Exercise tolerance and cardiorespiratory adjustments at peak work capacity in cystic fibrosis

Exercise tolerance and cardiorespiratory adjustments at peak work capacity (PWC) were determined in 20 patients with cystic fibrosis (CF) during progressive cycle ergometry. The results were related to resting lung function tests, expressed by a pulmonary function score (PFS) that ranged from 0 (no pulmonary dysfunction) to 18 (extreme dysfunction). Patients with CF with no (PFS < 3), mild (PFS 3-7), or moderate (PFS 8-12) pulmonary dysfunction exercised as well as normal subjects. When the PFS exceeded 12, PWC was reduced on the average by 51%, peak heart rate (PHR) was reduced by 15%, and peak ventilation (PV̇E) was reduced by 39%. Severely affected patients developed arterial desaturation at PWC (-7.3%), CO₂ retention (end-tidal P(CO₂) + 5 mmHg), and an increase in the PHR/PWC ratio. In most patients with CF the PV̇E/PWC ratio was elevated, suggesting wasted V̇E and a probable increase in dead space ventilation. The results indicate that whenever pulmonary disease in CF is advanced, there are decreases in exercise tolerance and cardiorespiratory reserves, exercise-induced ventilation-perfusion abnormalities, arterial desaturation, and alveolar hypoventilation. In view of the abnormal physiologic adaptations to exercise in patients with CF with advanced lung disease (PFS > 12), they should engage in exercise training programs and strenuous physical activity with caution and only after their cardiorespiratory reserves and adjustments to exercise have been objectively evaluated.