Figure 1.

A-D, Diagram showing RV pressure-volume analysis in patients with abnormal pulmonary vascular response to exercise with vs without contractile reserve. A, Schematic of RV pressure-volume loop in a patient without apparent RV dysfunction at rest. B, Schematic of RV pressure-volume response to exercise in a patient with RV contractile reserve in the setting of increased afterload during exercise. Red indicates rest and blue indicates exercise. Contractility (E_es) increases such that even with increased afterload (E_A), ventricular-arterial coupling is maintained. C, Schematic of RV pressure-volume loop in a patient with increased RV afterload apparent at rest. Relative to the patient without apparent RV dysfunction (A), contractility (E_es) is increased to maintain ventricular-arterial coupling in the face of increased afterload (E_A). D, Schematic of RV pressure-volume response from rest (red) to exercise (blue) in a patient with insufficient RV contractile reserve in the setting of increased afterload during exercise. Contractility (E_es) fails to increase in response to increased afterload (E_A), resulting in reduced ventricular-arterial coupling. Increased RV end-systolic and end-diastolic volumes are observed. E_A = arterial elastance, a measure of RV afterload determined by the slope between end-systolic coordinates and the end-diastole volume-axis intercept, or the quotient of end-systolic pressure and stroke volume^13,17; E_es = end-systolic elastance, a measure of RV contractility defined by the slope of the end-systolic pressure-volume relationship; RV = right ventricular.