Genesis of Bolus Pressure During Primary Peristalsis: Key to Understanding "Functional Dysphagia".

Background: During swallowing, the bolus passes through the esophagus during the relaxation phase of peristalsis-termed the bolus domain (BD)-before being cleared by sequential contractions. Bolus pressure (BP) in BD results from the compartmentalization of the bolus between the advancing contraction and the lower esophageal sphincter. This study aimed to evaluate the genesis of BP in the BD using high-resolution impedance manometry (HRMZ), distension-contraction plots, and high-frequency ultrasound imaging in healthy subjects and "functional dysphagia (FD)" patients.

Methods: We analyzed HRMZ recordings from 30 healthy controls and 30 FD patients. Swallows of 5 mL and 10 mL saline were recorded in the supine and Trendelenburg positions. BP was measured in the BD (from upper esophageal sphincter relaxation to the 20-mmHg isocontour onset of contraction). Automated tools extracted BP, luminal cross-sectional area (CSA), and the percentage of BD area with CSA ≤ 50 mm² (no-bolus area). Ultrasound images evaluated the timing of luminal distension and wall changes during the bolus domain and contraction.

Key results: Controls showed luminal distension in most of the BD. On the other hand, FD patients exhibited higher BP and a significantly larger percentage of no-bolus areas in the BD (p < 0.001) compared to controls. ROC analysis revealed high diagnostic accuracy in distinguishing patients from controls (AUC = 0.898) for the percentage of no-bolus area in the BD; a 16.5% threshold yielding 86.7% sensitivity and 80.0% specificity. Ultrasound imaging confirmed luminal collapse during the bolus domain in patients with FD.

Conclusions & inferences: In patients with FD, bolus pressure is partly related to the compression of the manometry catheter by the esophageal wall. The proportion of BP-positive, bolus-negative areas in the BD distinguishes FD patients and controls.