title: Influence of respiratory instability during neurocardiogenic presyncope on cerebrovascular and cardiovascular dynamics.
abstract: OBJECTIVE
  To analyse the influence of breathing activity on cerebrovascular dynamics during presyncope.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  38 subjects developing neurocardiogenic syncope (syncope group), and 61 age-matched control subjects with negative tilt.
  
  
  METHODS
  Middle cerebral artery mean blood flow velocity (MCFV), continuous non-invasive blood pressure (BP), end-tidal CO(2) (CO(2)-et) and minute ventilation were measured before and during 45' 60 degrees tilting.
  
  
  METHODS
  Respiratory and cerebrovascular variability, cerebrovascular resistance (CVR)-absolute and corrected for CO(2)-et at 40 mm Hg (CVR-40)-and dynamic cerebrovascular regulation (CVR-dyn: transfer function phase analysis between MCFV and BP), obtained during supine rest (baseline), first 5 minutes of tilt (early tilt), early- and late presyncope (first and second half, respectively, of 4 minutes preceding syncope in syncope group, and equivalent time in controls).
  
  
  RESULTS
  Tilting induced a mean (SE) CVR decrease in controls (baseline 1.20 (0.04); late presyncope 1.12 (0.06) mm Hg x s/cm, p<0.05) but not in the syncope group (baseline 1.09 (0.04); late presyncope 1.09 (0.06) mm Hg x s/cm, p = NS). However, CVR-40 showed similar reduction in both groups (controls: from 1.15 (0.04) to 0.96 (0.04) mm Hg x s/cm; syncope group: from 1.01 (0.04) to 0.83 (0.04) mm Hg x s/cm, p = NS). CVR-dyn of the two groups was also similar (p = NS). Respiratory variability increased in the syncope group, from early tilt to late presyncope (p<0.05 or better), preceding hyperventilation and being significantly correlated with an increase in MCFV and BP variability (p<0.01).
  
  
  CONCLUSIONS
  During presyncope, the development of respiratory instability and hypocapnia impairs MCFV, thus facilitating the onset of syncope despite preserved cerebrovascular regulation.
authors.affiliation: Department of Internal Medicine, University of Pavia and IRCCS Ospedale S Matteo, Pavia, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Porta
authors.forename: G
authors.initials: G
authors.lastname: Casucci
authors.forename: S
authors.initials: S
authors.lastname: Castoldi
authors.forename: A
authors.initials: A
authors.lastname: Rinaldi
authors.forename: L
authors.initials: L
authors.lastname: Bernardi
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000502:physiology; D002319:Cardiovascular System / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D016857:Hypocapnia / Q000150:complications / Q000503:physiopathology*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D012189:Retrospective Studies; D013575:Syncope / Q000150:complications / Q000503:physiopathology*; D019462:Syncope, Vasovagal / Q000150:complications / Q000503:physiopathology; D018667:Tilt-Table Test / Q000379:methods
chemical_list: D002245:Carbon Dioxide