Introduction
In cystic fibrosis (CF) regular physical activity represents an integral part of disease management,1 and as reduced exercise capacity has been shown to be prognostically disadvantageous, identifying patients in need of exercise counselling seems important.2 Pulmonary disease, eventually progressing to respiratory failure, is the leading cause of death in the CF population. Forced expiratory volume in 1 s (FEV1) is used as the single most important variable to monitor the development and progression of pulmonary disease in patients with CF, and its decline is negatively associated with survival.3–5 Although rising, the life expectancy of patients with CF it is still markedly reduced compared with the general population in the western hemisphere.6
Clinical exercise testing7 is recommended performed annually in the follow-up of patients with CF,8–10 and a standardised cardiopulmonary exercise test (CPET) is the most reliable method for determining cardiorespiratory fitness (CRF) by non-invasively measuring cardiopulmonary response during incremental exercise to maximum effort.7 11 Peak oxygen uptake (VO2peak) is considered the most important variable during CPET and provides valuable information about the cardiorespiratory system, the causes of dyspnoea and the prognosis of the patient.2 12 Desaturation during exercise testing is known to correlate with both accelerated lung function decline and increased likelihood of hospitalisation.13 It has recently been shown that the VO2peak and other CPET derived measures represent independent and significant predictors of death or lung-transplant at 10-year follow-up.2
Several studies have described CRF in the adult CF population.2 14–25 However, most of these studies were based on a limited number of participants,14–16 19–22 or described results in a population below the age of 30 years.14–23 In addition, CPET was conducted using a cycle ergometer2 14–19 21–25 in all but one study.20 Cycle ergometry, which is recommended for individuals with CF aged >10 years, is the preferred method at most CF centres.10 Although not shown in CF, a higher VO2peak is obtained on a treadmill then when using cycle ergometry in both patients with chronic obstructive pulmonary disease and healthy subjects.26 27 To the authors’ knowledge, no previous studies have described CRF and cardiopulmonary response during maximal exercise on a treadmill in a large number of adult patients with CF of varying age.
The objectives of the present study were (1) to describe the CRF determined by treadmill testing in an adult CF population related to sex and age, (2) to evaluate the causes of decreased CRF and (3) to study the association between VO2peak and FEV1 in all individuals and longitudinally in patients having performed three or more tests.