FIGURE 2 a) The association between diffusing capacities of the lung for nitric oxide (DLNO) and carbon monoxide (DLCO) measured at rest (single-breath; average breath-hold time was ∼6 s). Several published studies were used [57, 106, 107]. DLNO=4.65·(DLCO)+3.8, R2 0.90, standard error of the estimate (see) 11.8, p<0.001, 95% CI of the slope 4.51–4.79; n=493 healthy subjects. b) The association between pulmonary diffusing capacity and alveolar volume (VA) measured at rest (single-breath; average breath-hold time was ∼6 s). Several published studies were used [57, 106, 107]. DLNO=23.0·(VA)+2.4, R2 0.64, see 21.9, p<0.001, 95% CI of the slope 21.4–24.5; n=493. DLCO=4.63·(VA)+1.55, R2 0.62, see 4.5, p<0.001, 95% CI of the slope 4.31–4.94; n=493. All healthy subjects. c) The association between pulmonary diffusing capacity and cardiac output (Q) measured at rest and during exercise by rebreathing. Data from two published studies [35, 109], including ∼45% of previously unpublished data. DLNO=6.3·(Q)+58.2, R2 0.42, see 31.3, p<0.001, 95% CI of the slope 5.5–7.2; n=76, four data points per subject. DLCO=2.0·(Q)+9.0, R2 0.71, see 5.3, p<0.001, 95% CI of the slope 1.8–2.1; n=76, four data points per subject. All healthy subjects. When using rebreathing manouvres, DLCO is more tightly associated with cardiac output than DLNO (comparison of correlation coefficients z-statistic 5.52, p<0.01); however, DLNO is more tightly related to alveolar volume compared to DLCO (comparison of correlation coefficients z-statistic 2.27, p=0.023). The association between DLNO and DLCO in relation to VA during rebreathing manouvres (r=0.73 between DLNO versus VA, and r=0.63 between DLCO versus VA) is not shown here.