title: Closed circuit rebreathing to achieve inert gas wash-in for multiple breath wash-out.
abstract: Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be delivered and it would not alter wash-out parameters. Computer modelling was used to assess the impact of the rebreathe method on wash-in efficiency. Clinical testing of open and closed circuit wash-in-wash-out was performed in healthy controls and adult patients with cystic fibrosis (CF) using a circuit with an effective CO2scrubber and a refined wash-in protocol. Wash-in efficiency was enhanced by rebreathing. There was no difference in mean lung clearance index between the two wash-in methods for controls (6.5versus6.4; p=0.2, n=12) or patients with CF (10.9versus10.8; p=0.2, n=19). Test time was reduced by rebreathe wash-in (156versus230 s for CF patients, p<0.001) and both methods were well tolerated. End wash-in CO2was maintained below 2% in most cases. Rebreathe-wash-in is a promising development that, when correctly deployed, reduces wash-in time and facilitates portable MBW testing. For mild CF, wash-out outcomes are equivalent to an open circuit.
authors.affiliation: Institute of Inflammation and Repair, Education and Research Centre, University of Manchester, Manchester, UK; Manchester Adult Cystic Fibrosis Centre, University Hospital of South Manchester, Manchester, UK.
authors.forename: Alex R
authors.identifier: 0000-0003-1828-0058
authors.initials: AR
authors.lastname: Horsley
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: O'Neill
authors.affiliation: Belfast City Hospital, Belfast Health and Social Care Trust, Belfast, UK.
authors.forename: Damian G
authors.initials: DG
authors.lastname: Downey
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast, UK; Belfast City Hospital, Belfast Health and Social Care Trust, Belfast, UK.
authors.forename: J Stuart
authors.initials: JS
authors.lastname: Elborn
authors.affiliation: Bristol Royal Infirmary, University Hospitals Bristol NHS Foundation Trust, Bristol, UK.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Bell
authors.affiliation: Institute of Inflammation and Repair, Education and Research Centre, University of Manchester, Manchester, UK.
authors.forename: Jaclyn
authors.initials: J
authors.lastname: Smith
authors.affiliation: School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
authors.forename: John
authors.initials: J
authors.lastname: Owers-Bradley