The objective: to determine the effect of prolonged oxygen therapy (POT) on changes in the clinical and functional status of patients with chronic obstructive pulmonary disease (COPD) and severe hypoxemic chronic respiratory failure. Subjects and methods. 30 patients with COPD were examined during the period of remission of the disease, the average age was 64.8 ± 6.9 years. After the initial examination, patients were prescribed POT at home for 16 hours/day. As a basic therapy, all patients received a combined bronchodilator of long-acting indacaterol/glycopyrronium at a dose of 110/50 μg once a day in combination with beclomethasone dipropionate (BDP) at the dose of 200-400 μg/day. The patients were examined repeatedly 3 times with a 1-year interval. Clinical indicators, gas composition of arterial blood, results of spirometry and ultrasound examination of the diaphragm were evaluated. Results. Initially, disorders of the functional state of the diaphragm were detected in COPD patients with hypoxemia (decrease in the thickening fraction and relaxation rate). After the first year of using POT, an increase in the rates of contraction and relaxation of the diaphragm muscle under tidal respiration was observed. On the 2nd and 3rd year of using POT, it was noted that indicators of the functional state of the diaphragm stabilized. As a result of POT, the number of exacerbations went down and mortality in COPD patients with hypoxemia decreased. Against the background of basic therapy with indacaterol/glycopyrronium in combination with low doses of BDP, no adverse events were observed for the entire period of follow-up. Conclusions. POT in combination with a double long-acting bronchodilator and low-dose inhaled glucocorticosteroids in COPD patients with hypoxemic chronic respiratory failure helps to reduce dyspnea, the number of severe exacerbations, as well as improve pulmonary ventilation functions, blood gas content, and the diaphragm function during the first year of its use. Further, the indicators continued to stabilize.