Cerebral versus systemic hemodynamics during graded orthostatic stress in humans.
Key result
Progressive lower body negative pressure in healthy men caused a 15.5% decrease in middle cerebral artery blood flow velocity and a 17.2% increase in pulsatility, indicating mild vasoconstriction.
Why the study?
Does progressive lower body negative pressure induce significant cerebral vasoconstriction compared to systemic vascular changes in healthy humans?
Population
16 healthy subjects
Comparison
Progressive lower body negative pressure to… vs Baseline (rest) and hyperventilation alone
Design
Other
Authors
Discussion
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Implication
Mild cerebral vasoconstriction during orthostatic stress is unlikely to cause syncope without hypotension; leaves open its contribution in neurocardiogenic syncope.
Structured PICO
Does progressive lower body negative pressure induce significant cerebral vasoconstriction compared to systemic vascular changes in healthy humans?
P
Population
16 healthy subjects (13 healthy men, mean age 27 +/- 7 years in the main group, and a separate group of 3 subjects)
I
Intervention
Progressive lower body negative pressure (LBNP) to induce graded reductions in central blood volume
C
Comparator
Baseline (rest) and hyperventilation alone
O
Outcome
Changes in brain blood flow velocity in the middle cerebral artery (VMCA) and pulsatility (index of distal cerebral vascular resistance)surrogate
Mild cerebral vasoconstriction occurs during orthostatic stress in healthy humans, but its magnitude is small compared to systemic changes and is unlikely to cause syncope without concomitant hypotension.
Cite This Study
Levine et al. (1994) studied Healthy humans (n=16). Progressive lower body negative pressure (LBNP) vs. Rest was evaluated on Changes in middle cerebral artery blood flow velocity (VMCA) and pulsatility. Progressive lower body negative pressure in healthy men caused a 15.5% decrease in middle cerebral artery blood flow velocity and a 17.2% increase in pulsatility, indicating mild vasoconstriction.