Reference values for alveolar membrane diffusion capacity and pulmonary capillary blood volume

The reference values for diffusion capacity of the alveolar capillary membrane (Tm,CO) and pulmonary capillary volume (Qc) are scarce, while the standard deviations of the equations are large. New equations and residual standard deviations (RSDs) were determined in a sample of healthy subjects. Tm,CO and Qc values were measured in 117 (72 females, 45 males) nonsmoking healthy subjects. The carbon monoxide transfer factor (TL,CO) was determined when the volunteer was breathing room air and subsequently, when the volunteer was breathing 100% oxygen. From these data, Tm,CO and Qc values were calculated. The females' TL,CO was 3.15 mmol x min(-1) x kPa(-1) lower than the males', apparently caused by lower female lung volume. Tm,CO and Qc were lower in females, but correction for lung volume eliminated this difference. Qc(-1) reference equations for females and males, respectively, are 4.375 x 10(-2) - 1.085 x l0(-2) x height and 4.455 x 10(-2) -1.085 x 10(-2) x height (RSD for both sexes: 2.544 x 10(-3)). Tm,CO(-1) reference equations for females and males, respectively, are 0.111+3.304 x 10(-4) x age-4.753 x 10(-2) x height and 0.127+3.304 x 10(-4) x age-4.753 x 10(-2) x height (RSD for both sexes: 1.085 x 10(-2)). The general character of these equations complies with earlier publications, the only difference being that the RSDs are 1.18-2.76 times lower. New reference equations for diffusion capacity of the alveolar capillary membrane and pulmonary capillary volume are available with considerably smaller residual standard deviations.