The goal of this clinical trial is to learn if inspiratory muscle training (IMT) works to treat on clinical symptom severity and quality of life in patients with Non-erosive reflux disease (NERD). The main questions it aims to answer are:

Does drug IMT lower the clinical symptom severity ? Does drug IMT improve quality of life? Researchers will compare high intensity IMT to a sham-IMT (a IMT device with no resistance) to see if IMT lower the clinical symptom severity and improve improve quality of life.

Participants will perform the following protocol:

The IMT protocol will consist of home-based high-intensity training using a Threshold IMT device: two sets of 30 breaths with a 1-minute rest, twice daily for 4 weeks. The study group will train at 60% of baseline maximum inspiratory pressure (MIP), with weekly adjustments based on modified Borg scores (4-6), while the control group will perform sham IMT without resistance.

The IMT protocol consisted of home-based high-intensity daily training - two cycles of 30 breaths with a 1-minute rest between sets, twice a day for 4 weeks using an IMT Threshold device (Threshold IMT Philips® Respironics, Inc). The IMT was performed twice a day, 7 days/week, for 4 weeks. The study group performed IMT at 60% of their baseline MIP and was adjusted weekly based on the modified Borg scale from 4 to 6 regarding respiratory effort performed during the session, while the control group performed a sham-IMT without applied resistance. Patients are evaluated before the inspiratory muscle training and after 4 weeks of training.

Inclusion Criteria:

• A clinical diagnosis of NERD,
• No erosive lesions on endoscopy,
• Presence of reflux symptoms for at least 3 months.

Exclusion Criteria:

• Current use of proton pump inhibitors (PPIs) or failure to complete a minimum 2-week washout period before enrollment.
• With known gastroduodenal ulcers
• Diagnosed with erosive esophagitis
• With hiatal hernia
• With a history of gastrointestinal malignancy
• With infectious or inflammatory gastrointestinal diseases
• With malabsorption syndrome or gastrointestinal obstruction
• With a history of major gastrointestinal surgery (including anti-reflux, gastric, or duodenal surgery)
• With systemic sclerosis or other systemic connective tissue diseases
• With severe cardiovascular, pulmonary, renal, or hepatic disease
• With chronic respiratory diseases such as asthma or COPD
• Having had an acute respiratory tract infection within the past 4 weeks
• With neuromuscular diseases
• With active tuberculosis
• Pregnancy