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Biomedical subjects

J A Schaefer

Publications and source records attributed to J A Schaefer.

At least 19 recordsLinked to original sources
PubMed2006

Electronic structure of the surface of the ionic liquid [EMIM][Tf(2)N] studied by metastable impact electron spectroscopy (MIES), UPS, and XPS.

The near-surface electronic structure of the room-temperature ionic liquid (RT-IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf(2)N]) has been investigated with the combination of the electron spectroscopies metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS (HeI and HeII)), and monochromatized X-ray photoelectron spectroscopy (XPS). We find that the top of the valence band states originates from states of the cation (see also ref 1). The ultimately surface-sensitive technique MIES proves that the surface layer consists of both cations and anions. The temperature dependence of the spectra has been measured between about 160 and 610 K. Information on the glass transition and the possibility for low-temperature distillation of [EMIM][Tf(2)N] at reduced pressures is derived from the present results.

Journal Article↗
PubMed2003

Understanding and tuning the epitaxy of large aromatic adsorbates by molecular design.

If the rich functionality of organic molecules is to be exploited in devices such as light-emitting diodes or field-effect transistors, interface properties of organic materials with various (metallic and insulating) substrates must be tailored carefully. In many cases, this calls for well-ordered interfaces. Organic epitaxy-that is, the growth of molecular films with a commensurate structural relationship to their crystalline substrates--relies on successful recognition of preferred epitaxial sites. For some large pi-conjugated molecules ('molecular platelets') this works surprisingly well, even if the substrate exhibits no template structure into which the molecules can lock. Here we present an explanation for site recognition in non-templated organic epitaxy, and thus resolve a long-standing puzzle. We propose that this form of site recognition relies on the existence of a local molecular reaction centre in the extended pi-electron system of the molecule. Its activity can be controlled by appropriate side groups and--in a certain regime--may also be probed by molecularly sensitized scanning tunnelling microscopy. Our results open the possibility of engineering epitaxial interfaces, as well as other interfacial nanostructures for which specific site recognition is essential.

Journal Article↗
PubMed2001

Repeated latex aeroallergen challenges employing a hooded exposure chamber: safety and reproducibility.

BACKGROUND: Bronchial, nasal, and conjunctival challenges are useful for clarifying discordant clinical history (Hx) and skin and/or serologic tests and in assessing semiquantitative changes in biologic sensitivity over time. The objective of this study was to determine the safety and reproducibility of repeated latex-allergen challenges with a hooded exposure chamber (HEC). METHODS: The HEC system comprises a powered forced-air respirator with a fitted face shield and hood that uses glove-derived latex-allergen associated cornstarch particles (LAC) to expose simultaneously the conjunctiva, nose, and lungs. Serial control and incremental LAC challenges are conducted until an endpoint based on upper and/or lower respiratory tract symptoms and peak expiratory flow rates is reached. Six latex-allergic (Hx and puncture skin test [PST]- and 5/6 radioallergosorbent test [RAST]-positive) subjects were challenged on three separate occasions at least 2 weeks apart. Serial latex PST midpoints and serum anti-latex IgE by RAST were monitored at each visit and at a fourth follow-up visit. RESULTS: All subjects responded to LAC, but not to air or control cornstarch administered as controls. All responses were confined to mild symptoms of allergic rhinoconjunctivitis and/or asthma that either resolved spontaneously or were reversed with inhaled albuterol. No subject experienced a systemic or delayed reaction. There were no significant changes in the endpoint LAC doses over the three challenge visits (P>0.2). The mean coefficient of variation for log2 endpoints within-subjects was 17.3+/-17.2% (SD). The serum latex-specific IgE was not significantly boosted by the three challenges (P>0.2). The concentration of latex extract necessary to produce an 8-mm wheal by PST was not significantly changed during the study (P>0.1), indicating that latex sensitivity was not affected by the repeated LAC exposures. CONCLUSIONS: The results of this study indicate that repeated HEC latex-allergen challenges are both reproducible and safe, and do not increase latex sensitivity.

Administration, Inhalation↗
PubMed2001

A hooded exposure chamber method for semiquantitative latex aeroallergen challenge.

BACKGROUND: Allergen challenges are useful in adjudicating discordant clinical histories and skin test responses, serologic test responses, or both, as well as in determining the degree of allergic reactivity. Latex allergen challenges have been developed but have limitations that reduce their usefulness. OBJECTIVE: We sought to develop a novel hooded exposure chamber (HEC) system to allow safe, sensitive, and semiquantitative evaluation of respiratory latex allergy. METHODS: The HEC system uses an impinger to produce a particle cloud of cornstarch isolated from powdered latex gloves. The particles are air driven into a face shield and hood to simultaneously challenge the subject's conjunctiva, nose, and lungs during 3 minutes of normal tidal breathing. A cloud of respirable latex allergen-associated cornstarch particles (LACs) is consistently produced in the HEC during challenges. Twenty-three subjects with latex allergy (history and positive skin test response, positive serologic test response, or both) and 3 atopic control subjects not allergic to latex (history and negative skin test response, negative serologic test response, or both) were sequentially exposed to air, control cornstarch, and then progressive 2-fold increments of LACs in a single-masked fashion. A positive challenge result was defined as (1) a peak expiratory flow rate decline of 15% or greater from baseline; (2) a peak expiratory flow rate decline of 10% or greater and an increase of either the rhinoconjunctivitis or chest symptom score scale of 3 or more points from baseline; or (3) an increase of either the rhinoconjunctivitis or chest symptom score scale of 6 or more points from baseline. RESULTS: Twenty-two of the 23 subjects with latex allergy reached threshold criteria for a positive challenge at LAC titers of 1:8 or greater, giving a sensitivity of 0.96. Challenge endpoints were moderately corrected with skin test sensitivity (r (s) = -0.55, P =.01) but not with RAST reactivity. None of the 3 control subjects responded to LACs at the 1:8 dilution. No patient or control subject responded to the air or control cornstarch control exposures. All responses were confined to mild symptoms of allergic rhinoconjunctivitis, asthma, or both that either resolved spontaneously or were easily reversed with inhaled albuterol. No subject experienced a systemic or late-phase reaction. CONCLUSION: The HEC procedure is a safe, sensitive, and specific method for masked semiquantitative latex aeroallergen challenges that mimic occupational latex exposure to powdered latex gloves.

Administration, Inhalation↗
PubMed2000

A facilitated early return to work program at a large urban medical center.

An Early Return to Work Program was initiated at The Johns Hopkins Hospital and Associated Schools of Medicine, Hygiene and Nursing in Baltimore, Maryland, in April 1992 as part of a comprehensive effort to control the incidence and costs of work-related illnesses and injuries. The program was similar to others that incorporate employee and supervisory training and job accommodation, but it also included an industrial hygienist trained in ergonomics to facilitate the placement of individuals with restrictions. The return to work program was studied over a 10-year period, comparing the number of lost workday cases, lost workdays, and restricted duty days before (1989 to 1992) and after (1993 to 1999) initiation of the program. A significant decrease (55%) was observed in the rate of lost workday cases before versus after the return to work program. Furthermore, the number of lost workdays decreased from an average of 26.3 per 100 employees before, to 12.0 per 100 employees after, the return to work initiative, and the number of restricted duty days went from an average of 0.63 per 100 employees to 13.4 per 100 employees (a twentyfold increase). The study suggests that a well-structured early return to work program is an integral part of a comprehensive effort to control the duration of disability associated with occupational injuries and illness. It also indicates that to be most effective, an early return to work program must include participation by medical providers, safety professionals, injured employees, and supervisors. Our work suggests that even with these elements in place, the effectiveness of return to work programs may be increased by including an individual trained in ergonomics to facilitate the job placement process.

Accidents, Occupational↗
PubMed1999

An ergonomics program designed to reduce the incidence of upper extremity work related musculoskeletal disorders.

In 1992, the Johns Hopkins Hospital and University initiated a program aimed at the early diagnosis and treatment of potential upper extremity work related musculoskeletal disorders (UEWMSDs), ergonomic assessment and abatement of work areas where individuals with UEWMSDs are employed, as well as the identification and correction of areas throughout the hospital and university where UEWMSDs could possibly occur. The program resulted in an initial increase in the number and cost for the treatment of UEWMSDs. Subsequently, there was a significant decrease in the number of UEWMSDs reported and virtual elimination of the need to use surgical procedures to correct these conditions. This article suggests that a coordinated program of medical care, ergonomic assessment, and intervention can be efficacious in the primary, secondary, and tertiary prevention of UEWMSD.

Continuity of Patient Care↗
PubMed1996

Effects of work stressors and work climate on long-term care staff's job morale and functioning.

Relationships between work stressors and work climate, and job morale and functioning were examined. Initial and 8-month follow-up data were obtained from 405 staff in 14 long-term care facilities. Relationship and workload stressors were related to less job satisfaction and intent to stay in the job, and more job-related distress, depression, and physical symptoms. Patient care task stressors were associated with better outcomes. More positive work climates were linked to higher job morale. Initial work stressors predicted poorer functioning, and coworker cohesion predicted more intent to stay in the job at follow-up.

Adult↗
PubMed1995

Presentation and clinical investigation of mitochondrial respiratory chain disease. A study of 51 patients.

Defects of the mitochondrial respiratory chain are associated with a great variety of clinical disorders. Whilst recognition of these conditions is increasing, the need for sophisticated biochemical and molecular studies has tended to limit both their investigation and diagnosis to a few specialist centres. Using a group of 51 patients with histochemically, biochemically and/or genetically defined respiratory chain defects, we have examined both the clinical heterogeneity of these disorders and how they may be investigated most effectively in non-specialist centres. We evaluated the use of the following routinely available clinical investigations--fasting intermediary metabolites (lactate, pyruvate, ketone bodies, etc.) in blood and cerebrospinal fluid, serum creatine kinase estimation, EMG, EEG, CT, MRI and histological/histochemical muscle biopsy analysis. Our studies show that, in addition to well-recognized syndromes (e.g. chronic progressive external ophthalmoplegia, mitochondrial encephalopathy lactic acidosis and stroke like episodes, and myoclonus epilepsy with ragged red-fibres, a significant number of patients present with non-specific encephalopathic disorders. Furthermore, even within those categories of respiratory chain disease which have been genetically defined, a wide variation of presenting symptoms and signs were found. Where there was initial doubt concerning the diagnosis, the following clinical features were helpful in suggesting respiratory chain disease: ophthalmoplegia; a maternal pattern of inheritance; the presence of myopathy or deafness in association with encephalopathy. Of the clinical investigations we assessed, elevated lactate in blood or cerebrospinal fluid and low density lesions in the basal ganglia were helpful in identifying patients with respiratory chain dysfunction. Histochemical analysis of muscle was, however, the single most useful investigation being diagnostic in patients with chronic progressive external ophthalmoplegia, Kearns-Sayre syndrome and myopathy, and of significant importance in patients presenting primarily with central nervous system disease. The results of our study are used to discuss the most appropriate approach to diagnosis of this group of disorders.

Adolescent↗
PubMed1993

Occupational chemical exposures in an academic medical center.

Although the risks of certain chemical agents in the hospital environment are well known, problems associated with the entire spectrum of chemicals are not. To address this issue, we analyzed incident reports generated in response to chemical exposures in an academic medical center. We also reviewed workers' compensation clinic logs and the OSHA 200 log to obtain information on medical follow-up and severity. A total of 253 exposures occurred during the 3 years from 1988 to 1990. The overall incidence rate was 8.0 per 1000 person-years. Exposure rates by job title were highest for housekeepers (60.1 per 1000 person-years), followed by maintenance workers (18.6), and laboratory technicians (13.1). The most frequently involved chemical groups were disinfectants (25.9%), solvents (16.8%), and cleaning compounds (12.1%). Exposure by the dermal route was most common (37.9%). Thirteen percent of the exposures resulted in lost time and a similar percentage was reported on the OSHA log. Medical treatment was obtained by 53%. Implications for hazard communication, recordkeeping, and prevention are discussed.

Academic Medical Centers↗
PubMed1992

Neurocysticercosis in an Orthodox Jewish community in New York City.

BACKGROUND AND METHODS: From June 1990 through July 1991, intracerebral infection with the larval stage of the pork tapeworm Taenia solium was diagnosed in four unrelated persons in an Orthodox Jewish community in New York City. None of the patients had eaten pork, and only one had traveled to a country in which T. solium infection was endemic. We investigated this outbreak, screened serum samples from family members and household contacts for antibodies to cysticercosis, and examined stool specimens from household employees for eggs of taenia species. RESULTS: The four patients had recurrent seizures and brain lesions that were radiologically consistent with the presence of cysticerci. The diagnosis was confirmed in two patients by a brain biopsy, and in two by immunoblot assays for cysticercus antibodies. Of 17 immediate family members screened serologically, 7 from two families had cysticercus antibodies. Magnetic resonance imaging of the brain showed cystic lesions in two of the seropositive family members, one of whom had had a seizure. Examinations of six domestic employees from all four households revealed an active infection with taenia species in one and a positive serologic test in another. Since these women had recently emigrated from Latin American countries where T. solium infection is endemic, they were the most likely sources of infection in the members of these households. CONCLUSIONS: A diagnosis of neurocysticercosis should be considered in patients with seizures and radiologic evidence of cystic brain lesions, even in those who do not eat pork and who have not traveled to a country in which T. solium infection is endemic. Recent emigrants from countries in which T. solium infection is endemic should be screened for tapeworm infection in their stools before they are employed as housekeepers or food handlers.

Adolescent↗
PubMed1985

An in vitro study of the accuracy and precision of Breathalyzer models 900, 900A, and 1000.

Ninety Breathalyzer instruments (Model 1000) and twenty instruments (Models 900, 900A) were studied using a protocol described by the Department of Transportation's "Standard for Devices to Measure Breath Alcohol." Although the mean of each of three concentrations tested (0.05, 0.10, and 0.15 g/210 L) compared favorably in both series, the standard deviation was consistently higher for the Model 1000 instruments. The Model 1000 instruments also produced a significant number of test results which exceeded the normally expected scientific deviation.

Alcoholic Intoxication↗
PubMed1984

Relative lesion detection ability of Tc-99m HMDP and Tc-99m MDP: concise communication.

To compare the efficacy of Tc-99m HMDP and Tc-99m MDP to define skeletal lesions, 28 adult patients were examined in a double-blind, randomized, crossover study. Each patient was imaged with both agents over a period of 7-14 days. Both quantitative and qualitative evaluations were performed on the resulting images. Both agents detected the same number of skeletal lesions, and the number of lesions detected was the same whether the imaging was performed 2 or 4 hr after injection. Relative uptake of the tracer in the lesion relative to normal bone was also the same for both agents. Lesions were easier to see at 4 hr after injection than at 2 hr, presumably because soft-tissue levels were lower. Retention of tracer in bone compared with soft tissue was greater, and image quality was judged to be better, with Tc-99m HMDP than with Tc-99m MDP.

Adult↗
PubMed1977

Ultrastructural characteristics of the brain and blood-brain barrier in experimental seizures.

During experimental seizures, the blood-brain barrier (BBB) is broken; tracer substances such as I131-albumin, Evans blue and horseradish peroxidase (HRP) geographically locate the barrier breakdown primarily in the diencephalon. Using rats, we have induced seizures with electroshocks and demonstrated the breakdown of the BBB with Evans blue and HRP. We have shown that (1) the BBB breakdown is proportional to the number of electroconvulsant shocks (ES) given; (2) the mechanism of increased barrier permeability is primarily by micropinocytosis in the cerebral capillaries, arterioles, and, to a lesser extent, venules; and (3) the stimulus for micropinocytosis and hence BBB breakdown is associated with the abrupt rise in systemic blood pressure and cerebral vasodilatation that accompanies each ES. If the systolic hypertension is abolished via cervical cordotomy, there is little to no breakdown in the BBB.

Animals↗
PubMed1976

Spontaneous rupture of the stomach in the newborn: clinical and experimental evaluation.

Our study presents an experimental model for studying gastric rupture in the newborn. We showed that gastric rupture could be produced in eight newborn rodents and in three puppies less than 10 days old after injection of 120 ml air at 100 mm Hg pressure in the rodents and 175 ml air at 240 mm Hg pressure in the puppies. Gastric rupture occurred with animals supine and with approximately 20 ml barium injected into the stomach. Positioning of the animal in the supine position permitted the barium to pool in the antral-pyloric region of the stomach.

Age Factors↗