Numerical Study of Blood Flow at the End-to-Side Anastomosis of a Left Ventricular Assist Device for Adult Patients

Ventricular assist devices (VADs) have been used for years in adult patients with end-stage heart failure, during bridge-to-transplant, and they have recently shown promise in aiding in myocardial recovery [1]. While the fluid mechanics within VADs has been studied extensively [2], an area which must be more adequately addressed is the outflow cannula attached as an end-to-side anastomosis to the aorta. This attachment may lead to unnaturally high and low shear stresses, turbulence, flow separation, and stagnant flows. As a result, platelet activation and thrombus formation may occur. May-Newman et al. [3] developed a laminar, continuous, computational fluid dynamics (CFD) model to study how different outflow cannula anastomoses affect flow patterns in an adult aortic model. Turbulent flows, however, were not considered. The effects of the anastomosis on the flows in the secondary vessels were neglected as well. There is a lack of detailed description of the flow field across the cannulated adult aorta based on different VAD outflow cannula configurations and operating conditions. As a result, we have developed a comprehensive model to simulate turbulent blood flow in three-dimensional models of the cannulated adult aorta under continuous flow conditions and to study the impact of the secondary vessels on the aortic arch.

The blood vascular system of the gills of pholas dactylus l . (mollusca, bivalvia, eulamellibranchia)

Scanning electron microscopical studies of acrylic corrosion casts of the blood vascular system of the gills of Pholas dactylus and of critical-point dried preparations of whole gills, supplemented by histological preparations and observations on whole animals, show that the blood vascular system has two interconnecting pathways, one frontal and one abfrontal, both of which arise and terminate in the primary vessels of the gills. In the abfrontal pathway both afferent and efferent primary vessels give rise to secondary vessels at right angles to them. There is no regular alternation of afferent and efferent secondary vessels and both occur in the ascending and descending lamellae. Tertiary vessels, circumferential to the interlamellar spaces, link the secondary vessels. In the filamentary frontal pathway blood is conveyed to or from the primary vessels via perforations in their ventral walls which open into labyrinthic blood spaces; the filamentary frontal channels of descending lamellae empty into these spaces whereas those of ascending lamellae are filled from the spaces. The two systems are joined by many short, D-shaped spaces within the filaments, which connect the filamentary frontal channels to the circumferential, tertiary vessels. Movement of blood in the gills is more oscillatory than unidirectional. Factors that might affect the flow of blood in the two systems and in different parts of the gills are considered.

The developmental anatomy of Conopholis americana (Orobancaceae) seedlings and tubercles

Germinated and attached seedlings of the phanerogamic parasite Conopholis americana (L.) Wallroth are described for the first time. The morphogenetic changes which characterize the transition from seedling to preflowering tubercle, as well as the anatomy of the mature tubercle, including endogenous floral buds, are also described. Conopholis seedlings were found attached only to mycorrhizal oak roots. The primary haustorium attached to and penetrated the fungal sheath, pushing aside epidermal and cortical cells of the host as it grew toward the host stele. Cells of the endophyte contacted host xylem and differentiated directly into reticulately thickened tracheary elements. Concomitantly a cambial are of parasite origin was established within the young tubercle, aligned with the vascular cambium of the host root. The cambium of the tubercle gave rise to xylem centripetally, which differentiated into tracheary elements juxtaposed to host secondary vessels, and cortical parenchyma centrifugally. Sieve elements could not be unequivocally demonstrated in seedlings or tubercles. Tissues and cell types of the parasite could be distinguished from those of the host by both morphological and histochemical criteria. The parasite to host transition zone was characterized by direct tracheary element connections and delimited by densely cytoplasmic parasite parenchyma cells that had greatly enlarged centrally located nuclei.

Xylary union between elongating lateral branches and the main stem in Populus deltoides

The vasculature of elongating lateral branches was examined to determine how vessels produced in the branch unite with those produced in the main stem axis to form a continuous transport system. In a previous study it was found that differentiation of both primary and secondary xylem in a lateral bud or branch is independent of that in the main axis; i.e., xylem does not differentiate into the bud or branch from the main axis. When serial sections of the nodal region are followed downward, the bud vascular cylinder merges with that of the main axis and the adaxially situated bud traces (those nearest the stem) enter the bud gap margin first. The primary vessels of these bud traces differentiate in an oblique downward path along the margins of the bud gap, and they form radial files of primary vessels that lie adjacent to primary xylem of leaf traces in the stem. Traces situated more abaxially in the bud (those farther from the stem) contribute to other radial files of primary vessels, each of which lies progressively closer to the bud gap. Secondary xylem is initiated in the stem before it is in the branch. Consequently, the last-formed metaxylem vessels of the bud traces are continuous with secondary vessels of the stem. These latter vessels lie in the stem secondary xylem immediately external to primary xylem from the bud. Secondary xylem in the branch is initiated when foliage leaves and internodes mature. Secondary vessels formed in the branch traces are continuous with secondary vessels in the stem; these vessels are embedded in a matrix of fibers. Because cambial activity is more vigorous in the stem than in the branch, two vessels that are radially adjacent in the branch may be widely separated by fibers in the stem. The central trace of the axillant leaf enters the gap immediately below the last branch traces; at this level in the stem the leaf trace vasculature is entirely primary. The stem secondary xylem that overlies the leaf trace is continuous with that in the axillary branch.

Ultrastructure of wilt syndrome caused by Verticillium dahliae. VII. Correlated light and transmission electron microscope identification of vessel coatings and tyloses

Thin cross sections of petioles from wilted leaves of chrysanthemums infected with Verticillium dahliae were fixed in glutaraldehyde + FeCl3 and embedded for electron microscopy. Alternate thick (LM) and thin (TEM) sections were cut. The thick sections were stained with (1) the Prussian blue reaction, (2) Sudan black B, (3) toluidine blue O, or (4) Schiff s reagent. Correlated LM and TEM of exactly the same vessels showed that tylosis walls, smooth coating, fibrillar coating, and bubbly coating stained differentially. The tyloses are more abundant than formerly anticipated but are restricted to the primary vessels; fungal cells and coating on vessel walls are confined to smaller secondary vessels.

Micro- and macrovascular changes as the direct cause of parenchymal destruction in congenital murine hydrocephalus

✓ Microangiotomography was used to identify the normal and pathological pattern of cerebral vessels in the hy-3 murine mutant mouse (normal and hydrocephalic) at various developmental stages from birth through 21 days of life. The technique employed allows resolution, in the range of 7 to 10 µ of the surface and in-traparenchymal (perforating) microvasculature. Ventricular enlargement causes displacement of primary cerebral arteries, followed by both stretching and a decrease in the caliber of primary, secondary, and tertiary vessels (arterial and venous). Ultimately, there is a reduction in the number and caliber of the microvasculature, resulting in diminished cerebral blood flow and cerebral edema. Tissue destruction leading to ependymal rupture, parenchymal cavitation, and the formation of porencephalic cysts within the edematous parenchyma ensues. External ventricular drainage, by decompressing the ventricles, resulted in rapid restoration of the filling of the primary and secondary vessels, thereby suggesting the primary role of vascular changes in the production of brain damage. This study offers experimental evidence that early diversion of the cerebrospinal fluid interrupts this chain of events in congenital murine hydrocephalus.