The purpose of this study was to elucidate the effects of the tongue-hold swallow (THS) on the pharyngeal wall by quantifying posterior pharyngeal wall (PPW) anterior bulge during the THS. In addition, the effect of tongue protrusion length on the extent of pharyngeal wall anterior bulge was analyzed.
Thirteen healthy subjects (6 males and 7 females, 23-43years) underwent 320-row area detector CT during saliva swallow (SS) and THS at two tongue protrusion length (THS1-protrude the tongue as much as 1/3 of premeasured maximum tongue protrusion length (MTP-L) and THS2-protrude the tongue as much as 2/3 of MTP-L). To acquire images of the pharynx at rest, single phase volume scanning was performed three times during usual breathing with no tongue protrusion (rest), protrusion of the tongue at 1/3 of MTP-L (rTHS1), and protrusion of the tongue at two thirds of MTP-L (rTHS2). Length from cervical spine to PPW (PPW-AP) and the volume of pharyngeal cavity was measured and was compared between rest, rTHS1, and rTHS2 and between SS, THS1, and THS2. Correlation between MTP-L and PPW-AP were calculated in three conditions; SS, THS1, and THS2.
PPW-AP at rest, rTHS1, rTHS2 was 2.9±0.6mm, 3.0±0.5mm, 3.0±0.5mm, respectively, showing no significant differences across swallows. PPW-AP at the maximum pharyngeal constriction was 8.1±2.0mm, 9.1±2.4mm, 8.7±2.0mm in SS, THS1, THS2, respectively. Compared to SS, PPW-AP in THS1 was significantly larger (p=0.04) and PPW-AP in THS 2 was not significantly different (p=0.09). Pharyngeal volume at rest, rTHS1, and rTHS2 was 16.4±5.2mm , 18.4±4.5mm , 21.3±6.2mm , respectively. It was significantly larger during rTHS2 compared to rest or rTHS1 (rTHS2-rest p=0.007, rTHS2-rTHS1 p=0.007). Pharyngeal volume was completely obliterated (zero volume) at maximum pharyngeal contraction in all except one subject. There was no correlation between MTP-L and PPW-AP in any of the three conditions (SS, THS1 and THS2).
This study demonstrated that the expanded pharyngeal cavity due to the tongue protrusion was completely obliterated by the increase of anterior motion of pharyngeal wall during THS. It also became clear that the degree of tongue protrusion did not linearly correlate with the movement of PPW during THS. There was no relationship between PPW motion and the MTP-L, suggesting that the effect of tongue protrusion is better determined in each subject by analyzing the motion of PPW using imaging tools.

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