The role of the cerebral capillaries in acute ischemic stroke: the extended penumbra model.

The pathophysiology of cerebral ischemia is traditionally understood in relation to reductions in cerebral blood flow (CBF). However, a recent reanalysis of the flow-diffusion equation shows that increased capillary transit time heterogeneity (CTTH) can reduce the oxygen extraction efficacy in brain tissue for a given CBF. Changes in capillary morphology are typical of conditions predisposing to stroke and of experimental ischemia. Changes in capillary flow patterns have been observed by direct microscopy in animal models of ischemia and by indirect methods in humans stroke, but their metabolic significance remain unclear. We modeled the effects of progressive increases in CTTH on the way in which brain tissue can secure sufficient oxygen to meet its metabolic needs. Our analysis predicts that as CTTH increases, CBF responses to functional activation and to vasodilators must be suppressed to maintain sufficient tissue oxygenation. Reductions in CBF, increases in CTTH, and combinations thereof can seemingly trigger a critical lack of oxygen in brain tissue, and the restoration of capillary perfusion patterns therefore appears to be crucial for the restoration of the tissue oxygenation after ischemic episodes. In this review, we discuss the possible implications of these findings for the prevention, diagnosis, and treatment of acute stroke.

A comparison of technologies for database-driven websites for medical education.

Static web pages may be easy to setup using text processors or user-friendly web editing software. However, some basic knowledge of the implementation (HTML) is usually needed for final editing and maintenance. As a result many static web pages are left without appropriate updating. With a database driven, dynamic approach web contents may change through user interaction, the pages are usually easier to maintain, and design elements are separated from contents. Database driven solutions (or content management systems) for larger organizations may be purchased at many different levels of complexity. For smaller systems, such as separate courses or projects, they may, however, be developed locally. The present study compares four alternative technologies for database driven web pages. Each technology offers advantages and disadvantages and many issues need to be considered when selecting platform. The present study demonstrates that database driven web pages may be effectively deployed using free Open Source software. Details may be found at www.intermed.dk/datadriven.