The interaction between cardiovascular and posture controls and the effects of ageing

Fainting during quiet standing is a serious problem in syncopal youth and prominent in elderly individuals. This thesis examined the possible interaction of the cardiovascular and posture control systems during quiet stance and the effect of ageing. We hypothesized that there exists a bidirectional interaction between blood pressure (BP) and posture changes through the activation of skeletal muscle pump via the calf muscles. In study one, the analysis methods for non-stationary signals were explored and the wavelet transform coherence method was validated for its applicability. In study two, cardiovascular variables, stabilogram data and posture muscle electromyography (EMG) data were compared to each other. The EMG and BP signals showed discrete regions of high coherence during quiet stance. In a third study, the effect of ageing on the relationship between these two systems was investigated. Age was found to have a statistically significant affect on the relationship between these two systems