Fig. 2.

Variability of initiation of the esophageal phase of swallowing. A–C: effects of water injected into the nasopharynx on pharyngeal and esophageal phases of swallowing. Note large difference in delays to initiation of the esophageal phase after injection of 1 ml (A) vs. 4 ml (B) of water. Injection of 1 ml of water always activated the pharyngeal phase, but did not always activate the esophageal phase (C). Therefore, if initiation of the esophageal phase of swallowing was independent of peripheral feedback, then the high variability of occurrence, even to the point of lack of activation of the esophageal phase, would not occur. GH, geniohyoideus; TH, thyrohyoideus; CP, cricopharyngeus; CT, cricothyroideus; E1-E, EMG activity of the esophagus at 1 cm from the CP; E1-M and E4-M, motility of the esophagus at 1 and 4 cm from the CP, respectively.