xxiv List of abbreviations AHI Apnoea–hypopnoea index AIDS Acquired immunodeficiency syndrome BAL Bronchoalveolar lavage BMI Body mass index BPD Bronchopulmonary dysplasia CF Cystic fibrosis CFTR Cystic fibrosis transmembrane conductance regulator COPD Chronic obstructive pulmonary disease CPAP Continuous positive airway pressure CT Computed tomography ECG Electrocardiogram ENT Ear, nose and throat FEV1 Forced expiratory volume in 1 s FRC Functional residual capacity FVC Forced vital capacity GOR Gastro-oesophageal reflux HIV Human immunodeficiency virus HRCT High-resolution computed tomography ILD Interstitial lung disease KCO Transfer coefficient of the lung for carbon monoxide LCI Lung clearance index MRI Magnetic resonance imaging NIV Noninvasive ventilation OSA(S) Obstructive sleep apnoea (syndrome) PaCO 2 Arterial carbon dioxide tension PaO 2 Arterial oxygen tension PCD Primary ciliary dyskinesia PCR Polymerase chain reaction PEEP Positive end-expiratory pressure PFT Pulmonary function test PSG Polysomnography PtcCO 2 Transcutaneous carbon dioxide tension RV Residual volume SaO 2 Arterial oxygen saturation SpO 2 Oxygen saturation measured by pulse oximetry TB Tuberculosis TLC Total lung capacity TLCO Transfer factor of the lung for carbon monoxide V'E Minute ventilation