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the paucity of high-quality studies examining the clinical relevance of impedance findings. Thus, the aim of our study was to determine if on therapy impedance values assessing for nonacid reflux can be predicted from the traditionally recognized and commonly employed clinical markers of reflux based on off therapy upper endoscopy, manometry, or pH monitoring. MATERIALS AND METHODS The study was performed in accordance with the Declara- tion of Helsinki, Good Clinical Practice, and applicable regulatory requirements. The Vanderbilt Institutional Review Board approved this clinical trial (IRB# 090872). STUDY DESIGN AND PATIENT POPULATION The study population consisted of patients with sus- pected reflux-associated extraesophageal symptoms refractory to PPI therapy referred to the Esophageal Motility Center at Vanderbilt University Medical Center for evalua- tion and treatment. Refractory symptoms were defined as less than 50% improvement in the chief complaint after at least 12 weeks of twice-daily PPI therapy. This group was chosen since they represent the patient population for whom pH and/or impedance monitoring is currently indicated. 14,15 In order to assess the severity and frequency of their extrae- sophageal symptoms, patients were asked to complete a questionnaire previously described in the literature. 16 The following information were collected for all patients: pres- ence, severity, and frequency of GERD symptoms (heartburn 6 regurgitation) and extraesophageal symptoms (cough, hoarseness, throat clearing, sore throat, globus sensation, postnasal drip symptoms, chest pain), current medications, demographic data (age, sex, race, body mass index), history of alcohol and tobacco use, and presence of voice/laryngeal and nasal symptoms. Patients underwent esophagogastroduodenoscopy (EGD), wireless 48-hour pH monitoring, and esophageal manometry off acid suppression to assess the baseline esophageal mucosal integrity, motility, and acid expo- sure. They also underwent 24-hour impedance/pH monitoring while on twice daily PPI therapy to deter- mine the presence of acid and nonacid reflux in the setting of acid suppression. The presence and size of a hiatal hernia were determined at endoscopy; the pres- ence and severity of esophagitis was graded by the Los Angeles Classification; and the presence of Barrett’s esophagus was also noted. 17 Inclusion criteria were age greater than 18 years and chronic EER symptoms re- fractory to PPI therapy. Patients were excluded from the study if they were unwilling to undergo testing, were pregnant, had undergone surgery for reflux or peptic ulcer disease, or if they had a serious illness that would interfere with study participation. Wireless pH Monitoring Ambulatory pH monitoring was performed for 48 hours using a wireless monitoring device (Given Imag- ing, Duluth, GA). Patients were instructed to stop taking all PPIs and H2-receptor antagonists (H2RAs) for at least 7 days prior to undergoing testing. Wireless

capsules were calibrated by submersion in buffer solu- tions at pH 7.0 and pH 1.0, and then activated by magnet removal. Patients underwent EGD with con- scious sedation for visual anatomic inspection and distance measurements from the incisors to the squamo- columnar junction (SCJ). Capsules were then placed using the manufacturer’s delivery system at 6 cm above the SCJ and attached with vacuum suction. Capsule placement was confirmed with endoscopy. After success- ful placement, patients were given wireless pH recorders to wear about their waists, or to keep within 3 feet to 5 feet at all times. Recording devices receive pH data sam- pling transmitted by the capsule at 433 Hz with 6 second sampling intervals. Patients were instructed to perform their normal daily activities and dietary prac- tices. Distal esophageal pH recording was conducted for a total of 48 hours. During this time patients kept dia- ries of meal times, symptoms, and supine positioning. After completion of the 48-hour study, data were downloaded from recording devices to dedicated com- puters. Patient diary information was manually entered into the computer-based record. Measurements of the total, upright, and supine percentage time when esopha- geal pH was below 4 were determined over day 1 and day 2 of the wireless study. Total acid exposure time (% total time pH less than 4) greater than 5.5% was consid- ered abnormal, while greater than 8.2% was considered abnormal for the upright state and greater than 3.0% was considered abnormal for the supine state. 18 Esophageal Motility Testing High-resolution manometry (Given Imaging, Duluth, GA) was used to measure the location of the lower esoph- ageal sphincter prior to placement of the impedance-pH catheter. A solid-state assembly with 36 circumferential sensors spaced at 1-cm intervals (outer diameter 4.2 mm) was used. This device detects pressure over a length of 2.5 mm in each of the 12 radially dispersed sectors of the 36 pressure-sensing elements. The sector pressures are averaged, making the sensors a circumferential pressure detector. Prior to recording the transducers were cali- brated at 0 and 100 mm Hg using externally applied pressure. Using this device the lower esophageal sphinc- ter was measured and the proximal location noted for placement of the impedance-pH catheter. Combined Impedance-pH Monitoring Patients underwent impedance-pH monitoring while on at least twice daily PPI therapy for 1 month prior to evaluation. They were instructed to fast for 4 hours before testing. Each patient’s primary symptom complaint was recorded as part of the preprocedure evaluation. Patients were given diaries to record the timing of initiation and completion of meals and position changes (upright or supine) during 24-hour impedance and pH monitoring. Impedance testing was performed using a combined impedance-pH monitoring device (Sandhill Scientific Inc; Highlands Ranch, CO) comprising a data recorder (Sleuth System; Sandhill Scientific Inc.) and a 2.1-mm diameter

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