Aerospace medicine and biology: A continuing bibliography with indexes, supplement 203

This bibliography lists 150 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1980

Simulation of Pulsatile Flow in Cerebral Aneurysms: From Medical Images to Flow and Forces

In this chapter we present a numerical model for the simulation of blood flow inside cerebral aneurysms. We illustrate the process of predicting flow and forces that arise in vessels and aneurysms starting from patient-specific data obtained using medical imaging techniques. Once the three-dimensional geometry is reconstructed, we discuss fluid properties of blood which allows to compute the flow. The flow of an incompressible Newtonian fluid in the human brain is simulated by using a volume penalizing immersed boundary method, in which the aneurysm geometries are represented by the so-called masking function. We impose pulsatile flow forcing, based on the direct measurement of the mean flow velocity in a vessel during a cardiac cycle and focus on effects due to changes in the flow regimes. In slow or very viscous flows the pulsatile forcing dominates the fluid dynamical response, while at faster or less viscous flows the intrinsic unsteadiness of natural incompressible flow is dominant over the pulsatile flow forcing effect. We consider a full range of physiologically relevant conditions and show high frequencies to emerge in the pulsatile response. The strong qualitative transitions in flow behavior and shear stress levels inside an aneurysm cavity at increased flow rates may contribute to the long-term risk of aneurysm rupture

A new mechanism for glymphatic flow of interstitial fluid in branched perivascular spaces of the brain

Objective. To explore the biophysics of interstitial tissue fluid flow in the brain, based upon the anatomy and mechanics of the perivascular spaces, in order to better understand how glymphatic flow happens. Methods. The dynamics of fluid flow at cardiac frequencies are investigated in rapidly computable, branched, geometric models of brain tissue at multiple scales. The models are supplied by intermingled trees of penetrating arteries and veins. They include pulsatile changes in intracranial pressure and intravascular pressure, elastic expansion of brain tissue, and nonlinear changes in resistance to flow of cerebrospinal fluid along the axis of the Virchow-Robin space. Resulting changes in periarterial and perivenous pressures and the resulting bulk flow of interstitial fluid from arteriolar to venular perivascular spaces are calculated on a laptop computer. Results. Under typical physiological conditions a time averaged positive pressure of ~ 0.5 mmHg develops between the smaller, distal periarteriolar and perivenous branches. Based on tissue geometry and hydraulic resistance, the resulting flow is sufficient to refresh the interstitial fluid once every 1 to 10 hours. The effect is degraded by increasing radial widths of the perivascular spaces. The calculated average glymphatic flow through the whole brain is similar to the measured production of new cerebrospinal fluid by the arachnoid villi. Conclusions. When the branching structure of perivascular trees is properly considered, their classical anatomy has surprising emergent properties. Biologically meaningful amounts of advective flow can happen between smaller, distal branches of periarteriolar and perivenous spaces

NASA Thesaurus Supplement: A three part cumulative supplement to the 1982 edition of the NASA Thesaurus (supplement 3)

The three part cumulative NASA Thesaurus Supplement to the 1982 edition of the NASA Thesaurus includes Part 1, Hierarchical Listing, Part 2, Access Vocabulary, and Part 3, Deletions. The semiannual supplement gives complete hierarchies for new terms and includes new term indications for entries new to this supplement

Brain solute transport is more rapid in periarterial than perivenous spaces

Fluid flow in perivascular spaces is recognized as a key component underlying brain transport and clearance. An important open question is how and to what extent differences in vessel type or geometry affect perivascular fluid flow and transport. Using computational modelling in both idealized and image-based geometries, we study and compare fluid flow and solute transport in pial (surface) periarterial and perivenous spaces. Our findings demonstrate that differences in geometry between arterial and venous pial perivascular spaces (PVSs) lead to higher net CSF flow, more rapid tracer transport and earlier arrival times of injected tracers in periarterial spaces compared to perivenous spaces. These findings can explain the experimentally observed rapid appearance of tracers around arteries, and the delayed appearance around veins without the need of a circulation through the parenchyma, but rather by direct transport along the PVSs.publishedVersio

LES of non-Newtonian physiological blood flow in a model of arterial stenosis

Large Eddy Simulation (LES) is performed to study the physiological pulsatile transition-to-turbulent non-Newtonian blood flow through a 3D model of arterial stenosis by using five different blood viscosity models: (i) Power-law, (ii) Carreau, (iii) Quemada, (iv) Cross and (v) modified-Casson. The computational domain has been chosen is a simple channel with a biological type stenosis formed eccentrically on the top wall. The physiological pulsation is generated at the inlet of the model using the first four harmonic series of the physiological pressure pulse (Loudon and Tordesillas [1]). The effects of the various viscosity models are investigated in terms of the global maximum shear rate, post-stenotic re-circulation zone, mean shear stress, mean pressure, and turbulent kinetic energy. We find that the non-Newtonian viscosity models enlarge the length of the post-stenotic re-circulation region by moving the reattachment point of the shear layer separating from the upper wall further downstream. But the turbulent kinetic energy at the immediate post-lip of the stenosis drops due to the effects of the non-Newtonian viscosity. The importance of using LES in modelling the non-Newtonian physiological pulsatile blood flow is also assessed for the different viscosity models in terms of the results of the dynamic subgrid-scale (SGS) stress Smagorinsky model constant, C<sub>s</sub>, and the corresponding SGS normalised viscosity

Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties

The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids

Aerospace Medicine and Biology: a Continuing Bibliography with Indexes (supplement 330)

This bibliography lists 156 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System during November 1989. Subject coverage includes: aerospace medicine and psychology, life support system and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance