Non-invasive evaluation of left ventricular afterload, part 2 : arterial pressure-flow and pressure-volume relations in humans

The mechanical load imposed by the systemic circulation to the left ventricle is an important determinant of normal and abnormal cardiovascular function. Left ventricular afterload is determined by complex time-varying phenomena, which affect pressure and flow patterns generated by the pumping ventricle. Left ventricular afterload is best described in terms of pressure-flow relations, allowing for quantification of various components of load using simplified biomechanical models of the circulation, with great potential for mechanistic understanding of the role of central hemodynamics in cardiovascular disease and the effects of therapeutic interventions. In the second part of this tutorial, we review analytic methods used to characterize left ventricular afterload, including analyses of central arterial pressure-flow relations and windkessel modeling (pressure-volume relations). Conceptual descriptions of various models and methods are emphasized over mathematical ones. Our review is aimed at helping researchers and clinicians obtain and interpret results from analyses of left ventricular afterload in clinical and epidemiological settings

On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement

Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement

Stability analysis of different combinations of time-integration schemes in fluid-structure interaction simulations

Partitioned fluid-structure interaction simulations often use different time-integration schemes to discretize the different sub-problems. As such, the flow and structural equations can be solved with schemes that are particularly suited for each individual problem. However, using incompatible schemes, these simulations can encounter stability problems. In this research an analytical stability analysis is performed for a model of blood flow in an artery. The backward Euler scheme is used for the time discretization of the flow equations. For the structure two schemes are used: the BE scheme and the Hilber-Hughes-Taylor operator in which the numerical damping is controlled by a single parameter alpha. The influence of this parameter and some physiological parameters on the stability and the damping of the spurious modes is studied. According to this analysis, the combination of the BE and HHT scheme is stable, but the wave number, the numerical damping and the flow and structural density can affect the damping of the spurious modes considerably. To verify the analytical results, a numerical study is performed using nonlinear two-dimensional axisymmetric FSI simulations

A fast 4D B-spline framework for model-based reconstruction and regularization in vector flow imaging

A generic framework for model-based regularization and reconstruction is described, with applications in a wide range of noisy measurement scenarios. The framework employs automatic differentiation and stochastic gradient optimizers to perform online measurement fitting and regularization, and was implemented as a scalable CPU and GPU library with highperformance operation even in compute- or memory-intensive contexts, such as for 4D cardiac vector flow imaging. The framework was demonstrated by reconstructing 4D vector flow mapping through the incorporation of the incompressible NavierStokes equations. Furthermore, the achieved performance was within bedside applicability requirements