The goal of this clinical trial is to evaluate whether two types of breathing training can improve symptoms of gastroesophageal reflux disease (GERD) in adults.

The main research questions are:

• Do volume-oriented incentive spirometry (VIS) or diaphragmatic breathing exercise (DBE) improve GERD symptoms compared with usual care?
• Do these breathing exercises reduce the symptoms of GERD?
• Does volume-oriented incentive spirometry (VIS) produce greater improvement in GERD symptoms compared with DBE?
• Do these exercises increase the strength of the lower esophageal sphincter (LES)?

Researchers will compare VIS training, DBE training, and usual care to determine whether breathing training can serve as a safe and effective non-pharmacological treatment option for GERD.

Participants will:

• Be randomly assigned to VIS training, DBE training, or usual care
• Perform their assigned breathing training (if in the intervention group) twice daily for 6 weeks
• Attend study visits at baseline and at week 7 for questionnaires and esophageal function tests
• Keep a diary of their symptoms and breathing practice

Gastroesophageal reflux disease (GERD) is a prevalent gastrointestinal disorder resulting from dysfunction of the lower esophageal sphincter (LES) and impaired anti-reflux barrier mechanisms. While proton pump inhibitors (PPIs) are effective in reducing gastric acid secretion, up to 30-40% of patients report persistent symptoms despite optimized medical therapy. Non-pharmacological interventions are therefore of growing clinical interest.

Diaphragmatic breathing exercise (DBE) targets abdominal breathing patterns to enhance diaphragmatic tone and coordination. This may improve the esophagogastric junction competence and reduce transient LES relaxations. Volume-oriented incentive spirometry (VIS), a device providing visual feedback during sustained deep inspiration, has been demonstrated to facilitate diaphragmatic recruitment and strengthen inspiratory effort. VIS has shown benefits in perioperative recovery, pulmonary rehabilitation, and post-COVID-19 recovery, but has not yet been systematically studied in GERD populations.

This randomized controlled trial adopts a parallel three-arm design, comparing VIS training, DBE training, and a usual care control group. Participants in the intervention arms will be instructed to perform their assigned breathing training twice daily for six weeks. Standardized protocols will be applied: VIS training will target 80-90% of predicted inspiratory capacity with 3-5 seconds of breath-hold at peak inspiration, while DBE will emphasize abdominal expansion and controlled diaphragmatic contraction.

Objective outcome measures include high-resolution manometry (HRM) to assess LES basal pressure and 24-hour pH-impedance monitoring to quantify esophageal acid exposure time (AET) and reflux episodes. GERD symptom severity will be evaluated using validated questionnaires (GERDQ). Assessments are scheduled at baseline and week 7 following the intervention.

The primary hypothesis is that both VIS and DBE will improve GERD symptoms compared with usual care, with VIS expected to demonstrate superior enhancement of diaphragmatic activation and LES pressure. Secondary outcomes will explore physiological changes in esophageal acid exposure, symptom-reflux association, and intervention feasibility.

This trial is expected to generate evidence supporting safe, low-cost, and accessible non-pharmacological strategies for GERD management, complementing or potentially reducing the need for long-term pharmacotherapy.

Inclusion Criteria:

• Adults aged 20 to 80 years
• Endoscopic finding of reflux esophagitis (LA grade A) with proton pump inhibitor (PPI) use > 2 months, or 24-hour pH monitoring showing acid exposure time (AET) > 6%, or endoscopic diagnosis of reflux esophagitis LA grade B or higher
• Willingness to comply with the full training and follow-up protocol

Exclusion Criteria:

• Pregnant or breastfeeding women
• History of anti-reflux surgery
• Severe cardiopulmonary dysfunction or respiratory disease
• Inability to perform the training exercises or attend follow-up visits

De-identified individual participant data (IPD) will be shared, including demographic characteristics, baseline clinical data, intervention adherence, and primary and secondary outcome measures (GERDQ scores, LES pressure, 24-hour pH-impedance results, and HRM parameters). No identifiable personal information will be included.

De-identified individual participant data and supporting information (study protocol, SAP) will be available beginning 6 months after publication of the primary results. Data will remain available for 3 years after publication.

Data will be available to qualified researchers for purposes of meta-analysis or secondary research related to gastroesophageal reflux disease. Requests should be submitted to the Principal Investigator by email. Access will be granted after review and approval of a reasonable research proposal, and a data use agreement may be required.

This study uses a single-blind design. Outcome assessors analyzing GERDQ questionnaires, high-resolution manometry, and 24-hour pH-impedance data are blinded to group assignments, while participants, care providers, and investigators are aware of interventions.