24‐hour multichannel intraluminal impedance‐pH monitoring
All subjects underwent 24hr MII‐pH monitoring using a multi-channel probe catheter for LPR (Sandhill Scientific, Inc., Highlands Ranch, CO, ZAI-BL-54, 55, 56, ComforTEC Z/PH single-use 2.3-mm-diameter probe). The catheter has four pairs of esophageal impedance electrodes, two pairs of pharyngeal impedance electrodes, and two proximal-distal-pH sensors. We placed the most proximal pharyngeal impedance electrodes 1 cm above the upper esophageal sphincter. We checked the number of pharyngeal reflux events, specific event time by 24-hour notation, and acidity of reflux contents. Mealtimes were excluded from analysis. The pharyngeal reflux was defined as any reflux episode reaching proximally to 1 cm above the upper border of UES.14 The pharyngeal reflux includes liquid reflux, and mixed reflux.15 Liquid reflux retrograde 50% decrease in impedance starting distally and propagating at least to the next 2 or more proximal impedance measuring segments. Mixed reflux was defined as a combination of the gas reflux and liquid reflux patterns. The number of pharyngeal reflux was manually analyzed by an otolaryngology specialist after automated pre-analysis with autoscan software (Bioview Analysis, Sandhill Scientific). We defined daytime as 06:00–18:00 and nighttime as 18:00–06:00. Pre- and post-prandial periods were defined as 2 h immediately before and after mealtime, respectively. The cut-off values of acidity classification were acid (pH < 4), weakly acidic (7 > pH > 4), and weakly alkaline (pH > 7).