Immediate effects of the MetaNeb® compared to huff and cough in adults with stable cystic fibrosis.

The MetaNeb® System (Hill-Rom, Inc. Batesville, Indiana, USA) is a relatively new device that has been developed to facilitate airway clearance in individuals with acute and chronic lung conditions, including cystic fibrosis (CF). It was introduced for clinical use in Australia in 2016. The MetaNeb® incorporates two modes; (i) continuous positive expiratory pressure (CPEP) and, (ii) continuous high frequency oscillation (CHFO). The CPEP mode assists with lung expansion and recruitment by delivering PEP, whereas the CHFO mode aids secretion clearance by providing pulsatile positive airway pressure at two different frequencies (similar to intrapulmonary percussive ventilation [IPV].)These modes deliver positive airway pressure and airway oscillation throughout both inspiration and expiration. The device also allows three varying levels of PEP to be applied at the mouthpiece, and a nebulised mucolytic (e.g. saline or hypertonic saline) to be delivered while the device is in use. Multiple interfaces can be used to deliver the therapy including a face mask, mouthpiece or tracheostomy. In this study we will be using the mouthpiece only. For the experimental intervention undertaken during visit 1, participants will be asked to complete 30 minutes of supervised physiotherapy in sitting, using the MetaNeb® system (Hill-Rom, Inc. Batesville, Indiana, USA) with their usual inhaled mucolytics (either normal or hypertonic saline). The 30 minute MetaNeb treatment session will comprise breathing in and out of the mouthpiece for 5x 5 minute cycles of MetaNeb® therapy (2.5 mins each of CPEP and CHFO modes) interspersed with 1 minute of sputum clearance using huff and/or cough. This treatment will be used on the first study visit only. Each participant will have the settings of the MetaNeb® titrated to optimise comfort and these settings will be recorded. All treatment sessions will occur in the Radiology department at Sir Charles Gairdner Hospital (SCGH) and will be conducted by either the PhD candidate or another trained member of the SCGH CF Physiotherapy team. Across both study visits, the 30-minute intervention period and 30-minute rest period will be video recorded (camera will be placed behind the participant and will not capture their face). This video recording will be used to: (i) count the number of number of huff and coughs performed during visit 1 and standardise this variable at visit 2 and (ii) provide the gold standard (criterion measure) of the number of coughs and huffs taken to establish agreement with the Spire Health Tag. Each visit will be separated by at least 48 hours and be within a two-week period (washout period). During the washout period participants will be asked to maintain their usual medications, airway clearance techniques and exercise habits. When first designing the study, our team did consider randomisation. However, this is not possible. This is because, in order to determine the true effect of the MetaNeb®, we need to use an experimental design in which the only difference between the two sessions is the use of the MetaNeb®. Every other factor that can influence airway clearance, such as the number of huffs and coughs the participant does, must be standardised between sessions. During the treatment session with the MetaNeb®, the participant will huff and cough. They will do this on request (by the treating physiotherapist), but this will also occur spontaneously. We have no control over spontaneous huffing and coughing during the MetaNeb® session (this is a reflex response to the changes in pressure and flow within the airways). Based on our clinical experience doing ACT with these patients, in some people, the MetaNeb® is likely to induce a lot of spontaneous huffing and coughing, and in other people, will not induce any. We will not know how the participant will respond until we perform the MetaNeb® session. For this reason, we must perform the MetaNeb® session first, so we can count the number of ‘requested’ and ‘spontaneous’ huffs and coughs so this can be standardised at the next session. This methodological consideration is well accepted in the literature, and has been described in earlier work (Dwyer et al 2019)