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Biomedical subjects

A R Baker

Publications and source records attributed to A R Baker.

At least 19 recordsLinked to original sources
PubMed2005

Copper and zinc removal from aqueous solution by mixed mineral systems II. The role of solution composition and aging.

This study investigates Cu and Zn removal onto binary mixed mineral sorbents from simulated wastewater, relevant to streams impacted by acid mine drainage and effluents. Mixed suspensions of kaolinite/montmorillonite and kaolinite/goethite exhibited different sorption behavior from the single mineral components, reducing Cu and Zn removal (except Cu sorbed on montmorillonite/goethite) over the range of pH investigated. Cu and Zn removal by the electrolyzed systems showed a complex response to increased ionic strength, which increased solid concentration, leading to lower Cu and Zn sorption. Enhanced Cu sorption on the montmorillonite/goethite as age increased may be attributed to increased hydroxylation of the mineral surface resulting in the formation of new reactive sites.

Journal Article↗
PubMed2005

Copper and zinc removal from aqueous solution by mixed mineral systems I. Reactivity and removal kinetics.

This study investigates the reactivity and removal kinetics of Cu and Zn onto mixed mineral systems from aqueous solution related to acid mine drainage impacted areas. The sorbents used were kaolinite, Al-montmorillonite, goethite, and their mixtures. The effects of surface charge, proton coefficient, and sorption kinetics were studied at room temperature (23+/-2 degrees C). Using an empirical model, mineral mixing reduced the exchange of protons for sorbing ions and the acidity of the reactive sites, thus impeding Cu and Zn removal by proton exchange. Based on the amount of Cu and Zn sorbed on the mixed mineral suspensions at ionic strength 0.01 to 0.1 M and pH 4, it is suggested that Cu and Zn removal from aqueous solution was by both inner and outer sphere complexation. Mineral mixing reduced the transfer rate of Cu relative to the single mineral suspensions in both slow and fast reaction phases. The behavior of the mixed suspensions in Cu and Zn sorption suggest that different reactive sites were involved at the onset of sorption, becoming similar to those of the single mineral components over time.

Journal Article↗
PubMed2005

Global iron connections between desert dust, ocean biogeochemistry, and climate.

The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the "Earth system": a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.

Atmosphere↗
PubMed2004

Homotypic variation of canine flexor tendons: implications for the design of experimental studies in animal models.

Water, collagen and glycosamimoglycan contents, cross-sectional area, stiffness and elastic modulus were carefully quantitated in flexor digitorum superficialis tendons from mature canines. From these data the within- and between-animal variability was estimated and used to demonstrate sample size calculations for both two-group and paired (within-animal) study designs. The estimated between-dog variance was typically 50% or less of the total variance for the parameters investigated. In other words, the correlation among the tendons within an animal for most measures was not strong. Therefore, for some variables (e.g., elastic modulus) in this animal and tendon model, there is no appreciable gain in statistical power by using a paired study design. A two-group design could be used, but any within-animal correlation must be accounted for in the analysis. For other variables such as collagen content, a paired design would gain substantial power.

Animals↗
PubMed2001

Reaction of carbon monoxide with the reduced active site of bacterial nitric oxide reductase.

Bacterial nitric oxide reductase (NOR), a member of the superfamily of heme-copper oxidases, catalyzes the two-electron reduction of nitric oxide to nitrous oxide. The key feature that distinguishes NOR from the typical heme-copper oxidases is the elemental composition of the dinuclear center, which contains non-heme iron (FeB) rather than copper (CuB). UV-vis electronic absorption and room-temperature magnetic circular dichroism (RT-MCD) spectroscopies showed that CO binds to Fe(II) heme b3 to yield a low-spin six-coordinate species. Photolysis of the Fe(II)-CO bond is followed by CO recombination (k(on) = 1.7 x 10(8) M(-1) x s(-1)) that is approximately 3 orders of magnitude faster than CO recombination to the active site of typical heme-copper oxidases (k(on) = 7 x 10(4) M(-1)x s(-1)). This rapid rate of CO recombination suggests an unimpeded pathway to the active site that may account for the enzyme's high affinity for substrate, essential for maintaining denitrification at low concentrations of NO. In contrast, the initial binding of CO to reduced heme b3 measured by stopped-flow spectroscopy is much slower (k(on) = 1.2 x 10(5) M(-1) x s(-1)). This suggests that an existing heme distal ligand (water/OH-) may be displaced to elicit the spin-state change observed in the RT-MCD spectrum.

Binding Sites↗
PubMed1999

Management of symptomatic malignant melanoma of the gastrointestinal tract.

BACKGROUND: Melanoma metastatic to the gastrointestinal (GI) tract is asymptomatic or presents with pain, bleeding, or obstruction. To determine whether surgery influences outcomes, we reviewed our experience with this patient population. METHODS: Medical records of patients with metastatic melanoma to the GI tract were reviewed. Patients were divided into four groups, i.e., complete resection, partial debulking, unresectable, or unexplored. Analysis was performed using the Kaplan-Meier method. RESULTS: Fifty patients with melanoma metastatic to the GI tract were identified (40 men and 10 women; mean age, 44 years). Presenting symptoms included pain (62%), bleeding (28%), and obstruction (18%). Diagnosis was confirmed using contrast studies (38%), endoscopy (20%), or computed tomography (30%). Thirty-six patients (61%) underwent a total of 39 operations. Seventeen patients underwent complete resection, whereas 14 underwent partial debulking. Five patients had unresectable lesions, and 14 patients did not undergo exploration because of medical contraindications. The operative mortality rate was 2.5% (1 of 39). The mean survival times for the unexplored and unresected groups were similar (4.1 months). Patients who underwent partial resection exhibited a longer mean survival time (8.9 months) than did patients in the unresected group (P < .001). The complete-resection group demonstrated a mean survival time of 23.5 months, which was significantly longer than that for patients who underwent less than complete resection (P < .0001). CONCLUSIONS: Metastatic melanoma to the GI tract can result in significant morbidity and death. Surgical resection can be performed safely. Patients for whom all sites of disease are completely resected experience significant improvements in survival times, compared with patients who undergo less than complete resection. For selected patients, surgical treatment of metastatic melanoma involving the GI tract is appropriate therapy.

Adult↗
PubMed1999

In vivo measurement of solute transport rates in a bioartificial organ.

A radioactive tracer technique was used to evaluate the in vivo mass transfer properties of a tissue engineered bioartificial organ. To obtain these measurements, bioartificial organs were first implanted in ten rats and allowed to vascularize for 4 weeks. After vascularization, radioactive inulin was placed within the cell chamber of the device. Following the addition of tracer, blood samples were taken over a 4-h time period and inulin levels were determined. The results of these experiments were interpreted using a compartmental model that describes the transport of inulin from the cell chamber, across the immunoisolation membrane, and into the neovascularized region contained within the adjacent scaffold material. Nonlinear regression analysis of the plasma inulin levels using a four-compartment pharmacokinetic model provided estimates of the membrane permeability, the product of the capillary wall surface area and capillary permeability, and the glomerular filtration rate (GFR). The permeability of the membrane was found to be 3.50 x 10(-5) +/- 1.15 x 10(-5) cm/sec (95% confidence interval, n = 10), which compares favorably to previous in vitro permeability data for this membrane. The capillary wall permeability was found to be 0. 0087 6 0.0029 cm(3)/sec/100 g of tissue. This compares well to a reported value for inulin of 0.01 cm(3)/sec/100 g of tissue. The GFR was found to be 0.44 +/- 0.07 ml/h/g BW, which compares well with a reported value of 0.40 ml/hr/g BW. The inulin tracer technique reported here is a useful tool for assessing the in vivo transport characteristics of a bioartificial organ as well as the vascularization within tissue engineered structures.

Animals↗
PubMed1998

Military service and migration in nineteenth-century France: some evidence from Loir-et-Cher.

"Military service in France during the nineteenth century removed many young men from their own localities for long periods. The widely accepted claim that few conscripts returned home after completing their period of service is based on little evidence. The paper examines the conscription classes of 1856 and 1891 in two cantons in the departement of Loir-et-Cher. In those cases, there was not a significant relationship between conscription and migration, nor between literacy and migration. Instead, migration of youths in their twenties was linked partly to prior experiences of migration but principally to their occupations."

Adolescent↗
PubMed1998

Randomized prospective study of the benefit of adjuvant radiation therapy in the treatment of soft tissue sarcomas of the extremity.

PURPOSE: This randomized, prospective study assesses the impact of postoperative external-beam radiation therapy on local recurrence (LR), overall survival (OS), and quality of life after limb-sparing resection of extremity sarcomas. PATIENTS AND METHODS: Patients with extremity tumors and a limb-sparing surgical option were randomized to receive or not receive postoperative adjuvant external-beam radiotherapy. Patients with high-grade sarcomas received postoperative adjuvant chemotherapy whereas patients with low-grade sarcomas or locally aggressive nonmalignant tumors were randomized after surgery alone. RESULTS: Ninety-one patients with high-grade lesions were randomized; 47 to receive radiotherapy (XRT) and 44 to not receive XRT. With a median follow-up of 9.6 years, a highly significant decrease (P2 = .0028) in the probability of LR was seen with radiation, but no difference in OS was shown. Of 50 patients with low-grade lesions (24 randomized to resection alone and 26 to resection and postoperative XRT), there was also a lower probability of LR (P2 = .016) in patients receiving XRT, again, without a difference in OS. A concurrent quality-of-life study showed that extremity radiotherapy resulted in significantly worse limb strength, edema, and range of motion, but these deficits were often transient and had few measurable effects on activities of daily life or global quality of life. CONCLUSION: This study indicates that although postoperative external-beam radiotherapy is highly effective in preventing LRs, selected patients with extremity soft tissue sarcoma who have a low risk of LR may not require adjuvant XRT after limb-sparing surgery (LSS).

Extremities↗
PubMed1997

Reaction of variant sperm-whale myoglobins with hydrogen peroxide: the effects of mutating a histidine residue in the haem distal pocket.

The reaction of hydrogen peroxide with a number of variants of sperm-whale myoglobin in which the distal pocket histidine residue (His64) had been mutated was studied with a combination of stopped-flow spectroscopy and freeze-quench EPR. The rate of the initial bimolecular reaction with hydrogen peroxide in all the proteins studied was found to depend on the polarity of the amino acid side chain at position 64. In wild-type myoglobin there were no significant optical changes subsequent to this reaction, suggesting the rapid formation of the well-characterized oxyferryl species. This conclusion was supported by freeze-quench EPR data, which were consistent with the pattern of reactivity previously reported [King and Winfield (1963) J. Biol. Chem. 238, 1520-1528]. In those myoglobins bearing a mutation at position 64, the initial bimolecular reaction with hydrogen peroxide yielded an intermediate species that subsequently decayed via a second hydrogen peroxide-dependent step leading to modification or destruction of the haem. In the mutant His64-->Gln the calculated electronic absorption spectrum of the intermediate was not that of an oxyferryl species but seemed to be that of a low-spin ferric haem. Freeze-quench EPR studies of this mutant and the apolar mutant (His64-->Val) revealed the accumulation of a novel intermediate after the first hydrogen peroxide-dependent reaction. The unusual EPR characteristics of this species are provisionally assigned to a low-spin ferric haem with bound peroxide as the distal ligand. These results are interpreted in terms of a reaction scheme in which the polarity of the distal pocket governs the rate of binding of hydrogen peroxide to the haem iron and the residue at position 64 governs both the rate of heterolytic oxygen scission and the stability of the oxyferryl product.

Amino Acid Sequence↗
PubMed1997

Sciatic nerve: paradoxic hypertrophy after amputation in young patients.

PURPOSE: To evaluate the appearance of the sciatic nerve after leg amputation. MATERIALS AND METHODS: Magnetic resonance (MR) images were obtained in seven patients (age at amputation, 11-19 years) who underwent above-knee amputation to treat osteogenic sarcoma. Images were evaluated for sciatic nerve enlargement. Findings were correlated with the time after amputation. RESULTS: All seven patients were found to have a markedly enlarged sciatic nerve in the stump of the amputated leg. The enlargement extended proximally from the point of nerve transection to a level posterior to the femoral neck (8-27 cm) depending on the length of the stump. No evidence of sciatic nerve enlargement was found in the opposite leg or on preoperative MR images that were available in three of the patients. Moreover, in one patient with a sarcoma who underwent a leg-sparing procedure, no sciatic nerve enlargement was seen postoperatively. The thickness of the distal sciatic nerve was related to the time after amputation. CONCLUSION: Hypertrophy of the sciatic nerve occurred after above-knee amputation in young patients. This finding differed from atrophy of the nerve that has been reported previously in older patients.

Adolescent↗
PubMed1997

Strategies to control Salmonella and Campylobacter in raw poultry products.

Foodborne illness is a major public health concern. The largest number of foodborne illness cases attributed to poultry and poultry products are caused by paratyphoid serotypes of Salmonella and by Campylobacter jejuni. The effective prevention of foodborne disease requires an understanding that contamination can be introduced into foods at numerous points along the food chain. Since multiple entry points exist for foodborne pathogens, multifaceted intervention approaches are required to successfully control contamination of poultry during the various phases of the growth period and processing procedure of broiler chickens. Strategies during the grow-out period (the period during which day-old chicks are raised to six- to seven-week-old broiler chickens) include sanitation, biosecurity, vaccine and drug therapy, and biological control procedures, such as those aimed at preventing colonisation. There are also many critical control points identified in the processing plant which reduce contamination. These include temperature controls (washer and product), chemical interventions, water replacements and counter-flow technology in the scalder and chiller, and equipment maintenance. Transportation and food handling at retail outlets and by the consumer (i.e., storage at the proper temperature and adequate cooking) are the final critical control points in the farm-to-table continuum. It is important to apply risk reduction strategies throughout the food chain. These include: easing the development and implementation of voluntary animal production 'best management practices', implementing in-plant hazard analysis and critical control point systems, developing effective transportation and refrigeration standards, working to facilitate adoption of the model Food Code in all States and providing educational materials and support for public health activities nationwide.

Animals↗
PubMed1996

Local expression of human growth hormone in bone results in impaired mechanical integrity in the skeletal tissue of transgenic mice.

The effect of local production of human growth hormone on murine cortical bone was investigated using a transgenic mouse model. Femora and humeri from human growth hormone transgenic mice and littermate control mice were obtained, and the geometrical, biomechanical, compositional, and histomorphometric properties of all specimens were determined. The goals were to investigate the effects of local expression of human growth hormone on skeletal integrity, including the functional geometry of long bone and its related structural and mechanical behavior, as well as tissue composition and integrity. As expected, local production of human growth hormone by osteoblasts indeed resulted in longer femora with significantly greater mid-diaphyseal cross-sectional geometry in the transgenic mice (16% increase in cross-sectional area and 29% increase in bending moments of inertia). However, the significant increase in geometry was not associated with a proportional increase in bending stiffness and other structural properties, which suggested that the mechanical properties of the cortical bone tissue may have been inferior. Microspecimen bending tests verified this prediction, given that transgenic cortical bone tissue had significantly lower apparent elastic modulus and ultimate strength (52 and 68%, respectively, of control values). These defects in the whole bone structural and tissue mechanical properties of transgenic specimens were associated with a smaller fraction of ash, larger fractions of woven bone and cartilage islands, and greater porosity in the mid-diaphyseal cortices. These results suggest that local production of human growth hormone by osteoblasts is indeed anabolic for bone, but at the expense of bone tissue integrity.

Adaptation, Physiological↗
PubMed1995

Laser Doppler study of porcine cauda equina blood flow. The effect of electrical stimulation of the rootlets during single and double site, low pressure compression of the cauda equina.

STUDY DESIGN: This study involved a model of spinal claudication to assess the effect of single and double site compressions on blood flow in porcine cauda equina. Real-time monitoring of blood flow was achieved by using laser Doppler probes. OBJECTIVES: To ascertain the difference between single and double site compressions on blood flow and nerve conduction in the cauda equina. Also, to provide possible explanations for the mechanisms underlying the pathophysiology of neurogenic claudication. SUMMARY OF BACKGROUND DATA: The model used was based on that of K. Olmarker. Double as compared with single site compression of cauda equina showed impaired nerve impulse propagation and decreased blood flow. METHOD: Pigs weighing 22-27 kg were anesthesized and the cauda equina was exposed by dorsal laminectomy of the sacral and first three coccygeal vertebrae. Polyethylene balloons were placed over the rootlets at the first and third coccygeal segments, and stimulating electrodes were positioned on the rootlets proximally to evoke motor activity. Electromyographic activity was monitored from tail musculature. Laser Doppler probes monitored blood flow in the cauda equina both between and distal to the two compression sites. RESULTS: Single site, low level compression did not affect blood flow whereas double site compression decreased it profoundly. Proximal stimulation caused a marked increase in blood flow, which was not sustained during prolonged compression. Electromyographic activity diminished concomitantly during this compression. CONCLUSIONS: Low pressure, double site compression significantly reduces cauda equina blood flow and prevents the sustained increase in blood flow required to maintain normal neurologic rootlet function. Local blood flow failure may therefore be responsible for claudication symptoms.

Animals↗
PubMed1994

Influence of compression stockings on lower-limb venous haemodynamics during laparoscopic cholecystectomy.

Lower-limb venous haemodynamics were studied prospectively in 40 patients (24 women, 16 men of median age 52 years) undergoing laparoscopic cholecystectomy. Patients were randomized to wear compression stockings during surgery or no stockings. All received subcutaneous heparin prophylaxis. Venous capacitance and outflow were measured non-invasively before, during and after pneumoperitoneum. In the group without compression stockings (20 patients) venous capacitance and outflow decreased during pneumoperitoneum in most patients. In the group wearing stockings (20 patients) the changes were less pronounced or abolished. There was a significant difference between the groups in venous capacitance and outflow ratios at mid-operation: median (interquartile range) 0.89 (0.56-1.16) and 0.89 (0.56-1.15) respectively in the group without stockings versus 1.48 (1.09-2.19) and 1.71 (1.20-2.19) respectively in that with stockings (P < 0.001). Pneumoperitoneum creates a significant resistance to venous return. Compression stockings counteract the changes observed.

Adult↗
PubMed1994

Metastatic malignant melanoma of the oral cavity. A retrospective study.

Metastatic malignant melanoma of the oral cavity is rarely reported in the dental literature. This retrospective study identified metastatic oral lesions in 3.0% of 809 patients with melanoma treated at the National Institutes of Health between 1953 and 1989. Fifteen cases met established rigorous criteria for metastatic tumors and were reviewed for disease course and outcome. Nine white men and six white women, with an average age of 40.6 years, had cutaneous primary tumors predominantly of the trunk and head and neck region that commonly presented as moles that were enlarging, bleeding, or showing both of these signs. A mean of 4.2 years elapsed between primary tumor and oral metastasis diagnosis. Tongue, buccal mucosa, and parotid gland were the predominant oral sites. Enlarging oral masses, pigmented lesions, and nonhealing extraction sites with masses were common oral presentations. Surgery, chemotherapy, radiation therapy, and immunotherapy were used in various combinations for treatment of the primary lesion and oral metastasis. Prognosis, although poor, was highly variable.

Adolescent↗