ATP Level and Cough Sensitivity to ATP in Subjects With Refractory/Unexplained Chronic Cough

Inclusion criteria for patients: 1. ≥18 years old 2. cough as sole symptom lasting ≥6 months 3. cough visual analogue score ≥30mm 4. diagnosed as RCC/UCC according to guidelines Exclusion criteria for patients: 1. smoking currently or in the past 6 months, or a smoking history of \>20 pack-year 2. a forced expiratory volume in 1 second/forced vital capacity ratio \<70%; 3. use of inhaled/oral corticosteroid, bronchodilators, anti-allergic medicine, antitussive medicine or anti-reflux treatment in the past 1 week; 4. a history of acute respiratory infection in the past 4 weeks; 5. a history of severe disease (cancer, acute coronary syndrome and so on). Healthy control aged ≥18 years old are included. Exclusion criteria are as follow: 1. smoking currently or in the past 6 months, or a smoking history of \>20 pack-year 2. a forced expiratory volume in 1 second/forced vital capacity ratio \<70% 3. a history of acute respiratory infection in the past 4 weeks 4. posstive findings of chest radiography 5. a history of chronic respiratory disease and allergic disease 6. any signs of cough hypersensitivity