title: Effect of non-invasive ventilation on the measurement of ventilatory and metabolic variables.
abstract: The effect of non-invasive ventilation (NIV) on the accuracy of measurements of ventilation, oxygen consumption (V˙O2) and carbon dioxide production (V˙CO2) was examined using a simulator. Known gas volumes of oxygen and carbon dioxide were delivered to a metabolic system that measured tidal volume, respiratory rate, V˙O2 and V˙CO2, both with and without NIV. Bland-Altman analyses were used to compare between conditions. NIV at pressure support (PS) 20cm H2O compared to without NIV showed: VT, mean difference (MD) 0mL (limits of agreement (LOA) -21 to 21) mL; V˙O2 MD -413 (LOA -810 to 16) mL/min; and V˙CO2 MD 32 (LOA -32 to 97) mL/min. For V˙O2 measurements during NIV, a correction was applied to account for increased air density due to PS. After correction, V˙O2 measurement accuracy improved; MD -46 (LOA -108 to 17) mL/min. Tidal volume and metabolic variables can be measured with acceptable accuracy during NIV, providing V˙O2 is corrected for altered gas density.
authors.affiliation: Faculty of Health Sciences, The University of Sydney, Sydney, Australia. Electronic address: cden2754@uni.sydney.edu.au.
authors.forename: C J
authors.initials: CJ
authors.lastname: Dennis
authors.affiliation: Department of Respiratory & Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Menadue
authors.affiliation: Faculty of Health Sciences, The University of Sydney, Sydney, Australia.
authors.forename: A R
authors.initials: AR
authors.lastname: Harmer
authors.affiliation: Department of Respiratory & Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia; Faculty of Medicine, The University of Sydney, Sydney, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Barnes
authors.affiliation: Faculty of Health Sciences, The University of Sydney, Sydney, Australia; Department of Physiotherapy, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Alison
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D004867:Equipment Design; D005080:Exercise Test; D006801:Humans; D008954:Models, Biological; D063087:Noninvasive Ventilation; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D011312:Pressure; D011659:Pulmonary Gas Exchange; D012119:Respiration; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Exercise; Gas density; Measurement accuracy; Oxygen consumption; Pressure support