Exercise hypoxaemia as a predictor of pulmonary hypertension in COPD patients without severe resting hypoxaemia.

BACKGROUND AND OBJECTIVE: Pulmonary hypertension (PH) in COPD is associated with morbidity and mortality. Previous studies showed a relationship between resting hypoxaemia and PH, but little is known about the relationship between exercise hypoxaemia and PH in COPD without resting hypoxaemia.

METHODS: A retrospective observational study of COPD patients without resting hypoxaemia was conducted to evaluate the relationships between exercise hypoxaemia and pulmonary haemodynamics. Clinical characteristics, pulmonary function, blood gas analysis, 6-min walk distance (6MWD) and oxygen saturation of peripheral artery (SpO2 ) at the end of the 6-min walk test (6MWT) were reviewed. Correlation analysis and stepwise regression analysis were performed to identify the predictor of mean pulmonary artery pressure (mPAP).

RESULTS: Eighty-four consecutive patients with a mean predicted forced expiratory volume in 1 s (FEV1 ) of 47 ± 21% were evaluated. In univariate analysis, mPAP had negative correlations with age (r = -0.27, P < 0.05), arterial partial pressure of oxygen (PaO2 , r = -0.24, P < 0.05), % predicted forced vital capacity (FVC, r = -0.28, P < 0.05), % predicted FEV1 (r = -0.40, P < 0.001), FEV1 /FVC ratio (r = -0.33, P < 0.005), % predicted diffusion capacity for carbon monoxide (DLCO , r = -0.40, P < 0.001), 6MWD (r = -0.40, P < 0.001) and SpO2 at the end of the 6MWT (r = -0.74, P < 0.001). In stepwise regression analysis, SpO2 at the end of the 6MWT and 6MWD remained as independent predictors of mPAP (R2  = 0.60). In receiver operating characteristic (ROC) analysis, SpO2 at the end of the 6MWT presented an area under the curve of 0.896 for the prediction of PH, with a sensitivity of 0.86 and specificity of 0.84 for the cut-off point of 81%.

CONCLUSION: In addition to 6MWD, exercise hypoxaemia indicates PH in patients with COPD without resting hypoxaemia.