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Byline: Pralay. Ghosh, Afzal. Azim, Sai. Saran, Arvind. Baronia, Banani. Poddar, Ratender. Singh, Mohan. Gurjar, Prabhaker. Mishra Introduction: Lung-protective ventilation strategy and prone positioning are the strategies practiced to manage [...]

Byline: Girish. Rajpal, Vikas. Naik Arterial dissection occurs when intraluminal blood penetrates into layers of the vessel wall. Cranio-cervical dissection accounts for 15-20% of causes of stroke in the young [...]

Angiogenesis: grow with the flow During embryogenesis, blood vessels are remodelled in response to blood flow. Nicoli et al. describe a genetic pathway that explains how this mechanosensory stimulus is integrated with early developmental signals to remodel aortic arch vessels in zebrafish. The flow-induced transcription factor klf2a is required for the induction of an endothelial cell-specific microRNA, miR-126, which promotes VEGF signalling and angiogenesis through repressing Spred1, an inhibitor of VEGF signalling. This demonstrates how blood flow modulates endothelial cell-signalling pathways and implicates a microRNA as a central integration point during this process. During embryonic development, blood vessels remodel in response to blood flow. Here, a genetic pathway is described through which this mechanosensory stimulus is integrated with early developmental signals to remodel vessels of the aortic arch in zebrafish. It is found that the flow-induced transcription factor klf2a is required to induce the expression of an endothelial-specific microRNA, activating signalling through the growth factor Vegf. Within the circulatory system, blood flow regulates vascular remodelling.sup.1, stimulates blood stem cell formation.sup.2, and has a role in the pathology of vascular disease.sup.3. During vertebrate embryogenesis, vascular patterning is initially guided by conserved genetic pathways that act before circulation.sup.4. Subsequently, endothelial cells must incorporate the mechanosensory stimulus of blood flow with these early signals to shape the embryonic vascular system.sup.4. However, few details are known about how these signals are integrated during development. To investigate this process, we focused on the aortic arch (AA) blood vessels, which are known to remodel in response to blood flow.sup.1. By using two-photon imaging of live zebrafish embryos, we observe that flow is essential for angiogenesis during AA development. We further find that angiogenic sprouting of AA vessels requires a flow-induced genetic pathway in which the mechano-sensitive zinc finger transcription factor klf2a.sup.5,6,7 induces expression of an endothelial-specific microRNA, mir-126, to activate Vegf signalling. Taken together, our work describes a novel genetic mechanism in which a microRNA facilitates integration of a physiological stimulus with growth factor signalling in endothelial cells to guide angiogenesis., Author(s): Stefania Nicoli [sup.1] , Clive Standley [sup.2] , Paul Walker [sup.3] , Adam Hurlstone [sup.3] , Kevin E. Fogarty [sup.2] , Nathan D. Lawson [sup.1] Author Affiliations: (1) Program [...]

Computational fluid dynamics (CFD) modeling of blood flow from image-based patient specific models can provide useful physiologic information for guiding clinical decision making. A novel method for the generation of image-based, 3-D, multiscale vascular surface models for CFD is presented. The method generates multiscale surfaces based on either a linear triangulated or a globally smooth nonuniform rational B-spline (NURB) representation. A robust local curvature analysis is combined with a novel global feature analysis to set mesh element size. The method is particularly useful for CFD modeling of complex vascular geometries that have a wide range of vasculature size scales, in conditions where 1) initial surface mesh density is an important consideration for balancing surface accuracy with manageable size volumetric meshes, 2) adaptive mesh refinement based on flow features makes an underlying explicit smooth surface representation desirable, and 3) semi-automated detection and trimming of a large number of inlet and outlet vessels expedites model construction. Index Terms--Hemodynamics, multiscale modeling, NURB surface, surface fitting, surface mesh generation, vascular modeling.

Byline: Rudranil. Nandi, Shekhar. Basu, Susanta. Sarkar, Rakesh. Garg Background and Aims: Haemodynamic responses to laryngoscopy and endotracheal intubation and their hazards are well documented. The purpose of the study [...]

Byline: Shahed. Omar, Ahmad. Ali, Yahya. Atiya, Rudo. Mathivha, Joel. Dulhunty Context: Severe sepsis or septic shock. Aims: The aim of this study is to examine the effect of a [...]

Functional magnetic resonance imaging (fMRI) is an important technique for neuroimaging. The conventional system identification methods used in fMRI data analysis assume a linear time-invariant system with the impulse response described by the hemodynamic responses (HDR). However, the measured blood oxygenation level-dependent (BOLD) signals to a particular processing task (for example, rapid event-related fMRI design) show nonlinear properties and vary with different brain regions and subjects. In this paper, radial basis function (RBF) neural network (a powerful technique for modelling nonlinearities) is proposed to model the dynamics underlying the fMRI data. The equivalence of the proposed method to the existing Volterra series method has been demonstrated. It is shown that the first- and second-order Volterra kernels could be deduced from the parameters of the RBF neural network. Studies on both simulated (using Balloon model) as well as real event-related fMRI data show that the proposed method can accurately estimate the HDR of the brain and capture the variations of the HDRs as a function of the brain regions and subjects. Index Terms--Event-related design, functional magnetic resonance imaging (fMRI), hemodynamic response (HDR), neural network, radial basis functions (RBF), Volterra kernels.

A clinical method for monitoring cardiac output (CO) should be continuous, minimally invasive, and accurate. However, none of the conventional CO measurement methods possess all of these characteristics. On the other hand, peripheral arterial blood pressure (ABP) may be measured reliably and continuously with little or no invasiveness. We have developed a novel technique for continuously monitoring changes in CO by mathematical analysis of a peripheral ABP waveform. In contrast to the previous techniques, our technique analyzes the ABP waveform over time scales greater than a cardiac cycle in which the confounding effects of complex wave reflections are attenuated. The technique specifically analyzes 6-min intervals of ABP to estimate the pure exponential pressure decay that would eventually result if pulsatile activity abruptly ceased (i.e., after the high frequency wave reflections vanish). The technique then determines the time constant of this exponential decay, which equals the product of the total peripheral resistance and the nearly constant arterial compliance, and computes proportional CO via Ohm's law. To validate the technique, we performed six acute swine experiments in which peripheral ABP waveforms and aortic flow probe CO were simultaneously measured over a wide physiologic range. We report an overall CO error of 14.6%. Index Terms--Arterial blood pressure, arterial tree, cardiac output, distributed effects, hemodynamics, mathematical modeling, pulse contour analysis, system identification, wave reflections, Windkessel.

The 'hemodynamic inverse problem' is the determination of arterial system properties from pressures and flows measured at the entrance of an arterial system. Conventionally, investigators fit reduced arterial system models to data, and the resulting model parameters represent putative arterial properties. However, no unique solution to the inverse problem exists--an infinite number of arterial system topologies result in the same input impedance ([Z.sub.in]) and, therefore, the same pressure and flow. Nevertheless, there are exceptions to this theoretical limitation; total peripheral resistance ([R.sub.tot]), total arterial compliance ([C.sub.tot]), and characteristic impedance ([Z.sub.o]) can be uniquely determined from input pressure and flow. [Z.sub.in] is determined completely by [C.sub.tot] and [R.sub.tot] at low frequencies, [Z.sub.o] at high frequencies, and arterial topology and reflection effects at intermediate frequencies. We present a novel method to determine the relative contribution of [Z.sub.o], [C.sub.tot], [R.sub.tot] and arterial topology/reflection to [Z.sub.in] without assuming a particular reduced model. This method is tested with a large-scale distributed model of the arterial system, and is applied to illustrative cases of measured pressure and flow. This work, thus, lays the theoretical foundation for determining the arterial properties responsible for increased pulse pressure with age and various arterial system pathologies. Index Terms--Apparent arterial compliance, hemodynamics, mathematical modeling, pulse wave reflection.

Byline: Ankur. Khandelwal, Rudrashish. Haldar, Arun. Srivastava, Prabhat. Singh The existence of neural connection between the limbic system (hypothalamus, hippocampus, amygdala, and other adjacent areas) and the autonomic nervous system [...]