Is there a direct link between cerebrovascular activity and cerebrospinal fluid pressure-volume compensation?
OBJECTIVE
Cerebral blood flow is coupled to brain metabolism by means of active modulation of cerebrovascular resistance. This homeostatic vasogenic activity is reflected in slow waves of cerebral blood flow velocities (FV) which can also be detected in intracranial pressure (ICP). However, effects of increased ICP on the modulation of cerebral blood flow are still poorly understood. This study focused on the question whether ICP has an independent impact on slow waves of FV within the normal cerebral perfusion pressures range.


METHODS
Twenty patients presenting with communicating hydrocephalus underwent a diagnostic intraventricular constant-flow infusion test. Blood flow velocities in the middle cerebral artery and posterior cerebral arteries were measured using Transcranial Doppler. Pulsatility index, FV variability of slow vasogenic waves (3 to 9 bpm), ICP, and arterial blood pressure were simultaneously monitored.


RESULTS
During the test, ICP increased from a baseline of 11 (6) mm Hg to a plateau value of 21 (6) mm Hg (P=0.00005). Although the infusion did not induce significant changes in cerebral perfusion pressures, FV, pulsatility index, or index of autoregulation, the magnitude of FV vasogenic waves at plateau became inversely correlated to ICP (middle cerebral artery: r=-0.58, P<0.01; posterior cerebral arteries: r=-0.54, P<0.01).


CONCLUSIONS
This study shows that even moderately increased ICP can limit the modulation of cerebral blood flow in both vascular territories within the autoregulatory range of cerebral perfusion pressures. The exhaustion of cerebrospinal fluid volume buffering reserve during infusion studies elicits a direct interaction between the cerebrospinal fluid space and the cerebrovascular compartment.
Haubrich
Christina
C
Department of Academic Neurosurgery, Box 167 Addenbrooke's Hospital, Cambridge, UK.
Czosnyka
Zofia
Z
Lavinio
Andrea
A
Smielewski
Piotr
P
Diehl
Rolf R
RR
Pickard
John D
JD
Czosnyka
Marek
M
D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002552:Cerebral Ventricles / Q000502:physiology; D002555:Cerebrospinal Fluid / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006849:Hydrocephalus / Q000134:cerebrospinal fluid / Q000503:physiopathology*; D019586:Intracranial Hypertension / Q000134:cerebrospinal fluid / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000502:physiology; D020769:Posterior Cerebral Artery / Q000502:physiology; D011673:Pulsatile Flow / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology