title: An increased endothelial-independent vasodilation is the hallmark of the neurally mediated syncope.
abstract: BACKGROUND
  The neurally mediated syncope (NMS) is sustained by complex cardiac and vascular reflexes, acting on and amplified by central autonomic loops, resulting in bradycardia and hypotension.
  
  
  OBJECTIVE
  Our aim was to assess whether the pathophysiology of NMS is also related to an abnormal peripheral vasoreactivity.
  
  
  METHODS
  We evaluated by ultrasound the flow-mediated vasodilation (FMD) and the nitrate-mediated dilation (NMD) in 17 patients with NMS, induced by drug-free tilt test in 6 subjects and by nitrate-potentiated tilt test in the other 11 cases; the syncope was classified as vasodepressive (VD) in 8 cases, cardioinhibitory (CI) in 7, and mixed in 2.
  
  
  RESULTS
  The FMD was not different from controls (10.2 ± 4.5 vs 11.4 ± 3.9, P = ns), with normal recovery times; the NMD was greater in fainting subjects than in controls (26.7 ± 7.3 vs 19.0 ± 3.6, P < 0.05), with higher values in VD than in CI syncope (31.1 ± 7.0 vs 23.1 ± 5.0, P = ns); compared to controls, subjects with NMS showed normal recovery times after FMD but longer recovery times after nitrate administration (13.0 ± 5.6 vs 6.3 ± 0.7 minutes, P < 0.05).
  
  
  CONCLUSIONS
  The evaluation of endothelial function supports evidence that NMS is characterized by a marked and sustained endothelial-independent vasodilation, in the presence of a normal FMD; vascular hyperreactivity in response to nitrate administration is particularly overt in vasodepressive syncope and can explain the high rate of responses to nitrate administration during tilt test.
authors: Division of Cardiology, Internal Medicine Department. lsantini@alice.it
authors: Luca
authors: L
authors: Santini
authors: Ambrogio
authors: A
authors: Capria
authors: Valentina
authors: V
authors: Brusca
authors: Arianna
authors: A
authors: Violo
authors: Francesca
authors: F
authors: Smurra
authors: Iside
authors: I
authors: Scarfò
authors: Giovanni B
authors: GB
authors: Forleo
authors: Lida P
authors: LP
authors: Papavasileiou
authors: Mauro
authors: M
authors: Borzi
authors: Francesco
authors: F
authors: Romeo
mesh_terms: D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000502:physiology; D004730:Endothelium, Vascular / Q000503:physiopathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D018667:Tilt-Table Test; D014463:Ultrasonography; D014664:Vasodilation / Q000502:physiology*