(947) – Muscular Efficiency in Patients With Idiopathic Pulmonary Arterial Hypertension (iPAH): Impact on Clinical Severity and Survival

Patients with idiopathic pulmonary hypertension (iPAH) have a severe cardiocirculatory limitation and severe impairment of respiratory efficiency. The current therapies have changed the course of the disease, and, in analogy with other chronic illness, we hypothisize that these patients could develop a reduced muscular efficiency (i.e. a larger oxygen consumption than a normal subject for the same external work) that could have a prognostic impact. Fifty-five consecutive stable iPAH patients (mean age 50+15 years; NYHA class II 62%, NYHA class III 38%) and 20 matched controls underwent a symptom limited cardiopulmonary exercise test. Muscular efficiency was assessed as Energetic Efficiency (EE) calculated as the ratio between total O2 consumption (integral VO2 dt during effort and recovery) and the external work (integral WR dt). After the test, patients were followed for period of 3 years in order to evaluate the survival. The EE had not correlation with BMI, VE/VCO2SLOPE, %VO2max, pulmonary hemodynamics and 6MWT . Patients with iPAH had a lower exercise capacity and EE significantly higher than the control group (0.33±0.09 ml/j vs 0.24±0.03ml/j, p<0.0001). In the iPAH patients who died during the follow-up EE was higher than the iPAH patients who remained alive (Dead 0.42±0.09 ml/j vs Alive 0.28±0.03 ml/j, p<0.0001). In the COX analysis EE, gender, and VO2 peak were independent risk factors for death. Using a ROC analysis we identify the value of EE > 0.35 ml/j as an important prognostic factor (RR 4.95, IC: 1.5-16.7, p<0.01). Our data show that iPAH patients not only have a reduced VO2 peak, but also a less efficient oxygen utilization than normal subjects. Notably the impairment of muscular efficiency has a relevant prognostic impact. Further studies are needed in order to clarify the mechanism of the impaired energy expenditure.