This study is planned to be conducted based on the cohort of patients with severe chronic obstructive pulmonary disease in our hospital. Based on gut microbiota, random forest was used to search for potential diagnostic biomarkers in patients with frequent acute exacerbation and controls with non frequent acute exacerbation; Construct a frequent acute exacerbation risk prediction model using random forest, support vector machine, and BP neural network models. The development of this study will provide valuable references for the clinical classification and prognosis evaluation of chronic obstructive pulmonary disease (COPD), and improve the health level of COPD patients by further searching for treatable targets.

Inclusion Criteria:

1. Patients who meet the diagnostic criteria for COPD of the global initiative for chronic obstructive lung diseases (GOLD 2022) and GOLD grading Ⅲ - Ⅳ (FEV1/FVC<70%, FEV1% predicted value ≤ 50% after Bronchiectasis)
2. Age>40 years old
3. COPD stable for more than 4 weeks
4. Short acting Bronchiectasis was not used within 24 hours before this experiment, long acting Bronchiectasis was not used within 48 hours, and glucocorticoids were not used throughout the body in the past month
5. Patient informed and signed consent form

Exclusion Criteria:

1. Asthma, active pulmonary tuberculosis, interstitial pneumonia and severe Bronchiectasis
2. Complicated with serious diseases (acute infection, diabetes, stroke, heart disease, liver and kidney dysfunction, cancer or autoimmune disease)
3. History of chronic diarrhea or constipation
4. History of Gastrointestinal Surgery
5. Using probiotics or antibiotics within the past 4 weeks
6. No history of using oral hormones or traditional Chinese medicine in the past three months
7. Pregnancy or lactation

A patient with severe chronic obstructive pulmonary disease who visited the Department of Respiratory and Critical Care Medicine, Beijing Chaoyang Hospital, Capital Medical University since January 2023