Impaired lung diffusing capacity for nitric oxide and alveolar-capillary membrane conductance results in oxygen desaturation during exercise in patients with cystic fibrosis

AbstractBackgroundExercise has been shown to be beneficial for patients with cystic fibrosis (CF), but for some CF patients there is a risk of desaturation, although the predicting factors are not conclusive or reliable. We sought to determine the relationship between the diffusion capacity of the lungs for nitric oxide and carbon monoxide (DLNO and DLCO) and the components of DLCO: alveolar-capillary membrane conductance (DM), and pulmonary capillary blood volume (VC) on peripheral oxygen saturation (SaO2) at rest and during exercise in CF.Methods17 mild/moderate CF patients and 17 healthy subjects were recruited (age=26±7 vs. 23±8 years, ht=169±8 vs. 166±8 cm, wt=65±9 vs. 59±8 kg, BMI=23±3 vs. 22±3 kg/m2, VO2PEAK=101±36 vs. 55±25%pred., FEV1=92±22 vs. 68±25%pred., for healthy and CF, respectively, mean±SD, VO2PEAK and FEV1 p<0.001). Subjects performed incremental cycle ergometry to exhaustion with continuous monitoring of SaO2 and measures of DLNO, DLCO, DM and VC at each stage.ResultsCF patients had a lower SaO2 at rest and peak exercise (rest=98±1 vs. 96±1%, peak=97±2 vs. 93±5%, for healthy and CF, respectively, p<0.01). At rest, DLNO, DLCO, DM were significantly lower in the CF group (p<0.01). The difference between groups was augmented with exercise (DLNO=117±4 vs. 73±3ml/min/mmHg; DLCO=34±8 vs. 23±8ml/min/mmHg; DM=50±1 vs. 34±1, p