The Prognostic Value of Exercise Testing in Patients with Cystic Fibrosis

Abstract

Previous studies have shown female sex, impaired pulmonary function, older age, malnutrition, and colonization of the respiratory tract by Pseudomonas cepacia to be associated with a poor prognosis in patients with cystic fibrosis. We sought to determine the prognostic value of exercise testing in addition to the other prognostic factors. A total of 109 patients with cystic fibrosis, 7 to 35 years old, underwent pulmonary-function and exercise testing in the late 1970s. They were followed for eight years to determine the factors associated with subsequent mortality. Survival rates were calculated with standard life-table methods. Cox proportional-hazards regression models were used to determine crude relative risks of mortality and relative risks adjusted for age, sex, body-mass index, forced expiratory volume in one second (FEV1), end-tidal partial pressure of carbon dioxide (PCO2) at peak exercise, and oxygen consumption at peak exercise (V̇o2peak). Patients with the highest levels of aerobic fitness (V̇o2peak, ≥82 percent of predicted) had a survival rate of 83 percent at eight years, as compared with rates of 51 percent and 28 percent for patients with middle (V̇o2peak, 59 to 81 percent of predicted) and lowest (V̇o2peak, ≤58 percent of predicted) levels of fitness, respectively. After adjustment for other risk factors, patients with higher levels of aerobic fitness were more than three times as likely to survive than patients with lower levels of fitness. Colonization by P. cepacia was associated with a risk of dying that was increased fivefold. Age, sex, body-mass index, FEV1, and end-tidal PCO2 at peak exercise were not independently correlated with mortality. Higher levels of aerobic fitness in patients with cystic fibrosis are associated with a significantly lower risk of dying. Although better aerobic fitness may simply be a marker for less severe illness, measurement of V̇o2peak appears to be valuable for predicting prognosis. Further research is warranted to determine whether improving aerobic fitness through exercise programs will result in a better prognosis. (N Engl J Med 1992;327: 1785–8.), THE prognosis for patients with cystic fibrosis has improved dramatically in the past two decades, with median survival increasing from 10.6 years in 1966 to 28.0 years in 1989.1 Several factors have been identified that seem to be associated with prognosis. For example, male sex2 and normal intestinal fat absorption3 appear to be associated with a better prognosis, whereas colonization of the respiratory tract with Pseudomonas cepacia 4 and poor nutritional status5 appear to be associated with a poorer prognosis. Exercise testing has been used in patients with cystic fibrosis for some 15 years, and the results of these tests correlate… © 1992, Massachusetts Medical Society. All rights reserved.