2002 Volume 6 Issue 2 Pages 179-186
Objectives ： When normal subjects eat solid food，the bolus is formed in the oropharynx prior to swallowing．When subjects chew liquid or a mixture of solid and liquid before swallowing，liquid frequently enters the hypopharynx before swallow onset．The purpose of this study was to determine whether transport to the hypopharynx is due to muscle activity (active transport) or gravity (passive transport)．
Methods ： Ten healthy volunteers were imaged with videofluorography in the lateral projection while consuming foods with barium (10 ml 50％ liquid barium，8 g corned beef hash [CBH]，and a mixture of 5 ml liquid barium with 4 g CBH [MIX]．With each food (including liquid) the subject was instructed to chew and then swallow．Recordings were made in upright and facedown postures．Videotapes were reviewed in slow motion and swallow onset defined as the onset of rapid hyoid elevation．The location of the leading edge of the barium was classified as follows： Oral cavity (OC)； Upper oropharynx (UOP，from the fauces to the inferior border of mandible) ； Valleculae (VAL) ； or Hypopharynx (HYP)．Swallows were divided into three groups based on position of the leading edge at swallow onset： UOP or more (UOP-om；in the UOP，VAL ，or HYP) ； Valleculae or more (VAL-om；in the VAL or HYP)； or Hypopharynx (HYP)．
Results： 1．Upright Posture：The “VAL-om” position was significantly more frequent for MIX (100％) than other foods (Liquid 65％，CBH 55％) and more frequent for Liquid than CBH．Frequency of HYP position differed significantly among all three test foods（Liquid 35％，CBH 0％，MIX 71％)．2． Facedown Posture：Position of the leading edge did not vary significantly among foods．3．Comparison of Upright and Facedown Postures： With MIX，the VAL-om and HYP positions were each significantly more frequent for upright than facedown swallows (VAL-om position： 100％ upright and 60％ facedown； Hypopharynx position： 71％ upright and 5% facedown)． With CBH and Liquid，position was not significantly affected by position．
Discussion ： The leading edge often reached the oropharynx before swallow onset in either posture，but commonly reached the hypopharynx before swallow in upright posture only．This suggests that pre-swallow food transport to the oropharynx is active，but transport to the hypopharynx due to gravity．Food in the hypopharynx before swallowing may increase aspiration risk because the larynx is open．Testing patients with mixed consistency foods may be useful in evaluation of swallow safety for dysphagic individuals．
