Effects of posture on cardiac dynamics during visual search

Abstract

Cardiovascular psychophysiologists are employing emerging non-invasive technologies to chart the changes in a variety of parameters of cardiac activity as psychological tasks are performed. One technique, impedance cardiography, makes it possible to assess cardiac output and contractile force while psychological tasks are being performed. This study was designed to determine if facilitating the venous return of blood from the legs would alter the pattern of cardiac changes that have been noted in earlier impedance cardiographic studies of the effects of psychological challenge. Twenty normotensive males performed visual search in upright, sitting and reclining positions and impedance cardiographic assessments of cardiac output and stroke volume, and an index of contractility were obtained. In addition, heart rate and two systolic time intervals were measured. As expected, decreases in stroke volume occurred as heart rate increased during visual search. Hence cardiac output (heart rate × stroke volume) remained stable. Higher levels of cardiac output, stroke volume and contractility were recorded in the reclining versus the upright position. However, the patterns of cardiac activity did not differ before, during and after performance when body position was altered. Hence, posture altered the absolute levels of several cardiac parameters, but did not affect the configuration of cardiac changes associated with performing a mildly challenging task.