Twenty-two volunteers (6 males and 16 females, aged 19–38 years, mean age = 22.4 years), who did not have a history of swallowing disorders, were enrolled in this study. The study design was reviewed and approved by the ethics committee of our institution. Informed consent was obtained from each volunteer before the VF images were taken.
Udon noodles and cooked white rice with barium sulfate contrast medium were prepared (Fig. ). The textural properties of the test foods were assessed using a texture analyzing system (RE-3305S, YAMADEN, Japan). A two-bite test of each sample was performed with a cylindrical plunger (10 mm in diameter). The speed of the plunger was 1.0 mm/s and the final sample deformation was set at one third of the original height of the sample. From the data of the compressive load, the software calculated the hardness, stickiness, and cohesiveness of the samples. Five measurements were taken for each sample.
Udon noodles and white rice
Volunteers sat on a special VF chair (Tomomi Kobou Inc., Japan) and lateral X-ray images were taken using a fluoroscopic unit (Finescope300, TOSHIBA, Japan). An automatic brightness control mode was used to adjust the X-ray exposure factor and the gain of an image intensifier detector. Each volunteer ate a morsel of test food in a manner of his/her choosing. The weight of the morsel of test food had been measured. Fluoroscopic images were recorded on digital videotape (SONY, Japan) and imported into a computer system (Mac Pro, Apple, USA) to observe and evaluate images.
The items measured from the VF images were (1) the number of chewing strokes until the first swallow motion occurred, (2) time between the beginning of mastication and the end of swallowing, (3) the number of partitioned swallows until the entire food bolus was cleared from the mouth, and (4) the frequency and degree of stage 2 transport of the food bolus.
Based on previous reports [2
], the degree of stage 2 transport of the food bolus is classified as follows (Fig. ): (a) the bolus remains in the oral cavity until the start of the swallowing reflex without stage 2 transport, (b) the leading edge of the forming bolus passes across the pillars of the fauces before initiation of the swallow on the way to the lower border of the mandible, (c) the leading edge passes across the lower border of the mandible on the way to the valleculae, and (d) the leading edge is at the area between the valleculae and the piriform sinus (entrance of the esophagus).
Fig. 2 Classification of the degree of stage 2 transport: (a) oral cavity, (b) between the pillars of the fauces and the lower border of the mandible, (c) between the lower border of the mandible and the valleculae, (d) between the valleculae and the piriform (more ...)
Differences between udon noodles and white rice were statistically analyzed using Student’s t test and Wilcoxon signed-ranks test, and significance was set at P < 0.05.