BEDSIDE AUTONOMIC FUNCTION TESTING IN PATIENTS WITH VASOVAGAL SYNCOPE

The factors that determine the individual susceptibility to vasovagal syncope [VVS] are largely unknown, including the role of the autonomic nervous system. We therefore studied common vagal and sympathetic ref lexes in 12 patients with WS (mean age 37 [18-75] years, 6 men). The V alsalva maneuver and deep breathing were performed to assess vagal res ponsiveness and mental arithmetic stress; the cold-pressor test and is ometric handgrip were performed to assess sympathetic responsiveness. Standing up was per-formed to assess the combined responsiveness. With the exception of a subnormal response to deep breathing in one patien t, all vagal tests were normal. In contrast, the response to mental st ress, the cold-pressor test, and isometric handgrip was subnormal in 4 patients, 6 patients, and 4 patients, respectively. The response to s tanding up was normal in all patients. It is concluded that many patie nts with WS are characterized by normal vagal responsiveness, but symp athetic hyporesponsiveness. Sympathetic hyporesponsiveness might expla in the inadequate vasoconstriction, which plays an important, early ro le in ws.