Long-term gas exchange characteristics as markers of deterioration in patients with cystic fibrosis

BACKGROUND AND AIM: In patients with cystic fibrosis (CF) the architecture of the developing lungs and the ventilation of lung units are progressively affected, influencing intrapulmonary gas mixing and gas exchange. We examined the long-term course of blood gas measurements in relation to characteristics of lung function and the influence of different CFTR genotype upon this process. METHODS: Serial annual measurements of PaO(2 )and PaCO(2 )assessed in relation to lung function, providing functional residual capacity (FRC(pleth)), lung clearance index (LCI), trapped gas (V(TG)), airway resistance (sR(eff)), and forced expiratory indices (FEV(1), FEF(50)), were collected in 178 children (88 males; 90 females) with CF, over an age range of 5 to 18 years. Linear mixed model analysis and binary logistic regression analysis were used to define predominant lung function parameters influencing oxygenation and carbon dioxide elimination. RESULTS: PaO(2 )decreased linearly from age 5 to 18 years, and was mainly associated with FRC(pleth), (p < 0.0001), FEV(1 )(p < 0.001), FEF(50 )(p < 0.002), and LCI (p < 0.002), indicating that oxygenation was associated with the degree of pulmonary hyperinflation, ventilation inhomogeneities and impeded airway function. PaCO(2 )showed a transitory phase of low PaCO(2 )values, mainly during the age range of 5 to 12 years. Both PaO(2 )and PaCO(2 )presented with different progression slopes within specific CFTR genotypes. CONCLUSION: In the long-term evaluation of gas exchange characteristics, an association with different lung function patterns was found and was closely related to specific genotypes. Early examination of blood gases may reveal hypocarbia, presumably reflecting compensatory mechanisms to improve oxygenation.