Figure 1. Invasive cardiopulmonary exercise test results. A, Analysis of the case vignette patient’s key functional performance measures demonstrates that the maximum respiratory exchange ratio, which compares the carbon dioxide (CO2) output to the oxygen (O2) uptake (V̇ CO2: V̇ O2) at maximum exercise is> 1.05, indicating an overall level of effort was performed by the patient that was sufficient to define a potential limitation to exercise through interpretation of iCPET findings. B, Spirometry performed at rest reveals a baseline restrictive lung disease, as evidenced by symmetrical, severely reduced functional vital capacity (FVC), total lung capacity (TLC), and forced expiratory volume in 1 second (FEV1). C, The patient’s low V̇ O2 at peak exercise is internally consistent with his severely reduced functional capacity as reported in A. D, Analysis of key respiratory data demonstrates an increase in minute ventilation at maximum exercise relative to maximum voluntary ventilation (at peak exercise, V̇ Emax: MVV> 0.7), suggesting a pulmonary mechanical limitation at maximum exercise. E, Pulmonary gas exchange data suggest hypoxemia and low end-tidal partial pressure of CO2 (PETCO2) on exercise, raising suspicion for pulmonary vascular disease. F, Analysis of advanced cardiopulmonary vital signs during exercise demonstrates a blunted increase in cardiac output, and an exaggerated increase in mean pulmonary arterial pressure, pulmonary vascular resistance, and mean right atrial pressure without a significant increase in pulmonary capillary wedge pressure compared with cardiopulmonary hemodynamics at rest. Collectively, these data suggest exercise-induced PAH, chronotropic insufficiency to exercise, and a secondary pulmonary mechanical limit to exercise by which to account for the patient’s diminished functional capacity. bpm indicates beats per minute; and N/A, not available.