Inter-rater agreement of novel high-resolution impedance manometry metrics: Bolus flow time and esophageal impedance integral ratio

Abstract

Background: Novel high-resolution impedance manometry (HRIM) metrics of bolus flow time (BFT) and esophageal impedance integral (EII) ratio have demonstrated clinical utility, though the reliability of their analysis has not been assessed. We aimed to evaluate the inter-rater agreement of the BFT and EII ratio.

Methods: HRIM studies including five upright, liquid swallows from 40 adult patients were analyzed by two raters using a customized MATLAB program to generate the BFT and EII ratio. Inter-rater agreement was assessed using the intraclass correlation coefficient (ICC) for median values generated per patient and also for all 200 swallows.

Key results: The ICC (95% confidence interval, CI) for BFT was 0.873 (0.759-0.933) for median values and 0.838 (0.778-0.881) for all swallows. The ICC (95% CI) for EII ratio was 0.983 (0.968-0.991) for median values and 0.905 (0.875-0.928) for all swallows. Median values for both BFT and EII ratio were similar between the two raters (P-values .05).

Conclusions and inferences: The BFT and EII ratio can be reliably calculated as supported by generally excellent inter-rater agreement. Thus, broader utilization of these measures appears feasible and would facilitate further evaluation of their clinical utility.

Keywords: achalasia; dysphagia; high-resolution manometry; impedance; reliability.

Figure 1. The bolus flow time and esophageal impedance integral (EII) ratio

A) The EII ratio was calculated by dividing the measurement region of interest (red-dashed box), which entailed the swallow to the completion of peristalsis or 12 seconds if peristalsis was absent, into two impedance domains: swallow (Z1) and post-swallow (Z2). The amount of bolus present (the EII) within each domain was quantified by measuring the impedance-pixel density (impedance value x time x axial length). The EII ratio was then calculated as the ratio of residual bolus volume (EII-Z2) relative to the intra-esophageal bolus volume immediately following the swallow, but before the deglutitive contraction (EII-Z1): EII ratio = (EII-Z2)/(EII-Z1). The area within the black-dashed box is enlarged in the top panel of B. B) The BFT was measured by positioning three impedance and three manometry signals through the EGJ at 1-cm intervals with the distal signals positioned within the hiatus as identified by crural contractions, top panel. The bolus presence time (BPT) at the EGJ was determined as the time from which the impedance dropped to 90% of the nadir until the impedance returned to 50% of the impedance baseline (middle panel). The BFT was then derived as the sum of all periods during the BPT when a flow-permissive pressure gradient (i.e. when the esophageal pressure was greater than both the crural and intra-gastric pressure signals) was present (bottom panel). If the impedance drop was not greater than 50% at each axial location and/or a flow-permissive pressure gradient was not achieved, the BFT was considered to be zero. Figure used with permission from the Esophageal Center at Northwestern. CD – crural diaphragm.