BAROREFLEX SENSITIVITY IN PATIENTS WITH VASOVAGAL SYNCOPE

Background In the present study, we tested the hypothesis that baroref lex sensitivity is reduced in patients with vasovagal syncope compared with normal control subjects. Methods and Results We investigated 30 patients with vasovagal syncope (mean age, 43.6+/-16.7 years, 14 men a nd 16 women) and 32 normal control subjects (mean age, 41.8+/-17.0 yea rs; 24 men and 8 women). Cardiopulmonary baroreceptor sensitivity was assessed by measuring the change in forearm vascular resistance during subhypotensive lower body negative pressure (LBNP). Carotid barorefle x sensitivity was assessed by measuring the change in RR interval duri ng the manipulation of carotid transmural pressure. Phenylephrine baro receptor sensitivity was assessed on the basis of the linear regressio n slope of the RR interval versus systolic arterial blood pressure dur ing the increment in blood pressure after intravenous administration o f phenylephrine. In patients with vasovagal syncope, during the applic ation of -10 mm Hg LBNP, forearm vascular resistance decreased by 0.7/-11.6 U versus an increase of 8.3+/-6.2 U in control subjects (P=.002 ). Phenylephrine baroreceptor sensitivity was 11+/-7 ms/mm Hg in patie nts versus 14+/-6 ms/mm Hg in control subjects (P=NS). Carotid baroref lex sensitivity was 4+/-6 versus 4+/-2 ms/mm Hg in patients and contro l subjects, respectively (P=NS). Conclusions In patients with vasovaga l syncope, during the application of subhypotensive LBNP, there is imp aired forearm vasoconstriction or paradoxical forearm vasodilation. Th is suggests impaired cardiopulmonary baroreceptor inactivation or para doxical activation of these receptors and is consistent with reduced c ardiopulmonary baroreceptor sensitivity.