Shin-ya Kawakami

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 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.

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.

Synchronization of masseter activity patterns between the right and left sides during chewing in healthy young males

Abstract Masseter activity patterns during chewing, which were quantitatively assessed using T50 values, were compared between the right and left sides of healthy young males. Surface electromyograms were recorded from both masseters, and each participant was asked to chew four different agar samples at his own pace across two separate sessions. The four agar samples, each possessing differing textural properties, consisted of two normal and two distinctive agar varieties. The Pearson’s correlation coefficient was calculated for each pair of T50 values to evaluate the degree of synchronization of activity patterns between both masseters. A three-way analysis of variance revealed significant main effects of the ‘participant’ and ‘experimental session’ factors, but not of the ‘test food’. The number of significant coefficients increased stepwise by increasing the number of chews per sequence. These results suggest the importance of the initial stages of chewing sequences in facilitating the synchronization of bilateral masseter activity patterns.