TRANSFER-FACTOR (DIFFUSING-CAPACITY) STANDARDIZED FOR ALVEOLAR VOLUME- VALIDATION, REFERENCE VALUES AND APPLICATIONS OF A NEW LINEAR-MODELTO REPLACE KCO (TL VA)/

Transfer factor (TL) varies with alveolar volume (Va), but not in the manner implied by the carbon monoxide transfer coefficient (KCO (TL/VA )), This paper considers two other simple models (one Linear and one e xponential) which might standardize TL for Va, and asks the questions: 1) Is either model valid? 2) What are appropriate reference values? a nd 3) Will the model be useful? The relationship of TL to VA within su bjects at different depths of inspiration, and between subjects having lungs of different sizes, were measured and compared. The subjects we re asymptomatic, nonsmoking, Caucasian adults, including 31 males asse ssed in the laboratory and 503 male and female participants in populat ion studies. The linear partial regression coefficients of TL on VA (L corrected for body temperature, atmospheric pressure and water satura tion (BTPS)) standardized for height (H) in metres, were similar withi n- and between- subjects; the coefficients applied over a wide range o f values for VA. This was not the case for the exponential model. The resulting reference equations in SI units for males and females were: TL = 11.52 H + 2.72 VA . H-2 - 0.051 Age -12.35, RSD 1.17; and TL = 4. 87 H + 2.29 VA . H-2 0.019 Age -3.03, RSD 0.92, respectively. The resi dual standard deviations (RSD) about the new relationships were less t han in other series. The new linear model could account for much of th e variation between different published reference values for TL; it co uld be useful clinically, in circumstances when Va deviates from the n orm. The model does not explain differences in TL associated with gend er. Inclusion of VA . H-2 as a covariate in the reference equation for transfer factor, in addition to age and height, improves the accuracy of prediction of normal transfer factor compared with current referen ce values; its use suggests that some of the differences between publi shed values is due to the volume term. The equations can be used clini cally, and eliminate the need for carbon monoxide transfer coefficient .