Cardiorespiratory fitness on a treadmill in an adult cystic fibrosis population.

Objectives: (1) To describe the cardiorespiratory fitness (CRF) in an adult cystic fibrosis population related to sex and age, (2) to evaluate the cause of low CRF and (3) to study the association between peak oxygen uptake (VOpeak) and forced expiratory volume in 1 s (FEV).

Methods: A total of 204 cardiopulmonary treadmill exercise tests (CPETs) performed by 116 patients were included. VOpeak, gas exchange, heart rate, oxygen saturation and ventilatory variables were measured.A low CRF was defined as a VOpeak <80% of predicted, ventilatory limitation was defined as a breathing reserve <15%, exercise hypoxaemia was defined as an oxygen saturation <88% and ventilation-perfusion mismatch was defined as a minute ventilation/ventilatory equivalent for carbon dioxide slope ≥34. In patients who had performed three or more CPETs, the annual change in FEV and VOpeak were calculated using linear regression.

Results: The VOpeak was 40.6±11.5 and 35.2±8.9 mL kg min, which was 87±23 and 93±20 in percentage of predicted for men and women, respectively. VOpeak was moderately affected by age, for men (r=-0.36, p<0.001) and women (r=-0.53, p<0.001), respectively. In 45 of 101 tests where CRF was low, no cardiorespiratory limiting factors were identified. The correlation coefficient between VOpeak and FEV was r=0.64 (p<0.001). In participants with a low CRF, FEV ranged from 20% to 112% of predicted.

Conclusions: The correlation between VOpeak and FEV was moderate. The majority of the tests resulted in a VOpeak within normal limits. Interestingly, 44% of the tests with a low VOpeak could be explained by deconditioning. Thus, exercise therapy may be beneficial for these patients.