Patient Inclusion Criteria:  Age ≥ 18 years BMI <30 kg/m¬2 Confirmed diagnosis of COPD Currently using domiciliary NIV with average reported compliance of at least 3hours Ability to provide informed consent Medical stability confirmed by recruiting physician Free of exacerbations for at least 2 weeks prior to enrolment Presence of expiratory flow limitation on forced oscillation technique criteria  Exclusion Criteria:  Current acute illness as determined by recruiting physician e.g. upper respiratory tract infection Presence of major medical comorbidity, e.g. severe heart failure (LVEF <30%), active malignancy, end-stage renal failure (CKD 4), and neuromuscular disease Subjects who have had surgery of the upper airway, nose, sinus, or middle ear within the previous 90 days. Psychosocial factors that would prevent compliance with study protocol  Healthy participant inclusion criteria:  Age ≥ 18 years No expiratory flow limitation on forced oscillation testing No acute illness on study day Ability to provide informed consent