Paradigms of Cardiovascular Control in Response to Sympathetic Stimulation by Simulated Orthostatic Stress

Abstract

BackgroundSympathetic stimulation by lower body negative pressure (LBNP) as surrogate of orthostatic stress augments heart rate (HR) and total peripheral resistance (TPR) in maintaining blood pressure (BP). This study addressed the variation in cardiovascular response to LBNP within and between subjects.MethodsIn 10 healthy subjects (5 female), BP (Nexfin), HR, stroke volume (SV), cardiac output (CO), TPR, BP/HR variability, and frequency domain baroreflex HR control (BRS) were quantified during three consecutive 5 minute runs of ‐50 mmHg LBNP (repeated after one week) to determine reproducibility.ResultsIn response to repeated LBNP runs, SV and HR demonstrated excellent and CO and TPR good within‐subject reproducibility. The cardiovascular response between subjects differed. Subjects with a marked decrease in SV (ΔSV>31%) demonstrated a higher resting HF/Ptot ratio as surrogate of parasympathetic activity and a more HR mediated response to LBNP. Contrary, a small SV decrease (ΔSV蠄31%) paralleled a higher resting LF/HF ratio as surrogate of sympathetic activity and a predominant increase in TPR in response to LBNP. BRS did not differ between groups.ConclusionConsiderable between‐subject variation in cardiovascular responses to LBNP indicates differences in blood pressure regulation and suggests subject‐specific strategies of autonomic cardiovascular control in young healthy individuals.