An impedance-manometry based method for non-radiological detection of pharyngeal postswallow residue

Postswallow residue is indicative of impaired pharyngeal bolus clearance. The integrated nadir impedance to impedance ratio (iZn/Z) is a novel functional variable that can be derived using automated impedance manometry (AIM). In this study, the postswallow pharyngeal iZn/Z was evaluated as a potential correlated postswallow residue and therefore predictor of ineffective swallowing.

Optimal iZn/Z criteria were determine using a database of 50 randomly selected bolus swallows recorded with impedance, manometry, and videofluoroscopy. The iZn/Z was derived for a region of interest (ROI), spanning the mid-point of the pharyngeal stripping wave to the upper esophageal sphincter proximal margin, and from 0.25 to 1.25 s after the peak of the pharyngeal stripping wave. Videofluorscopy was scored by four experts using a six-point bolus residue scale (BRS) score. Optimized criteria for iZn/Z were then applied to a much larger database of 225 swallows scored for residue by one expert observer.

Among individual database, swallows iZn/Z was significantly correlated with average expert BRS score (r = 0.748, P < 0.0001). An iZn/Z of ≥ 500 was optimally predictive of swallows with residue defined by a BRS score of 4 or more. Within the larger cohort, iZn/Z was higher in dysphagia patient swallows compared with controls [2 (1, 4) vs 1 (1, 3), P < 0.005] and swallows with an iZn/Z ≥ 500 had higher bolus residue scores [4 (1, 6) vs 2 (1, 4), P < 0.001].

The AIM derived iZn/Z is an easily determined objective non-radiological marker of clinically relevant postswallow residue and therefore has potential diagnostic relevance as a predictor of ineffective swallowing.