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Altered cerebral vasoregulation in hypertension and stroke

From the Division of Gerontology (Dr. Novak), Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA; Departments of Neurology (Dr. Slivka, and A. Chowdhary, B. Farrar, J. Braun, and R. Kanard) and Statistics (Dr. Nagaraja), The Ohio State University, Columbus, OH; and Department of Neurology (Dr. Novak), Boston University, MA.

Address correspondence and reprint requests to Dr. Vera Novak, Harvard Medical School, Division of Gerontology, Beth Israel Deaconess Medical Center, 110 Francis Street, Lowry Medical Building, Boston, MA 02215; e-mail: vnovak{at}caregroup.harvard.edu

Background: Autoregulation of blood flow that maintains steady perfusion over the range of systemic blood pressure is compromised by stroke.

Objectives: 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°. 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.

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