Inclusion Criteria:
* COPD group:
* Age：≥40
* Suspected COPD：COPD-SQ≥16，and no evidence of airflow limitation after bronchodilators
* Confirmed COPD：According to the diagnostic criteria in the 2021 Revised Edition of the Chinese Guidelines for the Diagnosis and Treatment of Chronic Obstructive Pulmonary Disease and the 2026 GOLD Report, a diagnosis requires the presence of symptoms (such as dyspnea, chronic cough, or sputum production), a history of exposure to risk factors (e.g., smoking, biomass fuels, occupational exposures, or air pollution), evidence of persistent airflow limitation (post-bronchodilator FEV1/FVC \< 0.70), and the exclusion of alternative diagnoses.
* Exclude acute exacerbation within the last month Asthma group：
* Age：≥3
* Suspected asthma：Patients with chronic respiratory symptoms but no evidence of variable airflow limitation
* Confirmed asthma：According to the diagnostic criteria in the 2024 Chinese Guidelines for the Prevention and Treatment of Bronchial Asthma and the 2025 GINA Report, diagnosis requires the presence of recurrent symptoms (such as wheezing, shortness of breath, chest tightness, and cough) that resolve spontaneously or with treatment; evidence of variable airflow limitation (e.g., a positive bronchodilator reversibility test, a positive bronchial provocation test, or an average daily diurnal PEF variability of \>10% over at least 7 consecutive days); and the exclusion of alternative diagnoses.
Healthy subjects:
* Age ≥ 3 (See Table 1 for details)
* No respiratory symptoms（cough, expectoration, shortness of breath, wheezing, etc）
* No history of serious cardiopulmonary or other systemic diseases, especially no history of respiratory diseases and surgery
* No history of respiratory infection within the past 4 weeks; non-smoker or total lifetime smoking \< 100 cigarettes
* No history of occupational exposure to harmful gases or dust, or serious pollution of the work or living environment
* No abnormalities on chest physical examination
* No abnormalities were found on chest imaging (X-ray, CT) records within the past year.
* Body mass index within the normal range (18.5\~24.9) Confirmed Bronchiectasis Group：
* Age ≥ 3 years
* Clinical history consistent with bronchiectasis, confirmed by CT scan
* No other concurrent or accompanying respiratory diseases at present Confirmed ILD Group：
* Age ≥ 3 years
* Fibrotic interstitial lung disease: HRCT scan shows fibrotic lung disease, defined as reticular abnormalities and traction bronchiectasis with or without honeycombing, and the disease extent \> 10%; or lung tissue biopsy indicates fibrotic interstitial changes
* No other concurrent or accompanying respiratory diseases at present Confirmed Upper Airway Obstruction Group：
* Age ≥ 3 years, gender not restricted
* History of upper airway inflammation, injury, endotracheal intubation or tracheotomy, burns, foreign body aspiration, tracheal tumor, or other conditions that can cause large airway obstruction
* Clinical manifestations are mainly dyspnea and shortness of breath, which are significantly aggravated after activity, and sometimes symptom exacerbation is related to body position
* Pulmonary function test shows significant limitation of inspiratory or expiratory flow in the F-V curve, presenting a characteristic plateau pattern
* At least one of the following evidences: chest CT scan or upper airway three-dimensional reconstruction confirms upper airway stenosis; laryngoscopy or bronchoscopy reveals tracheal/bronchial wall thickening and/or stenosis, intratracheal nodules or neoplasms, tumor infiltration, tracheal mucosal congestion, tracheal cartilage collapse, etc
Exclusion Criteria:
* • Contraindications for oscillometry testing and spirometry testing: Oscillometry testing: Severe and intolerable dyspnea, acute exacerbation of respiratory infection, uncontrolled epilepsy, oral or facial diseases or deformities preventing proper latching, tympanic membrane perforation, need for continuous oxygen therapy, indwelling gastric tube, tracheotomy with inability to close the tube, currently undergoing artificial ventilation and unable to temporarily stop the procedure; Spirometry testing: Recent severe cardiovascular disease, epileptic seizures, uncontrolled hypertension, aortic aneurysm, severe hyperthyroidism, heart rate \>120 bpm, tympanic membrane perforation, other respiratory infectious diseases, etc.;
* Other respiratory diseases that affect lung function results： such as lung cancer, pneumonia, active pulmonary tuberculosis, pulmonary embolism, etc.; Recent surgical history that affects lung function results, including open-chest surgery, pleural effusion surgery, etc.;
* Poor cooperation during basic lung function tests, failing to meet quality control requirements;
* Breastfeeding women;
* Participants deemed unlikely by the researcher to comply with research procedures and restrictions.
