Hemodynamic changes occurring during the progressive enlargement of abdominal aortic aneurysms.

The purpose of this study is to characterize the evolution of the hemodynamic forces acting on the arterial walls at progressive stages of enlargement of abdominal aortic aneurysms (AAA). The specific aims are twofold: first, to determine the magnitude of the "wall shear stresses" (WSS) and their spatial and temporal gradients at various stages of enlargement, and second, to identify the critical size at which the formation of regions of stasis and/or the transition to a turbulent state occur inside the AAA. A parametric in vitro study of the pulsatile blood flow was conducted in rigid models of AAA by systematically varying the hemodynamic conditions and the size of the aneurysm. The instantaneous flow characteristics inside the AAA models were measured along the cardiac cycle, using tomographic digital particle image velocimetry (TDPIV). The TDPIV measurements showed that even for the case of large dilatation ratios (internal diameter >4.5 mm), the flow inside the AAA remained fully attached to the walls during systole, but massively detached during diastole. A critical aneurysm aspect ratio (length-to-diameter ratio) was found, for which a transition to a turbulent state occurred. The formation of internal shear layers (internal jet) and slowly recirculating regions (stasis) generated large spatial gradients of WSS and regions of low and oscillating WSS. The formation of regions of flow stasis was observed even at very early stages in the aneurysm enlargement. These spatial and temporal variations in the hemodynamic forces, the formation of regions of stasis, and the transition to turbulence are postulated to play an important role in the etiology of the disease by activating endoluminar thrombus formation, lipid deposition, and certain inflammatory mechanisms.

Carotid arteries: contrast-enhanced US angiography--preliminary clinical experience.

B-mode ultrasonographic (US) angiography enhanced with a microbubble-based US contrast agent (FS069) was evaluated in human subjects with carotid artery disease. Results at contrast material-enhanced US angiography and duplex US were compared with those at conventional angiography. Both US angiography and duplex US accurately depicted stenoses of 70% or more compared with those depicted at conventional angiography. The percentage diameter stenosis of the internal carotid artery measured at US angiography strongly correlated with that measured at conventional angiography (r = 0.988). The percentage area stenosis measured at US angiography strongly correlated with ex vivo measurements of the resected carotid plaque at magnetic resonance imaging (r = 0.979). US angiography depicted unsuspected wall irregularities, ulceration, and dissection.

Surgical and endovascular treatment of lower extremity venous insufficiency.

Lower extremity venous insufficiency is a highly prevalent condition. Now it is understood that telangiectasias, reticular varicosities, and true varicose veins are physiologically similar and etiologically identical. The four main influences causing these abnormalities are heredity, female sex, gravitational hydrostatic forces, and hemodynamic muscular compartment pressure. There are clear indications and goals for intervention. A cornerstone in the treatment of venous insufficiency is elimination of sources of venous hypertension. One of these is the refluxing greater saphenous vein. Minimally invasive saphenous ablation can be achieved by radiofrequency energy and laser light energy. These new techniques eliminate the psychologic barrier to treatment caused by the term "stripping" and allow the objectives of surgery to be achieved with minimal invasion and quick recovery. Endovenous techniques show great promise. They provide minimal invasion, often under local anesthesia and intravenous sedation, thereby eliminating the need for general anesthesia. Objectives of venous insufficiency have been established and the endoluminal minimally invasive techniques developed in recent years appear to accomplish their goals.

Early experience using the Wallgraft in the management of distal microembolism from common iliac artery patholology.

Blue toe syndrome commonly occurs as a result of aneurysmal or atherosclerotic disease in the iliac arteries. Surgery, angioplasty, or intraarterial stent placement are the most common treatment options but the optimal management has not been defined. Here we report managing distal microembolization from iliac artery atherosclerosis associated with aneurysmal dilation with the Wallgraft Endoprosthesis, a self-expanding metallic stent covered with Dacron. Three common iliac arteries in two patients were treated using this device. A 79-year-old male presented with unilateral symptoms and an 83-year-old female with bilateral disease. Arteriography demonstrated complex plaque at the aortic bifurcation associated with aneurysmal dilation of the distal common iliac artery in both patients. This complex disease was successfully covered using the Wallgraft Endoprosthesis. Postoperatively the patients received aspirin, their toe lesions healed, and neither has had a recurrence after 16 months. Covered stents offer the theoretic advantage of completely excluding the diseased segment, preventing the escape of thrombus or plaque debris, and covering aneurysmal dilation in the artery.

Small-caliber mesothelial cell-layered polytetraflouroethylene vascular grafts in New Zealand white rabbits.

Reduction in the thrombogenicity of small-caliber synthetic vascular grafts by lining them with mesothelial cell has been suggested as a method to reduce thrombosis. The purpose of this research is to determine whether creation of a mesothelial lining on the inner surface of a synthetic vascular graft would improve the patency rate of a small-caliber vascular grafts. Carotid interposition grafting was performed using mesothelial-lined grafts (MLG) in 30 New Zealand rabbits and compared with similar carotid interposition grafts using non-mesothelial-lined grafts (NLG) on the contralateral side. The mesothelial lining was created by suturing a piece of harvested peritoneum with the visceral surface toward the lumen onto a 2-mm polytetraflouroethylene (PTFE) graft. Graft patency was studied by in vivo Dopler. In vitro evaluations were done with hematoxylin-eosin stains, broadband cytokeratin staining, and monoclonal antibodies for macrophages. Explanation of the grafts was done in terminal operation at 7, 14, and 21 days. The MLG showed progressive fibroblastic proliferation in direct proportion to the age of the graft, but this did not lead to graft occlusion. However, a significant number of NLG were not patent at each time period studied. We concluded that mesothelial cell lining of smallcaliber PTFE grafts could enhance the short-term patency more than using the PTFE without the mesothelial lining. The use of such hybrid small-caliber grafts has a potential for improving the patency of these artificial vascular graft substitutes.