What this trial measures

• Number of participants with unsafe swallowingBaseline

  Swallowing safety requires the ability to protect the airway to prevent penetration-aspiration (the entry of food or liquid material into the airway during swallowing). Swallowing safety will be measured using the Penetration-Aspiration Scale, an 8-point categorical scale which captures the depth to which any material enters the airway and whether or not the material is ejected. Levels 1 and 2 on the scale are considered safe, while levels \> 2 are considered unsafe. Actual scale scores (1-8) will be recorded and then converted to binary categorical scores (\< 3 vs \>/= 3). The frequency (count) of participants showing scores \> 2 will be reported by bolus consistency (thin, slightly thick, mildly thick, moderately thick and extremely thick liquids).

• Number of participants with impaired swallowing efficiencyBaseline

  Swallowing efficiency requires the ability to move a bolus of food or liquid from the mouth through the pharynx into the esophagus in a single swallow without leaving residue behind in the pharynx. Residue is material remaining behind in the pharynx after the swallow. Residue will be measured by tracing the area of barium visible on a lateral view x-ray (in pixels, using ImageJ software) and dividing that area by the squared length of the C2-C4 cervical spine. This cervical spine scalar provides a common anatomical reference that is a proxy for pharyngeal size, and enables the comparison of residue severity across different people with different neck length and pharynx size. In healthy swallowing, residue is expected to be minimal, i.e. less than 1% (C2-4)squared. The frequency (count) of participants showing residue above this threshold will be reported by bolus consistency (thin, slightly thick, mildly thick, moderately thick and extremely thick liquids).

• Number of participants with delayed airway closure ("Time-to-laryngeal-vestibule-closure")Baseline

  Swallowing safety requires the ability to protect the airway to prevent penetration-aspiration (the entry of food or liquid material into the airway during swallowing). Closure of the entrance to the airway ("laryngeal vestibule closure" or LVC) must be achieved in a timely manner. Time-to-LVC will be measured, i.e., the time interval between onset of the pharyngeal swallow (i.e. onset of the hyoid burst movement) and the first frame showing the most-complete closure of the laryngeal vestibule. In healthy adults, the upper limits (97.5th percentile value) for this measure are currently reported to be 267 ms on thin liquids, 367 ms on slightly thick liquids, 367 ms on mildly thick liquids, 300 ms on moderately thick liquids and 267 ms on extremely thick liquids. The frequency (count) of participants displaying time-to-LVC measures above these limits will be reported by bolus consistency (thin, slightly thick, mildly thick, moderately thick and extremely thick liquid).

• Number of participants with poor pharyngeal constrictionBaseline

  Efficient clearance of a bolus of food or liquid through the pharynx in swallowing requires constriction of the pharynx. In healthy adults, there is typically no unobliterated space visible in the pharynx on a lateral view x-ray image on the frame of maximum constriction. ImageJ software will be used to measure the area of unobliterated pharyngeal space, which is expressed as a % of an anatomical reference scalar defined as the squared length of the C2-C4 cervical spine \[%(C2-4)squared\]. Larger unobliterated area reflects impairment in pharyngeal constriction. In healthy adults, the upper limits (97.5th percentile) for this measure are currently reported to be 6.2%(C2-4)squared on thin, 5% on slightly thick, 7.5% on mildly thick, 4.9% on moderately thick and 3.8% on extremely thick liquids. The frequency (count) of participants with pharyngeal constriction area above these limits will be reported by bolus consistency.