List of abbreviations AHI apnoea–hypopnoea index BMI body mass index COPD chronic obstructive pulmonary disease COVID-19 coronavirus disease 2019 CPAP continuous positive airway pressure CT computed tomography ECG electrocardiography FEV1 forced expiratory volume in 1 s FVC forced vital capacity HRCT high-resolution computed tomography Hb haemoglobin K CO transfer coefficient of the lung for carbon monoxide (normalised for alveolar volume) MRI magnetic resonance imaging NIV noninvasive ventilation OSA(S) obstructive sleep apnoea (syndrome) PaCO2 arterial carbon dioxide tension PaO2 arterial oxygen tension PtcCO2 transcutaneous carbon dioxide tension SaO2 arterial oxygen saturation SARS-CoV-2 severe acute respiratory syndrome coronavirus 2 SpO2 arterial oxygen saturation measured by pulse oximetry TLC total lung capacity T LCO transfer factor of the lung for carbon monoxide V' E minute ventilation vii