The arterial baroreflex in neurogenic orthostatic hypotension

Excerpt

Reflex control of blood pressure (BP) is under primary control of the arterial baroreflex. The afferent limb of the baroreflex is mediated by vagal and glossopharyngeal fibers, providing information about changes in BP detected by carotid and aortic pressor sensors to the brainstem. The efferent output includes a vagal limb, regulating heart rate; and an adrenergic limb, regulating vasomotor tone/total peripheral resistance, as well as cardiac output. Traditionally, evaluation of baroreflex function in humans was done using the modified Oxford technique, which relates heart period change to a pharmacologically induced BP change [4, 5]. This method, which of course solely evaluates the vagal limb of the baroreflex, involves intravenous injection of a depressor agent (sodium nitroprusside) followed by a pressor agent (phenylephrine), resulting in large changes in BP. With development of non-invasive standardized autonomic function testing, we modified the approach to be applicable to routine autonomic testing, relating heart period change to the fall and rise in BP that occurs during and immediately following the Valsalva maneuver, and generated normative values [3, 7, 10]. …