title: Reduced systemic vascular resistance in healthy volunteers with presyncopal symptoms during a nitrate-stimulated tilt-table test.
abstract: BACKGROUND
  Nitrates may facilitate syncope through various pathways, but the precise mechanism of nitrate-induced syncope is still under debate. The purpose of the present study was to compare the underlying haemodynamic mechanisms in subjects without and with presyncopal symptoms during a nitroglycerin-stimulated tilt-table test.
  
  
  CONCLUSIONS
  A major decrease in systemic vascular resistance was documented in subjects with presyncope during 0.25 mg nitroglycerin-stimulated tilt-table test, in the absence of changes in cardiac output. These findings indicated that even a small dose of nitroglycerin significantly decreased arterial resistance and cardiac afterload. AIMS The mechanism of nitrate-induced syncope remains controversial. We examined the haemodynamic changes in healthy volunteers during nitroglycerin-stimulated tilt-table test.
  
  
  METHODS
  Continuous radial pulse wave analysis, whole-body impedance cardiography and plethysmographic finger blood pressure were recorded in a supine position and during head-up tilt in 21 subjects with presyncopal symptoms (6 male/15 female, age 43 ± 3 years) after 0.25 mg sublingual nitroglycerin and 21 control subjects (6 male/15 female, age 43 ± 2 years). The drug was administered in the supine position and a passive head-up tilt followed 5 min later. Additionally, nitroglycerin was only administered during head-up tilt in 19 subjects and the haemodynamics were recorded.
  
  
  RESULTS
  Supine and upright haemodynamics were similar before nitroglycerin administration in the two groups. During the nitroglycerin-stimulated tilt test, aortic and radial mean blood pressure decreased significantly more in the presyncope group when compared with the controls (P= 0.0006 and P= 0.0004, respectively). The decreases in systemic vascular resistance (P= 0.0008) and heart rate (P= 0.002), and increase in aortic reflection time (P= 0.0002) were greater in the presyncope group, while the change in cardiac index was not different between the groups (P= 0.14). If nitroglycerin was administered during the upright tilt and not in supine position, the haemodynamic changes were quite corresponding.
  
  
  CONCLUSIONS
  Presyncopal symptoms during nitrate-stimulated tilt test were explained by decreased systemic vascular resistance and increased aortic reflection time, while cardiac output remained unchanged. These findings indicated reduced arterial resistance in nitroglycerin-induced presyncope.
authors.affiliation: Department of Internal Medicine, Tampere School of Public Health, University of Tampere, Tampere, Finland. anna.tahvanainen@uta.fi
authors.forename: Anna
authors.initials: A
authors.lastname: Tahvanainen
authors.forename: Jenni
authors.initials: J
authors.lastname: Koskela
authors.forename: Miia
authors.initials: M
authors.lastname: Leskinen
authors.forename: Erkki
authors.initials: E
authors.lastname: Ilveskoski
authors.forename: Klaus
authors.initials: K
authors.lastname: Nordhausen
authors.forename: Mika
authors.initials: M
authors.lastname: Kähönen
authors.forename: Tiit
authors.initials: T
authors.lastname: Kööbi
authors.forename: Jukka
authors.initials: J
authors.lastname: Mustonen
authors.forename: Ilkka
authors.initials: I
authors.lastname: Pörsti
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D005996:Nitroglycerin / Q000008:administration & dosage; D013575:Syncope; D018667:Tilt-Table Test; D014655:Vascular Resistance / Q000187:drug effects*; D055815:Young Adult
chemical_list: D005996:Nitroglycerin