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Biomedical subjects

J R Schneider

Publications and source records attributed to J R Schneider.

At least 19 recordsLinked to original sources
PubMed2005

Amorphouslike diffraction pattern in solid metallic titanium.

Amorphouslike diffraction patterns of solid elemental titanium have been detected under high pressure and high temperature using in situ energy-dispersive x-ray diffraction and a multianvil press. The onset pressure and the temperature of formation of amorphous titanium is found to be close to the alpha-beta-omega triple point in the P-T phase diagram. Amorphous Ti has been found to be thermally stable up to 1250 degrees C for at least 3 min at some pressures. By analyzing the conditions for producing amorphous elemental Zr and Ti, we observed a multi-phase-point amorphization phenomenon for preparing single-element bulk amorphous metals. The results reported may open a new way to preparing single-element bulk amorphous metals with a high thermal stability.

Journal Article↗
PubMed2005

Prevalence of retinopathy in Caucasian type 2 diabetic patients from the South of Brazil and relationship with clinical and metabolic factors.

Diabetic retinopathy (DR) is a sight-threatening chronic complication of diabetes mellitus and is the leading cause of acquired blindness in adults. In this cross-sectional study, we investigated the prevalence of and the factors associated with DR in an analysis of 210 consecutive and unrelated Brazilian Caucasians with type 2 diabetes mellitus. Retinopathy was evaluated by ophthalmoscopy and/or biomicroscopy through dilated pupils. The relationship between clinical and metabolic variables and the presence of DR was assessed by logistic regression analysis. DR was detected in 99 of the 210 patients (47%). In the univariate logistic regression analyses, male sex, duration of diabetes, body mass index, glycated hemoglobin, C-peptide, LDL cholesterol, smoking, and albumin excretion rate were found to be associated with the presence of DR. However, the multiple logistic regression analysis showed that only duration of diabetes (odds ratio (OR) = 1.15, 95% CI = 1.09-1.22; P < 0.001), glycated hemoglobin (OR = 1.21, 95% CI = 1.01-1.46; P = 0.047) and albumin excretion rate > 100 microg/min (OR = 12.72, 95% CI = 3.89-41.56; P < 0.001) were independently associated with DR. Although DR was found to be frequent among Brazilian type 2 diabetic patients, its prevalence was within the range observed in other Caucasian populations. Our findings emphasize the need for good glycemic control in order to prevent or delay the onset of DR, since the most well-known risk factors for the development of this complication in type 2 diabetes mellitus, such as duration of diabetes, glycated hemoglobin and albumin excretion rate were independently related to DR.

Adult↗
PubMed2003

A targeted approach to the identification of candidate genes determining susceptibility to Plasmodium gallinaceum in Aedes aegypti.

The malaria parasite, Plasmodium, has evolved an intricate life cycle that includes stages specific to a mosquito vector and to the vertebrate host. The mosquito midgut represents the first barrier Plasmodium parasites encounter following their ingestion with a blood meal from an infected vertebrate. Elucidation of the molecular interaction between the parasite and the mosquito could help identify novel approaches to preventing parasite development and subsequent transmission to vertebrates. We have used an integrated Bulked Segregant Analysis-Differential Display (BSA-DD) approach to target genes expressed that are in the midgut and located within two genome regions involved in determining susceptibility to P. gallinaceum in the mosquito Aedes aegypti. A total of twenty-two genes were identified and characterized, including five genes with no homologues in public sequence databases. Eight of these genes were mapped genetically to intervals on chromosome 2 that contain two quantitative trait loci (QTLs) that determine susceptibility to infection by P. gallinaceum. Expression analysis revealed several expression patterns, and ten genes were specifically or preferentially expressed in the midgut of adult females. Real-time PCR quantification of expression with respect to the time of blood meal ingestion and infection status in mosquito strains permissive and refractory for malaria revealed a differential expression pattern for seven genes. These represent candidate genes that may influence the ability of the mosquito vector to support the development of Plasmodium parasites. Here we describe their isolation and discuss their putative roles in parasite-mosquito interactions and their use as potential targets in strategies designed to block transmission of malaria.

Aedes↗
PubMed2002

Generation of GW radiation pulses from a VUV free-electron laser operating in the femtosecond regime.

Experimental results are presented from vacuum-ultraviolet free-electron laser (FEL) operating in the self-amplified spontaneous emission (SASE) mode. The generation of ultrashort radiation pulses became possible due to specific tailoring of the bunch charge distribution. A complete characterization of the linear and nonlinear modes of the SASE FEL operation was performed. At saturation the FEL produces ultrashort pulses (30-100 fs FWHM) with a peak radiation power in the GW level and with full transverse coherence. The wavelength was tuned in the range of 95-105 nm.

Journal Article↗
PubMed2001

Leg symptoms in peripheral arterial disease: associated clinical characteristics and functional impairment.

CONTEXT: Persons with lower-extremity peripheral arterial disease (PAD) are often asymptomatic or have leg symptoms other than intermittent claudication (IC). OBJECTIVE: To identify clinical characteristics and functional limitations associated with a broad range of leg symptoms identified among patients with PAD. DESIGN, SETTING, AND PARTICIPANTS: Cross-sectional study of 460 men and women with PAD and 130 without PAD, who were identified consecutively, conducted between October 1998 and January 2000 at 3 Chicago-area medical centers. MAIN OUTCOME MEASURES: Ankle-brachial index score of less than 0.90; scores from 6-minute walk, accelerometer-measured physical activity over 7 days, repeated chair raises, standing balance (full tandem stand), 4-m walking velocity, San Diego claudication questionnaire, Geriatric Depression Score Short-Form, and the Walking Impairment Questionnaire. RESULTS: All groups with PAD had poorer functioning than participants without PAD. The following values are for patients without IC vs those with IC. Participants in the group with leg pain on exertion and rest (n = 88) had a higher (poorer) score for neuropathy (5.6 vs 3.5; P<.001), prevalence of diabetes mellitus (48.9% vs 26.7%; P<.001), and spinal stenosis (20.8% vs 7.2%; P =.002). The atypical exertional leg pain/carry on group (exertional leg pain other than IC associated with walking through leg pain [n = 41]) and the atypical exertional leg pain/stop group (exertional leg pain other than IC that causes one to stop walking [n = 90]) had better functioning than the IC group. The group without exertional leg pain/inactive (no exertional leg pain in individual who walks </=6 blocks per week [n = 28]) and the leg pain on exertion and rest group had poorer functioning than those with IC. Adjusting for age, sex, race, and comorbidities and compared with IC, participants with atypical exertional leg pain/carry on achieved a greater distance on the 6-minute walk (404.3 vs 328.5 m; P<.001) and were less likely to stop during the 6-minute walk (6.8% vs 36%; P =.002). The group with pain on exertion and rest had a slower time for completing 5 chair raises (13.5 vs 11.9 seconds; P =.009), completed the tandem stand less frequently (37.5% vs 60.0%; P =.004), and had a slower 4-m walking velocity (0.80 vs 0.90 m/s; P<.001). CONCLUSIONS: There is a wide range of leg symptoms in persons with PAD beyond that of classic IC. Comorbid disease may contribute to these symptoms in PAD. Functional impairments are found in every PAD symptom group, and the degree of functional limitation varies depending on the type of leg symptom.

Aged↗
PubMed2000

Carotid endarterectomy in octogenarians: comparison with patient characteristics and outcomes in younger patients.

OBJECTIVES: Carotid endarterectomy has been shown to be of clear benefit to selected patients. However, recent trials of carotid endarterectomy versus best medical therapy have excluded octogenarians, and some authors have suggested that carotid endarterectomy would have an unfavorable cost-benefit relationship in octogenarians. We compared patients and results for carotid endarterectomy in octogenarians and younger patients. METHODS: We reviewed the results for 582 primary carotid endarterectomies (90 in octogenarians and 492 in younger patients) performed in 528 patients between February 1, 1985, and January 31, 1998 (all data were collected prospectively for the most recent 301 carotid endarterectomies). Conventional surgical technique was used with general anesthesia, selective shunting, and selective patching. Main outcome measures were perioperative and late ipsilateral stroke and death. RESULTS: The two groups were similar with respect to indications for carotid endarterectomy and patient characteristics, except that octogenarians were more likely to have histories of congestive heart failure or hypertension and less likely to have histories of smoking or chronic lung disease. Carotid endarterectomy was performed for asymptomatic disease in 27% of the octogenarians and 33% of the younger patients (P =.31). Stenosis was >/=80% in 90% of the octogenarians and 78% of the younger patients (P =.014). Perioperative strokes, all of which were ipsilateral, occurred in one octogenarian (1.1%) and eight younger patients (1.6%, P = 1.00). No octogenarians and two younger patients died within 30 days of surgery (P = 1.00). Length of stay and direct costs associated with carotid endarterectomy were similar for octogenarians and younger patients. Late strokes occurred in two octogenarians (one ipsilateral) and four younger patients (two ipsilateral). Life table estimates of freedom from ipsilateral stroke at 2 years were 98% and 97% for octogenarians and younger patients, respectively (log-rank P =.69), and life table estimates of patient survival at 4 years were 81% and 89% for octogenarians and younger patients, respectively (P =.11). Octogenarians represented an increasing fraction of the carotid endarterectomies performed during the study period. CONCLUSIONS: Octogenarians selected for carotid endarterectomy were similar to younger patients with respect to indications for carotid endarterectomy and comorbidities. Early mortality, early and late neurologic outcome, complications, and resource utilization were similar for the two groups, and more than 75% of octogenarians survived 4 years after undergoing carotid endarterectomy. Cost-benefit analyses for carotid endarterectomy, which are highly sensitive to expected patient survival, might not be pertinent to individual patient situations. Intellectually intact octogenarians without unusually severe comorbidities are good candidates for and should be offered the benefits of carotid endarterectomy.

Age Factors↗
PubMed1999

Assessment of coagulation system activation using spot urine measurements.

Coagulation system activation is most commonly assessed by measuring levels of one or more proteins in peripheral blood. Because faulty blood-drawing can cause activation of the coagulation system, artifactual elevations of such markers have been reported. We have therefore investigated the possibility of using randomly collected ('spot') urine samples as a non-invasive means of assessing the state of coagulation system activation. Using a commercially available enzyme-linked immunosorbent assay kit designed to measure plasma levels of fragment 1 + 2, we found immunoreactive fragment 2 in healthy control subjects, and significantly increased levels in diabetic and non-diabetic pregnant subjects, and patients with venous thromboembolism, prostate cancer, and diabetes. Measurements of excretion of immunoreactive fragment 2 are worth further study as an adjunct or alternative to plasma-based assays designed to detect or quantify coagulation system activation.

Adult↗
PubMed1998

Beam-position monitors in the X-ray undulator beamline at PETRA.

At the 12 GeV storage ring PETRA, the first synchrotron radiation beamline uses a 4 m-long undulator. The beamline, with a length of 130 m between source and sample, delivers hard X-ray photons usable up to 300 keV. The photon beam has a total power of 7 kW. Combined with the high brilliance, the powerful beam is very critical for all beamline components. Copper, located at a distance of 26 m, hit by the full undulator beam, melts within 20 ms. Different monitors are described for stable, safe and reliable operation of beam and experiments.

Journal Article↗
PubMed1998

A triple-crystal diffractometer for high-energy synchrotron radiation at the HASYLAB high-field wiggler beamline BW5.

The triple-crystal diffractometer installed at HASYLAB beamline BW5 with a high-field wiggler of critical energy 27 keV for DORIS III, operated at 4.5 GeV electron energy, is described. Samples can be mounted in large cryostats or furnaces normally used in neutron scattering experiments. The instrument has been successfully applied to measure structure factors S(Q) in liquids and amorphous materials, to collect full data sets of highly accurate structure factors for charge-density work, to measure the spin component of the ground-state magnetization in transition-metal and rare-earth compounds, to study the diffuse scattering from stacking faults and dislocation loops in Si single crystals, and for the investigation of various aspects of structural phase transitions: critical scattering in SrTiO3, oxygen order and stripe order in high-To materials. A crossed-beam technique allows for local studies of texture, internal strain and phase changes in the bulk of materials.

Journal Article↗
PubMed1998

The pre-conditioning incidence of antiphospholipid antibodies is not significantly increased in patients with bone marrow transplant-related organ dysfunction.

Hepatic dysfunction resulting from hepatic veno-occlusive disease (VOD) is a common complication of bone marrow transplantation (BMT). Some investigators believe that hepatic dysfunction, along with pulmonary and central nervous system (CNS) dysfunction, is part of a systemic disorder called multiple organ dysfunction syndrome (MODS). Endothelial damage by pretransplant chemo-radiation and activation of hemostasis are considered early events in the development of hepatic VOD. The pathological mechanism leading to fibrous obliteration of hepatic vessels may also take place in pulmonary and CNS vessels. Since antiphospholipid antibodies (aPA) are associated with venous and arterial thrombosis, which can lead to vessel occlusion, we asked if the incidence of aPA before conditioning was greater in patients who developed MODS following BMT. Samples drawn before pretransplant chemo-radiation from 57 patients who subsequently developed MODS and 55 control patients who did not develop MODS were studied blindly for aPA by ELISA. The number of aPA-positive patients who developed MODS (10/57), compared to the number of aPA-positive patient controls who did not develop MODS (7/55) was not statistically significant (P = 0.48). Our data indicate that the incidence of aPA before conditioning was not greater in patients who developed MODS, including hepatic VOD, following BMT.

Antibodies, Antiphospholipid↗
PubMed1998

Which asymptomatic patients should have carotid endarterectomy?

Carotid endarterectomy for asymptomatic very-high-grade stenosis has been shown to be of clear benefit when compared with best medical treatment in recent prospective randomized studies. However, the benefit of carotid endarterectomy in these trials has been less than most vascular surgeons predicted based on prior nonrandomized studies. Furthermore, vascular surgeons often see patients who do not fit the inclusion criteria for any of the prospective randomized trials and whose potential benefit from endarterectomy may be different from that observed in those trials. Medical comorbidities or other patient characteristics that suggest even small increases in risk for carotid endarterectomy may negate the marginal benefit of the procedure in asymptomatic patients. Potential benefit is also highly dependent on surgeon-specific and hospital-specific perioperative morbidity and mortality. This article addresses some of the factors that may alter the potential benefit of carotid endarterectomy and the implications with respect to recommendations for or against carotid endarterectomy in the individual patient.

Age Factors↗
PubMed1997

Measurements of emittance and absolute spectral flux of the PETRA undulator at DESY Hamburg.

The first synchrotron radiation beamline using a 4 m-long undulator at the 12 GeV storage ring PETRA delivers hard X-ray photons usable up to 300 keV. The photon intensity is measured on an absolute scale in the energy range between 16 and 60 keV and compared with calculated intensities. The experimental set-up described is also used to measure the horizontal and vertical emittance of the source.

Journal Article↗
PubMed1997

Carotid endarterectomy in women versus men: patient characteristics and outcomes.

PURPOSE: To examine and compare the results of carotid endarterectomy in women and men in a single-group experience. METHODS: A review of a consecutive series of 426 carotid endarterectomy procedures performed over an 11-year period. RESULTS: Women and men who underwent carotid endarterectomy were remarkably similar in nearly all characteristics except that women were less likely to have clinically overt coronary artery disease. Women were more likely than men to undergo patch closure of the carotid artery, but details of surgery and hospital stay were otherwise similar. A trend toward higher perioperative stroke risk in women was not significant, and late ipsilateral stroke risk was comparable in women and men. Women enjoyed a better late survival rate, presumably related to their lower prevalence of coronary artery disease. CONCLUSIONS: Women enjoyed similarly low risks of perioperative and late stroke and a better long-term survival rate when compared with men who underwent carotid endarterectomy. Further experience and longer follow-up in prospective randomized trials may provide more definitive information regarding the comparative efficacy of carotid endarterectomy in women and men, but our results suggest that absolute results are similar and excellent in both women and men.

Adult↗
PubMed1997

Supraceliac versus infrarenal aortic cross-clamp for repair of non-ruptured infrarenal and juxtarenal abdominal aortic aneurysm.

Repair of abdominal aortic aneurysms may require aortic occlusion above the renal arteries. Despite fears of renal, hepatic and intestinal ischemia, recent publications have suggested that when repair would be difficult or impossible with infrarenal aortic clamping, supraceliac clamping may not be associated with significantly increased morbidity. Between February 1985 and January 1994, 169 patients underwent elective or urgent (symptomatic but not ruptured) repair of infra- or juxtarenal abdominal aortic aneurysm. Twenty-three patients (14%) required supraceliac clamping for juxtarenal abdominal aortic aneurysm, inflammatory abdominal aortic aneurysm, or other difficult exposure problems. Supraceliac clamping and infrarenal aortic clamping patients were indistinguishable with respect to age, gender, abdominal aortic aneurysm diameter, and other co-morbidities. There was a trend toward more frequent use of supraceliac clamping in urgent operations. Preoperative angiography was used selectively and was obtained more often in supraceliac clamping patients, reflecting suspected juxtarenal or renal involvement based on computed tomography findings, but the decision to employ supraceliac clamping was made at surgery. Mean (s.d.) supraceliac clamping clamp time was 22(5) (range 12-30) min. Similar numbers of supraceliac clamping and infrarenal aortic clamping patients required bifurcated grafts, operative times were comparable, and numbers of early complications were similar in the two groups. Transfusion requirements were slightly greater and length of stay was insignificantly shorter in supraceliac clamping patients (due to a few prolonged hospital stays in infrarenal aortic clamping patients). No supraceliac clamping patient required dialysis or suffered clinically apparent hepatic failure, coagulopathy, or intestinal ischemia. There were no operative deaths and all patients were discharged from the hospital. Supraceliac clamping was not associated with greater perioperative morbidity and may have contributed to a lack of mortality by facilitating repair of difficult abdominal aortic aneurysm. Supraceliac clamping should be considered for elective and urgent abdominal aortic aneurysm repair when there is inadequate length or quality of infrarenal aorta for anastomosis, severe associated pararenal atherosclerosis, inflammatory aneurysm, or previous aortic surgery. It is concluded that selective supraceliac clamping is safe and facilitates repair of difficult aortic problems.

Aortic Aneurysm, Abdominal↗
PubMed1996

Color duplex-guided compression therapy for postcatheterization pseudoaneurysms in a community hospital.

Diagnostic or therapeutic arterial catheterization may be complicated by postcatheterization pseudoaneurysm. Pseudoaneurysms have generally been treated surgically, but more recently, encouraging results with duplex-guided compression therapy (DGCT) of pseudoaneurysms have been reported from university hospitals. We reviewed our experience with DGCT to assess the applicability of DGCT in a community hospital setting. Sixty-two patients presented with 63 symptomatic postcatheterization pseudoaneurysms between January 1, 1990, and December 31, 1993. Prior to October 28, 1991, all pseudoaneurysms were treated surgically. Subsequently we initiated DGCT as primary treatment for pseudoaneurysms, reserving surgery for DGCT failures and unstable patients. DGCT patients were indistinguishable from primary surgery patients, and the number of pseudoaneurysms treated did not appear to increase during the study period. DGCT was initially successful in 27 (75%) of 36 patients. Three pseudoaneurysms recurred, yielding cumulative success in 24 (67%) of 36 patients. Three of 12 DGCT failures were due to patient intolerance. DGCT was unsuccessful in three of four intra-aortic balloon pump (IABP)-associated pseudoaneurysms. There was some variation in pseudoaneurysm volume between the successful and failed groups, and a trend toward failure with larger pseudoaneurysm was not significant (13 vs. 6 cm3, p > or = 0.25). DGCT failure appears more likely in post-IABP pseudoaneurysms and possibly with larger pseudoaneurysms. Anticoagulation, type of procedure (exclusive of IABP), obesity, and other patient characteristics examined did not appear to predict success or failure of DGCT. Treatment was reserved for symptomatic patients throughout the period of study and there was no evidence that patients were more likely to be treated for pseudoaneurysms after DGCT was initiated. We conclude that DGCT is usually successful and is appropriate primary treatment for all symptomatic postcatheterization pseudoaneurysms in stable patients.

Adult↗
PubMed1995

Telemetered temperature monitoring in preweanling Mongolian gerbils (Meriones unguiculatus).

Like most small mammals, Mongolian gerbils (Meriones unguiculatus) are born without the ability to maintain core body temperature (Tb). Breeding adults, juvenile alloparents, nest materials, and other litter mates probably contribute to the maintenance of core body temperature in neonates, but the relative role of each factor is unknown. We developed a procedure allowing biotransmitters to be implanted into 9-day-old pups for use with a radiotelemetry system. Experiment 1 demonstrated the development of thermoregulatory capacity over postpartum days 11, 15, and 19. Pups at 11 days of age lacked thermoregulatory capacity, and maintained Tb only slightly above the ambient temperature (15 degrees C) of the testing environment. The transition from poikilothermy to homeothermy was clearly accomplished by day 19, with pups maintaining Tb of 35.8 +/- 0.2 degrees C for at least 100 min. Experiment 2 measured Tb in 11- and 12-day-old pups during a thermal challenge (15 degrees C) in the presence of nest materials, litter mates, or both. Pups provided with either nest materials, litter mates, or both maintained higher Tb during a 40-min test than those without these resources. Our methodology minimizes disruptions and the thermal consequences associated with other invasive (rectal probe thermistors) and noninvasive (e.g., infrared thermography) procedures.

Animals↗