This research is designed to evaluate how long-term treatment with Bilevel Positive Airway Pressure (BiPAP) influences diaphragm function in patients with Chronic Obstructive Pulmonary Disease (COPD) who suffer from chronic hypercapnic respiratory failure. The diaphragm is the primary muscle of breathing, and its dysfunction is linked to unfavorable clinical outcomes such as higher mortality rates and frequent hospitalizations. In this prospective cohort study, COPD patients starting BiPAP therapy based on clinical indication will be monitored through repeated ultrasound assessments of diaphragm structure and function together with pulmonary function testing, respiratory muscle strength evaluation, dyspnea. The main outcome of interest is the change in diaphragm thickness in inspiration, thickness in expiration, diaphragm thickening fraction (DTF), diaphragm maximum contraction velocity and maximum relaxation velocity across a 6 weeks as a early time and 12 months for long time follow-up period. Secondary measures include hospital admissions, and one-year survival. The study is expected to generate valuable evidence about the link between non-invasive ventilation and diaphragm function, which may contribute to optimizing treatment strategies for COPD patients with advanced respiratory failure.