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).