EBC sampling
®
EBC was collected in a standardised manner using a cooling tube (RTube®, Respiratory Research Inc. Texas, USA) over a period of 10 min of passive tidal breathing whilst the participant wore a nose clip, stopping briefly to swallow saliva if needed, as per manufacturer’s guidance. The RTube® is a single-patient, single-use design, preventing cross contamination, and features a large ‘Tee’ section to separate saliva from exhaled breath, thereby ensuring collection of airway lining fluid and not secretions from the oropharynx. Once collected, samples were immediately separated into aliquots and stored at − 70 °C pending analysis.