Abstract 9677: Therapeutic Improvements in Pulmonary Arterial Hypertension Are Related to Cardiopulmonary Function but Not Skeletal Muscle Oxygen Extraction

Abstract

Introduction: World Symposium Group 1 pulmonary arterial hypertension (PAH) patients have impaired function from both central oxygen delivery and skeletal muscle oxygen extraction. The effect of PH-directed therapy on skeletal muscle oxygen extraction is unknown. The aim of this study is to determine if therapy associated changes in muscle extraction parallel changes in cardiopulmonary function. Methods: Retrospective analysis was performed on twenty-nine PAH patients (24 female, mean age 54±11.4 years) receiving prostacyclin therapy (18 on monotherapy). Subjects underwent invasive cardiopulmonary exercise testing (iCPET) for treatment response evaluation followed by repeat surveillance iCPET with mean follow-up of 10.4±5.2 months. Skeletal muscle oxygen extraction was quantified by arterio-venous difference indexed to hemoglobin (Ca-vO 2 /Hgb) and systemic oxygen extraction ratio (SER) (Ca-vO 2 /CaO 2 ). Central oxygen delivery (DO 2 ) was calculated as peak cardiac output X CaO2 at peak exercise. Functional capacity was semi-quantified by six-minute walk test (6MWT) distances between assessments (n=20). Subjects were stratified into two groups: those with improvement (n=10) vs unimproved (n=19) in currently accepted ERS/COMPERA score ( Figure ). Results: Improvements in ERS/COMPERA score were related to DO 2 (318.3±273.1 vs -38.3±684.9 mL/min, P=.016 ) and PVR (-4.8±3.0 vs -0.6±3.2 WU, P=.002 ) (Figure A & B). However, there was not a detectible difference between assessments in Ca-vO 2 /hgb (-0.01±0.14 vs 0.00±0.27 mL/g, P=.573 ), SER (-0.01±0.10 vs 0.00±0.20, P=.573 ), or 6MWT (7 improved, 13 unimproved) (77±115 vs 25±104 meters, P=.877 ) ( Figure C & D ). Conclusions: Although PH-directed therapy improves both PVR and oxygen delivery, its effects on skeletal muscle extraction are questionable. Clinicians should consider that oxygen extraction may influence functional capacity when evaluating therapeutic improvement.