CARDIORESPIRATORY ADAPTATIONS TO EXERCISE IN CYSTIC-FIBROSIS

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Abstract
Cardiorespiratory adaptations to exercise of 21 patients with cystic fibrosis (CF) were compared to those of 17 age-, height- and weight-matched subjects without lung disease. To assess differences in adaptations to exercise in patients with varying severities of pulmonary disease, they were grouped 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 (.ovrhdot.VE), arterial O2 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 O2 consumption than did patients with normal pulmonary functions or control subjects. Despite this high total .ovrhdot.VE, alveolar hypoventilation was observed in the severe groups, as evidenced by elevated end-tidal PCO2 [partial pressure], 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. The increased .ovrhdot.VE during exercise was an attempt to maintain alveolar ventilation in the face of increased dead space. The elevated .ovrhdot.VE was adequate to preserve normal gas exchange in all patients except those with severe lung disease, where CO2 retention and arterial desaturation were observed.

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