Architectonic arrangement of the vasa vasorum of the human great saphenous vein

Vasa vasorum interna in the carotid wall of active forms of Takayasu arteritis evidenced by ultrasound localization microscopy

Introduction: Takayasu arteritis (TA) is associated with microvascularization of the wall of large arteries and is related to inflammation. Ultrasound localization microscopy (ULM), combining ultrafast ultrasound imaging with microbubble (MB) injection, can track the path of MBs within the arterial wall and thus provide imaging of the vasa vasorum. From the analysis of MB tracks in the common carotid arteries of patients with active TA, we report the presence of microvessels in connection with the carotid lumen (i.e., vasa vasorum interna [VVI]). Methods: ULM maps were obtained on five patients with active disease in the observational single-center series of the TAK-UF study. MB tracks connected to the carotid lumen were automatically identified, allowing the reconstruction of VVI. Results: MB tracking allows us to observe a microvascular network on the inner part of the wall, with some vessels in communication with the carotid lumen. This type of vessel was identified in all patients with active TA (n = 5) with a median of 2.2 [1.1-3.0] vessels per acquisition (2D longitudinal view of 3 cm of the common carotid artery). The blood flow within these vessels is mainly centrifugal; that is, toward the adventitia (88% [54-100] of MB tracks with flow directed to the outer part of the wall). Conclusion: VVI are present in humans in the case of active TA and emphasize the involvement of the intima in the pathological process. ClinicalTrials.gov Identifier: NCT03956394.

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.

Excessive Adventitial and Perivascular Vascularisation Correlates with Vascular Inflammation and Intimal Hyperplasia

Albeit multiple studies demonstrated that vasa vasorum (VV) have a crucial importance in vascular pathology, the informative markers and metrics of vascular inflammation defining the development of intimal hyperplasia (IH) have been vaguely studied. Here, we employed two rat models (balloon injury of the abdominal aorta and the same intervention optionally complemented with intravenous injections of calciprotein particles) and a clinical scenario (arterial and venous conduits for coronary artery bypass graft (CABG) surgery) to investigate the pathophysiological interconnections among VV, myeloperoxidase-positive (MPO⁺) clusters, and IH. We found that the amounts of VV and MPO⁺ clusters were strongly correlated; further, MPO⁺ clusters density was significantly associated with balloon-induced IH and increased at calciprotein particle-provoked endothelial dysfunction. Likewise, number and density of VV correlated with IH in bypass grafts for CABG surgery at the pre-intervention stage and were higher in venous conduits which more frequently suffered from IH as compared with arterial grafts. Collectively, our results underline the pathophysiological importance of excessive VV upon the vascular injury or at the exposure to cardiovascular risk factors, highlight MPO⁺ clusters as an informative marker of adventitial and perivascular inflammation, and propose another mechanistic explanation of a higher long-term patency of arterial grafts upon the CABG surgery.

Pathological analysis of vascularization of the arterialized veins in failed arteriovenous fistulas among uremic patients

PURPOSE

To assess venous wall vascularization and its correlation with neointimal hyperplasia (NIH) in failed arteriovenous fistulas (AVFs).

METHODS

A total of 43 uremic patients who received a first AVF creation and 39 patients who received reconstruction of failed fistulas were enrolled in the study. A 5-10 mm vein segment adjacent to future fistula creation or reconstruction site was surgically removed and assessed using histopathological analyses and stained by immunohistochemistry to quantify vasa vasorum density (VVD).

RESULTS

Both the intimal thickness (70.68 [28.81-99.54] vs. 4.53 [2.69-7.30] μm, P < 0.001) and the intimal thickness/medial thickness ratio (2.20 [0.77-4.36] vs. 0.15 [0.10-0.30], P < 0.001) were higher in failed AVFs than in pre-access veins. CD31 and factor VIII marked VVDs both in the intima (6.31 [1.62-12.53] vs. 0.0 [0.0-0.0], P < 0.001; 7.82 [3.33-11.61] vs. 0.0 [0.0-0.0], P < 0.001) and media (10.0 [7.59-12.95] vs. 3.71 [2.44-4.87], P < 0.001; 8.33 [5.55-13.0] vs. 3.57 [2.53-4.82], P < 0.001), and the intimal VVD/medial VVD ratio (0.67 [0.19-1.08] vs. 0.0 [0.0-0.0], P < 0.001; 0.71 [0.39-1.14] vs. 0.0 [0.0-0.0], P < 0.001) were significantly higher in failed AVFs than in pre-access veins. There was also a positive relationship between the intimal VVD/medial VVD ratio and the intimal thickness/medial thickness ratio (P < 0.001). In addition, compared to pre-access veins, vascular endothelial cell growth factor-A (VEGF-A) expression was higher in failed AVFs.

CONCLUSIONS

Vascularization of the vessel wall was noticeably more developed in the arterialized veins, especially among the NIH regions in failed AVFs.

Pulsatile flow in venous perforators of the lower limb

Teaching traditionally asserts that the arterial pressure pulse is dampened across the capillary bed to the extent that pulsatility is non-existent in the venous circulation of the lower limbs. Herein, we present evidence of transmission of arterial pulsations across the capillary network into perforator veins in the lower limbs of healthy, heat-stressed humans. Perforator veins are connections from the superficial veins that drain into the deep veins. When assessed using ultrasound at rest, they infrequently demonstrate flow and a pulsatile flow waveform is not described. We investigated perforator vein pulsatility in ten young, healthy volunteers who underwent passive heating by +2 ºC deep body temperature via a hot-water-perfused suit, and five who also underwent active heating by +2 ºC via low-intensity cycling while wearing the hot-water-perfused suit. At +0.5 ºC increments in temperature, blood velocity in an ankle perforator vein was measured using duplex ultrasound. In all perforators with heating, sustained flow was demonstrated, with a pulsatile waveform that was synchronous with the cardiac cycle. The maximum velocity was 29 ± 14 cm/s with passive heating and approximately half with active heating (P=0.04). The small veins of the skin at the ankle also demonstrated increased perfusion with pulsatility, seen with low-velocity microvascular imaging technology. We consider explanations for this pulsatility and conclude that it is propagated from the arterial inflow through the skin microcirculation as a result of increased dilatation and flow volume, and that this a normal response to increased skin blood flow.

On vasa vasorum: A history of advances in understanding the vessels of vessels

The vasa vasorum are a vital microvascular network supporting the outer wall of larger blood vessels. Although these dynamic microvessels have been studied for centuries, the importance and impact of their functions in vascular health and disease are not yet fully realized. There is now rich knowledge regarding what local progenitor cell populations comprise and cohabitate with the vasa vasorum and how they might contribute to physiological and pathological changes in the network or its expansion via angiogenesis or vasculogenesis. Evidence of whether vasa vasorum remodeling incites or governs disease progression or is a consequence of cardiovascular pathologies remains limited. Recent advances in vasa vasorum imaging for understanding cardiovascular disease severity and pathophysiology open the door for theranostic opportunities. Approaches that strive to control angiogenesis and vasculogenesis potentiate mitigation of vasa vasorum-mediated contributions to cardiovascular diseases and emerging diseases involving the microcirculation.

[Comparative study of vasa vasorum and neointima in conduits for coronary artery bypass grafting]

AIM

This study was undertaken to investigate the preoperative incidence and severity of intimal hypertrophy, as well as the level of blood supply of arterial and venous conduits for coronary artery bypass grafting.

MATERIAL AND METHODS

Segments of the internal thoracic artery and great saphenous vein (n=13) were harvested pairwise during coronary artery bypass grafting and were then visualized by scanning electron microscopy in back-scattered electrons. The analysis of the incidence and thickness of intimal hypertrophy, as well as the calculation of the number and the area of the vasa vasorum were performed using the programme ImageJ.

RESULTS

Intimal hypertrophy was more characteristic for the great saphenous vein as compared with the internal thoracic artery (9/13 (69.2%) and 7/13 (55.8%), respectively), although this difference did not reach statistical significance. The maximal-to-minimal neointimal thickness ratio correlated with the percentage of stenosis (r=0.875, p<0.0001), the area (r=0.45, p=0.023) and the number (r=0.47, p=0.015) of the vasa vasorum in the conduits, thus confirming the hypothesis on possible participation of these vessels in the development of intimal hypertrophy, with the area of the vasa vasorum being greater in the vessels with >10% stenosis (p=0.051). The number of the vasa vasorum in the great saphenous vein exceeded that in the internal thoracic artery (p=0.0005), with this difference remaining significant after adjustment for the area of the adventitia (p=0.027). The number of the vasa vasorum per the percentage of stenosis in the great saphenous vein also exceeded that in the internal thoracic artery (p=0.039) and more strongly correlated with intimal hypertrophy in the great saphenous vein as compared with that in the internal thoracic artery (r=0.53 and r=0.27, respectively).

CONCLUSION

Intimal hypertrophy correlates with the area and number of the vasa vasorum in conduits. The great saphenous vein is characterised by a larger number and higher density of the vasa vasorum as compared with the internal thoracic artery. The number of the vasa vasorum is correlated with stenosis of the great saphenous vein more closely than with stenosis of the internal thoracic artery. This may be suggestive of significant predisposition of the great saphenous vein to the onset of adventitial inflammation followed by the development of intimal hypertrophy.

A Brief Comment on Vasa Vasorum of Human Saphenous Vein: relevance for Coronary Artery Bypass Surgery

The importance of the vasa vasorum and blood supply to the wall of human saphenous vein (hSV) used for coronary artery bypass grafting (CABG) is briefly discussed. This is in the context of the possible physical link of the vasa vasorum connecting with the lumen of hSV and the anti-ischaemic impact of this microvessel network in the hSV used for CABG.

The venous perforators of the lower limb - A new terminology

Latin anatomical terminology of venous perforators (communications between superficial and deep venous systems of the lower limb) was adopted as late as 2001 as an appendix to the official nomenclature following the clinicians’ request. Terminologia Anatomica, last version of the Latin anatomical nomenclature, published in 1998, unfortunately contains no terms concerning these veins. During the 14th World Congress of the International Union of Phlebology, a consensus document was laid to expand the nomenclature of the lower limb veins, above all 36 new terms for perforators of the lower limb, both in Latin and English languages. This consensus document will be incorporated in the next version of the Terminologia Anatomica. But there are more constant and well-described ones, especially in the foot, and this article reviews in particular the current knowledge on the anatomy of the venous perforators of the whole lower limb.

Vasa vasorum inside out/outside in communication: a potential role in the patency of saphenous vein coronary artery bypass grafts

The saphenous vein (SV) is the most commonly used conduit for revascularization in patients undergoing coronary artery bypass surgery (CABG). The patency rate of this vessel is inferior to the internal thoracic artery (ITA). In the majority of CABG procedures the ITA is removed with its outer pedicle intact whereas the (human) SV (hSV) is harvested with pedicle removed. The vasa vasorum, a microvessel network providing the adventitia and media with oxygen and nutrients, is more pronounced and penetrates deeper towards the lumen in veins than in arteries. When prepared in conventional CABG the vascular trauma caused when removing the hSV pedicle damages the vasa vasorum, a situation affecting transmural flow potentially impacting on graft performance. In patients, where the hSV is harvested with pedicle intact, the vasa vasorum is preserved and transmural blood flow restored at graft insertion and completion of CABG. By maintaining blood supply to the hSV wall, apart from oxygen and nutrients, the vasa vasorum may also transport factors potentially beneficial to graft performance. Studies, using either corrosion casts or India ink, have shown the course of vasa vasorum in animal SV as well as in hSV. In addition, there is some evidence that vasa vasorum of hSV terminate in the vessel lumen based on ex vivo perfusion, histological and ultrastructural studies. This review describes the preparation of the hSV as a bypass conduit in CABG and its performance compared with the ITA as well as how and why its patency might be improved by harvesting with minimal trauma in a way that preserves an intact vasa vasorum.

Vasa Vasorum Angiogenesis: Key Player in the Initiation and Progression of Atherosclerosis and Potential Target for the Treatment of Cardiovascular Disease

Plaque microvascularization and increased endothelial permeability are key players in the development of atherosclerosis, from the initial stages of plaque formation to the occurrence of acute cardiovascular events. First, endothelial dysfunction and increased permeability facilitate the entry of diverse inflammation-triggering molecules and particles such as low-density lipoproteins into the artery wall from the arterial lumen and vasa vasorum (VV). Recognition of entering particles by resident phagocytes in the vessel wall triggers a maladaptive inflammatory response that initiates the process of local plaque formation. The recruitment and accumulation of inflammatory cells and the subsequent release of several cytokines, especially from resident macrophages, stimulate the expansion of existing VV and the formation of new highly permeable microvessels. This, in turn, exacerbates the deposition of pro-inflammatory particles and results in the recruitment of even more inflammatory cells. The progressive accumulation of leukocytes in the intima, which trigger proliferation of smooth muscle cells in the media, results in vessel wall thickening and hypoxia, which further stimulates neoangiogenesis of VV. Ultimately, this highly inflammatory environment damages the fragile plaque microvasculature leading to intraplaque hemorrhage, plaque instability, and eventually, acute cardiovascular events. This review will focus on the pivotal roles of endothelial permeability, neoangiogenesis, and plaque microvascularization by VV during plaque initiation, progression, and rupture. Special emphasis will be given to the underlying molecular mechanisms and potential therapeutic strategies to selectively target these processes.

Smooth muscle cells of human veins show an increased response to injury at valve sites

OBJECTIVE

Venous valves are essential but are prone to injury, thrombosis, and fibrosis. We compared the behavior and gene expression of smooth muscle cells (SMCs) in the valve sinus vs nonvalve sites to elucidate biologic differences associated with vein valves.

METHODS

Tissue explants of fresh human saphenous veins were prepared, and the migration of SMCs from explants of valve sinus vs nonvalve sinus areas was measured. Proliferation and death of SMCs were determined by staining for Ki67 and terminal deoxynucleotidyl transferase dUTP nick end labeling. Proliferation and migration of passaged valve vs nonvalve SMCs were determined by cell counts and using microchemotaxis chambers. Global gene expression in valve vs nonvalve intima-media was determined by RNA sequencing.

RESULTS

Valve SMCs demonstrated greater proliferation in tissue explants compared with nonvalve SMCs (19.3% ± 5.4% vs 6.8% ± 2.0% Ki67-positive nuclei at 4 days, respectively; mean ± standard error of the mean, five veins; P < .05). This was also true for migration (18.2 ± 2.7 vs 7.5 ± 3.0 migrated SMCs/explant at 6 days, respectively; 24 veins, 15 explants/vein; P < .0001). Cell death was not different (39.6% ± 16.1% vs 41.5% ± 16.0% terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells, respectively, at 4 days, five veins). Cultured valve SMCs also proliferated faster than nonvalve SMCs in response to platelet-derived growth factor subunit BB (2.9 ± 0.2-fold vs 2.1 ± 0.2-fold of control, respectively; P < .001; n = 5 pairs of cells). This was also true for migration (6.5 ± 1.2-fold vs 4.4 ± 0.8-fold of control, respectively; P < .001; n = 7 pairs of cells). Blockade of fibroblast growth factor 2 (FGF2) inhibited the increased responses of valve SMCs but had no effect on nonvalve SMCs. Exogenous FGF2 increased migration of valve but not of nonvalve SMCs. Unlike in the isolated, cultured cells, blockade of FGF2 in the tissue explants did not block migration of valve or nonvalve SMCs from the explants. Thirty-seven genes were differentially expressed by valve compared with nonvalve intimal-medial tissue (11 veins). Peptide-mediated inhibition of SEMA3A, one of the differentially expressed genes, increased the number of migrated SMCs of valve but not of nonvalve explants.

CONCLUSIONS

Valve compared with nonvalve SMCs have greater rates of migration and proliferation, which may in part explain the propensity for pathologic lesion formation in valves. Whereas FGF2 mediates these effects in cultured SMCs, the mediators of these stimulatory effects in the valve wall tissue remain unclear but may be among the differentially expressed genes discovered in this study. One of these genes, SEMA3A, mediates a valve-specific inhibitory effect on the injury response of valve SMCs.

Nerve-perivascular fat communication as a potential influence on the performance of blood vessels used as coronary artery bypass grafts

Perivascular fat, the cushion of adipose tissue surrounding blood vessels, possesses dilator, anti-contractile and constrictor actions. The majority of these effects have been demonstrated in vitro and may depend on the vessel and/or the experimental method or species used. In general, the relaxant effect of perivascular adipose tissue is local and may be either endothelium-dependent or endothelium-independent. However, nerve stimulation studies show that, in general, perivascular adipose tissue (PVAT) has an anti-contractile vascular effect likely to involve an action of the autonomic vascular nerves. Apart from a direct effect of perivascular fat-derived factors on bypass conduits, an interaction with a number of neurotransmitters and other agents may play an important role in graft performance. Although the vascular effects of PVAT are now well-established there is a lack of information regarding the role and/or involvement of peripheral nerves including autonomic nerves. For example, are perivascular adipocytes innervated and does PVAT affect neuronal control of vessels used as grafts? To date there is a paucity of electrophysiological studies into nerve-perivascular fat control. This review provides an overview of the vascular actions of PVAT, focussing on its potential relevance on blood vessels used as bypass grafts. In particular, the anatomical relationship between the perivascular nerves and fat are considered and the role of the perivascular-nerve/fat axis in the performance of bypass grafts is also discussed.

Comparison of tissue processing methods for microvascular visualization in axolotls

The vascular system, the pipeline for oxygen and nutrient delivery to tissues, is essential for vertebrate development, growth, injury repair, and regeneration. With their capacity to regenerate entire appendages throughout their lifespan, axolotls are an unparalleled model for vertebrate regeneration, but they lack many of the molecular tools that facilitate vascular imaging in other animal models. The determination of vascular metrics requires high quality image data for the discrimination of vessels from background tissue. Quantification of the vasculature using perfused, cleared specimens is well-established in mammalian systems, but has not been widely employed in amphibians. The objective of this study was to optimize tissue preparation methods for the visualization of the microvascular network in axolotls, providing a basis for the quantification of regenerative angiogenesis. To accomplish this aim, we performed intracardiac perfusion of pigment-based contrast agents and evaluated aqueous and non-aqueous clearing techniques. The methods were verified by comparing the quality of the vascular images and the observable vascular density across treatment groups. Simple and inexpensive, these tissue processing techniques will be of use in studies assessing vascular growth and remodeling within the context of regeneration. Advantages of this method include:

•

Higher contrast of the vasculature within the 3D context of the surrounding tissue

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Enhanced detection of microvasculature facilitating vascular quantification

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Compatibility with other labeling techniques

News in Pathogenesis of Chronic Venous Insufficiency

This review article is concentrating on the news in the pathophysiology of chronic venous insufficiency (CVD). Despite ongoing progress in understanding the molecular aspects of CVD the exact mechanism of its development remains unclear. Many different factors may play role in the pathogenesis of CVD, including changes in hydrostatic pressure, valvular incompetence, increased capillary permeability, endothelial dysfunction, activation of leukocytes, deep venous obstruction, capillary microthrombosis, ineffective function of calf muscle pump, biochemical and structural changes in the vessel wall, extracellular matrix alteration, and several other mechanisms. A better understanding of the pathophysiology is an important step in the finding of new potential treatment.

Scavenger receptor class A member 5 (SCARA5) and suprabasin (SBSN) are hub genes of coexpression network modules associated with peripheral vein graft patency

OBJECTIVE

Approximately 30% of autogenous vein grafts develop luminal narrowing and fail because of intimal hyperplasia or negative remodeling. We previously found that vein graft cells from patients who later develop stenosis proliferate more in vitro in response to growth factors than cells from patients who maintain patent grafts. To discover novel determinants of vein graft outcome, we have analyzed gene expression profiles of these cells using a systems biology approach to cluster the genes into modules by their coexpression patterns and to correlate the results with growth data from our prior study and with new studies of migration and matrix remodeling.

METHODS

RNA from 4-hour serum- or platelet-derived growth factor (PDGF)-BB-stimulated human saphenous vein cells obtained from the outer vein wall (20 cell lines) was used for microarray analysis of gene expression, followed by weighted gene coexpression network analysis. Cell migration in microchemotaxis chambers in response to PDGF-BB and cell-mediated collagen gel contraction in response to serum were also determined. Gene function was determined using short-interfering RNA to inhibit gene expression before subjecting cells to growth or collagen gel contraction assays. These cells were derived from samples of the vein grafts obtained at surgery, and the long-term fate of these bypass grafts was known.

RESULTS

Neither migration nor cell-mediated collagen gel contraction showed a correlation with graft outcome. Although 1188 and 1340 genes were differentially expressed in response to treatment with serum and PDGF, respectively, no single gene was differentially expressed in cells isolated from patients whose grafts stenosed compared with those that remained patent. Network analysis revealed four unique groups of genes, which we term modules, associated with PDGF responses, and 20 unique modules associated with serum responses. The "yellow" and "skyblue" modules, from PDGF and serum analyses, respectively, correlated with later graft stenosis (P = .005 and P = .02, respectively). In response to PDGF, yellow was also associated with increased cell growth. For serum, skyblue was also associated with inhibition of collagen gel contraction. The hub genes for yellow and skyblue (ie, the gene most connected to other genes in the module), scavenger receptor class A member 5 (SCARA5) and suprabasin (SBSN), respectively, were tested for effects on proliferation and collagen contraction. Knockdown of SCARA5 increased proliferation by 29.9% ± 7.8% (P < .01), whereas knockdown of SBSN had no effect. Knockdown of SBSN increased collagen gel contraction by 24.2% ± 8.6% (P < .05), whereas knockdown of SCARA5 had no effect.

CONCLUSIONS

Using weighted gene coexpression network analysis of cultured vein graft cell gene expression, we have discovered two small gene modules, which comprise 42 genes, that are associated with vein graft failure. Further experiments are needed to delineate the venous cells that express these genes in vivo and the roles these genes play in vein graft healing, starting with the module hub genes SCARA5 and SBSN, which have been shown to have modest effects on cell proliferation or collagen gel contraction.

Characterization of the vasa vasorum in the human great saphenous vein: a scanning electron microscopy and 3D-morphometry study using vascular corrosion casts

The vasa vasorum (VV) of explanted segments of the human great saphenous vein (Vena saphena magna; HGSV), harvested during dissection for coronary bypass grafts or diseased vein segments from the "Salzburger Landesklinikum," were studied by scanning electron microscopy and three-dimensional morphometry of microvascular corrosion casts. The main objective of this study was to examine the VV's structural arrangement in order to find the most vital segments of the HGSV and in turn to improve the results of coronary bypass surgeries. The study presents a meticulous analysis of the whole microvascular system of the VV of the HGSV and its three-dimensional arrangement. It is one of the first studies yielding detailed quantitative data on geometry of the VV of the HGSV. A detailed insight into different vascular parameters such as vessel diameter, interbranching, intervascular distances, and branching angles at different levels of the VV's angioarchitecture and in different parts of the HGSV in health and disease is given. Further, the geometry of bifurcations was examined in order to compute the physiological optimality principles of this delicate vascular system based on its construction, maintenance, and function.

Distribution of orientation of smooth muscle bundles does not change along human great and small varicose veins

Wall remodeling in varicose veins is associated with hypertrophy of subendothelial tissue, increase in inner diameter, wrinkling and invagination of the endothelial layer. Due to structural alterations of the wall, the smooth muscle cells (SMCs) change their original circular and longitudinal orientations. Our aim was to quantify the volume fraction of circularly, longitudinally and obliquely oriented SMCs within both the inner and outer half of the wall of 11 great saphenous varicose veins and five small saphenous varicose veins. Using stereological methods applied on cross-sections of the vessels regularly gained each 5 cm along the vessel we determined the wall thickness (846 ± 319 μm, mean ± standard deviation), the volume fraction of circular SMCs in the inner (0.19 ± 0.13) and outer (0.06 ± 0.06) layers, the volume fraction of longitudinal SMCs in the inner (0.06 ± 0.05) and outer (0.05 ± 0.04) layers, the volume fraction of oblique SMCs in the inner (0.15 ± 0.08) and outer (0.09 ± 0.08) layers, and the total volume fraction of SMCs in the inner (0.4 ± 0.1) and outer (0.21 ± 0.09) layers. The volume fraction of SMCs with circular and oblique but not with longitudinal orientation was greater in the inner layer compared to the outer layer. The SMC orientation distribution was uniform along the varicose saphenous veins. With increasing wall thickness, the volume fraction of longitudinal and oblique SMC bundles increased in both layers at the expansion of circular SMC bundles. The main differences in the orientation of the SMCs in the inner and outer wall layers should be taken into account when computational modeling of varicose saphenous veins is attempted.

Vasa vasorum quantification in human varicose great and small saphenous veins

Recent research regarding saphenous vasa vasorum (VV) has focused on two main topics: the VV during varicogenesis in chronic venous insufficiency and the VV in saphenous grafts used in reconstructive vascular surgery. Our aim has been (i) to establish a technique for the histological quantification of the VV in human varicose great and small saphenous veins and (ii) to describe the density and distribution of the vasa vasorum within varicose veins. Great (n=11) and small (n=5) saphenous veins (length, 15-40cm) were collected from 12 patients who were undergoing venous stripping due to chronic venous insufficiency (Clinical-Etiology-Anatomy-Pathophysiology class 2-3). The veins were divided into 5-cm long segments. In total, 92 tissue blocks were collected to trace the variability of the density and distribution of the vasa vasorum in the proximo-distal direction. The endothelium was detected by immunohistochemistry using the von Willebrand factor. We quantified the number of microvessel profiles per section area and the relative distance of the microvessels from the outer border of the adventitia. The VV did not exhibit a preferential orientation in the varicose veins. VV density profiles were highest in the middle third of the venous wall and lowest in the inner third of the venous wall. Both the density and distribution of VV were uniform along the veins, and no differences were observed between the great and small saphenous veins. The VV density was statistically independent of the relative distance from the adventitia. The usability of this technique for perioperative frozen sections remains to be tested.

Varicose veins: role of mechanotransduction of venous hypertension

Varicose veins affect approximately one-third of the adult population and result in significant psychological, physical, and financial burden. Nevertheless, the molecular pathogenesis of varicose vein formation remains unidentified. Venous hypertension exerted on veins of the lower extremity is considered the principal factor in varicose vein formation. The role of mechanotransduction of the high venous pressure in the pathogenesis of varicose vein formation has not been adequately investigated despite a good progress in understanding the mechanomolecular mechanisms involved in transduction of high blood pressure in the arterial wall. Understanding the nature of the mechanical forces, the mechanosensors and mechanotransducers in the vein wall, and the downstream signaling pathways will provide new molecular targets for the prevention and treatment of varicose veins. This paper summarized the current understanding of mechano-molecular pathways involved in transduction of hemodynamic forces induced by blood pressure and tries to relate this information to setting of venous hypertension in varicose veins.

Morphological study on microvasculature of left ventricular wall in infant and adult yaks

Observations on the microvasculature in the left ventricular wall of infant and adult yaks under light and scanning electron microscope (SEM) were presented. Moreover, the diameter of different microvasculature and the density of the capillaries in three layers of the ventricular myocardium were measured using Image Pro-Plus 5.0. The results showed that the average luminal diameter of arterioles and precapillary arterioles in adult yak's hearts were, in most cases, larger than those in infant yaks. On the contrary, the diameters of the capillary in infant yak's hearts were larger than those in adult yaks. The density of capillary in the myocardium of adult yak's heart had significantly higher values (P<0.01) than those in infant yaks. Arterioles of yak's hearts were characterized by the bark-like structure and the impressions of endothelial cell nuclei, and it always gave rise to capillary after three to four grades of embranchment. The outer surface of capillaries cast in infant yak's hearts was smooth, and no constrictions were found. This was different from adult yak that always had some constrictions. The capillary anastomosis of "H" and "Y" usually existed in the myocardium of both adult and infant yaks; however, those in infant yaks were not typical as in adult yaks in their shape. The peculiar arrangement of the venules in infant yak was a "baggy" or "bulgy" arrangement, while in the adult yak, they had a root-like pattern. Our findings suggest that the patterns of microvasculature in yak's heart could be propitious to adapt better in their environment following their increase of age.

Blood vessels of the normal and pathologically changed wall of the human vena saphena magna

The vascular supply of the wall of human vena saphena magna was qualitatively studied by the use of several morphological methods on both normal and pathologically changed veins. The material was obtained from patients undergoing aortocoronary bypass or surgery of the varices, and material from cadavers. Under physiological conditions, the wall of vena saphena magna is supplied by delicate system of vasa vasorum, organized in a form of feeding vessels branched into an irregular loose adventitial mesh and continuing further as a microcirculatory network supplying the two outer thirds of the media. Small local dilatations and tortuosities of adventitial veins were found on heavy varicose veins. Slight increase of vasa vasorum growing into the innermost layer of media was detected, but the hyperplastic intima remained avascular. In patients with recurrent varices or with vein thrombophlebitis intimal hyperplasia, degradation of media and thrombosis, were found. Apparent massive increase of vasa vasorum growing into the whole media, hyperplastic intima and into the organizing thrombi, were regularly observed. The increase of vasa vasorum is a part of the complex of pathophysiological reactions of the vein wall on the hypoxia developing during the most serious pathological changes, and not as the primary varicogenic factor. The vascular supply of the wall of the human vena saphena magna was qualitatively studied by the use of several morphological methods on both normal and pathologically changed veins. The material was obtained from patients undergoing aortocoronary bypass grafting or surgery of varices, as well as materials from cadavers. Under physiological conditions the wall of vena saphena magna is supplied by a delicate system of vasa vasorum. It is organized in a form of feeding vessels branched into an irregular loose adventitial mesh, which continues further as a microcirculatory network supplying the outer two thirds of the media. Small local dilatations and tortuosities of adventitial veins were found on severe varicose veins. A slight increase of the vasa vasorum growing into the innermost layer of media was detected, but the hyperplastic intima remained avascular. In patients with recurrent varices or vein thrombophlebitis, intimal hyperplasia, degradation of media and thrombosis, were found. It was regularly observed that there was an apparent, massive increase of the vasa vasorum growing into the entire media, hyperplastic intima, and into the organizing thrombi. The increase of the vasa vasorum is due to the pathophysiological reaction of the vein wall as a result of hypoxia, which develops during the most serious pathological changes. The increase is not the primary varicogenic factor.