Investigating the Effect of Nasal High Flow Oxygen Therapy on Regional Lung Function

Nasal high flow (NHF) is a non-invasive breathing therapy that is based on the delivery of heated and humidified air at flow rates that exceed peak inspiratory flow, via a large-caliber nasal cannula. It delivers a fraction of inspired oxygen (FiO2) from 21% to 100%, with a flow rate up to 60 L·min-1. The therapy is used for a variety of disease conditions including chronic obstructive pulmonary disease (COPD). Patients with COPD frequently manifest flow limitation during resting tidal breathing, through dynamic compression of the airways, which is attributed to a loss of parenchymal tethering of the airways. In patients with severe COPD and respiratory failure, improved oxygenation and ventilation may reduce mortality. There are limited clinical data available in adult applications of NHF and on the effectiveness of NHF in patients with stable moderate or severe COPD. The mechanisms through which NHF affects the respiratory system are still being investigated. Two of the proposed mechanisms of action of NHF therapy are the generation of 3-5 cmH20 positive airway pressure during expiration and washout of the nasopharyngeal dead space. Positive airway pressure has been shown to improve oxygenation, ventilation-perfusion matching and respiratory rates, while nasopharyngeal washout reduces the anatomical dead space and thereby improves alveolar ventilation. Our working hypothesis is that positive nasopharyngeal pressure generated by NHF particularly during expiration can help maintain small peripheral airways patent, thereby reducing the amount of gas trapping. Gas trapping can be quantified based on densitometric analysis of registered computerized tomography images obtained at high and low lung volumes.