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Raised cerebrovascular resistance in idiopathic orthostatic intolerance: evidence for sympathetic vasoconstrictionPatients with idiopathic orthostatic intolerance (IOI) exhibit symptoms suggestive of cerebral hypoperfusion and an excessive decrease in cerebral blood flow associated with standing despite sustained systemic blood pressure. In 9 patients (8 women and 1 man aged 22 to 48 years) with IOI, we tested the hypothesis that volume loading (2000 cc normal saline) and alpha-adrenoreceptor agonism improve systemic hemodynamics and cerebral perfusion and that the decrease in cerebral blood flow with head-up tilt (HUT) could be attenuated by alpha-adrenoreceptor blockade with phentolamine. At 5 minutes of HUT, volume loading (-20+/-3.2 bpm) and phenylephrine (-18+/-3.4 bpm) significantly reduced upright heart rate compared with placebo; the effect was diminished at the end of HUT. Phentolamine substantially increased upright heart rate at 5 minutes (20+/-3.7 bpm) and at the end of HUT (14+/-5 bpm). With placebo, mean cerebral blood flow velocity decreased by 33+/-6% at the end of HUT. This decrease in cerebral blood flow with HUT was attenuated by all 3 interventions. We conclude that in patients with IOI, HUT causes a substantial decrease in cerebrovascular blood flow velocity. The decrease in blood flow velocity with HUT can be attenuated with interventions that improve systemic hemodynamics and therefore decrease reflex sympathetic activation. Moreover, alpha-adrenoreceptor blockade also blunts the decrease in cerebral blood flow with HUT but at the price of deteriorated systemic hemodynamics. These observations may suggest that in patients with IOI, excessive sympathetic activity contributes to the paradoxical decrease in cerebral blood flow with upright posture.
Document ID
20040142210
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Jordan, J.
(Clinical Research Center, Franz Volhard Clinic Berlin, Germany)
Shannon, J. R.
Black, B. K.
Paranjape, S. Y.
Barwise, J.
Robertson, D.
Date Acquired
August 22, 2013
Publication Date
October 1, 1998
Publication Information
Publication: Hypertension
Volume: 32
Issue: 4
ISSN: 0194-911X
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: RR00095
CONTRACT_GRANT: HL44589
CONTRACT_GRANT: P01-HL56693
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
Randomized Controlled Trial
NASA Discipline Regulatory Physiology
Clinical Trial

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