Can a vibroacoustic device help COPD patients get more sputum when they inhale saline mist

Inclusion Criteria:

1. Able and willing to give written informed consent.
2. Male and female participants, aged ≥40-70 years. Women of childbearing potential (i.e. not post-menopausal, defined as amenorrhoeic for at least 12 months, and without documented surgical sterilization such as hysterectomy, bilateral oophorectomy, or tubal ligation) must not be pregnant, as confirmed by a negative urine pregnancy test prior to each sputum induction procedure, and must not be breastfeeding.
3. Diagnosis of COPD based on post-bronchodilator spirometry, defined as FEV1/FVC \< 0.70, consistent with GOLD criteria.
4. FEV1 ≥50% of predicted (post-bronchodilator).
5. Body mass index between 18 and 38 kg/m2
6. Subgroup "Current Smokers": current smoking with at least 15 cigarettes per day over the past 12 months and a cumulative smoking history of at least 10 pack-years, confirmed by a positive urine cotinine test at screening.
7. Subgroup "Ex-smokers": no smoking for at least one year prior to screening and a cumulative smoking history of at least 10 pack-years, confirmed by a negative urine cotinine test at screening

Exclusion Criteria:

1. Any clinically relevant disease or condition which, in the opinion of the investigator, may significantly compromise participant safety, affect study outcomes, or prevent adherence to the protocol. Explicitly excluded is cystic fibrosis or interstitial lung disease.
2. Any condition that, as judged by the investigator, constitutes a contraindication or safety concern for the application of vibroacoustic chest therapy. This includes, but is not limited to:

   * Any implanted or external electronic-mechanical device in the thoracic projection area (e.g. cardiac pacemaker, implantable cardioverter-defibrillator, cardiac assist devices, implantable drug delivery pumps, neurostimulators)
   * Coronary heart disease with coronary stents or history of percutaneous coronary intervention or coronary artery bypass grafting
   * Mechanical heart valve prosthesis
   * Aortic stent graft or thoracic endovascular implant
   * Unstable angina pectoris or acute coronary syndrome within the past 6 months
   * Clinically significant cardiac arrhythmia requiring treatment (e.g. uncontrolled atrial fibrillation, ventricular tachycardia)
   * Known large pulmonary bullae (\>1 cm) or history of spontaneous pneumothorax
   * Unstable rib fractures or thoracic vertebral fractures
   * Active haemoptysis or known high risk of pulmonary haemorrhage
   * Therapeutic anticoagulation or known coagulation disorder with increased bleeding risk
   * Active thoracic malignancy
   * Thoracic surgery within the past 6 month
3. Initiation or discontinuation of mucolytic or expectorant agents (e.g., N-acetylcysteine, ambroxol) within 14 days prior to Visit 1 or between study visits. Participants on stable chronic mucolytic therapy (unchanged regimen for at least 4 weeks prior to Visit 1) may be enrolled provided they maintain the same regimen throughout the study.
4. Treatment with systemic corticosteroids or biological therapies within 6 months prior to screening
5. Treatment with antibiotics within 2 months prior to screening
6. Lower respiratory tract infection within 4 weeks prior to screening
7. Upper respiratory tract infection within 2 weeks prior to screening
8. History of drug or alcohol abuse within 12 months prior to screening
9. Participation in a clinical trial involving an investigational medicinal product within 6 months prior to screening
10. Any condition associated with an increased risk of non-compliance with study procedures (e.g. inability to hold the vibroacoustic emitters against the chest because of severe arthritis, neuromuscular disease, or other condition significantly limiting upper extremity function).