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The single breath transfer factor ( T l,co ) and the transfer coefficient ( K co ): a window onto the pulmonary microcirculation
Author(s) -
Hughes J.M.B.
Publication year - 2003
Publication title -
clinical physiology and functional imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.608
H-Index - 67
eISSN - 1475-097X
pISSN - 1475-0961
DOI - 10.1046/j.1475-097x.2003.00482.x
Subject(s) - medicine , pulmonary diffusing capacity , microcirculation , diffusing capacity , conductance , diffusion , respiratory physiology , lung , thermodynamics , lung function , combinatorics , mathematics , physics
Summary The transfer factor, T l,co (with the transfer coefficient, K co , also known as the transfer factor per unit alveolar volume, [ T l / V a ]), is one of the most useful clinical tests of pulmonary function, the only one which specifically focuses on pulmonary microcirculation. It was originally devised in 1909 as a physiological tool to assess the diffusive capacity of the lung as a gas exchanger. It was subsequently developed as a clinical tool, but cumbersome analytical techniques delayed its introduction into clinical medicine until 1950s. The physiology of the carbon monoxide transfer factor (also called the diffusing capacity D l,co ) is based on the Roughton–Forster equation which partitions D l,co , a conductance, into membrane ( D m ) and red cell ( θ V c ) diffusion conductances. Recent work (1987–2001) suggests that 70–80% of the resistance to CO (and O 2 ) diffusion may reside in the red cell fraction. The clinical implication is that T l,co and K co are ‘windows’ onto the pulmonary microcirculation. As regards reference values for clinical use, T l,co depends on age, height and gender. K co , which is actually a rate constant, is independent of gender, and is affected principally by age. A schema is presented for the clinical interpretation of T l,co . As T l,co is derived from the product of K co and the accessible alveolar volume ( V a ), examination of these two components ( K co and V a ) will usually suggest a specific pathophysiological mechanism as the explanation for a reduction in T l,co .