Impaired lung diffusing capacity for nitric oxide and alveolar-capillary membrane conductance results in oxygen desaturation during exercise in patients with cystic fibrosis.
BACKGROUND
Exercise 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 (D(M)), and pulmonary capillary blood volume (V(C)) on peripheral oxygen saturation (SaO(2)) at rest and during exercise in CF.


METHODS
17 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/m(2), VO(2PEAK)=101±36 vs. 55±25%pred., FEV(1)=92±22 vs. 68±25%pred., for healthy and CF, respectively, mean±SD, VO(2PEAK) and FEV(1) p<0.001). Subjects performed incremental cycle ergometry to exhaustion with continuous monitoring of SaO(2) and measures of DLNO, DLCO, D(M) and V(C) at each stage.


RESULTS
CF patients had a lower SaO(2) 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, D(M) 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; D(M)=50±1 vs. 34±1, p<0.001, for healthy and CF respectively). Peak SaO(2) was related to resting DLNO in CF patients (r=0.65, p=0.003).


CONCLUSIONS
These results suggest a limitation in exercise-mediated increases in membrane conductance in CF which may contribute to a drop in SaO(2) and that resting DLNO can account for a large portion of the variability in SaO(2).
Department of Pharmacy Practice and Science, University of Arizona, Tucson, Arizona, USA. wheatley@pharmacy.arizona.edu
Courtney M
CM
Wheatley
William T
WT
Foxx-Lupo
Nicholas A
NA
Cassuto
Eric C
EC
Wong
Cori L
CL
Daines
Wayne J
WJ
Morgan
Eric M
EM
Snyder
D000293:Adolescent; D000328:Adult; D015824:Blood-Air Barrier / Q000378:metabolism / Q000503:physiopathology; D002248:Carbon Monoxide / Q000378:metabolism*; D003550:Cystic Fibrosis / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology; D005080:Exercise Test / Q000009:adverse effects; D005260:Female; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D010092:Oximetry; D010100:Oxygen / Q000493:pharmacokinetics*; D011650:Pulmonary Alveoli / Q000378:metabolism / Q000503:physiopathology; D011659:Pulmonary Gas Exchange; D012129:Respiratory Function Tests; D012307:Risk Factors
D009569:Nitric Oxide; D002248:Carbon Monoxide; D010100:Oxygen