Figure 1 - Intrabolus pressure and maximal sagittal upper esophageal sphincter (UES) diameter expressed as a function of swallowed bolus volume.

Intrabolus pressure (top) and maximal sagittal UES diameter (bottom) both expressed as a function of swallowed bolus volume in patients with failed UES relaxation, compared with measures from patients with a fixed, structural UES opening disorder (Zenker's) and healthy aged controls. a: Intrabolus pressure is supranormal in both patient groups. The significant volume-pressure gradient seen in normals and Zenker's, however, is not observed in those with failed UES relaxation. b: Maximal sagittal UES diameters were diminished in both types of sphincter disorder, but the normal, bolus volume-dependent increase in sagittal diameter is preserved in patients with failed UES relaxation and in healthy controls. The capacity for increased UES opening of a nonrelaxing UES approaches normal for swallowed bolus volumes of 20 mL. In contrast, the extent of UES opening in Zenker's rapidly peaks at 5 mL but changes very little with further increases in swallowed bolus volume. (Numbers in parentheses denotes subjects able to swallow bolus volume specified.) (Source: Williams et al.,⁵ with permission from American Journal of Physiology.)