Chronic obstructive pulmonary disease (COPD) is characterized by periods of acute worsening of symptoms, called exacerbations. Severe exacerbations require hospitalization, increase vulnerability to new exacerbations, and recovery can be slow or incomplete. The management of COPD therefore aims at prevention of exacerbations, but early and reliable prediction is difficult. Home-based daily lung-function testing could play a major role in this, but spirometry, the gold standard, is less suitable since it is difficult and inconvenient for COPD patients. Therefore, this work presents a novel auto-calibrating method to measure scaled tidal flow-volume curves (during restful breathing) from pressure recordings obtained via a nasal cannula. Experiments demonstrate a high level of accuracy. Because tidal curves are hardly used in medical care, the relation with conventional (forced) spirometry is investigated. Methods are introduced to determine (a) the expected tidal flow-volume curve for a given value of the Tiffeneau-Pinelli index obtained from forced spirometry, and (b) the expected Tiffeneau-Pinelli index for a given shape of the tidal curve. The average shape varies in a characteristic way with varying index, leading to an objective ranking of tidal curves. Large variations of measured curve shapes with similar index might potentially be useful in the prediction of exacerbations. Lattice Boltzmann simulations with a large eddy scale model are performed to reveal the flow during a realistic, transient, breathing profile in an adult upper airway. Comparison of pressure data to experiments shows a good agreement on average. Nasal high-flow therapy (NHFT) can be used in the treatment of exacerbations. Two main effects, the washout of anatomical dead space and the provision of positive end-expiratory pressure (PEEP) are studied by measuring the pressure distribution in 3D printed upper airway geometries. NHFT jet penetration is found to be hardly dependent on cannula size or NHFT flow rate. PEEP is approximately proportional to the square of the flow rate. By adapting the model for spontaneuous breathing profiles, a method is presented to reconstruct tidal flow-volume curves during NHFT from pressure recordings in the NHFT system. Experimental validation in the 3D printed geometries shows a satisfying accuracy in the adult model with sufficiently large cannula, but inaccuracy in the infant models. Further research is required to improve clinical applicability.