title: Symptomatic presentation of carotid sinus hypersensitivity is associated with impaired cerebral autoregulation.
abstract: BACKGROUND
  Carotid sinus hypersensitivity (CSH) is associated with syncope, unexplained falls, and drop attacks in older people but occurs asymptomatically in 35% of community-dwelling elders. We hypothesized that impaired cerebral autoregulation is associated with the conversion of asymptomatic CSH to symptomatic CSH. We therefore conducted a case-control study evaluating individuals with CSH with and without the symptoms of syncope or unexplained falls, as well as non-CSH controls, to determine whether the blood pressure and heart rate changes associated with CSH are associated with symptoms only when cerebral autoregulation is altered.
  
  
  RESULTS
  Bilateral middle cerebral artery blood flow velocities (BFV) were measured in consecutive patients with symptomatic CSH (n=22) and asymptomatic controls with (n=18) and without CSH (n=14) using transcranial Doppler ultrasonography during lower body negative pressure-induced systemic hypotension. Within-group comparisons revealed significantly lower cerebrovascular resistance index (CVRi) at nadir for the asymptomatic CSH group (right, mean [95% CI]: 2.2 [1.8, 2.8] versus 2.6 [2.2, 3.0]; P=0.005; left: 2.8 [2.4, 3.3] versus 3.1 [2.7, 3.8]; P=0.016). Between-group comparisons showed higher mean BFV (right: estimated mean difference, B=5.49 [1.98, 8.80], P=0.003; left: 4.82 [1.52, 8.11], P=0.005) and lower CVRi (right: B=0.08 [0.03, 0.12], P=0.003, left: B=0.07 [0.02, 0.12], P=0.006) in asymptomatic CSH versus symptomatic CSH groups. There were no significant differences in bilateral mean BFV or right CVRi between the non-CSH and symptomatic CSH groups but differences were present for left CVRi (B=0.07 [0.02, 0.013], P=0.015).
  
  
  CONCLUSIONS
  Cerebral autoregulation is altered in symptomatic CSH and therefore appears to be associated with the development of hypotension-related symptoms in individuals with CSH.
authors.affiliation: Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia (M.P.T.).
authors.forename: Maw Pin
authors.initials: MP
authors.lastname: Tan
authors.affiliation: Institute of Health and Society, Newcastle University, United Kingdom (T.J.C.).
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Chadwick
authors.affiliation: Institute for Ageing and Health, Newcastle University and Falls and Syncope Service, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom (S.J.K., S.W.P.).
authors.forename: Simon R J
authors.initials: SR
authors.lastname: Kerr
authors.affiliation: Institute for Ageing and Health, Newcastle University and Falls and Syncope Service, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom (S.J.K., S.W.P.).
authors.forename: Steve W
authors.initials: SW
authors.lastname: Parry
mesh_terms: D000368:Aged; D058070:Asymptomatic Diseases; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology; D002346:Carotid Sinus / Q000503:physiopathology; D016022:Case-Control Studies; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D013575:Syncope / Q000150:complications / Q000503:physiopathology*; D017585:Ultrasonography, Doppler, Transcranial
keywords: arrhythmia; autonomic nervous system; baroreceptors; cerebrovascular circulation; syncope