A new hemodynamic model for the study of cerebral venous outflow.

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 ∼11.7 to ∼1.4 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.

Investigation of cerebral venous outflow in microgravity.

OBJECTIVE: The gravitational gradient is the major component to face when considering the physiology of venous return, and there is a growing interest in understanding the mechanisms ensuring the heart filling, in the absence of gravity, for astronauts who perform long-term space missions. APPROACH: The purpose of the Drain Brain project was to monitor the cerebral venous outflow of a crew member during an experiment on the International Space Station (ISS), so as to study the compensatory mechanisms that facilitate this essential physiological action in subjects living in a microgravity environment. Such venous function has been characterized by means of a novel application of strain-gauge plethysmography which uses a capacitive sensor. MAIN RESULTS: In this contribution, preliminary results of our investigation have been presented. In particular, comparison of plethysmography data confirmed that long duration spaceflights lead to a redistribution of venous blood volume, and showed interesting differences in the amplitude of cardiac oscillations measured at the level of the neck veins. SIGNIFICANCE: The success of the experiment has also demonstrated that thanks to its easy portability, non-invasiveness, and non-operator dependence, the proposed device can be considered as a novel tool for use aboard the ISS. Further trials are now under way to complete the investigation on the drainage function of the neck veins in microgravity.

Validation of a Hemodynamic Model for the Study of the Cerebral Venous Outflow System Using MR Imaging and Echo-Color Doppler Data.

BACKGROUND AND PURPOSE: A comprehensive parameter model was developed to investigate correlations between cerebral hemodynamics and alterations in the extracranial venous circulation due to posture changes and/or extracranial venous obstruction (stenosis). The purpose of this work was to validate the simulation results by using MR imaging and echo-color Doppler experimental blood flow data in humans. MATERIALS AND METHODS: To validate the model outcomes, we used supine average arterial and venous extracerebral blood flow, obtained by using phase-contrast MR imaging from 49 individuals with stenosis in the acquisition plane at the level of the disc between the second and third vertebrae of the left internal jugular vein, 20 with stenosis in the acquisition plane at the level of the disc between the fifth and sixth vertebrae of the right internal jugular vein, and 38 healthy controls without stenosis. Average data from a second group of 10 healthy volunteers screened with an echo-color Doppler technique were used to evaluate flow variations due to posture change. RESULTS: There was excellent agreement between experimental and simulated supine flows. Every simulated CBF fell inside the standard error from the corresponding average experimental value, as well as most of the simulated extracerebral arterial flow (extracranial blood flow from the head and face, measured at the level of the disc between second and third vertebrae) and venous flows. Simulations of average jugular and vertebral blood flow variations due to a change of posture from supine to upright also matched the experimental data. CONCLUSIONS: The good agreement between simulated and experimental results means that the model can correctly reproduce the main factors affecting the extracranial circulation and could be used to study other types of stenotic conditions not represented by the experimental data.

A simulation model to study the role of the extracranial venous drainage pathways in intracranial hemodynamics.

Alterations in the extracranial venous circulation due to posture changes, and/or extracranial venous obstructions in patients with vascular diseases, can have important implications on cerebral hemodynamics. A hemodynamic model for the study of cerebral venous outflow was developed to investigate the correlations between extracranial blood redistributions and changes in the intracranial environment. Flow data obtained with both magnetic resonance (MR) and Echo-Color Doppler (ECD) technique are used to validate the model. The very good agreement between simulated supine and upright flows and experimental results means that the model can correctly reproduce the main factors affecting the extracranial venous circulation.

Simulation of 3D objects into breast tomosynthesis images.

Digital breast tomosynthesis is a new three-dimensional (3D) breast-imaging modality that produces images of cross-sectional planes parallel to the detector plane from a limited number of X-ray projections over a limited angular range. Several technical and clinical parameters have not yet been completely optimised. Some of the open questions could be addressed experimentally; other parameter settings cannot be easily realised in practice and the associated optimisation process requires therefore a theoretical approach. Rather than simulating the complete 3D imaging chain, it is hypothesised that the simulation of small lesions into clinical (or test object) images can be of help in the optimisation process. In the present study, small 3D objects have been simulated into real projection images. Subsequently, these hybrid projection images are reconstructed using the routine clinical reconstruction tools. In this study, the validation of this simulation framework is reported through the comparison between simulated and real objects in reconstructed planes. The results confirm that there is no statistically significant difference between the simulated and the real objects. This suggests that other small mathematical or physiological objects could be simulated with the same approach.