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Dynamically assessing the arterial baroreflex by examining ramp responses to vasoactive agents

The arterial baroreflex in patients can be evaluated by examining the cardiovascular responses to vasoactive agents, a neck chamber device, and head tilting. Analyzing ramp responses to arterial blood pressure input more effectively enables the determination of baroreflex curves than does the examination of traditional step responses. The latter also requires the realization of steady-state conditions. Despite the advantages of ramp response analysis, however, a baroreflex test using ramp responses can induce various reactions because of the effect of input/output history with nonlinearity. In equilibrium analysis, for example, different ramp input speeds cause a misreading of baroreflex curves, in spite of stability in the central command of the baroreflex under hypertensive and hypotensive conditions. This study therefore intends to ascertain the optimal ramp speed during a baroreflex test by using a nonlinear response model. Here, a genetic algorithm was used to predict the nonlinear dynamic characteristics of the baroreflex on the basis of ramp responses; the system identification was classified into two processes (i.e., linear and nonlinear parts). An input speed lower than 0.5 mmHg/s was required to derive precise analytical results of a baroreflex test.