All patients with COVID-19 were divided into three groups according to their illness: mild patient who receive conventional oxygen therapy, severe patients who receive nasal high flow oxygen inhalation or non-invasive positive pressure ventilation，all the oxygen therapy will be used as part of the standard of care. Each group will enroll 10 patients, the treatment of all patients will be continuously optimized during observation, and the incidence of respiratory failure, intubation rate, 28 day mortality rate, ICU hospitalization days, etc will be recorded and analyzed so to optimize the treatment time window of sequential oxygen therapy

Inclusion Criteria:

• Patients diagnosed with COVID-19

  • Aged between 18-75 years;

    • Willing to sign the informed consent voluntarily.

Exclusion Criteria:

• Patients with active tuberculosis, idiopathic pulmonary fibrosis, bronchial asthma, bronchiectasis, pulmonary embolism, chronic respiratory failure or other serious respiratory diseases; ② patients with serious cardiovascular and cerebrovascular diseases (malignant arrhythmia, unstable angina, acute myocardial infarction, cardiac function grade 3 or above, stroke, cerebral hemorrhage, etc.); ③ Patients with serious hepatorenal diseases (serious liver diseases refer to cirrhosis, portal hypertension and varicose bleeding, and serious kidney diseases include dialysis and kidney transplantation); ④ tumor patients who have undergone resection, radiotherapy and chemotherapy within 5 years; ⑤ patients who have difficulty in activity due to neuromuscular diseases; ⑥ patients with serious arthritis; ⑦ patients with serious peripheral vascular diseases; ⑧ Pregnant and lactating women; ⑨ with severe cognitive and mental disorders; ⑩ the clinical researchers who were participating in other interventions within one month before selection;

Only patients diagnosed with COVID-19 will be enrolled, diagnosis will depend on RT-PRC provided by China CDC