title: Altered cerebral vasoregulation in hypertension and stroke.
abstract: BACKGROUND
  Autoregulation of blood flow that maintains steady perfusion over the range of systemic blood pressure is compromised by stroke.
  
  
  OBJECTIVE
  To determine whether cerebral vasoregulation is impaired in stroke during orthostatic stress.
  
  
  METHODS
  Subjects included 30 control subjects, 30 with hypertension, and 20 with minor stroke and were studied using transcranial Doppler. Bilateral blood flow velocities (BFVs) from middle cerebral arteries, heart rate, blood pressure (BP), and CO2 were obtained during hyperventilation and CO2 rebreathing during supine rest and tilt at 80 degrees. Side-to-side BFV difference, vasomotor range (VMR), and cerebrovascular resistance (CVR) were calculated during normo-, hypo-, and hypercapnia.
  
  
  RESULTS
  Mean BFVs were similar between groups in supine position but differed during tilt. BFV diminished on the stroke side during tilt with hyperventilation and CO2 rebreathing (p < 0.0001). CVR increased (p < 0.0001) and VMR decreased (p < 0.01) on the stroke side. Vasoregulation was preserved on the normal side. BFV asymmetry differentiated patients with stroke from the other groups (p < 0.0001). BFV difference between the normal vs stroke side was the largest in stroke-normotensive (n = 7) compared with stroke-hypertensive (n = 13) patients and the two other groups (p < 0.0001). BFV asymmetry in stroke was associated with lower orthostatic BP (p < 0.0001).
  
  
  CONCLUSIONS
  Cerebral vasoregulation is impaired with minor stroke, and cerebral blood flow depends on blood pressure. Decline of blood flow velocities during orthostatic stress may pose a risk of silent hypoperfusion.
authors.affiliation: Division of Gerontology, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA. vnovak@caregroup.harvard.edu
authors.forename: V
authors.initials: V
authors.lastname: Novak
authors.forename: A
authors.initials: A
authors.lastname: Chowdhary
authors.forename: B
authors.initials: B
authors.lastname: Farrar
authors.forename: H
authors.initials: H
authors.lastname: Nagaraja
authors.forename: J
authors.initials: J
authors.lastname: Braun
authors.forename: R
authors.initials: R
authors.lastname: Kanard
authors.forename: P
authors.initials: P
authors.lastname: Novak
authors.forename: A
authors.initials: A
authors.lastname: Slivka
mesh_terms: D001783:Blood Flow Velocity; D002545:Brain Ischemia / Q000503:physiopathology*; D002544:Cerebral Infarction / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D006985:Hyperventilation; D008297:Male; D008875:Middle Aged; D018667:Tilt-Table Test; D017585:Ultrasonography, Doppler, Transcranial