The cerebral hemodynamics of normotensive hypovolemia during lower-body negative pressure.
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.
Giller
C A
CA
Department of Neurosurgery, Southwestern Medical School, Dallas, Texas.
Levine
B D
BD
Meyer
Y
Y
Buckey
J C
JC
Lane
L D
LD
Borchers
D J
DJ
D000328:Adult; D001794:Blood Pressure; D001810:Blood Volume / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002560:Cerebrovascular Circulation; D004453:Echoencephalography; D006439:Hemodynamics; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D011673:Pulsatile Flow