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Biomedical subjects

A J Carter

Publications and source records attributed to A J Carter.

86 records · Page 5Linked to original sources
PubMed1978

Axial length and the Hirschberg test.

Axial lengths of 30 eyes (15 subjects), measured by ultrasonography, ranged from 20.6--26.3 mm. Using a fixed light source, each eye was photographed as monocular fixation was changed over an 8-deg range in 2-deg steps. Hirschberg ratios obtained from the photographs show a low correlation with axial length (0.07), and the mean value, 24 prism diopters per millimeter (S.D. = 7), further supports recent recommendations that the traditional ratio of 12 or 14/1 be replaced by a more correct ratio of 22/1.

Adult↗
PubMedDate not supplied

The degree of neointimal formation after stent placement in atherosclerotic rabbit iliac arteries is dependent on the underlying plaque.

The purpose of this study was to determine the effects of stent placement on the underlying arterial morphology and the relations of stent-vessel wall interactions with subsequent neointimal formation in an atherosclerotic artery. Seven New Zealand White rabbits with experimentally induced atherosclerosis underwent balloon angioplasty (n = 7) and stent placement after balloon angioplasty (n = 7) in the iliac arteries. Histologic analysis of the treated arteries was performed at 28 days to assess device interactions with the artery and the pattern of the neointimal response. The area within the external elastic lamina of the stented vessels was 66% greater than the arteries with balloon angioplasty alone (p = 0.001) which contributed to a significantly greater late lumen area (3.33 +/- 0.51 mm2 versus 1.33 +/- 0.20 mm2, p = 0.0028). Neointimal thickness was measured at 220 stent wire sites from 21 sections of stented arteries of which 139 (63%) had underlying plaque and 81 (37%) were adjacent to normal media. Rupture of the internal elastic lamina (IEL) occurred at only 9 (11%) of the 81 stent wire sites over normal media. The mean neointimal thickness was 0.16 +/- 0.01 mm lor all stent wire sites. The neointimal thickness was greater at the stent wire sites with underlying plaque (0.23 +/- 0.01 min) than at the stent wire sites adjacent to normal media (0.08 +/- 0.01 mm) or at sites with rupture of the internal elastic lamina (0.16 +/- 0.02 mm, p = 0.0001). The degree of neointimal formation within the stents strongly correlated with the area of the underlying atherosclerotic plaque (r = 0.76, p = 0.0007) and the extent of plaque or medial compression by the struts (r = 0.90, p = 0.006). The present study characterizes stent interactions in a model commonly employed to evaluate novel therapies for the prevention of restenosis. The neointimal response was influenced by the local arterial morphology and correlated with the extent of plaque or medial compression by the stent. These data may be useful for future studies in this model and understanding the mechanism of in-stent restenosis.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Dose and dose rate effects of beta-particle emitting radioactive stents in a porcine model of restenosis.

BACKGROUND: Radioactive stents have been proposed as a means to prevent in-stent restenosis by inhibiting intimal proliferation with continuous low-dose irradiation. OBJECTIVES: The purpose of this study is to determine the effects of cumulative dose and dose-rate delivery on neointimal formation using 32P and 90Y beta-particle emitting radioactive stents in a porcine coronary model of restenosis. METHODS AND MATERIALS: We compared the late histologic results of 0.25 to 32.0 microCi 90Y (half-life 64 hours) (n = 64 stents) and 0.1 to 57.6 microCi 32P (half-life 14.3 days) (n = 55 stents) Beta-particle emitting radioactive stents with non-radioactive (n = 40) stents in a porcine coronary model of restenosis. A computer-based dosimetry modeling program was used to determine the 28 day cumulative dose and dose-rate delivery for the beta-particle emitting radioactive stents at a distance of 0.1 mm from the stent surface. RESULTS: Continuous low dose-rate (1 to 5 cGy/hr) radiation delivery for > 2 weeks via a 0.1 to 0.5 microCi 32P radioactive stent effectively reduced in-stent neointimal hyperplasia at 90 days. Cumulative doses of > 55 Gy induced severe adventitial fibrosis, microvascular damage and promoted the formation of a matrix-rich neointima. Delayed vascular repair was evident at focal regions within the body of radioactive stents that delivered cumulative doses of > or = 140 Gy at 28 days and cumulative doses of 1,100 Gy at 90 days. CONCLUSIONS: These data may be useful in predicting safe and effective dose and dose rate delivery for beta-particle emitting radioactive stents.

Animals↗
PubMedDate not supplied

Pathology of radiation-induced coronary artery disease in human and pig.

PURPOSE: External beam mediastinal radiation-induced accelerated coronary atherosclerotic heart disease in humans has been recognized, especially when the condition occurs in young persons. The purpose of the present study was to compare external beam radiation-induced accelerated coronary atherosclerosis in humans with that seen in the pig coronary arteries following radioactive stent placement. METHODS: A literature review of radiation-induced coronary artery disease was performed. In addition, clinical records and coronary histology from the Armed Forces Institute of Pathology Registry were reviewed from patients who had received external beam radiation for mediastinal malignancies. Coronary arteries from pigs that had radioactive coronary stent placement were evaluated from our stent pathology laboratory and analyzed for comparison with the human disease. RESULTS: In humans, the characteristics of the intimal plaque in accelerated atherosclerosis postradiation therapy were similar to that seen in typical atherosclerotic coronary disease in the absence of radiation therapy. However, medial thinning and adventitial fibrosis were the distinguishing pathologic arterial changes secondary to radiation seen in humans. Radioactive stent placement in pig coronary arteries produced similar changes to that observed in humans post-external beam radiation, consisting of medial injury and adventitial thickening accompanied by intimal foam cell collections, calcification, and necrotic core formation containing cholesterol clefts resulting in severe luminal narrowing. CONCLUSIONS: Radiation, delivered via external beam or radioactive stent, induces changes of intimal atherosclerosis with medial thinning and adventitial scarring in human and pig. Therefore, pending completion of long-term clinical studies, caution should be exercised before the widespread use of brachytherapy is advocated for the treatment and prevention of coronary restenosis.

Animals↗
PubMedDate not supplied

Narcosis and nightshade.

Although this year marks the 150th anniversary of the discovery of modern surgical anaesthesia, surgery itself has a much longer history. It is well known that extracts from the opium poppy, Papaver somniferum, were used to dull the pain of surgery during ancient times but less well known that extracts from plants with sedative powers often accompanied them, producing primitive anaesthesia. Most of these sedative plants were members of a large botanical family, the Solanaceae. This paper describes some of them and discusses the ways in which they were administered. It also explains why, during the middle ages, these primitive techniques went out of use but how none the less they provided Shakespeare with the inspiration for some of his greatest plays. When the active principal of the Solanaceae was identified as scopolamine, it came to play a part in 20th century anaesthesia. The combination of omnopon and scopolamine lives on as a premedication, and the presence of poppy heads and mandrake roots on the arms of today's Association of Anaesthetists serves to remind us of the speciality's links with its past.

Anesthesiology↗
PubMedDate not supplied

Pathology of acute and chronic coronary stenting in humans.

BACKGROUND: Despite the increasing use of stents, few reports have described human coronary artery morphology early and late after stenting. METHODS AND RESULTS: Histology was performed on 55 stents in 35 coronary vessels (32 native arteries and 3 vein grafts) from 32 patients. The mean duration of stent placement was 39+/-82 days. Fibrin, platelets, and neutrophils were associated with stent struts </=11 days after deployment. In stents implanted for </=3 days, only 3% of struts in contact with fibrous plaque had >20 associated inflammatory cells compared with 44% of struts embedded in a lipid core and 36% of struts in contact with damaged media (P<0.001). Neointimal growth determined late histological success, and increased neointimal growth correlated with increased stent size relative to the proximal reference lumen area. Neointimal thickness was greater for struts associated with medial damage than struts in contact with plaque (P<0.0001) or intact media (P<0.0001). When matched for time since treatment, neointimal cell density in stented arteries was similar to that in unstented arteries that had undergone balloon angioplasty and showed similar proteoglycan deposition. CONCLUSIONS: Morphology after coronary stenting demonstrates early thrombus formation and acute inflammation followed by neointimal growth. Medial injury and lipid core penetration by struts result in increased inflammation. Neointima increases as the ratio of stent area to reference lumen area increases. Deployment strategies that reduce medial damage and avoid stent oversizing may lower the frequency of in-stent restenosis.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Comparative pathology: radiation-induced coronary artery disease in man and animals.

The occurrence of coronary artery disease following mediastinal radiation for malignancies has long been debated. However, the development of coronary pathology in young individuals following radiation who lack risk factors for atherosclerosis is highly suggestive of a cause-and-effect relationship. By far the most convincing pathologic changes are adventitial scarring and medial atrophy with severe intimal atherosclerotic disease consisting of necrotic core, fibrous tissue, and calcification. Initial clinical studies in patients with coronary atherosclerosis treated with intraluminal radiation following stenting hold great promise in the treatment and prevention of restenosis. There are little or no data, however, on long-term effects of intra-coronary radiation therapy in man. Therefore, it may be important to study the chronic effects of radiation in animal models in order to predict what is likely to occur in humans. We evaluated the effects of varying doses (0.15-23.0 microCi of 32P) of beta-particle-emitting radioactive stents in pig coronary arteries at 1 and 6 months. At 1 month, there were dose-dependent changes in the morphology of the intima and media. High activities (>3 microCi) caused medial necrosis with fibrin deposition in the media and intima, with interspersed red cells most marked in regions surrounding the stent struts. Only rare smooth muscle cells (SMCs) and inflammatory cells were seen away from the stent struts. In the intermediate (1 microCi) stent activity group, the neointima was expanded by SMCs and a proteoglycan-rich matrix with focal endothelialization of the luminal surface. Neovascular capillaries and extravascular red cells were present adjacent to stent struts. At low activities (<0.5 microCi), the neointima was significantly smaller than control stents and consisted of SMCs and matrix with complete endothelialization of the luminal surface. The neointimal cell density of the media and intima decreased with increasing doses of radiation. In pigs 6 months after radioactive stenting (activities ranging from 0.5-12 microCi 32P), >3.0 microCi radioactive stents induced marked neointimal thickening, with changes similar to atherosclerosis, consisting of necrotic debris containing cholesterol clefts surrounded by macrophage collections, fibrosis, and focal calcification. There was increased adventitial thickening in the radiated vs non-radiated arteries. The intermediate stent activity (1.0 microCi) also showed greater neointimal thickening (vs control stents) and consisted mostly of SMCs in a proteoglycan-rich matrix. At <1.0 microCi, there were minimal differences seen between radiated and control non-radiated stented arteries. The media was unevenly injured in all stent activities and varied from less than to significantly greater than controls. These data suggest that radiation-induced coronary atherosclerosis seen in man is partially simulated in normal porcine coronary arteries 6 months following high-dose beta-particle-emitting radioactive stent placement. There is greater fibrosis and thickness of the adventitia and focal attenuation of the media in man and severe luminal narrowing in pig coronary arteries treated with high doses of radiation. Only long-term clinical follow up and careful autopsy studies will determine if endoluminal or intra-arterial radiation is a viable means of reducing restenosis in man.

Animals↗