The Effect of Home and Hospital Mask Designs on Respiratory Variables in Healthy Volunteers

The goal of this randomized cross-over study is to investigate whether the design of non-invasive ventilation (NIV) mask impacts respiratory variables in healthy volunteers on NIV therapy. The main questions it aims to answer are: * To assess if mask design impacts the ventilatory ratio in healthy volunteers. * To assess if mask design impacts transcutaneous CO2, respiratory rate, and tidal volume in healthy volunteers. Participants will attend five study visits: * Visit 1. Participants will be fitted to use non-invasive ventilation briefly to acclimatize them to using the therapy. * Visit 2. Participants will receive NIV with one of four masks. They will be asked to breathe through their mouth or through their nose, with a break from NIV in between the two sessions of NIV. * Visits 3-5. Participants will receive NIV with one of the other three masks, repeating Visit 2.

The study compares breathing with four different NIV masks, the interventional mask and three conventional NIV masks. Participants will be monitored by transcutaneous carbon dioxide, heart rate, oxygen, and respiratory rate monitors. Participants will attend five study visits: * Visit 1. Participants will be fitted to use NIV briefly to acclimatize them to using the therapy and ensure the four study masks fit. Participants that fit the masks and tolerate NIV well will be invited to attend four further visits. * Visit 2. Participants will be randomized as to which order they receive the masks, and which order they conduct mouth breathing and nose breathing. Baseline readings of normal unsupported breathing will be taken prior to going on NIV. Participants will the receive NIV with one of four masks for ten minutes and will be instructed to either breathe through their mouth or their nose. There will then be a break from NIV of at least ten minutes until baseline values of respiratory parameters have returned. Then there will be a second ten-minute period of NIV when the participant will be instructed to breathe through the other way through the nose or mouth. Once NIV therapy has been removed the participant will remain attached to the study monitoring equipment until respiratory parameters have returned to normal. * Visits 3-5 are a repeat of Visit 2 with the other study masks. The study is then complete.