Figure 3 - Hypopharyngeal intrabolus pressure is an indirect measure of UES compliance.

The pressure record shown is from a recording site approximately 1 cm above the upper margin of the UES. The cartoons below are derived from video frames at three time points before, during, and after passage of the bolus in relation to that recording site. Note that the mid-intrabolus pressure (center) is that pressure recorded from within the bolus as the bolus is traversing the open UES. The intrabolus pressure domain is relatively low and precedes the much higher pressure resulting from the arrival of the pharyngeal contraction coincident with the tail of the bolus. The magnitude of the intrabolus pressure is most dependent on the resistance to flow offered by the UES, in turn determined mainly by the UES diameter during opening and the intrinsic tissue elasticity or compliance within the sphincter.