Abstract
The classic method for determining alveolar‐capillary membrane conductance (DM) and pulmonary capillary blood volume (VC) involves measurement of lung diffusing capacity for carbon monoxide (DLCO) at multiple inspired O2 tensions (FIO2). Recently, the technique has been simplified by simultaneously measuring DLNO (nitric oxide) to determine values at a single FIO2. Controversy exists over equations for calculation of θCO (reaction rate of CO with Hgb) and the correct diffusion ratio for NO and CO (α) in the calculation of DMCO. The purpose of this study was to investigate how various published equations and ratios influence DM & VC using both the multiple and single FIO2 methods. Eight healthy males were studied. DLCO & DLNO were measured using the rebreathe method (inspired vol. ~75% of inspiratory capacity, FIO2 18, 35, & 55%). DM & VC were first calculated using five reported equations for θCO. Once DM & VC were optimized based on reported predicted values, the DLNO method was compared using a range of α values. Using the multiple FIO2 method, depending on the equation for θCO, DM ranged from 47 to 103 ml/min/mmHg, and VC from 74 to 102 ml. For the calculation of DM & VC using the DLNO method, α ranged from 1.5 to 4.0 in order to optimize DM & VC values to the classic method. The determination of DM & VC is critically dependent on the equations used for θCO which in turn affects the optimal ratio used to correct the DLNO method. NIH HL71478
Published Version
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