Characterizing the afferent limb of the baroreflex
Alfrey, Karen D.
Clark, John W., Jr.
Doctor of Philosophy
In this study, we develop a model of left ventricular and near-systemic hemodynamics, together with a three-component model of the aortic baroreceptor (BR) using experimental data from rat. The hemodynamic model possesses a third-order Windkessel structure consistent with existing models of human and dog hemodynamics and produces good fits to left ventricular, aortic, and femoral pressure waveforms. The baroreceptor model includes subsystem models of the viscoelastic properties of the aortic wall, converting input pressure to strain impinging on embedded nerve terminal endings; the mechanotransduction properties of baroreceptor terminal endings, converting applied strain to generator potential; and the encoding properties of the first Node of Ranvier, converting generator potential into a train of action potentials (spikes), the frequency of which encodes both mean pressure and rate of change of pressure in the aortic arch. The model mimics the known static and dynamic nonlinearities of the BR, including threshold, saturation, post-excitatory depression, and frequency-dependent hysteresis, using a minimum of parameter adjustment. Because it enables the study of subsystems not easily accessed in an experimental setting, including wall-nerve coupling and mechanotransduction, the model provides an ideal testbed for suggesting detailed ionic mechanisms underlying these behaviors. Overall, the model provides a quantitative description of the mechanical, electrical, and chemical behavior of the sensory nerve and its interaction with the arterial wall in which it is imbedded. Model-generated data agrees quantitatively with single nerve recordings of rat arterial baroreceptors, and qualitatively with data from other species.
Neurosciences; Biomedical engineering; Electronics; Electrical engineering