A high-resolution computational model of the deforming human heart.

Modeling of the heart ventricles is one of the most challenging tasks in soft tissue mechanics because cardiac tissue is a strongly anisotropic incompressible material with an active component of stress. In most current approaches with active force, the number of degrees of freedom (DOF) is limited by the direct method of solution of linear systems of equations. We develop a new approach for high-resolution heart models with large numbers of DOF by: (1) developing a hex-dominant finite element mixed formulation and (2) developing a Krylov subspace iterative method that is able to solve the system of linearized equations for saddle-point problems with active stress. In our approach, passive cardiac tissue is modeled as a hyperelastic, incompressible material with orthotropic properties, and mixed pressure-displacement finite elements are used to enforce incompressibility. Active stress is generated by a model with force dependence on length and velocity of muscle shortening. The ventricles are coupled to a lumped circulatory model. For efficient solution of linear systems, we use Flexible GMRES with a nonlinear preconditioner based on block matrix decomposition involving the Schur complement. Three methods for approximating the inverse of the Schur complement are evaluated: inverse of the pressure mass matrix; least squares commutators; and sparse approximate inverse. The sub-matrix corresponding to the displacement variables is preconditioned by a V-cycle of hybrid geometric-algebraic multigrid followed by correction with several iterations of GMRES preconditioned by sparse approximate inverse. The overall solver is demonstrated on a high-resolution two ventricle mesh based on a human anatomy with roughly 130 K elements and 1.7 M displacement DOF. Effectiveness of the numerical method for active contraction is shown. To the best of our knowledge, this solver is the first to efficiently model ventricular contraction using an iterative linear solver for the mesh size demonstrated and therefore opens the possibility for future very high-resolution models. In addition, several relatively simple benchmark problems are designed for a verification exercise to show that the solver is functioning properly and correctly solves the underlying mathematical model. Here, the output of the newly designed solver is compared to that of the mechanics component of Chaste ('Cancer, Heart and Soft Tissue Environment'). These benchmark tests may be used by other researchers to verify their newly developed methods and codes.

Towards real-time simulation of cardiac electrophysiology in a human heart at high resolution.

We have developed the capability to rapidly simulate cardiac electrophysiological phenomena in a human heart discretised at a resolution comparable with the length of a cardiac myocyte. Previous scientific investigation has generally invoked simplified geometries or coarse-resolution hearts, with simulation duration limited to 10s of heartbeats. Using state-of-the-art high-performance computing techniques coupled with one of the most powerful computers available (the 20 PFlop/s IBM BlueGene/Q at Lawrence Livermore National Laboratory), high-resolution simulation of the human heart can now be carried out over 1200 times faster compared with published results in the field. We demonstrate the utility of this capability by simulating, for the first time, the formation of transmural re-entrant waves in a 3D human heart. Such wave patterns are thought to underlie Torsades de Pointes, an arrhythmia that indicates a high risk of sudden cardiac death. Our new simulation capability has the potential to impact a multitude of applications in medicine, pharmaceuticals and implantable devices.

The potential role of high mobility group-1 protein in the pathogenesis of sepsis-induced multiple organ dysfunction syndrome in rats / 中华外科杂志

<p><b>OBJECTIVE</b>To investigate the potential role of high mobility group-1 protein (HMG-1) in the pathogenesis of sepsis-induced multiple organ dysfunction syndrome in rats.</p><p><b>METHODS</b>Using a sepsis model by cecal ligation and puncture (CLP), 80 male Wistar rats were randomly divided into four groups: normal control (n = 10), sham operation (n = 10), CLP (subdivided into 2, 6, 12, 24, 48, 72 h post-CLP, n = 60), and sodium butyrate treatment (subdivided into 12, 24 h post-CLP, n = 20). At serial time points in each group, animals were sacrificed, and blood as well as tissue samples from the liver, lung, kidney and small intestine were harvested to measure organ function parameters and HMG-1 mRNA expression by the reverse transcription polymerase chain reaction (RT-PCR) taking GAPDH as an internal standard. Also, additional experiments were performed to observe the effect of treatment with sodium butyrate on survival rate in septic rats (n = 57).</p><p><b>RESULTS</b>HMG-1 mRNA levels significantly increased in various tissues during 6 - 72 h after CLP (P < 0.05 or 0.01), and were markedly inhibited by sodium butyrate at 12 h and 24 h (P < 0.05 or 0.01). Early treatment with sodium butyrate also could markedly reduce serum alanine aminotransferase, creatinine levels at 12 h post-CLP and pulmonary myeloperoxidase activities at 24 h. Furthermore, treatment with sodium butyrate could significantly improve the 1- to 6-day survival rates in animals subjected to CLP (P < 0.05 or 0.01).</p><p><b>CONCLUSIONS</b>HMG-1 might play an important role in the development of excessive inflammatory response and subsequent multiple organ dysfunction syndrome.</p>