The cerebral hemodynamics of normotensive hypovolemia during lower-body negative pressure.

Giller CA, Levine BD, Meyer Y, Buckey JC, Lane LD, Borchers DJ
J Neurosurg. 1992 76 (6): 961-6

PMID: 1588430 · DOI:10.3171/jns.1992.76.6.0961

Although severe hypovolemia can lead to hypotension and neurological decline, many patients with neurosurgical disorders experience a significant hypovolemia while autonomic compensatory mechanisms maintain a normal blood pressure. To assess the effects of normotensive hypovolemia upon cerebral hemodynamics, transcranial Doppler ultrasound monitoring of 13 healthy volunteers was performed during graded lower-body negative pressure of up to -50 mm Hg, an accepted laboratory model for reproducing the physiological effects of hypovolemia. Middle cerebral artery flow velocity declined by 16% +/- 4% (mean +/- standard error of the mean) and the ratio between transcranial Doppler ultrasound pulsatility and systemic pulsatility rose 22% +/- 8%, suggesting cerebral small-vessel vasoconstriction in response to the sympathetic activation unmasked by lower-body negative pressure. This vasoconstriction may interfere with the autoregulatory response to a sudden fall in blood pressure, and may explain the common observation of neurological deficit during hypovolemia even with a normal blood pressure.

MeSH Terms (11)

Adult Blood Pressure Blood Volume Brain Cerebrovascular Circulation Echoencephalography Hemodynamics Humans Lower Body Negative Pressure Male Pulsatile Flow

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