Effect of posture on spontaneous and thermally stimulated cardiovascular oscillations

Abstract

The aim of the study was to investigate the effect of posture on thermally stimulated cardiovascular oscillations. The effect of increased gravitational stress (rising from sitting to standing position) on the thermally stimulated cardiovascular oscillations was measured in young male volunteers. Extensive cardiovascular function data were obtained using a cardiovascular investigation protocol. The volunteers were five fit young men, aged 20-21 years. EXPERIMENTS AND MAIN RESULTS: Cardiovascular changes from sitting to standing indicated increased sympathetic and decreased parasympathetic influence on heart and skin blood vessels; mean heart rate increased, beat to beat heart rate variability diminished, high frequency periodic heart rate variability decreased, low frequency heart rate oscillations and ratio of low frequency to high frequency heart rate variability increased, mean skin blood flow and oscillations of skin blood flow decreased (all p less than 0.05). Thermal skin stimulation at 0.01-0.10 Hz frequency increased both sitting and standing 0.10 Hz periodic heart rate variability (p less than 0.05), and 0.10 Hz thermal stimulation entrained the heart rate oscillations in sitting and standing subjects (p less than 0.05). In contrast, skin blood flow oscillations in sitting subjects decreased, while in standing subjects it increased during 0.10 Hz thermal stimulation compared to the corresponding prestimulus values (p less than 0.04). On the basis of previous physiological experiments, these results suggest coupling between thermoregulatory and 0.10 Hz reflex activities.