Ventilatory Response to Exercise in Cystic Fibrosis

patients is presumably due to limited exercise tolerance, as indicated by the lower heart rates achieved by the CF patients at maximum exercise (W,,,). Unfortunately, no values are given in the manuscript for the W, of the patients studied and neither is the method used to determine exercise tolerance described. If the patients in the study had indeed attained W,,, one would expect the mean respiratory quotient (RQ) to be significantly greater than 1.0, as a result of anaerobic metabolism. It would be of interest to know if the authors found a correlation between W,, and resting pulmonary function parameters, as previous investigators (2) have noted a ventilatory limit to exercise in CF. It is certainly not surprising to find that some patients were able to reach or exceed their maximum voluntary ventilation (MVV) on exercise. This ability to achieve levels of ventilation in excess of MVV on exercise reflects a form of bronchial lability, unique to the disease. Previous work from this Institution (3) has shown that patients with C F may experience dramatic increases in peak flow rates (PFR) during exercise and only minimal bronchoconstriction after exercise. This bronchial lability is due mainly to flow transients which result in higher PFR (4). Finally, it is noteworthy that the C F patients in the study were malnourished, a factor which has previously been associated with reduced exercise performance in CF (5).