Pulmonary diffusion and aerobic capacity: Is there a relation? Does obesity matter?

Aim: We sought to determine whether pulmonary diffusing capacity for nitric oxide (DLNO), carbon monoxide (DLCO) and pulmonary capillary blood volume (Vc) at rest predict peak aerobic capacity (O_2peak), and if so, to discern which measure predicts better. Methods: Thirty-five individuals with extreme obesity (body mass index or BMI = 50 ± 8 kg m^-2) and 26 fit, non-obese subjects (BMI = 23 ± 2 kg m^-2) participated. DLNO and DLCO at rest were first measured. Then, subjects performed a graded exercise test on a cycle ergometer to determine O_2peak. Multivariate regression was used to assess relations in the data. Results: Findings indicate that (i) pulmonary diffusion at rest predicts O_2peak in the fit and obese when measured with DLNO, but only in the fit when measured with DLCO; (ii) the observed relation between pulmonary diffusion at rest and O_2peak is different in the fit and obese; (iii) DLNO explains O_2peak better than DLCO or Vc. The findings imply the following reference equations for DLNO: O_2peak (mL kg^-1 min^-1) = 6.81 + 0.27 × DLNO for fit individuals; O_2peak (mL kg^-1 min ^-1) = 6.81 + 0.06 × DLNO, for obese individuals (in both groups, adjusted R²=0.92; RMSE = 5.58). Conclusion: Pulmonary diffusion at rest predicts O_2peak, although a relation exists for obese subjects only when DLNO is used, and the magnitude of the relation depends on gender when either DLCO or Vc is used. We recommend DLNO as a measure of pulmonary diffusion, both for its ease of collection as well as its tighter relation with O_2peak.