title: Hypothesis: Why θNO could be finite in vitro but infinite in vivo.
abstract: There is controversy as to whether the lung Diffusing Capacity for Nitric Oxide (DLNO) is a direct measure of DM in the Roughton-Forster equation or whether θNO is finite and DM is greater than DLNO. Despite in vitro evidence that θNO is finite, some groups believe that it is infinite in vivo and that DMNO/DMCO (α) is greater than predicted by the combined Fick/Graham law of Gas Diffusion through a membrane. We here present a hypothesis applying the fundamental rules of combined diffusion and chemical reaction to a red cell to explain (i) why θNO could be finite in vitro but effectively infinite in vivo and (ii) why ∝ could appear greater than predicted. DLNO would mainly reflect the conductance of the alveolar capillary membrane with a smaller contribution from plasma and minimal contribution from the outermost layers of the red cell. If this hypothesis is correct DMCO and Vc could not be obtained from a combined DLNO and DLCO manoeuvre since these variables would differ for NO and for CO.
authors.affiliation: Department of Medicine, University of Cambridge and Hinchingbrooke Hospital, Huntingdon PE29 6NT, United Kingdom. Electronic address: colinborland@nhs.net.
authors.forename: Colin
authors.initials: C
authors.lastname: Borland
authors.affiliation: Department of Respiratory Physiology, Papworth Hospital, Papworth Everard, Cambridgeshire CB3 8RE, United Kingdom. Electronic address: S.Patel122619@rbht.nhs.uk.
authors.forename: Suhani
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke St, Cambridge CB2 3RA, United Kingdom. Electronic address: qz246@cam.ac.uk.
authors.forename: Qingyu
authors.initials: Q
authors.lastname: Zhu
authors.affiliation: Department of Anaesthetic Research, Papworth Hospital, Papworth Everard, Cambridgeshire CB3 8RE, United Kingdom. Electronic address: a.vuylsteke@nhs.net.
authors.forename: Alain
authors.initials: A
authors.lastname: Vuylsteke
mesh_terms: D002248:Carbon Monoxide; D004912:Erythrocytes / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008168:Lung / Q000502:physiology; D008955:Models, Cardiovascular; D008956:Models, Chemical; D009569:Nitric Oxide; D011653:Pulmonary Diffusing Capacity
chemical_list: D009569:Nitric Oxide; D002248:Carbon Monoxide