Blood flow velocities during experimental intracranial hypertension in pigs.
OBJECTIVE
A purely hydraulic mechanism consisting in the pulsatile cuff-compression effect, by the cerebrospinal fluid displacement induced by the arterial pulsation, on the final portion of the bridging veins, has recently been hypothesized. This mechanism is able to maintain  the constancy of cerebral blood flow (CBF) within the autoregulatory range, thus implying an exact balance between arterial inflow and venous outflow. In this study, we correlated arterial inflow and venous outflow during an experimentally induced condition of intracranial hypertension in  pigs.


METHODS
Mock cerebrospinal fluid (CSF) was progressively infused until a condition of brain tamponade was reached. Blood flow velocities at middle cerebral artery and sagittal sinus sites were evaluated simultaneously.


RESULTS
Mean intracranial arterial blood flow  velocity (IABFV), mean sagittal sinus blood flow velocity (SSBFV), and pulsatile-IABFV remained almost constant until cerebral perfusion pressure (CPP) dropped below 60-70 mmHg; then, a progressive decrease in mean IABFV and SSBFV, together with an increase in pulsatile-IABFV, was evident.


CONCLUSIONS
The strict similarity between mean IABFV and SSBFV patterns suggests that CBF decrement is mainly due to a decrease in the venous outflow, which, in turn, produces an obstacle to the arterial inflow. The correspondent increase in pulsatile-IABFV confirms the presence of a distal outflow obstruction.  All these findings point towards a purely hydraulic mechanism underlying the cerebral autoregulation which acts at the level of the so-called Starling resistor.
Institute of Neurosurgery, Catholic University of Rome, Italy.
Carmelo
C
Anile
Pasquale
P
De Bonis
Eduardo
E
Fernandez
Antonio
A
Ficola
Gianpaolo
G
Petrella
Pietro
P
Santini
Annunziato
A
Mangiola
D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D002536:Cerebral Arteries / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003392:Cranial Sinuses / Q000503:physiopathology; D004195:Disease Models, Animal; D005260:Female; D019586:Intracranial Hypertension / Q000503:physiopathology*; D011673:Pulsatile Flow / Q000502:physiology; D013552:Swine; D017585:Ultrasonography, Doppler, Transcranial