Satomi Miyaoka

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.

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.

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.

Constancy of Head Turning Recorded in Healthy Young Humans

This study evaluated the ‘constancy’ of head turning as recorded two-dimensionally by accelerometers. Fourteen healthy participants turned the head with his/her natural and comfortable speed. Maximum inclination angles (MIA) during head turning were measured in four (anterior, posterior, right, and left) directions of clockwise (CW) and counter-clockwise (CCW) conditions. Three indices were used for the evaluation: (1) standard deviations of MIA as an index of ‘spatial constancy,’ (2) anterior/posterior and right/left ratios from intervals among four MIA as indices of ‘temporal constancy,’ and (3) first derivatives from head turning trajectories as an index of ‘angular velocity.’ The spatial index varied from 0.15° to 9.96° (CW condition) and from 0.56° to 10.6° (CCW condition). The temporal index in the anterior–posterior direction varied from 0.711 to 1.103 (CW condition) and from 1.071 to 1.905 (CCW condition). The index in the right–left direction varied from 0.773 to 2.081 (CW condition) and from 0.842 to 1.226 (CCW condition). Characteristic hollows or protrusions were detected from the first derivatives of head turning trajectories and were regarded as abrupt changes in angular velocity during head turning. The results suggest that these three indices are appropriate tools for evaluation of the constancy of head turning.