The prognostic significance of inspiratory capacity in pulmonary arterial hypertension.

BACKGROUND: Patients with pulmonary arterial hypertension (PAH) present with an altered inspiratory capacity (IC) reflecting dynamic hyperinflation (DH) that leads to mechanical constraints and excessive ventilatory demand, particularly during exercise, resulting in exertional dyspnea. OBJECTIVES: Assessment of the long-term consequences of altered IC and DH in PAH. METHODS: 50 patients with newly diagnosed PAH were prospectively recruited. All patients were assessed by means of right heart catheterization, 6-min walking distance (6MWD) test, lung function and cardiopulmonary exercise testing, including the assessment of IC. RESULTS: 37 patients with idiopathic PAH and 13 patients with conditions associated with PAH (29 female; mean age 51.6 ± 15.1 years; World Health Organization, WHO class, 2.7 ± 0.6) presented with a mean pulmonary arterial pressure of 42.8 ± 15.9 mm Hg and pulmonary vascular resistance (PVR) of 737.2 ± 592.8 dyn*s/cm(5). The mean IC at rest was 87.2 ± 17.3% pred. Kaplan-Meier analysis revealed that patients with an IC at rest >89% pred. had a significantly better 5-year survival than those with lower values (94.1 vs. 75.1%; log-rank p = 0.036). Univariate analysis identified IC at rest (% pred.) as a predictor of survival with a hazard ratio (HR) of 5.05 (95% confidence interval, CI, 0.97-26.24, p = 0.054). In multivariate analysis including PVR, WHO class, 6MWD and peak oxygen uptake as covariates, IC at rest remained an independent predictor of survival (HR: 8.06, 95% CI 0.92-70.34; p = 0.059). DH expressed as ΔIC or static hyperinflation expressed as IC/total lung capacity at rest revealed no prognostic significance. CONCLUSION: In patients with PAH, IC at rest is of prognostic significance at the time of diagnosis.