E. Titianova 1,2, I. Velcheva 3, S. Karakaneva 1
1 Clinic of Functional Diagnostics of Nervous System, Military Medical Academy – Sofia,
2 Medical Faculty of Sofia University St. Kl. Ohridski – Sofia,
3 State University Hospital of Neurology and Psychiatry, Medical University – Sofia, Bulgaria

Objective: To study the orthostatic adjustment of cerebral hemodynamics in orthostatic intolerance (OI), based on classification of Thulesius (1976).

Material and Methods: Hemodymanic changes associated with orthostatic challenge were studied in 20 volunteers and 30 patients with OI using a specially designed protocol (E. Titianova and J. Nader, 1999) – a passive 70-degree tilt of the upper part of the body followed by a passive 90-degree whole body tilting and an active stand-up (each one lasting 10 minutes and followed by return to the lying position) were applied. Mean blood pressure (MBP), heart rate and mean blood flow velocity (BFV) of both middle cerebral arteries (MCA) were determined after 10 minutes of rest and after 1, 5 and 10 minutes of each orthostatic position.

Results: The pattern of orthostatic adjustment of the cerebral and systemic hemodynamics depended on the topic of the lesion, the type (“passive” or “active”) of the orthostatic challenge and the antigravity efficacy of the peripheral muscle pump. A paradoxical cerebral vasoconstriction due to hyperventilation was found in patients with postural tachycardia syndrome. In cases with pure autonomic failure the cerebral autoregulation seemed to be preserved if the MBP was maintained within the limit for brain autoregulation. During the induced neurally mediated syncope the selective loss of diastolic BFV and the increase in Pulsatility index were typically observed.

Discussion: TCD monitoring of cerebral autoregulation is an important approach for topical diagnosis of the orthostatic intolerance and may help for selecting the best therapeutic strategies.

Key words: orthostatic intolerance, orthostatic tests, peripheral muscle pump, TCD monitoring.

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