Relationship between airway obstruction, desaturation during exercise and nocturnal hypoxaemia in cystic fibrosis patients.

We measured pulmonary function, responses to exercise and oxygen saturation (So2) at rest, and also before and during sleep in 24 patients with cystic fibrosis in a varying degree of severity. The pulmonary function indices analysed were forced expiratory volume in one second (FEV1), total lung capacity (TLC), measured by body plethysmography (TLC box) and Helium dilution (TLC He), residual volume measured by body plethysmography (RV) and the amount of trapped air (TA = TLC box-TLC He). The exercise variables included symptom limited maximal oxygen uptake (Vo2max), maximum minute ventilation (VEmax) and So2, at rest in sitting position and during maximal exercise. So2 was measured by ear oximetry. The lowest mean So2 obtained in two consecutive nights over a period of 1 hour was taken as the indicator of nocturnal oxygen saturation. A high correlation existed between resting supine and sitting So2, and the degree of nocturnal hypoxaemia (0.84 and 0.76, respectively). Highly significant correlations existed also for the indices of airway obstruction, Vo2 max and lowest So2 at exercise versus the nocturnal lowest hourly mean So2. From all variables a resting So2 in the sitting position lower than 94% appeared to be most predictive of nocturnal desaturation and indicates a risk of nocturnal hypoxaemia in patients with cystic fibrosis.