Abstract

Ventricular volumes were measured in 10 normal subjects by using two independent methods: the stroke volume was obtained by the Fick principle and the ejection fraction by multigated radionuclide angiography. Data were collected at rest in the supine and upright positions and during an upright exercise test, which included three levels of increasing severity. The left and right ventricular end-diastolic volumes (EDV) were maximal in the supine posture; at rest both were significantly lower in the upright position. At maximal exercise, the ventricular end-diastolic volumes were similar or slightly lower than at rest in the upright position. During upright exercise, the end-systolic volumes (ESV) gradually decreased; simultaneously, the left ventricular ejection fraction (EF) and the right ventricular EF increased. Since during exercise in the upright position, the end-diastolic volumes are unchanged or tend to decrease, a Frank-Starling mechanism cannot be called upon; the cardiac response to upright exercise is thus mainly based on an increased venous return and on an increase in myocardial contractility reflected by the increase in ejection fraction and the decrease in end-systolic volumes. Verf.-Referat