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Biomedical subjects

A Whittemore

Publications and source records attributed to A Whittemore.

At least 19 recordsLinked to original sources
PubMed1999

Influence of environmental changes on degradation of chiral pollutants in soils.

Numerous anthropogenic chemicals of environmental concern--including some phenoxy acid herbicides, organophosphorus insecticides, polychlorinated biphenyls, phthalates, freon substitutes and some DDT derivatives--are chiral. Their potential biological effects, such as toxicity, mutagenicity, carcinogenicity, and endocrine disrupter activity, are generally enantiomer-selective, and different enantiomers are preferentially degraded (transformed) by micro-organisms in various environments. Here we use field and laboratory experiments to demonstrate that environmental changes in soils can alter these preferences, and to suggest that the preferences shift owing to different groups of related microbial genotypes being activated by different environmental changes. In Brazilian soils, almost all pasture samples preferentially transformed the non-herbicidal enantiomer of dichlorprop ((RS)-2-(2,4-dichlorophenoxy)propionic acid), while most forest samples either transformed the herbicidal enantiomer more readily or as rapidly as the non-herbicidal enantiomer. Organic nutrient enrichments shifted enantioselectivity for methyl dichlorprop ((RS)-methyl 2-(2,4-dichlorophenoxy)propionic acid) strongly towards preferentially removing the non-herbicidal enantiomer in soils from Brazil and North America, potentially increasing phytotoxicity of its residues relative to that of the racemate. Assessments of the risks chemical pollutants pose to public health and the environment need to take into account the chiral selectivity of microbial transformation processes and their alteration by environmental changes, especially for pesticides as up to 25 per cent are chiral.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1997

A new paradigm: the vascular center.

The vascular surgeon, in the absence of effective medical options for the treatment of atherosclerosis, has in the past assumed primary responsibility for the care of patients with peripheral vascular disorders. During the past two decades, management of these patients has become increasingly complex, the direct result of extraordinary proliferation of both our aging population and the expanding technological array of treatment options available. Such patients often require multiple medications with repeated encounters with a variety of specialists resulting in inefficient and not infrequently ineffective care. The concept of a truly integrated multidisciplinary effort to expedite the care of patients with peripheral vascular disease developed in the early 1980s. A vascular center was created at the Brigham and Women's Hospital involving the departments of Surgery, Medicine, and Radiology with their appropriate subspecialty divisions. The combined expertise of dedicated individuals interested in a disease-oriented perspective has resulted in a marked improvement in the efficiency and, it is hopeful, efficacy of management.

Arteriosclerosis↗
PubMed1992

The value of cerebral angiography in predicting cerebral ischemia during carotid endarterectomy.

OBJECTIVE: Temporary occlusion of the carotid artery during endarterectomy can result in ipsilateral cerebral ischemia if collateral blood flow is insufficient. This requires placement of a shunt across the carotid bifurcation, which is associated with increased operative risk. We retrospectively analyzed preoperative cerebral angiograms and intraoperative electroencephalographic recordings to determine if ischemia during carotid endarterectomy could be predicted from angiographic data. MATERIALS AND METHODS: The cerebral angiograms of 30 patients were examined. Collateral blood flow to the hemisphere on the side of surgery was determined to be present if both proximal segments of the anterior cerebral artery and the anterior communicating artery were visualized, or if filling and washout of the ipsilateral posterior cerebral artery could be seen. Collateral flow was determined to be inadequate if the anterior collateral system was incomplete, and if either the ipsilateral posterior communicating artery was absent or the posterior cerebral artery filled without washout. This information was compared with intraoperative electroencephalographic and shunting data. RESULTS: Of 15 patients who had demonstrable collateral blood flow, 14 had stable electroencephalograms and did not require a shunt during surgery. In all 15 patients in whom no collateral flow to the ipsilateral hemisphere could be shown, electroencephalographic changes prompted placement of an intraluminal shunt. CONCLUSION: We found that the angiographic determination of inadequate collateral cerebral circulation correlated strongly with the development of intraoperative ischemia. This implies that routine preoperative cerebral angiograms can be used to alert the surgeon to the potential need for shunt placement during carotid endarterectomy.

Aged↗
PubMed1990

Current techniques for infrainguinal arterial reconstruction.

Infrainguinal reconstruction for peripheral vascular occlusive disease comprises an increasingly complex array of interventions which provide unparalleled options for the salvage of threatened limbs. Conventional autogenous saphenous vein bypass remains the most durable revascularization with anticipated graft patency rates approaching 80 percent after five years and excellent long term limb salvage. These excellent results are equally applicable to vein grafts carried to infrapopliteal and even inframalleolar levels, possibly reflecting increased utilization of the in situ method. Although 20 per cent of grafts fail within five years, secondary intervention results in sustained limb salvage in the majority of patients. In the absence of autogenous vein, however, prosthetic material performs poorly such that new interventions consisting of percutaneous transluminal angioplasty, rotary atherectomy devices and laser systems are under aggressive development. Although initial results with these devices are encouraging, long term patency rates remain poor largely due to restenosis. Further progress seems to depend primarily on an increased understanding of the natural healing response of the injured artery.

Angioplasty, Laser↗
PubMed1990

Atherosclerosis, peripheral arterial disease and the vascular response to ketanserin.

Platelet activation releases thromboxane A2 and serotonin, which acts on blood vessels through a specific, 5-hydroxytryptamine (5-HT2) receptor. The development of ketanserin, the selective 5HT2 receptor blocker, has made it possible to explore the role of serotonin in patients with advanced atherosclerotic disease. Ketanserin in low doses (3 to 30 micrograms/kg) was administered intra-arterially to 23 patients with symptomatic peripheral occlusive vascular disease during peripheral angiography: an additional seven patients received a placebo. The angiographic response was evaluated by coded reading and by computer-assisted measurement of arterial segments in four anatomical regions (pelvis, thigh, knee, and lower leg). Hemodynamic changes were assessed by mercury strain gauge plethysmography and Doppler pressure measurement. Unequivocal vasodilatation was observed in zero of seven placebo-treated patients and in 13 of 23 (57%) treated patients primarily at the level of collateral vessels. Dilation of the geniculate arteries, a major source of collaterals to the calf, was associated with a significant increase in the blood flow delivery to the calf. There was a moderate drop of systemic blood pressure in patients who failed to respond with peripheral vasodilatation. Ketanserin induces hemodynamically significant vasodilatation in some patients with peripheral vascular disease, suggesting that serotonin may contribute to ischemia in some patients with advanced atherosclerosis.

Adult↗
PubMed1989

Salvage of occluded arterial bypass grafts by means of thrombolysis.

Seventy-two thrombosed peripheral arterial bypass grafts in 62 patients were treated by local intraarterial thrombolytic infusion. The initial success rate was 69% (50 of 72 grafts). Graft material and location had no significant effect on the initial results. Urokinase was used in 43 cases with a 84% success rate, and streptokinase was used in 29 cases with a 48% success rate. After a follow-up period that ranged from 2 to 58 months, 27 grafts remained patent, with an average patency duration of 15 months (median 8 months). Overall graft patency at the end of 1 year was 60% applying life-table analysis. Factors that were evaluated to determine their effect on long-term patency included graft age and material, graft location, and the presence or absence of an underlying correctable lesion. The most significant factor in long-term patency was the presence of a lesion that was correctable by surgical revision or balloon angioplasty. In 25 grafts with underlying stenotic lesions, the 1-year patency was 86% after successful treatment. Twenty-five grafts without detectable lesions had 37% 1-year patency.

Adult↗
PubMed1986

Thrombolysis of occluded femoropopliteal grafts.

In a series of 44 occluded femoropopliteal grafts, streptokinase was used for thrombolytic therapy in 22 cases and urokinase in 22 cases. In most cases, thrombolytic agents were administered via an indwelling arterial catheter directly into the proximal thrombus. The catheter tip was advanced as thrombolysis occurred. Compared with streptokinase infusions, urokinase bolus injection followed by infusion had better results (77% vs 41%) and fewer complications (23% vs 50%). During thrombolytic infusion, concomitant heparin infusion was usually used to reduce the frequency of thrombus formation on the infusion catheter or recurrent thrombosis of the graft, once the tip of the infusion catheter was advanced distally. Follow-up in 23 of 26 successful cases showed that 11 of the grafts remained open at an average follow-up of 12 months or until the patient died. The 12 grafts that reoccluded remained open an average of 3 months. In none of the 18 failures was simple surgical thrombectomy or thrombectomy with graft revision effective in revascularizing the distal limb. The advantages of thrombolysis compared with thrombectomy are less trauma to the graft, which is especially important in vein grafts, and improved distal runoff due to lysis of infrapopliteal thrombus. Even among cases considered failures in this series, the surgical approach was often simplified because of partial thrombolysis. Thrombolysis requires a considerable amount of time, effort, and expense, but in certain patients where thrombectomy is indicated for the treatment of occluded femoropopliteal grafts this technique offers important advantages.

Aged↗
PubMed1986

Femorofemoral bypass to relieve acute leg ischemia during intra-aortic balloon pump cardiac support.

This study reports our experience with 10 patients who underwent the emergent construction of a femorofemoral bypass graft to salvage an acutely ischemic lower extremity following the insertion of a transfemoral intra-aortic balloon pump catheter. All patients had excellent resolution of the ischemia and salvage of the extremity. Half of the procedures were done at the bedside with the remainder performed in the operating room. No long-term infections or ischemic sequelae resulted from the procedures in the nine patients available for long-term follow-up. The use of femorofemoral bypass grafting is, therefore, recommended in patients with severe ipsilateral limb ischemia who are dependent on an intra-aortic balloon pump to prevent extremity tissue loss as well as the systemic metabolic manifestations of ongoing tissue ischemia and necrosis. Patient selection, technical considerations, and postoperative management are discussed.

Adult↗
PubMed1982

A case-control study of pancreatic carcinoma.

The hospital records of 60 female and 56 male pancreatic cancer patients and 232 age-, race-, sex-, and hospital-matched controls were reviewed for evidence of prior thyroid disease, cholecystectomy, appendectomy, alcohol consumption and among females, for diseases for the endometrium and ovary. No statistically significant differences were detected between case and control groups. It may be of interest, however, that there were four patients with a history of thyrotoxicosis among the pancreatic cancer patients and only one in the control group. In females, a history of thyroidectomy was somewhat more common among the patients than the controls.

Alcohol Drinking↗