Impact of pulmonary hemodynamics on 6-min walk test in idiopathic pulmonary fibrosis

Objectives: Pulmonary hypertension (PH) has been associated with decreased functional capacity in patients with advanced idiopathic pulmonary fibrosis (IPF). We aimed to evaluate the true impact of altered pulmonary hemodynamics on functional capacity in a cohort of patients with IPF.

Methods: Between January 1990 and December 2007, 124 patients [73M/51F; 111 Caucasians] with IPF underwent right heart catheterization and 6-min walk test (6MWT). Pulmonary arterial hypertension (PAH) was defined as mPAP≥25 and pulmonary artery occlusion pressure (PAOP)≤15mmHg, and Pre-PH as mPAP>20 and <25mmHg with PAOP<15mmHg. Demographic, hemodynamic, spirometric, and 6MWT data were collected.

Results: Fifty four (44%) patients had PH. There were no significant differences between the PH and the non-PH groups in measures of pulmonary function other than PaO(2). Patients with PH and PAH had significantly lower 6-min walk distance (6MWD) (p=0.008 and p=0.03 respectively) and distance saturation product (DSP) (p=0.002 and p=0.006 respectively) compared to non-PH patients. Mean pulmonary arterial pressure (mPAP) was the best predictor of 6MWD by multivariate analysis (p=0.0006). Increasing mPAP was associated with a statistically significant decline in 6MWD (p=0.02) and DSP (p=0.01). Patients with 'Pre-PH' had lower 6MWD compared to patients with mPAP≤20mmHg (p=0.07).

Conclusions: Relative to measures of pulmonary function and hypoxia, altered pulmonary hemodynamics had a greater impact on 6MWD in patients with IPF. Higher mPAP was associated with more significant exercise impairment. Mild abnormalities in pulmonary hemodynamics (so called 'Pre-PH') were associated with reduced 6MWD.