Question

An executive in her late twenties visits the ambulatory care clinic reporting six months of progressively worsening shortness of breath with physical exertion. She denies chronic cough, orthopnea, daytime fatigue, or prior lung disease. She has no significant medical history and takes only oral contraceptives. Vital signs are within normal limits, with an oxygen saturation of $96\%$ on ambient air. Physical examination reveals a prominent pulmonic component of the second heart sound and a faint parasternal heave. The lung fields are clear to auscultation, and there is no peripheral edema. Electrocardiography reveals right axis deviation and an incomplete right bundle branch block. A chest radiograph demonstrates prominent central pulmonary arteries without parenchymal infiltrates. Echocardiography shows a structurally normal left ventricle with an ejection fraction of $65\%$, normal valvular function, and right ventricular enlargement with an estimated right ventricular systolic pressure of $52$ mmHg. Pulmonary function testing demonstrates a normal forced vital capacity, normal FEV1/FVC ratio, and a slightly reduced diffusion capacity for carbon monoxide (DLCO). Which of the following is the most appropriate next step in evaluating this patient's condition?