Contrasting Cardiopulmonary Responses to Incremental Exercise in Patients with Schistosomiasis-Associated and Idiopathic Pulmonary Arterial Hypertension with Similar Resting Hemodynamic Impairment

It has been reported that schistosomiasis-associated PAH (Sch-PAH) has a more benign clinical course compared with idiopathic PAH (IPAH). We therefore hypothesized that Sch-PAH subjects would present with less impaired cardiopulmonary and metabolic responses to exercise than IPAH patients, even with similar resting pulmonary hemodynamic abnormalities. The aim of this study was to contrast physiologic responses to incremental exercise on cycle ergometer between subjects with Sch-PAH and IPAH. We performed incremental cardiopulmonary exercise tests (CPET) in subjects newly diagnosed with IPAH (n = 9) and Sch-PAH (n = 8), within 1 month of the hemodynamic study and before the initiation of specific therapy for PAH. There were no significant between-group differences in cardiac index, pulmonary vascular resistance or mean pulmonary artery pressure. However, mean peak oxygen uptake (VO2) was greater in Sch-PAH than IPAH patients (75.5±21.4 vs 54.1±16.1% predicted, p = 0.016), as well as the ratio of increase in VO2 to work rate (8.2±1.0 vs 6.8±1.8 mL/min/W, p = 0.03). Additionally, the slope of the ventilatory response as a function of CO2 output was lower in Sch-PAH (40.3±3.9 vs 55.6±19.8; p = 0.04), and the heart rate response for a given change in VO2 was also diminished in Sch-PAH compared to IPAH (80.1±20.6 vs 123.0±39.2 beats/L/min; p = 0.02). In conclusion, Sch-PAH patients had less impaired physiological responses to exercise than IPAH subjects with similar resting hemodynamic dysfunction. Our data suggest a more preserved cardiopulmonary response to exercise in Sch-PAH which might be related to its better clinical course compared to IPAH.