Abstract 12350: Pressure-flow Relationship of Pulmonary Circulation Determines Six-minute Walk Distance in Connective Tissue Disease

Abstract

Introduction: The 6-minute walk distance (6MWD) as a surrogate of exercise capacity is often shown to be the best predictor of mortality in pulmonary hypertension (PH). Recent studies have described that mean pulmonary artery pressure (mPAP) - cardiac output (CO) relationships have a potential to assess the detail of pulmonary circulation. Hypothesis: We hypothesized that pressure-flow relationships of the pulmonary circulation (mPAP/CO) would be associated with 6MWD in connective tissue disease (CTD). Methods: We prospectively performed 6-minute walk test and echocardiographic studies in 202 CTD patients (56±14 years; 11% male) with measurements of cardiac output using electric cardiometry. We have calculated the pulmonary artery pressure-cardiac output relationships as mPAP divided by CO (mPAP/CO). Results: Firstly, we have checked the accuracy of CO by electric cardiometry. In our cohort with invasive data, there is a good correlation between right heart catheter and electric cardiometry values of cardiac output (r=0.85; p <0.001) with electric cardiometry measurements slightly underestimating cardiac output (bias -14% of the mean). Correlates of 6MWD were age (partial R= -0.19, p=0.009), early-diastolic mitral annular motion velocity (e’, partial R= 0.20, p=0.005), E/e’ (partial r= -0.16, p=0.028) and CO (partial r= 0.21, p=0.019) in the univariate analysis. In multivariate analysis, the mPAP/CO was strongly associated with 6MWD (t= -2.06, p= 0.042). Male gender and early-diastolic tricuspid annular motion velocity were also associated with 6MWD (t= 2.09, p=0.038 and t =2.92, p =0.004, respectively). Conclusions: Elevated mPAP/CO was associated with reduced 6MWD independent from LV and RV diastolic function. These results may recommend that we would assess not only the pressure but also the pressure-flow relationships of the pulmonary circulation in high risk group of PH.