Nonlinear analysis of dynamic cerebral autoregulation in humans under orthostatic stress

摘要

The effects of orthostatic stress on cerebral autoregulation are assessed by examining the dynamic relationship between spontaneous fluctuations of cerebral blood flow and arterial blood pressure under various levels of Lower Body Negative Pressure (LBNP) in healthy humans. The Laguerre-Volterra network methodology for modeling nonlinear systems is employed to this purpose. Results are obtained in the form of Volterra kernels as well as in the form of the dynamic modes of the system. Three significant modes are identified, one of them residing mostly in the linear system dynamics, and the other two residing in the nonlinear system dynamics. The obtained results reveal that the latter are affected mainly in the low frequency range (below 0.04 Hz), whereas they remain unaffected in the intermediate frequency range (between 0.04 and 0.08 Hz) and are affected moderately above 0.08 Hz.