An impedance-manometry based method for non-radiological detection of pharyngeal postswallow residue
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INTRODUCTION: Post-swallow 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 post-swallow pharyngeal iZn/Z was evaluated as a potential correlate post-swallow residue and therefore predictor of ineffective swallowing. METHODS: 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 UES proximal margin and from 0.25-1.25sec after the peak of the pharyngeal stripping wave. Videofluorscopy was scored by four experts using a six point bolus residue scale (BRS) score. Optimised criteria for iZn/Z were then applied to a much larger database of 225 swallows recorded scored for residue by one expert observer. RESULTS: Amongst individual data-base 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 to 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). CONCLUSION: The AIM derived iZn/Z is an easily determined objective non-radiological marker of clinically relevant post swallow residue and therefore has potential diagnostic relevance as a predictor of ineffective swallowing.
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