Multiscale time irreversibility to predict orthostatic intolerance in older people

摘要

Orthostatic intolerance (OI) is a clinical syndrome, which is characterized by symptoms and loss of consciousness before impeding syncope and that it has been reported that is caused by orthostatic hypotension (OH). The phenomenon of irreversibility is specific for non-equilibrium systems and is presented in the complexity of cardiovascular system control signals. This study is focused to quantify the effect of the OI on the time irreversibility of the heart rate (HR), cardiac output (CO) and and systolic blood pressure (SBP) time series, during six-minutes walking distance test in symptomatic older people, who were compared by the following multiscale time irreversibility Porta's index and Euclidean distance. We analyzed 65 older subjects, of whom 42 were women. There was no significant differences in age and gender between symptomatic and asymptomatic OI participants, 44.6% (n=29) had symptoms of OI and 55.4% (n=36) did not. Results show higher indexes in non-OI groups, specially during the descent phase and during the subsequent passive phase. This study shows the irreversibility indexes as useful measure to extract non-linearity properties in hemodynamic parameters in order to find out differences during orthostatism.