| SIIIDTG g·mol−1·L−1 | AUC g·%·mol-1 | Peak g·mol−1 | |
| Healthy adults | |||
| Flow L·s−1 | 0.133 (0.056–0.210)*** | 10.43 (5.71–15.15)*** | −0.49 (−0.65–0.33)*** |
| VT L | 0.262 (0.181–0.345)*** | −6.15 (−15.81– −8.26)*** | −0.15 (−0.31–0.01) |
| FRC L | −0.028 (−0.049– −0.007)* | 1.69 (0.63–2.74)* | 0.06 (0.02–0.10)* |
| Constant | −0.307 | 10.43 | 0.25 |
| Intraclass correlation | 0.81 | 0.87 | 0.69 |
| R2 | 0.89 | 0.91 | 0.79 |
| COPD patients | |||
| Flow L·s−1 | −0.228 (−0.543–0.088) | 0.79 (−9.27–10.85) | 0.03 (−0.20–0.26) |
| VT L | 0.494 (0.145–0.842)* | −2.84 (−14.16–8.47) | −0.04 (−0.30–0.22) |
| FRC L | −0.037 (−0.101–0.028) | 1.65 (−0.44–3.74) | 0.05 (0.00–0.09) |
| Constant | −1.203 | 29.90 | 0.66 |
| Intraclass correlation | 0.92 | 0.97 | 0.94 |
| R2 | 0.96 | 0.98 | 0.96 |
Data are presented as β (95% CI), unless otherwise stated. Effects of flow, tidal volume (VT) and functional residual capacity (FRC) on main dual tracer gas single-breath washout parameters (phase III slope (SIIIDTG), area under the curve (AUC) and absolute peak concentration (peak)) in 40 healthy adults (20 chronic obstructive pulmonary disease patients) calculated by fitting a linear mixed-effects model with random intercept. Calculations are based on averaged values of three individual measurements of all test occasions. Flow, VT and FRC were considered as fixed effects, and individual subjects as random effects to account for repeated measurements. Estimates of random effects are not shown. The variance components of random and fixed effects were calculated with residual maximum likelihood. The intraclass correlation equals the proportion of total residual variance explained by random effects. For additional illustration of these effects, see online supplementary figure 5. R2: proportion of total quadratic variation that can be explained by fixed effects after correction for random effects. *: p<0.05; ***: p<0.001.