Background-The clinical relevance of exercise-induced pulmonary arterial hypertension (PAH) is uncertain, and its existence has never been well studied by direct measurements of central hemodynamics. Using invasive cardiopulmonary exercise testing, we hypothesized that exercise-induced PAH represents a symptomatic stage of PAH, physiologically intermediate between resting pulmonary arterial hypertension and normal. Methods and Results-A total of 406 consecutive clinically indicated cardiopulmonary exercise tests with radial and pulmonary arterial catheters and radionuclide ventriculographic scanning were analyzed. The invasive hemodynamic phenotype of exercise-induced PAH (nϭ78) was compared with resting PAH (nϭ15) and normals (nϭ16). Log-log plots of mean pulmonary artery pressure versus oxygen uptake (V O 2 ) were obtained, and a "join-point" for a least residual sum of squares for 2 straight-line segments (slopes m1, m2) was determined; m2Ͻm1ϭ"plateau," and m2Ͼm1ϭ"takeoff" pattern.

Left ventricular myocardial volume was determined by magnetic resonance imaging (MRI) in 14 volunteers with different levels of cardiac function. In addition left ventricular myocardial volume (mass) was determined in 10 postmortem human hearts by MRI. In vivo determination of left ventricular myocardial volume (mass) showed that estimated left ventricular mass determined at systole and at diastole came close to the theoretical ratio of one in all cases (r = 0.95, p < 0.0001). There was good agreement between left ventricular myocardial volume determined by MRI and the true mass obtained by weighing the isolated left ventricle. Left ventricular mass index determined by MRI was higher in the patients with ischemic heart disease than in the controls. No difference was observed between left ventricular mass index in the controls in the two series. These results demonstrate the feasibility of measuring myocardial mass by magnetic resonance in humans and suggest a clinical relevance of such studies in patients with left ventricular disease.