Effect of volitional inhibition and chewing on pharyngeal swallowing

Abstract

【Objective】In 2002，we reported that a bolus which mixed liquid and solid food promptly moved to the hypopharynx prior to swallowing when it was chewed and swallowed．The purpose of this study was to identify influence of chewing and to endoscopically identify factors related to the swallowing reflex．

【Subjects and Methods】Subjects were nine healthy volunteers (mean age of 28.8 years)．An elastic 4-Fr tube was inserted through the left nostril and fixed so that the tube was at the level of the palatopharyngeal muscle． Greencolored water was injected using a syringe pump at the rate of 6.5 ml/min (slow)，or 11.5 ml/min (fast)．We recorded suprahyoid muscle EMG and endoscopically observed fluid transport and recorded the images on a digital videotape．We measured the time from the start of injection to initiation of swallow reflex under six different conditions；food was either chewed or not chewed ，food was either swallowed spontaneously or volitionally delayed and liquid injection speed was slow or fast．

【Results】Latencies were significantly different only between spontaneous and volitionally delayed swallowing (p＜0.01) or between slow and fast infusions (p＜0.05)．There was no significant difference between chewing and no chewing．When subjects volitionally delayed swallowing，adduction of the arytenoids and expansion of the pharynx were seen in all subjects．In spontaneous swallows，swallow initiation was elicited when liquid reached pharyngoepiglottic band or filled the half of pyriform sinus．In volitionally delayed swallows，swallow initiation was elicited when liquid overflowed the pyriform sinus into the aryepiglottic fold or interarytenoid notch．

【Discussion】Chewing had no effect on the duration between the onset of liquid infusion and initiation of the swallow reflex．Volitional delay of swallowing altered the anatomy of the pharynx to accommodate the increased bolus volume and avoid aspiration but not alter threthold of swallow reflex．This interesting finding will be useful Dysphagia rehabilitation．