Paul Simoens

From Vascular Corrosion Cast to Electrical Analog Model for the Study of Human Liver Hemodynamics and Perfusion

Hypothermic machine perfusion (HMP) is experiencing a revival in organ preservation due to the limitations of static cold storage and the need for better preservation of expanded criteria donor organs. For livers, perfusion protocols are still poorly defined, and damage of sinusoidal endothelial cells and heterogeneous perfusion are concerns. In this study, an electrical model of the human liver blood circulation is developed to enlighten internal pressure and flow distributions during HMP. Detailed vascular data on two human livers, obtained by combining vascular corrosion casting, micro-CT-imaging and image processing, were used to set up the electrical model. Anatomical data could be measured up to 5-6 vessel generations in each tree and showed exponential trend lines, used to predict data for higher generations. Simulated flow and pressure were in accordance with literature data. The model was able to simulate effects of pressure-driven HMP on liver hemodynamics and reproduced observations such as flow competition between the hepatic artery and portal vein. Our simulations further indicate that, from a pure biomechanical (shear stress) standpoint, HMP with low pressures should not result in organ damage, and that fluid viscosity has no effect on the shear stress experienced by the liver microcirculation in pressure-driven HMP.

The pulmonary veins of the pig as an anatomical model for the development of a new treatment for atrial fibrillation.

The layout of the porcine atriopulmonary junction and immediately adjacent structures was investigated by gross anatomical and vascular corrosion casting studies to meet the need for more in‐depth anatomical insights when using the pig as an animal model in the development of innovative approaches for surgical cardiac ablation in man. The veins from the right cranial and middle lung lobes drain through a common ostium in the left atrium, whereas a second ostium receives the blood returning from all other lung lobes, although limited variation to this pattern was observed. Surrounding anatomical structures that are most vulnerable to ablation damage as reported in man are located at a safer distance from the pulmonary veins in pigs, yet a certain locations, comparable risks are to be considered. Additionally, it was histologically confirmed that myocardial sleeves extend to over a centimetre in the wall of the pulmonary veins.

Immunohistochemical detection of the angiopoietins during porcine metanephric kidney development

Angiopoietins are growth factors involved in vascular development. They also play an important role in the development of the kidney vasculature. The localization of these growth factors was immunohistochemically investigated in developing porcine metanephric kidneys. Angiopoietin 1 was predominantly present in the maturing glomeruli, while angiopoietin 2 was observed in the early developing glomeruli as well as in maturing glomeruli. Furthermore, angiopoietin 2 was observed in the muscle layer of renal arteries, in the convoluted tubules and in the loops of Henle. In contrast to the situation in the mouse in which angiopoietin 2 has been reported to be mainly expressed in mesangial cells near the glomerular hilus, expression of angiopoietin 2 in the porcine metanephric kidney was observed in the podocytes of early developing glomeruli, but not in the cells near the glomerular hilus. The results of this study support the hypothesis that the angiopoietins play an important role during mammalian metanephric development and during glomerulogenesis in particular, but indicate that species specific characteristics must be taken into account when evaluating their involvement in glomerulogenesis.

Stereology and computer assisted three-dimensional reconstruction as tools to study probiotic effects of Aeromonas hydrophila on the digestive tract of germ-free Artemia franciscana nauplii

Aims:  Validation of stereology and three‐dimensional reconstruction for monitoring the probiotic effect of Aeromonas hydrophila on the gut development of germ‐free Artemia franciscana nauplii.

Distribution of the Lingual Lymphoid Tissue in Domestic Ruminants

With 6 figures

Topography and ultrasonographic identification of the equine pulmonary vein draining pattern

Information on ultrasound examination of equine pulmonary veins is scarce due to a lack of in-depth anatomical information. Each pulmonary vein drains a specific lung lobe region, after which those veins merge into a collecting antrum, before opening into the left atrium through their respective ostia. The aim of this study was, by using anatomical dissection and silicone casting of equine cardiopulmonary sets, to study the venous drainage of both lungs and the position of the ostia and to investigate whether the ostia can be identified and differentiated using ultrasound. Three out of the four ostia could be observed echocardiographically in the standing horse. The ostium draining the most caudal aspects of both lungs showed little variability, while the ostium draining the rest of the right lung could be used as an easily recognisable landmark, since it was located adjacent to the interatrial septum. The identification of the equine pulmonary vein ostia using ultrasound might allow for the determination of size and flow patterns in the assessment of cardiovascular disease.

Stereological and immunogold studies on TIE1 and TIE2 localization in glomeruli indicate angiopoietin signaling in podocytes

Angiopoietins and their TIE receptors are important regulators of vascular stability and remodeling. These molecules are involved not only in the normal development of kidney glomeruli, but also in disease, thus making them promising targets for therapies. Although TIE receptors are mainly found in endothelial cells, some reports observed TIE2 expression in glomerular podocytes as well. This suggests a role of angiopoietins in the regulation of podocytes. In the present study, we aimed to map the subcellular localization of TIE receptors in metanephric glomeruli of fetal pigs using high-resolution immunogold electron microscopy and the relative labeling index stereological approach. TIE1 and TIE2 antibody labeling was detected on the abluminal side of endothelial cell membranes. In endothelial cells, 4.5% of TIE2 was observed close to cell-cell contacts and 11.9% of TIE2 was found in closely associated pairs, which suggests the presence of homodimers. Interestingly, both receptors were also expressed in podocyte foot processes indicating that TIE1 and TIE2 may play a similar role in podocytes as in endothelial cells.

Anatomical Description of the Presence and Variability of the Digital Manica Flexoria in the Equine Digital Flexor Tendon Sheath.

During endoscopy (tenoscopy) of the distal aspect of the equine digital flexor tendon sheath (DFTS), the digital manica flexoria can be visualized connecting the distal branches of the superficial digital flexor tendon. However, this structure has been inconsistently described and variably named in the veterinary literature. The objectives of this study were to describe the presence, configuration and variability of the digital manica flexoria in the equine distal limb. Dissection of 144 equine cadaveric limbs revealed the presence of this structure in all the feet, although different types and conformations were identified. In the forelimbs, a membranous digital manica flexoria predominated (94%; P < 0.001), in particular a synovial bridge type (83%; P < 0.001). In the hindlimbs, a tendinous digital manica flexoria predominated (93%; P < 0.001), in particular the oblique‐crossing of tendinous bundles (61%; P < 0.001). Passage dorsal to the digital manica flexoria towards the distal DFTS was only possible in 22 of the 144 limbs, all forelimbs. Clinicians should be aware of the intra‐ and inter‐individual anatomical variations of the digital manica flexoria to avoid misinterpretation during ultrasonographic and tenoscopic examinations of the DFTS.

The Omental Pedicle Flap in Dogs Revised and Refined: A Cadaver Study.

OBJECTIVE To expand current knowledge on the canine omental vasculature and refine the existing lengthening technique of the canine omentum. STUDY DESIGN Ex vivo study. ANIMALS Canine cadavers (n=20). METHODS In 10 canine cadavers the omental arteries were mapped using intravascular latex injection and these results were used to create an omental pedicle flap based on the splenic artery in 10 additional cadavers. The operating range of the flap was recorded with particular attention to the main regions of interest for omental transposition in dogs (axillary and inguinal regions). RESULTS The superficial and deep omental leaves were each predominantly supplied by a left and a right marginal omental artery that anastomosed near the caudal omental border into a superficial and a deep omental arch, respectively. Anastomoses between arteries of the superficial and the deep omental leaves were weak and inconsistent, except for 1 anastomosis that was found in 8 of 10 dogs. By transposing the intact omentum, the right axilla could be reached in 3 dogs, both axillae in 1 dog, and both groins in all cadavers. In all cases, the omental pedicle reached to and beyond the axillary and inguinal regions. By unfolding the pedicle leaves, the width of the pedicle tip could be doubled. CONCLUSION When lengthening the omentum is necessary to reach extra-abdominal structures, the omental pedicle flap based on the splenic artery appears to preserve the omental vascular supply. These observations warrant further clinical trials to evaluate this new omtental flap technique in vivo.

Morphology of the Canine Omentum Part 1: Arterial Landmarks that Define the Omentum

Although the omentum remains an enigmatic organ, research during the last decades has revealed its fascinating functions including fat storage, fluid drainage, immune activity, angiogenesis and adhesion. While clinicians both in human and veterinary medicine are continuously exploring new potential omental applications, detailed anatomical data on the canine omentum are currently lacking, and information is often retrieved from human medicine. In this study, the topographic anatomy of the canine greater and lesser omentum is explored in depth. Current nomenclature is challenged, and a more detailed terminology is proposed. Consistent arteries that are contained within folds of the superficial omental wall are documented, described and named, as they can provide the anatomical landmarks that are necessary for unambiguous scientific communication on the canine omentum. In an included dissection video, the conclusions and in situ findings described in this study are demonstrated.