Oxygen Saturation During Exercise in Cystic Fibrosis

Cystic fibrosis (CF) is often associated with low hemoglobin oxygen saturation and with limited exercise tolerance, yet published reports do not agree on the effect of exercise on oxygenation in CF. We studied oxygen saturation (SaO2) by ear oximetry in 91 patients with CF during progressive exercise to exhaustion. Only 13 of 91 patients changed SaO2 by 5% or more; of these, 4 patients increased SaO2 by 5% or more, whereas 9 decreased by 5% or more. Small changes in SaO2 did not relate to resting pulmonary function, but large decreases in SaO2 were much more likely to be found in patients with forced expiratory volume in one second (FEV1) less than 50% of VC than in those with better pulmonary function (desaturation of 5% or greater was found in only 1 of 62 patients with FEV1 greater than 50% of VC, but in 8 of 29 patients with FEV1 less than or equal to 50% VC). However, even in severely affected patients, modest increases or no change in saturation were more common than large decreases, and 17 of 29 patients with FEV1 less than 50% VC ended exercise with SaO2 greater than 90%, including 3 patients with initial SaO2 below 90%. No single resting pulmonary function test or combination of tests could predict oxygen changes with exercise. Most patients with CF tolerate even maximal exercise without significant desaturation, but patients with FEV1 less than 50% of VC should have supervised exercise testing with ear oximetry before undertaking an exercise program.