The association between cardiorespiratory fitness and pulmonary diffusing capacity.

Pulmonary diffusing capacity for nitric oxide (DL,NO) and carbon monoxide (DL,CO) measured at rest (mL/min/mmHg) is strongly associated with aerobic capacity (cardiorespiratory fitness or peak oxygen uptake, VO2peak) measured in L/min. Data from healthy, non-obese individuals from various studies (n=121 males and 81 females) were combined to examine this association. Subjects that were above the upper limit of normal (ULN, 97.5th percentile for age and sex and height) for DL,NO and DLCO had a higher median VO2peak compared to subjects below the ULN (Above the ULN=4.2-4.5L/min or 54-56mL/kg/min; below the ULN=3.0-3.2L/min, 45-46mL/kg/min, p<0.001). Those that were classified as Superior or Excellent in cardiorespiratory fitness (≥80th percentile in VO2peak for the person's age and sex) increased their odds of being above the ULN for DL,NO and DL,CO by about 6-fold and 8-fold, respectively, compared to those not classified as being Superior or Excellent in cardiorespiratory fitness. Approximately 65-68% of the variance in DL,NO and DL,CO, respectively, was shared by VO2peak (L/min) (p<0.001). However, after controlling for alveolar volume, sex, height, body mass, and age, the shared variance between pulmonary diffusing capacity and VO2peak decreased to 16-20% (95% CI=8-30%), and yet, remained statistically significant (p<0.001). The reasons for the shared variance between pulmonary diffusing capacity and VO2peak are discussed.