Exposure to thrombus diminishes endothelial derived relaxation in the rabbit carotid artery.

PURPOSE: Thrombus is believed to be deleterious to intimal function. However, few studies have directly examined this effect. This study examines the effect of thrombus on endothelial-dependent and -independent vasorelaxation in the rabbit carotid artery. METHODS: Twelve male New Zealand white rabbits (3.5-4.5 kg) were divided into two groups of six. Thrombosis was induced in group I by segmental right carotid artery ligation. Group II underwent segmental right carotid ligation immediately followed by removal of thrombus with normal saline flush through an arteriotomy. The left carotid arteries were exposed in both groups and served as internal controls. After 4 h, left and right carotid arteries were harvested, sectioned into 6-mm rings, and mounted on isometric force transducers in a physiologic bath. Thrombus was removed from the arteries in group I during the ring preparation process. Neither group I nor group II had thrombus in contact with endothelium during ex vivo testing. The arterial rings were constricted with norepinephrine (1 x 10(-4) M). Endothelium-dependent and -independent vasorelaxation to acetylcholine (Ach) and s-nitrosoacetylpenicillamine, respectively, were measured in a dose-response manner. Results were expressed as a percentage of vasorelaxation. Statistical analysis was performed using an analysis of variance. RESULTS: Endothelial-dependent vasorelaxation, which tests for endothelial cell function, was decreased in the thrombus and endothelial ischemia group (I) compared to control as noted by vasorelaxations of 22% vs 34% at 1 x 10(-4) molar concentration Ach, and 33% vs 48% at 1 x 10(-3) molar concentration Ach, respectively (P = 0.05). By comparison, there was no difference in the endothelial-dependent vasorelaxation of the endothelial ischemia group (II) versus control. Endothelial-independent vasorelaxation, which tests for smooth muscle function, was not affected by either the thrombus and endothelial ischemia group (I) or the endothelial ischemia group (II) compared to the control group. The controls in group I and group II were slightly different. When this difference was removed, the resulting comparison of treatments in group I and group II approached significance at molar concentrations of 1 x 10(-4), 1 x 10(-5), and 1 x 10(-6) (P = 0.07, 0.06, 0.06). CONCLUSIONS: The presence of thrombus within the rabbit carotid artery for a period of 4 h decreases endothelial-dependent relaxation. Four hours of endothelial ischemia without thrombus did not change endothelial-dependent vasorelaxation. Neither thrombus nor ischemia alone had any effect on the endothelium-independent vasorelaxation. We conclude that thrombus is deleterious to endothelial function independent of smooth muscle function in the acute setting as measured by endothelial-dependent vasorelaxation.

A parallel architecture for discrete relaxation algorithm.

Discrete relaxation techniques have proven useful in solving a wide range of problems in digital signal and digital image processing, artificial intelligence, operations research, and machine vision. Much work has been devoted to finding efficient hardware architectures. This paper shows that a conventional hardware design for a Discrete Relaxation Algorithm (DRA) suffers from O(n2m3) time complexity and O(n2m2) space complexity. By reformulating DRA into a parallel computational tree and using a multiple tree-root pipelining scheme, time complexity is reduced to O(nm), while the space complexity is reduced by a factor of 2. For certain relaxation processing, the space complexity can even be decreased to O(nm). Furthermore, a technique for dynamic configuring an architectural wavefront is used which leads to an O(n) time highly concurrent DRA3 architecture.

Intraoperative fibrinolytic therapy: experimental evaluation.

Percutaneous intra-arterial infusion of fibrinolytic agents has emerged as an alternative to embolectomy in selected patients with acute arterial occlusions. The combination of fibrinolytic therapy and embolectomy may be superior to either modality alone. This experiment was designed to determine safety and efficacy of intraoperative fibrinolytic therapy as an adjunct to catheter embolectomy. Forty hind limbs in 20 adult mongrel dogs were embolized with thrombus created in vitro. After 24 hours, bilateral transfemoral embolectomy was followed by intra-arterial, intraoperative infusion. Fifteen limbs (control) received 250 ml of saline solution during a 30-minute period; 25 limbs (experimental) received an arterial infusion of 60,000 units of streptokinase during a 30-minute period (SK 30'). In five limbs of each group, 500 units of heparin (H) was added. In five experimental limbs the streptokinase infusion time was increased to 60 minutes (SK 60'). Arteriograms and blood flow measurements were obtained before and after embolectomy (PE) and after infusion (PI); the results were compared. Improvement between the PE and PI angiograms was seen in 20% (3 of 15 dogs) of control subjects. In contrast, improvement after the infusion was evident in 100% (5 of 5 dogs) of dogs given SK plus H 30' (p less than 0.01), in 80% (12 of 15 dogs) of dogs given SK 30' (p less than 0.01), and in 20% (1 of 5 dogs) of dogs given SK 60'. A trend toward increased blood flow was noted in the experimental group. There were no intraoperative complications with hemostasis or postoperative bleeding (36-hour observation). We conclude that intraoperative fibrinolytic therapy in dogs is safe and effective as an adjunct to thromboembolectomy. A human clinical trial is recommended.

Efficient 3-d object representations for industrial vision systems.

The representation of 3-D objects is an important step in solving many problems in scene analysis. One of the most successful techniques is that based on the surfaces of objects. We describe several methods for obtaining such surface representations from various types of intrinsic images. In particular, previous work is reviewed and an algorithm based on region growing is investigated in terms of its efficiency in segmenting a set of points in 3-D space into planar faces. Information on the neighborhood structure of the points in the form of a spatial proximity graph is used to direct the segmentation. Applications to industrial objects are demonstrated.

Hierarchical constraint processes for shape analysis.

A major application of syntactic pattern recognition is the analysis of two-dimensional shape. This paper describes a new syntactic shape analysis technique which combines the constraint propagation techniques which have been so successful in computer vision with the syntactic representation techniques which have been successfully applied to a wide variety of shape analysis problems. Shapes are modeled by stratified shape grammars. These grammars are designed so that local constraints can be compiled from the grammar describing the appearance of pieces of shape at various levels of description. Applications to the analysis of airplane shapes are presented.