Autonomic Nervous System (ANS) is organized as functional reflex arcs. Sensory signals from specific receptors are relayed to the relative centres located into the spinal cord, brain stem, or hypothalamus. After a complex local intergration, the impulses are transmitted to the visceral organs, to control their activities. Cardiovascular reflexes (CR) play major role in regulating cardiovascular functions and the efferent pathways are mainly directed to heart and arterial walls to control heart rate (HR) and blood pressure (BP). In clinical practice, the 5 non-invasive CR tests described by Ewing and Clarke more than 30 years ago, are considered yet the cornerstone of diagnosis. They are noninvasive tool, well-standardized and fairly cheap, but they are time-consuming and often difficult to interpret correctly. They can detect the presence or not of ANS dysfunction, its severity, and they are right for the follow-up, providing good sensitivity, specificity, and reproducibility. However it’s mandatory to work in dedicated lab.s by using a well-calibrated poligraphic system and a beat-to-beat non-invasive BP recorder. The technicians must explain to the patient what will happen. The patients must be acclimatated, not assuming large meals, coffee, drugs or other substances that could modify HR or BP.
The tests of parasympathetic cardiovagal function include HR analysis in the standing position (the 30:15 ratio), HR variation with deep breathing, and the Valsalva ratio (VR). Tests of sympathetic adrenergic function include BP evaluation in the standing position, better by using a tilt table, the Valsalva maneuver and the sustained handgrip.
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