Mathematical modeling of the hematocrit influence on cerebral blood flow in preterm infants

Premature birth is one of the most important factors increasing the risk for brain damage in newborns. Development of an intraventricular hemorrhage in the immature brain is often triggered by fluctuations of cerebral blood flow (CBF). Therefore, monitoring of CBF becomes an important task in clinical care of preterm infants. Mathematical modeling of CBF can be a complementary tool in addition to diagnostic tools in clinical practice and research. The purpose of the present study is an enhancement of the previously developed mathematical model for CBF by a detailed description of apparent blood viscosity and vessel resistance, accounting for inhomogeneous hematocrit distribution in multiscale blood vessel architectures. The enhanced model is applied to our medical database retrospectively collected from the 254 preterm infants with a gestational age of 23–30 weeks. It is shown that by including clinically measured hematocrit in the mathematical model, apparent blood viscosity, vessel resistance, and hence the CBF are strongly affected. Thus, a statistically significant decrease in hematocrit values observed in the group of preterm infants with intraventricular hemorrhage resulted in a statistically significant increase in calculated CBF values.

Models to predict the parameters of ship voyages in the Arctic: existing approaches and possible ways of development

Any information support system for Arctic shipping requires a ship transit model as one of the key elements that allows for strategic analysis, operational planning of vessel voyages, and ice routing of a ship. At the same time, there is no single recognized approach to develop such a model, due to the complexity of ice cover in terms of its impact on shipping. In this article, we have identified and analyzed three principal approaches to predict the parameters of vessel voyages in the Arctic. They are (1) semi-empirical models to estimate the vessel resistance in ice and then calculate propulsion performance, (2) numerical methods to model ship-ice interaction and calculate ice resistance, (3) statistical models to assess the ship speed based on regression equations or neural networks. Analysis of the strengths and weaknesses of each approach allowed us to propose a concept to develop the ship transit model for practical application.

Theoretical grounds for determining optimal trim of river-sea vessels

The article presents the theoretical substantiation of using the optimal trim of “river- sea” vessels in order to improve the propulsion of vessels of various types and purposes navigating on seas and rivers. There has been carried out the analysis of the optimal trim for different types of ships in operation. The given calculations prove the possibility of designing new ships with improved sailing characteristics. The scheme of damping the bow shear wave coming from the stem of the “river-sea” vessel is illustrated using the shear wave coming from the bow bulb, with a differential to the bow. It is proved that trimming of a “river-sea” vessel without a bow bulb is effective for slow-moving and high-speed vessels due to the reduction of components and total drag, compared to the resistance to the movement of a vessel with a conventional trim. An integral similar to Mitchell integral for the wave drag of a vessel with a bow bulb is proposed, by means of which the conditions for damping a bow shear wave (coming from the stem) using the bow bulb of a “river-sea” vessel are determined. The elements composing resistance to the vessel propulsion are investigated in detail: total resistance of the medium to the movement of the vessel, resistance of friction, shape, protruding parts, wave, and aerodynamic resistance. There are considered the criteria of the optimal bow draft of the vessel and optimal trim of the vessel, the criteria of the efficient use of the optimal trim for the “river-sea” vessels on the sea sections. An equation is given that determines the value of the optimal length of the wave-forming part of the bow bulb or the condition for the optimal trim. The pictures illustrating a sea vessel bulb, the bow of which is capable of effectively forming a shear wave at a given differential are shown. Conclusions are made about the possibility of using the optimal trim for river-sea vessels on river and sea sections, recommendations are given that contribute to saving fuel and time, increasing the speed to two knots while reducing the total resistance by up to 20%.

Abstract P61: Pulsatility Index Outperforms Conventional Imaging Markers in the Association With Cognition in Community Subjects

Increase in pulsatility index (PI), measured by the transcranial Doppler (TCD), correlates with cognitive impairment and is associated with progression of non-demented patients into Alzheimer’s disease (AD) with dementia, suggesting that increase in small vessel resistance is a critical marker of cognitive decline. No study compared PI and MRI markers for small vessel disease or AD that have been shown to be associated with worse cognitive functions. The objectives of this study include: (i) compare PI against conventional MRI markers in its association with cognition, and (ii) investigate the association of PI and cognition in the presence of vascular risk factors. We measured clinical data and PI in the middle cerebral artery in 331 stroke- and dementia-free community subjects. General cognition was assessed using Hong Kong-Montreal Cognitive Assessment. Conventional imaging markers (including lacunes, white matter hyperintensities (WMH), brain parenchymal fraction (BPF), cerebral microbleeds, Alzheimer’s Disease Resemblance Atrophy Index (ADRAI)) were assessed by MRI. Linear regression models were used to compare the sensitivity of PI against conventional MRI markers (including WMH, BPF, ADRAI, lacune and cerebral microbleeds count), with age and years of education entered as covariates. PI was negatively associated with cognition (standardised b=-0.122, p=0.01). PI outperformed (standardised b=-0.118, p=0.012) other imaging markers and contributes to 1.1% change in the variance. PI was associated with higher systolic blood pressure (standardised b=0.122, p=0.028), and level of triglyceride (standardised b = 0.126, p = 0.021). To conclude, PI is associated with cognition, higher levels of blood pressure and triglycerides, suggesting a vascular component in cognitive decline. PI outperforms conventional MRI markers in the association with cognition in community subjects without dementia. As TCD is non-invasive, portable with a lower cost than MRI, PI may serve as a simple marker in monitoring cerebral small vessel resistance and cognition in older people.

Numerical Study on the Resistance and Sinkage of Inland Vessels Passing Through Navigable Tunnel

While passing through a navigable tunnel, a vessel usually undergoes a steady forward motion at low speed. Due to the limited size of the navigable tunnel, the restricted water conditions of small section-coefficient will have an adverse impact on vessel navigation safety. A bottom suction effect on vessels may occur for the risk of grounding and harming the maneuvering performance. Thus, it is particularly important to reveal the effect of the navigable tunnel scale on the vessel sinkage. In this paper, a numerical model of the representative 1000-ton vessel of the Wujiang channel under construction is established. Numerical simulations of the vessel are conducted based on RANS equations in deep water, both in fixed condition and free condition (i.e. the trim and sinkage are allowed). And the validity of the method is verified by comparing the calculation results with the experimental ones. Subsequently, for diverse water depths, water widths and vessel speeds, the parameters such as the vessel resistance and sinkage are predicted and compared. The calculation results are analyzed to obtain the trend of vessel motion at different tunnel scales. In addition, the effect of the tunnel scale on vessel navigation performance is also investigated.

Properties of Cladding With Respect to RPV Integrity

Inner surface of most of primary circuit components in PWR/BWR/WWER type reactors is covered by austenitic cladding that serves primarily as anticorrosion protection. This is also supported by the requirements for stress analysis of the vessel by most of the codes — austenitic cladding is not taken into account in the calculation of vessel wall thickness and on allowance of stress intensities for operating conditions. Its effect is taken, in some codes like for WWER components, in fatigue calculation and also for evaluation of vessel resistance against fast fracture during pressurized thermal shock (PTS) events.

Analysis of Generic IGBEM for Lifting Hydrofoils

Today the most crucial aspect in the preliminary vessel design stage is to make it as green/blue as possible. One of the exciting goals is the minimisation of vessel resistance. The use of hydrofoils to reduce the vessel draught and consequently, reduction in the vessel resistance is today one of the hottest design topics, especially for catamaran passenger vessels. In the present work, we discuss the issues related to the implementation of Isogeometric Analysis (IGA) Boundary Element Method (BEM) for the calculation of the hydrodynamic properties of lifting hydrofoils. The use of IGBEM allows numerical calculation of foil hydrodynamic properties without the traditional step of mesh generation using the CAD geometry directly. The analysis relies on the NURBS basis function with the generic Galerkin approach allowing identical solutions procedures for 2D or 3D problems. Method accuracy and computational times for a different number of Degrees of Freedom (DOF) in 2D are investigated.

Coupling of a cardiovascular model with a thermoregulation model to predict human blood pressure under unsteady environmental conditions

We coupled a cardiovascular model with a thermoregulation model to predict human blood pressure in unsteady environmental conditions. Our cardiovascular model is a lumped parameter model and consists of 42 segments, which include the entire artery and vein system, divided into 18 segments; the heart, divided into 4 segments; and the pulmonary artery and vein. The vessel parameters were adjusted on the basis of local body blood volume and flow of the thermoregulation model in a thermoneutral environment. Blood pressure under unsteady environmental conditions is predicted by changing the heart rate and vessel resistance of the cardiovascular model which is controlled by blood flow that the thermoregulation model predicts. It is possible to predict the increase in blood pressure under cold environmental conditions and the increase in cardiac output under hot environmental conditions and when bathing. The model was validated by simulating bathing experiments. As the result, the model predicted the peak blood pressure later than the experimental data in a cold environment. To improve the accuracy of the model, it is necessary to consider a method for controlling the heart rate, vessel resistance, and gravity effects after a change in posture.

Arterial hypertension and unusual ascending aortic dilatation in a neonate with acute kidney injury: mechanistic computer modelling

Background: Neonatal asphyxia caused acute kidney injury and severe hypertension in a newborn patient. An unusually dilatated ascending aorta developed within a few weeks. Dialysis and hypertensive treatment led to partial recovery of the aortic diameters. It was hypothesized that the aortic dilatation may be associated with cardiovascular changes induced by the acute kidney injury. Mathematical modelling was used to better understand the underlying mechanisms of hypertension and aortic dilatation.Methods: Patient observation included systolic blood pressure recording and echocardiographic exams. To explore underlying mechanisms of aortic dilatation and hypertension, a previous whole-body lumped parameter hemodynamics model was adapted to this study. Computer simulations were designed to permit dissection of individual mechanisms. The hypertension inducing effects of altering systemic vascular resistances, stiffnesses, and heart rate on blood flows and pressures were simulated.Results: In agreement with our clinical diagnosis, the mathematical model showed that an increase of systemic small vessel resistance is the prime cause of hypertension. Further, aortic stiffening may also cause hypertension, it was found to be secondary to the potency of systemic small vessel resistance. The cardiac output, as quantified using pressure-volume loop area, reduced significantly due to hypertension. Simultaneous left ventricle hypertrophy and small vessel blocking increased ascending aorta blood flow as well as pressure indicating an enlarged ascending aorta. In contrast, increased arterial stiffness appeared to lower the aortic blood flow and pressures.Conclusions and discussion: Systemic small vessel resistance is an important factor in arterial hypertension, and may also be a key clinical therapeutic target. Left ventricle hypertrophy may also be simultaneously ameliorated when treating systemic small vessels. Treatment of arterial stiffness appears to provide significant benefit but may be secondary to treatment of the systemic small vessels. The quantitative grading of pathophysiological mechanisms provided by the modelling may contribute to treatment recommendations. Further development and individualization of the model will augment its applicability in clinical practice.