Heart rate and stroke volume response patterns to augmented orthostatic stress

Abstract

Combined head up tilt (HUT) and lower body negative pressure (LBNP) can be used to exploit the full spectrum of cardiovascular control mechanisms and to reveal characteristics of individual blood pressure control. We studied whether the response to combined HUT and LBNP was reproducible within subjects and whether characteristic response patterns could be distinguished between different subjects. Ten healthy young males were subjected to combined HUT and graded LBNP to achieve a presyncopal end point in four tests, each separated by more than 2 weeks. Heart rate, blood pressure and thoracic impedance were monitored, cardiac output and peripheral vascular resistance were computed. From supine control to presyncope, heart rate, mean arterial blood pressure, pulse pressure and stroke index changed as expected. The time courses of heart rate and stroke volume as well as orthostatic tolerance times (15 +/- 6 to 18 +/- 7 minutes, n.s) appeared reproducible between trials within subjects but different between different subjects. LBNP-tilt approach was repeatable in time and pattern. Furthermore, differences observed between subjects indicated preferred activation of selected pathways of blood pressure control in different individuals while at the same time, reproducibility measured within the same subject showed that preferential mechanisms were highly conserved within the same individual. These characteristics are a prerequisite to use the combined graded orthostatic paradigm for hemodynamic testing and identification.