Effect of barometric pressure on single-breath carbon monoxide diffusing capacity

Abstract

BackgroundSingle-breath diffusing capacity for carbon monoxide (DLCO) quantifies gas transfer in the lungs. DLCO measurement is affected by barometric pressure (Pb) and alveolar partial pressure of oxygen (PAO2). The current equations for adjusting DLCO for Pb and PAO2 may not be accurate given advances in test performance and technology. We quantify changes in DLCO with alterations in Pb in normal and COPD subjects, determine the accuracy of the current Pb and PAO2 adjustment equations and develop updated adjustment equations. MethodsWe measured DLCO in 13 normal and 10 COPD subjects at 1330 m altitude and in a hypobaric/hyperbaric chamber at altitudes of sea-level and 2500 m; six normal subjects were tested at 3600 m. We determined if there were significant differences in DLCO between altitudes. We developed an equation for adjusting DLCO for changes in Pb from sea-level. We compared this equation with the existing Pb adjustment equation in normal and COPD subjects. We determined the accuracy of the current PAO2 adjustment equation and developed a new PAO2 adjustment equation. ResultsDLCO significantly increased with decreasing Pb. We developed a Pb adjustment equation that adjusts DLCO measured at altitudes between 1330 m and 3600 m to sea-level values. This Pb adjustment equation yields DLCO results that are not significantly different than the currently recommended equation. We developed a more accurate PAO2 adjustment equation. ConclusionDLCO measurement is significantly affected by altitude. We developed equations that accurately adjust DLCO for changes in Pb and PAO2 in normal and COPD subjects.