Diffusional support of arteries

Updates in aortic wall pathology

Several studies have investigated the pathogenesis of aortic wall abnormalities such as aortic dissection or aneurysm; however, the comprehensive pathological in situ event involved in the development of the disease is not understood well. The vasa vasorum form a network of capillaries or venules around the adventitia and outer media, which play an important role in the aortic wall structure and function. Impairment of their function may induce tissue hypoxia, impede the transfer of cellular nutrients, and cause aortic medial degeneration, which is considered the major predisposing factor to this aortic wall pathology. This review updates our understanding of the pathological changes in the aortic media and vasa vasorum of patients with aortic dissection and aortic aneurysm.

Ascending aorta of hooded seals with particular emphasis on its vasa vasorum

The pressure-volume relationship in the ascending aorta (“windkessel”) of the hooded seal was determined and the morphology of its vasa vasorum described in some detail. We found that the ascending aorta has a high compliance and can easily accommodate the entire stroke volume when the peripheral vascular resistance becomes much increased and maintain perfusion pressure during the much extended diastole and thereby reduce cardiac stroke work during diving. We also found that the 3- to 5-mm thick wall of the ascending aorta had a very elaborate vasa vasorum interna with a hitherto undescribed vascular structure that penetrates the entire vascular wall. If similar structures with similar importance for the nutrition of the wall of the vessel are found in humans, important implications for the understanding of pathological conditions, such as aneurisms, may be indicated.

Quantification of Adventitial Vasa Vasorum Vascularization in Double-injury Restenotic Arteries

BACKGROUND

Accumulating evidence indicates a potential role of adventitial vasa vasorum (VV) dysfunction in the pathophysiology of restenosis. However, characterization of VV vascularization in restenotic arteries with primary lesions is still missing. In this study, we quantitatively evaluated the response of adventitial VV to vascular injury resulting from balloon angioplasty in diseased arteries.

METHODS

Primary atherosclerotic-like lesions were induced by the placement of an absorbable thread surrounding the carotid artery of New Zealand rabbits. Four weeks following double-injury induced that was induced by secondary balloon dilation, three-dimensional patterns of adventitial VV were reconstructed; the number, density, and endothelial surface of VV were quantified using micro-computed tomography. Histology and immunohistochemistry were performed in order to examine the development of intimal hyperplasia.

RESULTS

Results from our study suggest that double injured arteries have a greater number of VV, increased luminal surface, and an elevation in the intima/media ratio (I/M), along with an accumulation of macrophages and smooth muscle cells in the intima, as compared to sham or single injury arteries. I/M and the number of VV were positively correlated (R2 = 0.82, P < 0.001).

CONCLUSIONS

Extensive adventitial VV neovascularization occurs in injured arteries after balloon angioplasty, which is associated with intimal hyperplasia. Quantitative assessment of adventitial VV response may provide insight into the basic biological process of postangioplasty restenosis.

Recanalisation of the internal carotid artery via the vasa vasorum after coil occlusion

Antegrade recanalisation of a completely occluded internal carotid artery (ICA) via the vasa vasorum is extremely rare. Here, we report such a case after proximal endovascular coiling in a case of dissected (i.e. non-atherosclerotic) ICA. A 42-year-old man presented with thromboembolic stroke of the left frontal lobe owing to pseudo-occlusion of the left ICA manifesting as motor aphasia and right hemiparesis. There were abundant floating thrombi in the petrous portion of the left ICA. Because of good collateral flow in the left middle cerebral artery territory through the anterior communicating artery and external carotid artery system, endovascular coil embolisation of the left ICA was performed for prevention of further thromboembolic stroke. The patient showed progressive recovery following endovascular treatment, and was discharged with mild right hemiparesis 1 month later. He maintained a regimen of aspirin and physical rehabilitation. At follow-up, 38 months later, the patient was asymptomatic. Angiography demonstrated occlusion of the left ICA and multiple serpiginous vessels originating from the proximal internal and external carotid arteries and which filled the ICA distal to the occlusion. This case suggests that an ICA occluded by proximal coil embolisation-even in a non-atherosclerotic case-might be recanalised via the vasa vasorum.

Quantification of plaque neovascularization using contrast ultrasound: a histologic validation

AIMS

The density of vasa vasorum within atherosclerotic plaque correlates with histologic features of plaque vulnerability in post-mortem studies. Imaging methods to non-invasively detect vasa vasorum are limited. We hypothesized that contrast ultrasound (CUS) can quantify vasa vasorum during atherosclerosis progression.

METHODS AND RESULTS

New Zealand white rabbits received a high-fat diet for 3 weeks, and bilateral femoral artery stenosis was induced by balloon injury. Contrast ultrasound femoral imaging was performed at baseline and 2, 4, and 6 weeks post injury to quantify adventitial videointensity. At each imaging time point 10 vessels were sectioned and stained with haematoxylin and eosin and von-Willebrand factor. Adventitial vasa vasorum density was quantified by counting the number of stained microvessels and their total cross-sectional area. Plaque size (per cent lumen area) progressed over time (P < 0.001), as did adventitial vasa vasorum density (P < 0.001). Plateau peak videointensity also progressed, demonstrating a strong linear correlation with histologic vasa vasorum density (P < 0.001). Receiver operating characteristic analysis indicated that a three-fold increase in median adventitial videointensity had a sensitivity of 100% and specificity of 88% for predicting abnormal neovascularization.

CONCLUSION

We have histologically validated that CUS quantifies the development of adventitial vasa vasorum associated with atherosclerosis progression. This imaging technique has the potential for characterizing prognostically significant plaque features.

Role of vasa vasorum in transendothelial solute transport in the coronary vessel wall: a study with cryostatic micro-CT

Using cryostatic microscopic computed tomography (micro-CT), we sought to determine the role of coronary vasa vasorum (VV) in transendothelial solute transport in arteries with normal and increased permeability due to high plasma cholesterol levels. In 6-mo-old pigs on a normal (n=23) and 2% high cholesterol (HC) diet (n=8), 2-cm segments of the proximal left anterior descending coronary arteries were removed in vivo after a selective injection of X-ray contrast solution. Harvesting of the specimens occurred at 0, 15, 25, 35, or 45 s after completion of the contrast injection. Specimens were snap frozen and scanned in our cryostatic micro-CT. The spatial distribution of contrast in the coronary artery wall was quantified using the CT images. Right coronary arteries were infused with Microfil to determine VV density (VV/mm2) and the cumulative lumen surface area (mm2/mm3). Transendothelial diffusion of contrast into the coronary vessel wall is a dynamic process starting at both the subintima and the adventitia. The subintimal opacification moves as a wave toward the adventitia, whereas the adventitial wave resolves. The coronary vessel wall in animals on a HC diet shows higher opacification than in normal coronary arteries without an increase of VV total luminal surface area. The loss of endothelial integrity in hypercholesterolemia significantly alters VV solute washin to, and washout from, the coronary artery wall.

Enhanced coronary vasa vasorum neovascularization in experimental hypercholesterolemia

Coronary arteries contain a network of vasa vasorum in the adventitia. The three-dimensional anatomy of the vasa vasorum in early coronary atherosclerosis is unknown. This study was designed to visualize and quantitate the three-dimensional spatial pattern of vasa vasorum in normal and experimental hypercholesterolemic porcine coronary arteries, using a novel computed tomography technique. Animals were killed after being fed either a high cholesterol diet (n = 4) or a control diet (n = 4) for 12 wk. The proximal left anterior descending coronary artery was removed from the heart, scanned, and reconstructed, and quantitation of vasa vasorum density was performed. Two different types of vasa vasorum were defined: first-order vasa vasorum ran longitudinally parallel to the vessel and second-order originated from first-order vasa circumferentially around the vessel wall. Compared with controls in hypercholesterolemic coronary arteries, there was a significant increase in the area of the vessel wall (3.86+/-0.22 vs. 8.07+/-0.45 mm2, respectively, P < 0.01) and in the density of vasa vasorum (1. 84+/-0.05/mm2 vs. 4.73+/-0.24/mm2; respectively, P = 0.0001). This occurred especially by an increase of second-order vasa vasorum and disorientation of normal vasa vasorum spatial pattern. This study suggests that adventitial neovascularization of vasa vasorum occurs in experimental hypercholesterolemic coronary arteries and may be a part of the early atherosclerotic remodeling process.

Effects of aortic pressure and vasoactive agents on the vascular resistance of the vasa vasorum in canine isolated thoracic aorta

1. We have developed a new preparation for continuously measuring changes in vascular resistance of the vasa vasorum of the canine isolated thoracic aorta perfused at a constant flow rate with Krebs-bicarbonate solution. 2. An increase of more than 150 mmHg in aortic pressure caused a significant increase in the vascular resistance of the vasa vasorum. 3. 5-Hydroxytryptamine (5-HT), noradrenaline (NA), adrenaline and dopamine caused dose-dependent increases in the vascular resistance of the vasa vasorum. The decreasing order of potency in the vasoconstrictor responses was as follows: 5-HT >> NA = adrenaline >> dopamine. The 5-HT- and adrenaline-induced vasoconstrictor responses were inhibited by methysergide and by phentolamine plus propranolol, respectively. 4. Acetylcholine (ACh), isoprenaline (ISP), histamine (His), ATP, ADP and adenosine produced dose-related decreases in the vascular resistance of aortic vasa vasorum perfused with the Krebs solution containing 10(-5) M-NA. The decreasing order of potency in the response was as follows: ACh = ISP > His >> adenosine = ATP = ADP. The ACh-, ISP- and His-induced vasodilator responses were antagonized by atropine, propranolol and famotidine, respectively. 5. The results suggest that the preparation described is useful for studying the regulation of vascular resistance of aortic vasa vasorum and that aortic pressure and vasoactive compounds may directly regulate the vascular resistance of the vasa vasorum in canine isolated thoracic aorta.