Title:
Esophageal impedance baseline according to different time intervals.

Abstract:
The impedance baseline has been shown to reflect esophageal integrity, and to be decreased in patients with esophagitis. However, different methods for the determination of the impedance baseline have not been compared.
The median impedance baseline was calculated in 10 consecutive multichannel intraluminal impedance recordings in children with non-erosive reflux disease. All children underwent an endoscopy with a biopsy as part of the clinical work-up to exclude esophagitis. The impedance baseline was obtained both by including and excluding all impedance episodes (IE; reflux, swallows and gas episodes) during the full recording, and during the first 1-minute period without an IE every hour (method 1), every 2 hours (method 2) or every 4 hours (method 3). The impedance baseline obtained during the full recording was set at 100%, and the variation (difference in impedance baseline for the different methods) and variability (difference in impedance baseline during one analysis period) were assessed.
None of the participants had esophagitis. The mean difference over the six channels between the impedance baseline over the total recording with and without IE was approximately 2.5%, and comparable for each channel (range 0.47% to 5.55%). A mean of 1,028 IEs were excluded in each tracing, and it took between 4 and 24 hours to delete all events in one tracing. The difference in the impedance baseline obtained with and without IEs was mainly caused by the gas episodes in the upper channels and swallows in the lower channels. The median impedance baseline according to the three one-minute analysis methods was comparable to the median impedance baseline according to the 24 hour analysis.
The automatic determination of the median impedance baseline over the total tracing including IEs is an adequate method. In isolated tracings with numerous IEs, the calculation of the median impedance baseline over one minute every 4 hours is an alternative option. Companies should develop software to calculate the median impedance baseline during the whole registration deleting all IEs for the analysis.