Association between pulmonary function and peak oxygen uptake in elderly: the Generation 100 study

BACKGROUND Although reduced function of the respiratory system limits peak oxygen uptake in diseases affecting the lungs or airways, the healthy respiratory system is thought to have a spare capacity for oxygen transport and uptake, and is not considered a limiting factor for peak oxygen uptake in healthy people. However, lung function declines with age and could theoretically limit peak oxygen uptake in elderly. We examined the association between peak oxygen uptake and lung function indices in an elderly population with the hypothesis that lung function indices would be associated with VO2peak up to a threshold value situated above the lower limits of normal lung function for our population. METHODS Spirometry, gas diffusion tests and incremental work tests were performed in 1443 subjects (714 women) aged 69-77 years. Association between lung function indices and peak oxygen uptake was studied with hockey-stick regression. RESULTS Forced expiratory volume in 1 s (FEV1) had a positive association with peak oxygen uptake up to, but not above, a threshold value of 2.86 l for men, and 2.13 l for women (lower limit of normal 2.73 and 1.77 l respectively). A corresponding threshold was found for diffusing capacity of the lung for carbon monoxide (DLCO) for men at 9.18 mmol/min/kPa (lower limit of normal 6.84 mmol/min/kPa). DLCO for women and DLCO divided by alveolar volume (DLCO/VA) for both sexes had a significant linear relationship to VO2peak (p < 0.05), but no significant threshold value was found in these associations. CONCLUSIONS Threshold values for FEV1 for both sexes and DLCO for men were identified. These lung function indices had a positive association with VO2peak up to these threshold values, but not above. The identified threshold values were above lower limits of normal for FEV1 and DLCO.