Nasal High Flow at 25 L/min or Expiratory Resistive Load do Not Improve Regional Lung Function in Patients with COPD: A Functional CT Imaging Study

Abstract Background: Nasal high flow (NHF) is a non-invasive breathing therapy that is based on the delivery via a large-caliber nasal cannula of heated and humidified air at flow rates that exceed peak inspiratory flow. It is thought that positive airway pressure generated by NHF can help reduce gas trapping and improve regional lung ventilation. There are no data to confirm this hypothesis at flow rates applicable in stable COPD patients.Methods: In this study, we used non-rigid registration of CT images acquired at maximal expiration and inspiration to compute regional lung attenuation changes (ΔHU), and lung displacement (LD), indices of regional lung ventilation. Eight COPD patients were assessed at baseline (BL) and after 5 min of NHF and expiratory resistive loading (ERL).Results: ΔHU was: BL: 81.7±28.8; NHF: 77.3±28.1; ERL: 70±26.7 HU (p=0.164) and LD: 30.2±12.7; 21.9±10.1 and 20.6±5.8 mm (p=0.044) in the 3 conditions, respectively. Respiratory rate significantly decreased with both treatments (BL:17.6±2.9; NHF:13±3.6; ERL: 11.6±2.8 bpm; p<0.001) while end-expiratory volume tended to increase.Conclusions: Neither NHF at 25 L/min nor ERL significantly improve the regional lung ventilation of stable COPD patients with gas trapping, based on the registration of expiratory and inspiratory CT images. Further studies are needed to assess the potential effect of higher flow rates of NHF.Trial registration: This study was registered with https://clinicaltrials.gov/ under: NCT03821311.