Blood flow velocities during experimental intracranial hypertension in pigs.

OBJECTIVES: 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. CONCLUSION: 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.

An experimental study on artificially induced CSF pulse waveform morphological modifications.

OBJECTIVE: The analysis of cerebrospinal fluid (CSF) pulse pressure waveform has been considered as a reliable method to investigate the intracranial system (ICS) dynamics. We have examined the morphological changes of the CSF pulse wave and of the sagittal sinus pressure (SSP) wave during a progressive increase in intracranial pressure (ICP) in order to investigate the ICS dynamics. METHODS: Four dogs were anesthetized. Blood pressure, ICP, and SSP were simultaneously recorded. Two vertical tubes were inserted inside one lateral ventricle, thus allowing the half-opening (one tube open) and opening (both tubes open) of the ICS. ICP was modified by varying the height of the liquid column into the tubes. Pressures were analyzed by applying the fast Fourier transformation on each pulse pressure wave. We distinguished two peaks (first and second peaks) and a notch in each pulse pressure wave. The pressure was raised from resting pressure up to 50 mmHg. RESULTS: A progressive and distinct change in the CSF pulse pressure shape was evident when opening the ICS to the atmosphere: a reduction in the height of the dicrotic notch and in the amplitude of the second peak and a corresponding positive shift of the first harmonic with respect to the onset of the CSF pulse pressure wave. DISCUSSION: A decrease in the amplitude of the CSF pulse waveform second peak and a positive phase shift of its first harmonic indicate an opening of the ICS to the atmosphere, i.e. an increase in the intracranial compliance.

An architecture for rapid prototyping of control schemes for artificial ventricles.

This paper presents an experimental system aimed at rapid prototyping of feedback control schemes for ventricular assist devices, and artificial ventricles in general. The system comprises a classical mock circulatory system, an actuated bellow-based ventricle chamber, and a software architecture for control schemes implementation and experimental data acquisition, visualization and storing. Several experiments have been carried out, showing good performance of ventricular pressure tracking control schemes.