AGA Abstracts Su1099 DISTENSIBILITY OF THE GASTROESOPHAGEAL JUNCTION HIGH- PRESSURE ZONE IN NON-GERD SUBJECTS PRE AND POST ATROPINE AND IN PATIENTS WITH GERD Anil Vegesna, Daren Chen, Barry P. McMahon, Petros C. Benias, Anjali Pillai, Larry S. Miller Background: Distensibility of the gastroesophageal junction high-pressure zone (GEJHPZ) has been shown to be greater in GERD patients than in non-GERD patients by using functional luminal imaging (FLIP) and yield pressures. In GERD patients, the pressure generated by the clasp and sling muscle fibers of the esophagus are lower, and the pressure of the lower esophageal circular smooth muscle (LEC) is attenuated. Aim: The aim of this project is to evaluate the distensibility of the GEJHPZ by using FLIP in GERD subjects, and non-GERD subjects before and after muscarinic blockade with atropine. Methods: Following anesthesia, a FLIP probe was passed trans-orally into the stomach and positioned across the GEJHPZ in 7 GERD subjects, and 8 non-GERD subjects before and after atropine administra- tion. Each balloon contained 16 impedance sensors spaced 5 mm apart. The balloon was positioned so that at least one distal sensor was in the stomach and at least one proximal sensor was in the esophagus. Minimum cross sectional area (CSA) at each impedance sensor and the pressure within the FLIP balloon were recorded as the balloon was sequentially filled to 40 ml by 10 ml increments. Key Results: CSA and pressures at 20, 30, and 40 ml were collected and analyzed. The distensibility plot was located significantly to the left in non-GERD post-atropine subjects and in GERD subjects when compared to non-GERD pre-atropine subjects. The GERD subjects' distensibility plot was further to the left than the non-GERD post-atropine subjects' plot (Fig. 1). The slopes of the distensibility plots from 20 to 40 ml of non-GERD pre-atropine, post-atropine, and GERD subjects were 1.2, 2.0, and 4.8 mm 2 /mmHg respectively (Fig. 1). Distensibility of the GEJHPZ was significantly less in the GERD patients compared to the non-GERD subjects both pre- and post-atropine at 40 ml (Table 1). Both GERD patients and non-GERD post-atropine subjects show signifi- cantly lower balloon pressures at all balloon volumes. Conclusions: Atropine increased the distensibility of the GEJHPZ in non-GERD subjects suggesting that tone and distensibity are influenced by vagal innervation in addition to passive tone. The increased distensibility in GERD subjects compared to the non-GERD subjects both pre- and post atropine suggests that there are other factors, in addition to loss of muscarinic tone, that contribute to increased distensibility in GERD patients. Average narrowest CSA in Non-GERD subjects and GERD patients This table shows the averages and standard error of means in non-GERD subjects and GERD patients. * Significant compared to non-GERD pre-atropine (p<0.05) # Significant compared to non-GERD post-atropine (p<0.05) This graph shows changes of CSA in non-GERD subjects and GERD patients. The X-axis represents pressure and Y-axis represents cross sectional area. S-488 AGA Abstracts Su1100 BASELINE IMPEDANCE MEASURED DURING WATER-PERFUSED HIGH RESOLUTION IMPEDANCE MANOMETRY: CLINICAL UTILITY AND PATHOPHYSIOLOGICAL IMPLICATION IN GERD Chien-Lin Chen, Tso-Tsai Liu, Chih-Hsun Yi, Wei-Yi Lei, Jui-Sheng Hung, Ming-Wun Wong Background/aim: Baseline impedance measured during solid-state HRIM (high resolution impedance manometry) can reliably discriminate patients with gastroesophageal reflux dis- ease (GERD) from controls. However, it is unknown whether similar measurement is applica- ble by using water-perfusion HRIM. We aimed to investigate the hypothesis whether baseline impedance measured during water-perfused HRIM can help discriminate GERD patients from the controls. We also aimed to test the hypothesis whether baseline impedance can predict proton pump inhibitors (PPIs) response in GERD patients. Methods: We enrolled consecutive patients with typical reflux symptoms and asymptomatic controls for HRIM. Baseline impedance was measured over 15 seconds during the landmark period of HRIM. All patients were given PPIs after upper endoscopy and their PPIs response was assessed 8 weeks after the treatment. Results: Among 18 GERD patients and 17 controls, baseline mucosa impedance measured during HRIM was lower in GERD patients than the controls (1861±183 vs. 3371± 250V, p < 0.001). Baseline impedance during water perfusion HRIM had moderate diagnostic accuracy for symptomatic GERD with an area under the curve (AUC) of 0.853 on receiver operating characteristics (ROC) analysis. A threshold of 2530 V for baseline impedance had a sensitivity of 88.3% and specificity of 82.4% for GERD with a positive predictive value of 83.4% and negative predictive value of 87.6%. Among all GERD patients, poor PPI responders had higher baseline impedance than those without it (2340±260 vs. 14791± 189 V, p = 0.02). There was no difference in base impedance regarding EGD or motility findings. BMI negatively correlated to base impedance in either controls (r= -0.59, p= 0.012) or GERD patients (r= -0.47, p = 0.047). Conclusion: Our work demonstrates that baseline impedance measurement during water perfusion HRIM has moderate diagnostic accuracy to distinguish GERD patients from controls. The results support early notion that baseline impedance measurement is clinicaly useful in predicting PPI response. The finding of reverse association between BMI and baseline impedance indicates that obesity might play a pathophysiological role in human esophageal integrity. Su1101 PATHOGENESIS OF VONOPRAZAN-RESISTANT NON-EROSIVE REFLUX DISEASE (NERD) AND THE ACID-SUPPRESSIVE EFFECT OF VONOPRAZAN IN THE PRESENCE OR ABSENCE OF HELICOBACTOR PYROLI INFECTION Shintaro Hoshino, Noriyuki Kawami, Yoshimasa Hoshikawa, Hiroki Ohno, Tadamichi Kawano, Mitsuru Kaise, Katsuhiko Iwakiri Background: Vonoprazan (VPZ) is a potassium-competitive acid blocker (P-CAB) with potent acid-suppressive effects, and became available in 2015. Despite the use of VPZ, reflux symptoms remain unresolved in some patients. The objective of this study was to clarify the details of the pathogenesis of VPZ-resistant NERD. In addition, the mechanism of reflux symptoms and suppression of gastric acid secretion in the presence or absence of Helicobacter pylori infection were investigated in patients with symptoms related to liquid reflux. Methods: Forty-three patients (21 men, mean age: 57.9±2.4) with vonoprazan-resistant NERD were enrolled in the study. VPZ (20 mg/day for 2-4 weeks) was administered to NERD patients who had severe reflux symptoms for at least twice a week and whose symptoms did not resolve despite taking standard-dose PPI for 4 weeks. Patients with symptoms despite VPZ treatment were diagnosed with VPZ-resistant NERD. Esophageal mucosa biopsy and esophageal manometry were performed to exclude patients with eosinophilic esophagitis and primary esophageal motility disorders. When eosinophilic esophagitis and primary esophageal motility disorders were ruled out, esophageal impedance pH monitoring of the esophagus was performed during VPZ therapy. Reflux was classified as acidic (pH<4), weakly acid (4#pH<7), or weakly alkaline (pH$7), and reflux symptoms were evaluated based on the Symptom Index (SI). All patients were tested for the presence of H. pylori infections. For patients who were SI-positive for liquid reflux, the mechanism of SI positivity and the percent time with intragastric pH >4 in the presence or absence of Helicobacter pylori infection were investigated. Results: One of the 43 patients (2.3%) was diagnosed with primary esophageal motility disorder (Jackhammer esophagus). Nineteen patients (44.2%) were SI- positive for liquid reflux, 3 patients (7.0%) were SI-positive for gas reflux, and the remaining 20 patients (46.5%) had functional heartburn. Symptoms in patients SI-positive for liquid reflux were associated with weak acid reflux, regardless of the presence of H. pylori infection. Over a 24-h period, the percent time with intragastric pH >4 was 78.2±4.4% (mean ± SE) and 98.1±0.8% in H. pylori-negative and positive patients, respectively, indicating a sufficient acid suppression effect. Conclusion: 2.3% (n=1) of the VPZ-resistant NERD patients had a primary esophageal motility disorder, 51% (n=22) were SI-positive for liquid or gas reflux, and 47% (n=20) had functional heartburn. Our findings suggested that gastric acid suppression by 20-mg VPZ was sufficient irrespective of H. pylori infection, resulting in none of the patients being SI-positive for acid reflux. Therefore, it is possible to prevent acid-related symptom by administration of 20-mg VPZ for 2-4 weeks ("VPZ test"). Su1102 THE STUDY OF SWALLOWING PATTERN, GASTROESOPHAGEAL REFLUX(GER) CHARACTERISTICS IN PATEINTS WITH LOW (XEROSTOMIA) AND NORMAL SALIVARY FLOW RATE Jeerawat Maytapa, Kasidit Norasettkul, Sureeporn Jangsirikul, Tanisa Patcharatrakul, Sutep Gonlachanvit Swallow plays role on esophageal acid clearance and can induce reflux. The swallowing process involves adequate saliva flow. However, the association between saliva flow and swallowing pattern, esophageal acid clearance, and reflux characteristics are unknown.