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polyvinyl catheter embedded by one pH and six imped- ance sensors at predefined positions. The pH sensors were calibrated before placement using standardized buffer solutions at pH 4.0 and 7.0, as recommended by the manufacturer. The catheter was placed intranasally so that the esophageal pH sensor was positioned 5 cm above the manometrically defined upper border of the lower esophageal sphincter. Intraluminal impedance was measured at 3, 5, 7, 9, 15, and 17 cm above the lower esophageal sphincter. Data sampling frequency for both impedance and pH sensors was 50 Hz. Studies were per- formed for 24 hours, after which patients returned to the lab for catheter removal and data review. Data were downloaded from the recorder and ana- lyzed using BioView Analysis software (Sandhill Scientific Inc). Reflux episodes were identified by compu- terized detection (Autoscan; Sandhill Scientific Inc.) of proximally directed decreases in impedance. Tracings were then manually reviewed by an experienced investi- gator (MFV) to confirm accuracy and correct any errors. Total, upright, and supine reflux events were recorded. Acid reflux events were defined as those occurring with pH less than 4.0, and nonacid reflux events were defined as those occurring at pH of 4.0 or greater. For imped- ance parameters, total number of reflux events greater than 48 was considered abnormal. 19–22 Statistical Analysis Data were collected and stored at the secure Web- based Vanderbilt Digestive Disease Center REDCap (Research Electronic Data Capture) (1 UL1 RR024975 NCRR/NIH). REDCap is an application designed to sup- port data capture for research studies providing: 1) an intuitive interface for validated data entry; 2) audit trails for tracking data manipulation and export proce- dures; 3) automated export procedures for seamless data downloads to common statistical packages; and 4) proce- dures for importing data from external sources. There was strict control and supervision of the data entry and access for this study. Continuous variables were summarized using the median, 25th, and 75th percentiles. Categorical varia- bles were summarized using percentages. We used separate Kruskal-Wallis tests to determine if the total number of impedance events and the percent total time pH less than four differed by esophagitis and pH groups. Spearman’s rank correlation was used to estimate the overall association between impedance events (on ther- apy) and percent total time pH less than 4 (off therapy). Multivariable linear regression was used to assess the relationship between on -therapy impedance parameters and off -therapy pH parameters, manometry findings, and upper endoscopy findings. All analyses were con- ducted using the R statistical program.

Fig. 1. Individual and group median (IQR) % total time pH < 4 for the three patient subgroups. As expected, acid reflux was signifi- cantly less in those with normal endoscopy and pH than those with abnormal pH or esophagitis.

monitoring off PPI therapy and 24-hour impedance/pH monitoring on PPI therapy between 2005 and 2012. Their chief complaints included: cough (53%), asthma (12%), hoarseness (7%), throat clearing (6%), pulmonary fibrosis (6%), sore throat (6%), postnasal drip (5%), and sinusitis (5%). A total of 58/75 (77%) of patients were female, 71/75 (95%) were Caucasian, with a median (IQR) age of 55 (45–64) years, and median (IQR) body mass index of 29 (25–33). Hiatal hernias greater than 1 cm in size were present in 29/75 (38%), of which 61% were 2 to 3 cm in size, and 39% were 4 cm or greater. Esophagitis was present in 14/75 (19%) of patients, of which 90% were grade A or B by Los Angeles Classifica- tion. None of the patients were found to have endoscopic evidence of possible Barrett’s esophagus. Impedance and pH Parameters Overall. Median (IQR) total, upright, and supine impedance events on PPI therapy were 39 (20–54), 29 (6–12), and 4 (1–8), respectively. The impedance events were predominantly mixed gas and liquid of nonacidic nature (pH > 4) and were abnormal (greater than 48 reflux events) in 35% of tested subjects. Abnormal acid reflux was not present in any of the subjects when tested on PPI therapy. Wireless pH testing off PPI ther- apy showed a median (IQR) % time pH < 4 of 9% (7%– 13%) in total, 11% (8%–16%) in the upright state, and 2% (1%–8%) in the supine state. Eighty-four percent of patients had abnormal wireless pH testing results off therapy. Subgroups. Patients were divided into three sub- groups based on endoscopic and pH findings: Esophagitis, normal endoscopy but abnormal pH (referred to as ‘‘pH þ ’’ in Figures 1 and 2), and normal endoscopy with normal pH (referred to as ‘‘pH ’’ in Figures 1 and 2). Figures 1 and 2 depict individual and group results on the degree of

RESULTS Demographics and Endoscopic Findings

Seventy-five patients with suspected extraesopha- geal reflux underwent testing with 48-hour wireless pH

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