Transfer factor (diffusing capacity) standardized for alveolar volume: validation, reference values and applications of a new linear model to replace KCO (TL/VA). D.J. Chinn, J.E. Cotes, R. Flowers, A-M. Marks, J.W. Reed. ERS Journals Ltd 1996.ABSTRACT: 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 exponential) which might standardize TL for VA, and asks the questions: 1) Is either model valid? 2) What are appropriate reference values? and 3) Will the model be useful?The relationship of TL to VA within subjects at different depths of inspiration, and between subjects having lungs of different sizes, were measured and compared. The subjects were asymptomatic, nonsmoking, Caucasian adults, including 31 males assessed in the laboratory and 503 male and female participants in population studies.The linear partial regression coefficients of TL on VA (L corrected for body temperature, atmospheric pressure and water saturation (BTPS)) standardized for height (H) in metres, were similar within-and between-subjects; the coefficients applied over a wide range of values for VA. 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 reference values; its use suggests that some of the differences between published values is due to the volume term. The equations can be used clinically, and eliminate the need for carbon monoxide transfer coefficient. Eur Respir J., 1996Respir J., , 9, 1269Respir J., -1277 When an individual subject performs measurements of transfer factor (TL, which is also called diffusing capacity) by the single-breath method, the result is found to vary with the depth of inspiration, and hence with the alveolar volume (VA) during breatholding. This was first observed by KROGH [1] who, in 1915, reported that "with increasing lung volumes above mean capacity, the permeability factor k (i.e. diffusing capacity per unit lung volume) remained practically constant". Based on this observation the carbon monoxide transfer coefficient (KCO), hereafter designated TL/VA, has been equated with transfer factor standardized for alveolar volume. However, subsequent studies, reviewed by STAM and coworkers [2], have shown that between functional residual capacity and total lung capacity, TL/VA was not constant; instead, it was negatively correlated with alveolar volume. On this account, the usefulness of TL/VA as a means for standardizing TL has been questioned [3,4].The Krogh model (TL/VA) can be represented as TL= mVA, where m is a constant. It is invalid because m is not independent of VA. In this paper, two other simple models are considered, an exponential model of the form TL=mVA δ , and a linear model which can be represented as TL=mVA + c ( fig. 1). To be valid, the parameters of the equations should be independe...
En la naturaleza existen distintos fenómenos, los cuales pueden clasificarse como determinísticos y estocásticos (o aleatorios): los primeros tienen la característica de que bajo las mismas condiciones iniciales para su realización siempre se obtiene el mismo resultado, mientras que los clasificados como aleatorios al observar el mismo fenómeno se obtienen distintos resultados, e incluso existe una infinidad de fenómenos de los cuales es imposible saber el resultado antes de su realización. En la vida real un fenómeno adquiere la característica de aleatorio debido a las condiciones iniciales bajo las cuales ocurre, principalmente porque éstas pueden ser números muy grandes, tales que no pueden controlarse todas a la vez. Por esta razón, al observar el mismo fenómeno se tienen distintos resultados. A los fenómenos con ésta característica se les conoce como fenómenos estocásticos o aleatorios.
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