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(Stroke. 1997;28:1677-1685.)
© 1997 American Heart Association, Inc.

Articles

Cerebrovascular and Cardiovascular Responses to Graded Tilt in Patients With Autonomic Failure

Roberta L. Bondar, MD, PhD; Paul T. Dunphy, PEng; Peyman Moradshahi, PEng; Mahmood S. Kassam, DrUniv, PEng; Andrew P. Blaber, PhD; Flo Stein, PhD, RVT; R. Freeman, MD

From the University of Western Ontario, Faculty of Kinesiology (R.L.B., A.P.B.), Thames Hall, London, Ontario, Canada; the Centre for Advanced Technology Education, Ryerson Polytechnic University (P.T.D., P.M., M.S.K., F.S.), Toronto, Ontario, Canada; and The Autonomic and Peripheral Nerve Laboratory, Department of Neurology, Beth Israel Deaconess Medical Center-West Campus (R.F.), Boston, Mass.

Background and Purpose Patients with autonomic nervous system failure often experience symptoms of orthostatic intolerance while standing. It is not known whether these episodes are caused primarily by a reduced ability to regulate arterial blood pressure or whether changes in cerebral autoregulation may also be implicated.

Methods Eleven patients and eight healthy age- and sex-matched control subjects were studied during a graded-tilt protocol. Changes in their steady state middle cerebral artery mean flow velocities (MFV), measured by transcranial Doppler, brain-level mean arterial blood pressures (MABP_brain), and the relationship between the two were assessed.

Results Significant differences between patients and control subjects (P<.05) were found in both their MFV and MABP_brain responses to tilt. Patients' MFV dropped from 60±10.2 cm/s in the supine position to 44±14.0 cm/s at 60° head-up tilt, whereas MABP_brain fell from 109±11.7 to 42±16.9 mm Hg. By comparison, controls' MFV dropped from 54±7.8 cm/s supine to 51±8.8 cm/s at 60°, whereas MABP_brain went from 90±11.2 to 67±8.2 mm Hg. Linear regression showed no significant difference in the MFV-MABP_brain relationship between patients and control subjects, with slopes of 0.228±0.09 cm · s^–1 · mm Hg^–1 for patients and 0.136±0.16 cm · s^–1 · mm Hg^–1 for control subjects.

Conclusions The present study found significant differences between patients and control subjects in their MFV and MABP_brain responses to tilt but no difference in the autoregulatory MFV-MABP_brain relationship. These results suggest that patients' decreased orthostatic tolerance may primarily be the result of impaired blood pressure regulation rather than a deficiency in cerebral autoregulation.

Key Words: autonomic nervous system • autoregulation • cerebral blood flow • ultrasonics

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