Pilot Physiological Evaluation of an Investigational Mask with Expiratory Washout.

The goal of this pilot randomized cross-over study is to compare the effect of a full-face mask with expiratory washout to a conventional full face mask on non-invasive ventilation (NIV) in patients with acute hypercapnic, and acute hypoxemic, respiratory failure. The main questions it aims to answer are: * Does a mask with expiratory washout improve minute ventilation in patients using non-invasive ventilation compared with a conventional single-limb NIV mask * How does a mask with expiratory washout affect respiratory variables compared with a dual-limb NIV mask. Participants already prescribed NIV will undergo 3 arms of the investigation in a randomized order: * Single-limb NIV with investigation mask (with expiratory washout) * Single-limb NIV with conventional mask * Dual-limb NIV with conventional mask