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Biomedical subjects

A D Callow

Publications and source records attributed to A D Callow.

123 records · Page 7Linked to original sources
PubMedDate not supplied

New graft materials and current approaches to an acceptable small diameter vascular graft.

Prosthetic graft material has not been successful for small artery bypass. Mechanical, cellular, and humoral factors have all been implicated as a cause of failure. In vitro, ex vivo, and in vivo methods have been developed to assess platelet and fibrinogen deposition, measure compliance, and study other factors theorized to relate to graft failure. Cell culture techniques have been used to determine the role of cellular mitogens. The goal of an arterial substitute that can maintain patency in a 3-4 mm diameter low-flow configuration and that is not associated with the development of anastomotic hyperplasia has yet to be reached. A variety of solutions are being researched. New nonthrombogenic polymers are being tested as are new coatings for standard materials. Endothelial cell seeding has been accomplished in animals and is being tried in human clinical studies. Problems and results of endothelial seeding trials are reviewed. Other biologic approaches include the in vitro construction of a blood vessel model using cell coculture techniques and the implantation of bioabsorbable prosthetics into animals. The role of pharmacologic agents in maintaining graft patency is addressed.

Animals↗
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EEG surveillance as a means of extending operability in high risk carotid endarterectomy.

Some patients who have transient ischemic attacks are denied operation because severe occlusive lesions in other extra-cranial arteries may be inappropriately interpreted as constituting an unacceptable surgical risk, or because the lesion is so distal as to make its removal hazardous. Failure of endarterectomy is usually due to incomplete removal of the lesion or to thrombosis upon the frayed intima. Such lesions require excellent visualization and meticulous surgical technique -- not always possible with a shunt. Among 130 consecutive carotid endarterectomies performed under general anesthesia, EEG changes consistent with cerebral ischemia appeared in only nine (7%). These patients required a shunt. In 11 patients normal EEG tracings were obtained during endarterectomy despite contralateral carotid occlusion. None of these patients had a neurological deficit. Continuous EEG monitoring is a reliable method of detecting changes in cerebral perfusion, permits a more meticulous endarterectomy in high-lying lesions without a shunt, and extends operability in high risk patients. Angiographical findings may be an unreliable predictor concerning risk of endarterectomy.

Aged↗
PubMedDate not supplied

Healing after arterial dilatation with radiofrequency thermal and nonthermal balloon angioplasty systems.

Thermal balloon angioplasty has been proposed as a means of reducing acute and delayed reclosure of arteries after percutaneous transluminal balloon angioplasty. A radiofrequency (rf) balloon catheter was used to perform thermal balloon angioplasty on canine arteries in vivo. The histologic appearance of rf-treated sites was compared with that of control sites treated by conventional percutaneous transluminal angioplasty. Acutely, rf-treated sites showed a reduced medial cellularity with preservation of internal elastic lamina except at the transitional zone between thermal injury and normal artery, where localized internal elastic lamina disruption was found. Nonthermal sites showed generalized disruption of internal elastic lamina and normal medial cellularity. Both thermal and nonthermal sites displayed a return of intimal cover commencing at 1 to 2 weeks and completed by 4 weeks. Diffuse myointimal hyperplasia appeared by 2 weeks after injury at breaks in the internal elastic lamina along the nonthermal vessels but was localized to the transitional zone in thermal injury sites. In rf-treated vessels, repopulation of the acellular thermally modified media had commenced by 4 weeks, and by 8 weeks the media was diffusely repopulated by spindle-shaped cells resembling smooth muscle cells lying between and aligned with preserved connective tissue laminae. Overall, the distribution and extent of the proliferative response after rf thermal balloon angioplasty were less than those seen after nonthermal balloon angioplasty. Thermal sites, which underwent reintimalization before medial cells returned, were considerably less prone to the development of myointimal hyperplasia. These results suggest that this modality may have beneficial effects on arterial healing after angioplasty.

Angiography↗
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Pulmonary emboli from blood-biomaterial interaction.

The problem of surface thrombosis and subsequent embolization remains entrenched as a yet incompletely surmounted barrier to the development of truly satisfactory intravascular prosthetic devices. A baboon ex vivo shunt was used to determine the interaction of Indium-111 platelets and potential biomaterials. The uptake of Indium-111 platelets was monitored continuously by gamma camera scanning. Several of the materials tested demonstrated a saw-toothed pattern of platelet activity, with accumulation followed by rapid decline. Neither PTFE nor Dacron exhibited this pattern. Post shunt scans of the animals' chests showed discrete foci of platelet activity in the lungs, corresponding to each embolic event noted on the material's scan. In conclusion, the search for a smooth surface as a blood material interface may produce a material which accumulates and then sloughs significant platelet aggregates. It is crucial that these materials be subjected to vigorous testing to determine their safety prior to initiation of clinical trials.

Animals↗
PubMedDate not supplied

Problems in the construction of a small diameter graft.

Hyperplasia at the graft host artery anastomosis is probably the commonest cause of intermediate and late failure and is seen most frequently and most severely in small diameter grafts. An arterial substitute with an internal diameter of less than 4 mm which can maintain patency in a flow rate not in excess of 50 cc per minute is the sought after graft. Contributing to the formation of this hyperplastic lesion are activated platelets, activated monocytes, dedifferentiated endothelial cells, and probably other elements which under these circumstances of activation produce smooth muscle cell and other mitogens. A multidisciplinary approach utilizing the information from polymer chemistry, fluid engineering, cell biology, and the essentials of thrombosis is required.

Biocompatible Materials↗
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Costs and benefits of prosthetic vascular surgery.

For a variety of reasons, primary amputation is often advised in the elderly individual with a severely ischemic leg. Reinforcing this recommendation is the perception that reconstructive arterial surgery in this group is far more expensive than the primary amputation. Living more than only one more year after amputation, professional nursing care cost approaches $100,000. In two recent studies, the cost for patients undergoing primary below the knee amputations plus rehabilitation was almost identical to the mean patient cost for arterial reconstruction. In addition, under the prospective payment systems, substantial financial loss accrues to hospitals caring for these patients.

Actuarial Analysis↗
PubMedDate not supplied

The effect of suture material on platelet deposition onto prosthetic material.

Previous studies have demonstrated the importance of employing prosthetic material with minimal thrombogenicity. However, the role of different suture materials in early thrombotic events on prosthetic materials has not been examined. Experiments were designed to analyze the effects of suture on platelet graft interaction using an in vivo baboon hemocompatability screen. 111Indium labeled, autologous platelet deposition was determined on expanded polytetrafluoroethylene (ePTFE) containing suture lines of polypropylene (Prolene), polybutester (Novafil), and ePTFE (Gore-Tex). A significant increase in platelet deposition was noted not only at the suture line, but proximal and distal to it as well. The results were different for each of the sutures employed and suggest that the suture line may influence early platelet deposition in the perianastomotic region, not only at the suture line, but proximally and distally as well.

Animals↗
PubMedDate not supplied

Restenosis after carotid artery surgery.

From an English language review and a review of the author's experience, the incidence of recurrent stenosis after carotid artery surgery is reported as varying from 0.5 to as high as 19%. Two types of lesions are identified: fibromuscular hyperplasia occurring after less than two years and secondary atherosclerosis beyond that period of time. The response to injury of the arterial wall is reviewed at the cellular level with speculations as to etiology of the lesions. Careful, thorough follow-up examination is strongly recommended.

Angiography↗