Biomedical subjects

B Ene-Iordache

Publications and source records attributed to B Ene-Iordache.

3 recordsLinked to original sources

PubMed2001

Automatic generation of glomerular capillary topological organization.

Glomerular structural changes are conventionally investigated by optical or electron microscopy on two-dimensional (2D) sections. To understand the relationship between functional and structural changes of glomerular capillary networks in more detail, three-dimensional (3D) investigation of the capillary tufts is required. Since confocal microscopy and scanning electron microscopy cannot completely show the 3D topological organization of the capillary tuft, we have developed an automatic method to obtain a 3D model of the glomerular capillary lumen structure and to derive its topological organization. Serial semithin sections of a glomerular tuft, from rat kidney tissue, were digitized at high resolution. Capillary lumens were digitally outlined and segmented images were automatically aligned. A 3D model of the capillary tuft was automatically generated using the Visualization Toolkit library and the Marching Cubes algorithm. We then developed an original algorithm for automatic 3D skeletonization of capillary lumen volume to identify capillary segments and bifurcations and to obtain the topological organization of the network and geometric parameters of capillary segments (length, radius, and spatial configuration). Capillary segment connectivity was graphically presented in a 2D layout with an automatic procedure, revealing the lobular organization of the network. This technique, successfully applied to serial sections of a glomerular capillary, can be used to study a population of glomerular capillaries to disclose the structural effects of pathological conditions. The methodology can be extended to other vascular structures, such as the microcirculation of neoplastic tissues.

Algorithms↗

PubMed2001

Computational fluid dynamics of a vascular access case for hemodialysis.

Vascular accesses (VA) for hemodialysis are usually created by native arteriovenous fistulas (AVF) or synthetic grafts. Maintaining patency of VA continues to be a major problem for patients with end-stage renal disease, since in these vessels thrombosis and intimal hyperplasia often occur. These lesions are frequently associated with disturbed flow that develops near bifurcations or sharp curvatures. We explored the possibility of investigating blood flow dynamics in a patient-specific model of end-to-end native AVF using computational fluid dynamics (CFD). Using digital subtraction angiographies of an AVF, we generated a three-dimensional meshwork for numerical analysis of blood flow. As input condition, a time-dependent blood waveform in the radial artery was derived from centerline velocity obtained during echo-color-Doppler ultrasound examination. The finite element solution was calculated using a fluid-dynamic software package. In the straight, afferent side of the radial artery wall shear stress ranged between 20 and 36 dynes/cm2, while on the inner surface of the bending zone it increased up to 350 dynes/cm2. On the venous side, proximal to the anastomosis, wall shear stress was oscillating between negative and positive values (from -12 dynes/cm2 to 112 dynes/cm2), while distal from the anastomosis, the wall shear stress returned within the physiologic range, ranging from 8 to 22 dynes/cm2. Areas of the vessel wall with very high shear stress gradient were identified on the bending zone of the radial artery and on the venous side, after the arteriovenous shunt. Secondary blood flows were also observed in these regions. CFD gave a detailed description of blood flow field and showed that this approach can be used for patient-specific analysis of blood vessels, to understand better the role of local hemodynamic conditions in the development of vascular lesions.

Arteriovenous Anastomosis↗

PubMed1995

Capillary network structure does not affect theoretical analysis of glomerular size selectivity.

Anatomical studies have demonstrated that the glomerular capillaries are complex and heterogeneous networks. Conventional models of glomerular size selectivity, however, are based on the assumption of simplified geometries. We developed a theoretical model of glomerular size-selective function based on the geometric data obtained in a previous reconstruction of a glomerular network from a normal Munich-Wistar rat. This heterogeneous model was compared with the homogeneous model conventionally used to calculate membrane selective parameters from the fractional clearance of two test solutes, neutral dextran and Ficoll. For both models we assumed a hypothetical log-normal distribution of pore sizes and calculated optimal membrane pore-size parameters using previously published values of fractional clearances. The difference between the sieving coefficients calculated with the two models was negligible, never exceeding 5.5%. Since the homogeneous model does not consider the pressure drop along the glomerular capillary, we also computed fractional clearances with the homogeneous model, assuming the same pressure drop as in the heterogeneous one. The differences in computed fractional clearances using the homogeneous model with and without a pressure drop were less than 1.2%. We concluded that models based on identical capillary networks can therefore be used for interpreting sieving coefficients for macromolecules.

Animals↗