P171 Implications Of A Non-constant Resistance-compliance Product In Pulmonary Arterial Hypertension

Abstract

Introduction Pulmonary vascular resistance (PVR) is traditionally used to describe pulmonary haemodynamic characteristics. However, it does not take into account pulmonary artery compliance (Ca) or pulsatile flow. The product of PVR and Ca is known as RC-time. RC-time reflects the exponential decay of pressure in the pulmonary arteries during diastole. The right ventricle (RV) oscillatory power fraction (RVOPF) is the ratio of oscillatory power to total power generated by the RV. Oscillatory power is not used to generate stroke volume. Consequently the RVOPF is a measure of cardiac inefficiency. Previous small studies have suggested that both RC-time and RVOPF are constant. We hypothesised that RC-time is not constant and changes in RC-time affect cardiac efficiency. Methods Right heart catheters performed in PapworthHospital over a 6 year period were analysed. Patients were divided into normal pulmonary haemodynamics (NPH) and pulmonary arterial hypertension (PAH) groups. RC-time and RVOPF (≈ 1 − (mean pulmonary artery pressure/systolic pulmonary artery pressure) were calculated. Results RC-time for the NPH group (0.47 ± 0.1s) is lower than the PAH group (0.56 ± 0.2s; p 2 = 0.33; NPH group: r 2 = 0.27). Conclusions RC-time is not constant between health and pulmonary vascular disease. A reduction in RC-time, in the context of PAH, is associated with a decrease in cardiac efficiency. RVOPF is lower in the NPH group compared to the PAH group. This implies better cardiac efficiency in the NPH group possibly due to less pulsatile loading of the RV. Haemodynamic assessments which include measures of compliance may be of utility in understanding the progression of right heart failure in PAH.