Intraluminal impedance detects failure of pharyngeal bolus clearance during swallowing: a validation study in adults with dysphagia

Multichannel intraluminal impedance (MII) detects bolus flow through a healthy pharynx. The aim of this study was to determine whether the technique detects bolus flow and retention in patients with pharyngeal dysphagia; develop appropriate impedance-based criteria for assessing patients and to provide some preliminary insights into the clinical utility of the technique. Pharyngo-oesophageal pressure and impedance were recorded simultaneously with video-fluoroscopy (VF) during swallows in six patients with dysphagia. Agreement, as to the presence or absence of bolus material, between the VF and MII was expressed using the Cohen's Kappa statistic. To test whether the impedance criteria for the detection of bolus passage in dysphagia could be improved, a Kappa statistic was calculated in an iterative process for a range of impedance values (100%-0%) defining bolus head entry and bolus tail clearance from the pharynx. Bolus presence according to the MII criteria previously derived by us in healthy controls demonstrated a modest correlation with VF when applied to this dysphagia population [0.37, 0.5 and 0.58 in the hypopharynx, upper oesophageal sphincter (UOS) and proximal oesophagus respectively]. In the patient population, the optimal impedance criteria were 50% for bolus head entry and 20% for bolus tail clearance. Adopting these criteria demonstrated enhanced agreement between VF and impedance; yielding Kappa coefficients of 0.42 in the hypopharynx, 0.54 in the UOS and 0.62 in the proximal oesophagus. With the adoption of appropriate criteria, pharyngeal impedance measurement can accurately detect bolus passage and failed or impaired clearance during swallowing in patients with dysphagia.