A Physical Model of the Intracranial System for the Study of the Mechanisms of the Cerebral Blood Flow Autoregulation

This paper introduces a novel physical model of the intracranial system, which was built with the specific purpose of gaining a better insight into the fundamental mechanisms involved in the cerebral circulation. Specifically, the phenomena of passive autoregulation of the blood flow and the variation of the intracranial compliance as a function of the mean intracranial pressure have been investigated. The physical model allows to go beyond state-of-the-art mathematical models that are often based on strong assumptions or simplifications on the physical mechanisms governing the cerebral circulation. Indeed, the physical model based on passive components was able to correctly replicate some fundamental mechanisms of the blood flow autoregulation. In particular, it allows to highlight the role of the venous outflow, which behaves as a Starling resistor. The physical model can be employed as a demonstrator for educational purpose and to test the behavior of shunts for the therapy of hydrocephalus

The intracranial system: A new interpretation of the Monro-Kellie doctrine

In this paper we have reported our experience in several years in whom we have studied the phenomena correlated with the intracranial pressure. We have started to study different types of animals during an experimental condition of intracranial hypertension; we have observed many different configurations in spontaneous pathologic&nbsp; humans, and, eventually, in last years we have passed to confirm our ideas modelling an intracranial system in a physical phantom made by a centrifugal pump, stainless steel for base, glass for the wall, elastic tube for the cerebrovascular tree and collapsible tubes for venous drainage.We have noted that there is some confusion about the so-called Monro-Kellie doctrine; the major part of the scientist believe in a sort of static interpretation given by the sum of the compartment which constitute the intracranial system (parenchyma, blood and cerebrospinal fluid). But we believe in a dynamic interpretation in which there is a constant balance between the arterial inflow and venous outflow during each cardiac cycle.In this paper we have focused on the results, obtained in the different preparations, animals, humans and in vitro, all confirming the assumption that there is no difference between arterial inflow and venous outflow.</p

A preliminary experimental analysis of V-tail quad-rotor dynamics

Standard quad-rotors are the most common and versatile Unmanned Aerial Vehicles (UAVs) thanks to their simple control and mechanics. However other configurations with distinct capabilities exist. We present a preliminary systematic study of an alternative configuration known as V-tail, which is still mechanically simple, with four fixed rotors, but whose back rotors are tilted by a known angle. Mathematical modelling and field experiments suggest that this configuration is able to achieve better performance in manoeuvring control, while losing some power only in the stationary hovering task. In addition, these increases in performance are obtained with the same attitude control of the standard quad-rotor, making this configuration very easy to setup

Modelling and simulation of a quadrotor in V-tail configuration

Standard quad-rotors are the most common and versatile unmanned aerial vehicles (UAVs) thanks to their simple control and mechanics. However, the common coplanar rotor configurations are designed for maximising hovering and loitering performances, and not for fast and aggressive manoeuvrings. Since the expanding field of application of micro aerial vehicles (MAVs) requires ever-increasing speed and agility, the question whether there are better configurations for aggressive flight arises. In this work, we address this question by studying the energetics and dynamics of fixed tilted rotor configurations compared to standard quad-rotor. To do so we chose a specific configuration, called V-tail, which is as mechanically simple as the standard X-4 quad-rotor, but has back rotors tilted by a known fixed angle, and developed the dynamical model to test its properties both through software simulation and with actual experiments. Mathematical modelling and field experiments suggest that this configuration is able to achieve better performance in manoeuvring control, while losing some power in hovering owing to less vertical thrust. In addition, these increases in performance are obtained with the same attitude control as the standard quad-rotor, making this configuration very easy to set up

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 resisto