Changes in sensation of swallowing by increasing and decreasing bolus volume－Experiments with tea

Abstract

Motor aspects of swallowing have been intensively studied by several kinds of methods (for example, EMG, ultrasonic, and videofiuoroscopic examinations), but far fewer investigations have focused upon sensory aspects, thus many problems remain unresolved. Since it is scientifically and clinically important to understand how swallowing of bolus is perceived by individuals, the present study was designed to examine 1）the optimal volume for a swallow (OVS), 2) the maximum volume for a swallow (MVS), and 3) changes in the subjective ease of swallowing (SES) in relation to bolus volumes. A total of 67 healthy young females were subjects in the present experiment, and they were divided into ExperimentⅠ (Exp I , n＝28) and Experiment II (Exp II, n＝39). A kind of tea at room temperature was used as a ‘simulated’ bolus. ln Experiment Ⅰ, OVS and MVS were measured by a free access condition, and the obtained values were 17.9 ± 1.58 mL (mean ± SEM) and 35.4 ±2.26 mL, respectively. Changes in SES caused by increasing or decreasing the volume of a swallow were measured by the magnitude estimation method in both experiments. OVS in each subject in Experiment I was adopted as the standard stimulus (SS), and 7 volumes varying from (SS - 6) mL to (SS + 6) mL of the SS were used as the comparative stimuli (CS). In Experiment II，18 mL (averaged OVS in Exp I) was adopted as the SS in all of the subjects, and 7 volumes varying from 6 mL to 24 mL were used as the CS．ln both experiments， the sublects were initially instructed to quantify the SES for the SS as ‘10’ , and were then instructed to evaluate the SES for the CS by integers in comparison with that of the SS. The major findings were that：1) the SES decreased by both decreasing and increasing bolus volume，2）a reversed‐U curve was plotted at the center of which was the SES for the volume of 15 mL, and 3）the SES for (SS + 6) mL in ExperimentⅠand those for 6 mL and 24 mL in Experiment II were significantly smaller than that for the SS. The present study provides experimental evidence with a psychometric method for the experiential fact that an extremely small or large volume of bolus makes swallowing difficult.