Quantitative relationship between liquid bolus flow and laryngeal closure during deglutition.

We employed digital image analysis to assess the relative movements of the hyoid, larynx, and bolus as a function of liquid bolus volume (2-15 ml), and synchronized these measurements with intrapharyngeal manometry. Comparisons were performed of bolus head and tail movement in relation to the timing of hyoid movement, contact between the arytenoid and epiglottic cartilages, and intrabolus pressures. Bolus head movement in the distal pharynx, as determined from flow plots, was relatively rapid. Initial bolus tail movement in the distal pharynx was delayed proportional to bolus volume, and once initiated, was slower than bolus head movement. Laryngeal exposure time, defined as the interval between bolus head arrival and tail departure at the hypopharyngeal recording sensor, increased as a function of bolus volume. The time interval between the initial anterior hyoid movement and bolus arrival at the larynx, determined by concurrent plotting of hyoid excursion and bolus head position, was constant despite increasing bolus volume. Similarly, the interval between epiglottic-arytenoid contact and bolus arrival was constant despite increased bolus volume. The early phase of intrabolus pressure was temporally associated with posterior movement of the tongue base and varied as a function of bolus volume, whereas late intrabolus pressure was temporally associated with initial pharyngeal wall movement and was not significantly volume dependent. These data indicate that the temporal relationship between laryngeal closure and bolus head flow remains constant despite changes of laryngeal exposure time to the bolus as a function of volume.