Effect of non-invasive ventilation on the measurement of ventilatory and metabolic variables

•Non invasive ventilation can be used in conjunction with cardio pulmonary exercise testing equipment.•Cardio pulmonary exercise testing metabolic variables are unaffected by pressure support with provided the gas density changed is accounted for.•Oxygen uptake can be measured after correcting for gas density. This should be applied to future studies examining oxygen uptake with non invasive ventilation.

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) 20 cm H2O compared to without NIV showed: VT, mean difference (MD) 0 mL (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.