Lege Artis Medicinae

[Hemodynamic changes during simulated orthostasis]


MAY 01, 2000

Lege Artis Medicinae - 2000;10(05)

[INTRODUCTION – „Lower body negative pressure" (LBNP, simulated orthostasis) is an experimental method to simulate orthostatic stress. METHODS – The aim of this study was to quantitate hemodynamic and thoracic bioimpedance changes with four levels of LBNP (-15, -35, -55, -65 mmHg) in 7 healthy men in supine position 20 min before (pre-LBNP), 30 min during, and 20 min after suction as well as without suction (rest control). RESULTS - Thoracic bioimpedance computed stroke volume index continuously decreased with time by the end of simulated orthostasis of -15, -35, -55 and -65 mmHg. The decrease of cardiac index was largest at LBNP of -15 and -35, where the highest relative increase of total peripheral resistance index occurred. Mean arterial pressure did not change in any systematic way with lower LBNP levels, but increased at the end of LBNP -55 and -65. Heart rate remained unchanged at LBNP-15, but increased continuously with simulated orthostasis duration at higher levels by the end of LBNP-35, -55, and -65. Having finished simulated orthostasis, heart rate fell below pre-stimulus levels and also below rest control levels for 25 min; computed stroke volume index transiently returned to pre-stimulus levels, whereas mean arterial pressure increased above pre-LBNP level after finishing the stimulus. CONCLUSIONS - Different levels of lower body negative pressure produced quantitatively different time course and dose-response patterns and subjects remained non-hypotensive up to -65 mmHg suction. The heart rate was depressed after simulated orthostasis, while arterial blood pressure and impedance computed total peripheral resistance exceeded pre-stimulus levels indicating an altered cardiovascular (neuro-humoral) state after 30 min of simulated orthostasis. ]


  1. Volume Regulation and Space Medicine Research Group, Department of Physiology, School if Medicine, Karl-Franzes University, Graz, Austria
  2. Institute for Adaptive and Spaceflight Physiology, Austrian Society for Aerospace Medicine and Life Sciences, Graz, Austria



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