle fruit and apply their saliva to the oral mucosae. They were asked to score the sweetness elicited by the five liquids relative to a sucrose standard at 0, 15, 25 and 35 min thereafter. The citric acid-based liquids were perceived as being sweeter than the acetic acid-based liquids at all timepoints. Thus, commercial sour liquids that mainly contain citric acid are more effective than acetic acid-based liquids in eliciting a perception of sweetness after the miracle fruit application, while the sugars in the liquids seemed to play a minimal role as determinants of sweetness.

Effects of damage of the l-XII nerve that innervates tongue retractive muscles in rats.

The aim of this study was to examine whether sectioning of the lateral branches of the hypoglossal nerves (l-XII) in young male rats affects regulation of body weight, food intake and water intake in their period of growth by using a linear fixed effects model or not. Three groups of the rats were prepared according to treatments applied at about 4 weeks after birth to the l-XII innervating the hyoglossus, styloglossus and inferior longitudinal muscles: bilaterally sectioned (n = 9), unilaterally sectioned (n = 3) and sham-operated (n = 6) groups. Changes in body weight, food intake and water intake of the rats in the three groups were measured for 32 days before and after the treatments. To test the abilities of eating and drinking, the amounts of food and water intake were also measured for 1 and 2 min, respectively, after 20 h food and water deprivation at the final stage of the experiment. The major findings obtained were that (i) bilateral sectioning of the l-XII in the young rats significantly reduced body weight and the amount of water, not food, intake consumed and (ii) the bilateral sectioning affected the ability of eating and bilateral and unilateral sectioning affected that of drinking. The results suggest that bilateral sectioning of the lateral branches of XII nerve in young male rats affects regulation of body weight and water intake in their period of growth.

Applicability of piezoelectric sensors for speech rehabilitation

The applicability of piezoelectric sensors for speech rehabilitation was examined by setting vocalizing tasks for seven healthy young adults (four men and three women). A piezoelectric sensor was attached to the front of the neck and each seated subject was instructed to vocalize /a/ with subjective low and high tones and /pa/, /ta/, and /ka/ with a subjective middle tone. The three major findings were: (1) slow potential changes recorded at the start of these tasks were followed by rapid changes; (2) the tasks did not differ in the average range of the slow changes; (3) female subjects had higher average frequencies of rapid changes than male subjects. The frequencies and phases of the rapid changes paralleled the sound waves recorded in the neck during the tasks. Swallowing tasks verified the appropriateness of the recording system. The advantages of using piezoelectric sensors in the clinic are discussed.