Casual interactions between blood pressure and cardiac inter-beat intervals in older people with orthostatic intolerance

The aim of our study was to analysed the proportion of both casual direction between inter-beat interval (R-R) and non-invasive beat to beat blood pressure (BP) during six minutes walking distance test between symptomatic and asymptomatic participants of orthostatic intolerance (OI). We analysed 65 older subjects, of whom 42 were women. The participants underwent a supine to stand orthostatic test with non-invasive beat-to-beat systolic blood pressure and diastolic blood pressure and R-R monitoring. Transfer Entropy (TE) method was applied to identify relationship between hemodynamical variables. The directionality index quantifies the preferred direction of information flow from difference between both directional couplings. Results show a higher symmetric bidirectional couplings in asymptomatic OI group. These results show that systolic blood pressure affects heart rate; nevertheless directional coupling between these cardiovascular signals is altered depending on changes in autonomic control introduced by the orthostatic test.