Graded lower-body negative pressure up to -50 mm Hg reduced middle cerebral artery flow velocity by 16% ± 4% and increased the pulsatility ratio by 22% ± 8%.
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 et al. (Mon,) conducted a other in healthy volunteers (n=13). graded lower-body negative pressure was evaluated on Middle cerebral artery flow velocity and pulsatility ratio. Graded lower-body negative pressure up to -50 mm Hg reduced middle cerebral artery flow velocity by 16% ± 4% and increased the pulsatility ratio by 22% ± 8%.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: