Quantifying the effect of posture on intracranial physiology in humans by MRI flow studies.
OBJECTIVE
To quantify the effect of posture on intracranial physiology in humans by MRI, and demonstrate the relationship between intracranial compliance (ICC) and pressure (ICP), and the pulsatility of blood and CSF flows.


METHODS
Ten healthy volunteers (29+/-7 years old) were scanned in the supine and sitting positions using a vertical gap MRI scanner. Pulsatile blood and CSF flows into and out from the brain were visualized and quantified using time-of-flight (TOF) and cine phase-contrast techniques, respectively. The total cerebral blood flow (tCBF), venous outflow, ICC, and ICP for the two postures were then calculated from the arterial, venous, and CSF volumetric flow rate waveforms using a previously described method.


RESULTS
In the upright posture, venous outflow is considerably less pulsatile (57%) and occurs predominantly through the vertebral plexus, while in the supine posture venous outflow occurs predominantly through the internal jugular veins. A slightly lower tCBF (12%), a considerably smaller CSF volume oscillating between the cranium and the spinal canal (48%), and a much larger ICC (2.8-fold) with a corresponding decrease in the MRI-derived ICP values were measured in the sitting position.


CONCLUSIONS
The effect of posture on intracranial physiology can be quantified by MRI because posture-related changes in ICC and ICP strongly affect the dynamics of cerebral blood and CSF flows. This study provides important insight into the coupling that exists between arterial, venous, and CSF flow dynamics, and how it is affected by posture.
Alperin
Noam
N
Department of Radiology, University of Illinois at Chicago, Chicago, Illinois 60612, USA. alperin@uic.edu
Lee
Sang H
SH
Sivaramakrishnan
Anusha
A
Hushek
Stephen G
SG
D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000098:blood supply* / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007427:Intracranial Pressure / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011187:Posture / Q000502:physiology*; D011673:Pulsatile Flow / Q000502:physiology; D013223:Statistics as Topic