BackgroundThe quantification of the flow returning from the head through the cervical veins and the collaterals of the internal jugular vein (IJV), is becoming of prominent interest in clinical practice. We developed a novel model to calculate the cerebral venous return, normalized to the arterial inflow, in the different segments of the IJV.MethodsWe assessed, by established Echo Colour Doppler (ECD) methodology, the head inflow (HBinF) defined as the sum of common carotids and vertebral arteries, as well as the cerebral flow (CBF) defined as the sum of internal carotid and vertebral arteries. We also assessed the head outflow (HBoutF) defined as the sum of the measurements at the junction of the IJV and the vertebral veins. In addition, we also calculated the collateral flow index (CFI) by estimating the flow which re-enters directly into the superior vena cava as the amount of blood extrapolated by the difference between the HBinF and the HBoutF. We preliminarily tested the model by comparing ten healthy controls (HC) with ten patients affected by chronic cerebral spinal venous insufficiency (CCSVI), a condition characterized by some blockages in the IJV which are bypassed by collateral circulation.ResultsIn HC the HBinF was 956+-105ml/min, whereas the HBoutF was > 90% of the HBinF, leading to a final CFI value of 1%. The last result shows that a very small amount of blood is drained by the collaterals. In upright we confirmed a reduction of the outflow through the IJV which increased CFI to 9%. When we applied the model to CCSVI, the HBinF was not significantly different from controls. In supine, the flow of CCSVI patients in the IJV junction was significantly lower (p < 0.001) while the correspondent CFI value significantly increased (61%, p < 0.0002).ConclusionsOur preliminary application of the novel model in the clinical setting suggests the pivotal role of the collateral network in draining the blood into the superior vena cava under CCSVI condition.

We developed a mathematical model of the cerebral venous outflow for the simulation of the average blood flows and pressures in the main drainage vessels of the brain. The main features of the model are that it includes a validated model for the simulation of the intracranial circulation and it accounts for the dependence of the hydraulic properties of the jugular veins with respect to the gravity field, which makes it an useful tool for the study of the correlations between extracranial blood redistributions and changes in the intracranial environment. The model is able to simulate the average pressures and flows in different points of the jugular ducts, taking into account the amount of blood coming from the anastomotic connections; simulate how the blood redistribution due to change of posture affects flows and pressures in specific points of the system; and simulate redistributions due to stenotic patterns. Sensitivity analysis to check the robustness of the model was performed. The model reproduces average physiologic behavior of the jugular, vertebral, and cerebral ducts in terms of pressures and flows. In fact, jugular flow drops from ϳ11.7 to ϳ1.4 ml/s in the passage from supine to standing. At the same time, vertebral flow increases from 0.8 to 3.4 ml/s, while cerebral blood flow, venous sinuses pressure, and intracranial pressure are constant around the average value of 12.5 ml/s, 6 mmHg, and 10 mmHg, respectively. All these values are in agreement with literature data. mathematical modeling; cerebral outflow; posture dependence; jugular veins collapse; collateral routes THE EXTRACRANIAL VENOUS SYSTEM represents an important determinant of the brain circulation, but its role in the pathology of the central nervous system is not fully understood yet (4,26). It is recognized that, in supine position, the jugular veins represent the main outflow route for the cerebral circulation (2,6,25,36,38), being able to carry most of blood flow from the brain and from other extracerebral territories (ϳ700 -720 ml/ min; Refs. 27, 33) with respect to a cerebral blood inflow of ϳ750 ml/min (45). However, the jugular venous system exhibits important flow limitation during upright posture changes, because the jugular veins tend to collapse as a consequence of the decrease of transmural pressure due to the gravitational field, causing a significant increase in resistance (3,7,12,14,26). In the absence of other routes for extracranial outflow, this flow limitation would have dramatic effects on the cerebral circulation, since, apart from brief transient time intervals, the average cranial arterial inflow is expected to be equal to the cranial venous outflow for the mass preservation.As a consequence, large attention has been devoted to the venous circulation in the upright state, in an effort to understand which alternative routes can carry the brain venous outflow. It has long been postulated that the vertebral venous system may provide an important alternative route for venous outflow when standing or sitting; this was f...

No abstract

No abstract

No abstract