Exertional hypoxemia in stable COPD is common and predicted by circulating proadrenomedullin.

BACKGROUND: The prevalence of exertional hypoxemia in unselected COPD patients is unknown. Intermittent hypoxia leads to adrenomedullin (ADM) up regulation through the HIF-1 pathway. We aimed to assess the prevalence and the annual probability to develop exertional hypoxemia in stable COPD. We also hypothesized that increased ADM might be associated with exertional hypoxemia and envisioned that adding ADM to clinical variables might improve its prediction in COPD. METHODS: 1233 6-minute walking tests and circulating proadrenomedullin levels from 574 patients with clinically stable, moderate to very severe COPD enrolled in a multinational cohort study and followed-up for 2 years were concomitantly analyzed. RESULTS: The prevalence of exertional hypoxemia was 29.1%. In a matrix derived from a fitted-multi-state model, the annual probability to develop exertional hypoxemia was 21.6%. Exertional hypoxemia was associated with greater deterioration of specific domains of health-related QoL, higher severe exacerbation and death annual rates. In the logistic linear and conditional Cox-regression multivariable analyses, both FEV1% predicted and proADM proved independent predictors of exertional hypoxemia (p<0.001 for both). Adjustment for comorbidities, including cardiovascular disorders, and exacerbation-rate did not influence results. Relative to using FEV1% pred alone, adding proADM resulted in a significant improvement of the predictive properties (p=0.018). Based on the suggested non-linear nomogram, patients with moderate COPD (FEV1 predicted=50%) but high proADM levels (>2nmol/l) presented increased risk (>30%) for exertional desaturation. CONCLUSIONS: Exertional desaturation is common and associated with poorer clinical outcomes in COPD. Adrenomedullin improves prediction of exertional desaturation as compared to the use of FEV1%pred alone.