The DLNO/DLCO ratio: Physiological significance and clinical implications

J M B Hughes; A T Dinh-Xuan

doi:10.1016/j.resp.2017.01.002

The DL_NO/DL_CO ratio: Physiological significance and clinical implications

Respir Physiol Neurobiol. 2017 Jul:241:17-22. doi: 10.1016/j.resp.2017.01.002. Epub 2017 Jan 11.

Authors

J M B Hughes¹, A T Dinh-Xuan²

Affiliations

¹ National Heart and Lung Institute, Imperial College, London, United Kingdom. Electronic address: mike.hughes@imperial.ac.uk.
² Department of Physiology, Cochin Hospital, Assistance Publique, Hôpitaux de Paris, Medical School, Paris Descartes University, Paris, France. Electronic address: anh-tuan.dinh-xuan@aphp.fr.

PMID: 28088638
DOI: 10.1016/j.resp.2017.01.002

Abstract

DL_NO/DL_CO directly measures the ratio of the diffusing capacities of the lung for nitric oxide (NO) and carbon monoxide (CO). In terms of the Roughton and Forster (1957) equation, 1/DL=1/Dm+1/θVc, where Dm is the membrane (Dm) and θVc is the red cell component of the overall diffusing conductance (DL); DL_NO mostly reflects the Dm component and DL_CO the θVc red cell component. The DL_NO/DL_CO ratio is positively related to the Dm_CO/Vc ratio and the CO red cell resistance (1/θCOVc) as a percentage of the total resistance (1/DL_CO), independent of the absolute values of DL_NO or DL_CO. In clinical studies, a raised DL_NO/DL_CO ratio (≥110% predicted versus a control group), plus a low DL_NO and DL_CO (<67% pred), predicts pulmonary vascular disease, while a low DL_NO/DL_CO ratio, with similarly reduced DL_NO and DL_CO, is associated with interstitial lung disease with fibrosis. More clinical studies are needed, and reference values need to be better defined.

Keywords: Carbon monoxide; Diffusing capacity; Gas exchange; Lung function; Nitric oxide; Transfer factor.

Publication types

Review

MeSH terms

Animals
Carbon Monoxide*
Humans
Lung / physiology
Models, Cardiovascular
Nitric Oxide*
Pulmonary Diffusing Capacity*

Substances

Nitric Oxide
Carbon Monoxide