Cardiorespiratory adaptations to exercise in cystic fibrosis

We compared the cardiorespiratory adaptations to exercise of 21 patients with cystic fibrosis (CF) with those of 17 age-, height-, and weight-matched subjects without lung disease. To assess differences in adaptation to exercise in patients with varying severities of pulmonary disease, we grouped them on the basis of their lung function test results. Exercise consisted of a progressive, incremental cycle ergometer work test. Work load increased every 2 min until the subject could not continue. During exercise, heart rate, end-tidal and mixed expired O₂ and CO₂ tensions, minute ventilation (V̇E), arterial oxygen saturation, and blood pressure were monitored. The patients breathed significantly larger volumes than normal subjects at work loads > 0.8 W/kg. Patients with mild, moderate, or severe disease ventilated more per unit of oxygen consumption than did patients with normal pulmonary functions or control subjects. Despite this high total V̇E, alveolar hypoventilation was observed in the severe groups, as evidenced by elevated end-tidal P(CO₂), and contributed to arterial desaturation. Resting heart rate was higher in the severe group. The rate of changes in heart rate with increasing work load was the same in all groups. We conclude that the increased V̇E during exercise was an attempt to maintain alveolar ventilation in the face of increased dead space. The elevated V̇E was adequate to preserve normal gas exchange in all patients except those with severe lung disease, where CO₂ retention and arterial desaturation were observed.