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Biomedical subjects

T A Hall

Publications and source records attributed to T A Hall.

At least 37 records · Page 2Linked to original sources
PubMed1999

Assessment of medical personnel exposure to nitrogen oxides during inhaled nitric oxide treatment of neonatal and pediatric patients.

OBJECTIVE: This study was an assessment of potential exposures of medical personnel to nitrogen oxides during simulated and actual inhaled nitric oxide treatment of newborn and pediatric patients. DESIGN: Breathing zone exposures to nitric oxide (NO) and nitrogen dioxide (NO(2)) were monitored using data-logging personal dosimeters during simulated and actual administration of NO gas to patients in an intensive care setting. Sample. A total of 28 bedside nurses and 18 respiratory therapists were monitored during 6 different patient treatments. ANALYSIS: The highest measured concentrations of NO and NO(2) in the personal breathing zones of the nurses and respiratory therapists were peak readings (<1 minute in duration) of 6.7 parts per million (ppm) NO and 3.1 ppm NO(2). Exposures averaged throughout 15 minutes and throughout the work shift were below the limit of detection (0.8-ppm NO and 0.5-ppm NO(2)). CONCLUSION: Detectable exposures to NO and NO(2) were brief, infrequent, and well below Occupational Safety and Health Administration permissible exposure limits or any other exposure guideline, eg, American Conference of Governmental Hygienists Threshold Limit Values.

Administration, Inhalation↗
PubMed1995

Air pollution and daily mortality in Philadelphia.

Many recent analyses have reported associations between air pollution and mortality in U.S. cities. In this paper, we present the results of regression analyses of daily mortality in Philadelphia during the period 1973-1988. Pollution variables included in the analyses were total suspended particulates (TSP), sulfur dioxide, and ozone. We controlled for the effects of weather on mortality by analyzing mortality separately for each season and explicityly including quintiles of temperature in the regression models. In regression models that consider weather and pollution variables simultaneously, daily mortality is associated with hot days in summer [relative risk (RR) for highest quintile of temperature = 1.07; 95% confidence interval (CI) = 1.04-1.10], and with cold days in spring (RR for lowest quintile of temperature = 1.07; 95% CI = 1.04-1.10), fall (RR for lowest quintile of temperature = 1.05; 95% CI = 1.02-1.08), and winter (RR for lowest quintile of temperature = 1.04; 95% CI = 1.01-1.07). When all three pollution covariates and weather are considered simultaneously in the regression model, ozone is associated with mortality in summer (RR = 1.15; 95% CI = 1.07-1.24) and sulfur dioxide is associated with mortality in spring (RR = 1.19; 95% CI = 1.06-1.33), fall (RR = 1.14; 95% CI = 1.00-1.29), and winter (RR = 1.21; 95% CI = 1.09-1.35), where the relative risks are for incremental changes of 100 parts per billion in ozone and sulfur dioxide on the previous day.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗
PubMed1994

The neuroepidemiology of styrene: a critical review of representative literature.

Because exposure to styrene occurs commonly in some industries and styrene is highly lipid soluble, it is reasonable to be concerned about the possibility that styrene is neurotoxic. Styrene, like many other solvents, volatile anesthetics, and drugs, does, at certain concentrations, produce acute changes in consciousness with consequent alterations of feelings, cognition, and psychomotor functioning. Such acute actions do not imply that styrene also would produce reversible or irreversible damage to the nervous system; the evaluation of long-term exposures to styrene also is necessary to draw conclusions about the full range of neural effects that styrene might produce. To that end, several studies of workers exposed to styrene for up to 30 years have been undertaken in factories in many parts of the world. Epidemiologists have suggested that neuropsychological deficits such as slowing of reaction time, loss of color vision, and vestibulooculomotor dysfunction are reliably induced by styrene at levels near or below current exposure standards, which range from 20 to 50 ppm in most of the world. However, the workers so studied always were described as healthy, and the effects noted were considered to be subclinical. A detailed evaluation of much of the neuroepidemiological literature on styrene (38 papers and related literature), however, indicated that the findings were, almost universally, false positive outcomes due to (1) type I statistical error, (2) the action of some factor other than styrene, and (3) misinterpretation of data. Despite the study of workers exposed for many years, no indications of persisting damage to the nervous system were evident from this review. The conclusions of this review of the neuroepidemiology of styrene are consistent with those based on critical reviews of the solvent literature in general, with specific reference to the probable absence of such an entity as the "painter's syndrome" or "chronic toxic encephalopathy". Because the results on styrene neurotoxicity that provide an inclination to lower the current threshold limit values (TLVs) are false positive findings, there is no scientific basis for a reduction in the current TLV.

Animals↗
PubMed1991

AIDS series--paper III-B. Prevention of HIV transmission in the workplace: categorization of jobs and tasks by risk of HIV infection.

The risk to workers of exposure to HIV or other blood-borne infectious diseases on the job is dependent upon the likelihood of exposure to blood, body fluids, or tissues while performing the tasks required by the job. Three categories of workplace-associated risk of HIV exposure have been defined. These categories can be summarized as follows. Category I--Regular or Frequent Exposure Potential. Applies primarily to health-care workers, including emergency medical workers. These workers are at greatest risk of occupationally acquired HIV disease. Category II--Intermittent Exposure Potential. Applies to persons such as police officers, fire fighters, and correctional facility personnel. Category III--Rare or No Exposure Potential. Applies to most jobs in the service and manufacturing industries, including office personnel. These workers are at no greater risk than the general public for exposure to HIV. As there is definite risk to Category I and II workers of becoming infected with HIV while performing duties required by their jobs (their risk of acquiring HBV is much greater), it is important for employers in these workplaces to establish procedures to prevent the exposures that may lead to infections. The first step in this process is to analyze carefully tasks performed within the workplace to identify Category I and II tasks, as described in the DOL/DHHS Joint Advisory Notice. Once this has been done, the DOL/DHHS document and pertinent CDC recommendations should be used to develop specific procedures for those workers at risk.

HIV Infections↗
PubMed1991

Procedures to protect health-care workers from HIV infection: category I (health-care) workers.

At the heart of the recommendations to prevent HIV transmission in workers who perform high-risk tasks are the universal blood and body fluid precautions. These precautions are meant to be followed by all health-care workers in the care of all patients and by public safety workers (e.g., firefighters, police officers, and correctional facility personnel) whenever they perform specific tasks that expose them to blood, body fluids, or tissues. Universal precautions apply to blood, semen, vaginal secretions, body tissues, cerebrospinal fluid, synovial fluid, pleural fluids, peritoneal fluid, pericardial fluid, and amniotic fluid. These fluids have either been implicated in HIV transmission or their risk of transmission is unknown. Other fluids or excretions are excluded from universal precautions because epidemiologic studies have failed to implicate them in HIV transmission. These include feces, nasal secretions, sputum, sweat, tears, urine, vomitus, breast milk, and saliva, unless they contain visible blood. However, routine precautions (handwashing, gloves, etc.) to prevent exposure to other diseases transmitted by these media should be followed. Other precautions are directed at health-care workers who perform specialized at-risk procedures, e.g., surgeons, dentists, laboratory workers, etc. In general, recommendations for these workers include the universal precautions plus additional emphasis on the use of barrier measures. Although the risk of environmentally mediated HIV transmission is negligible, it is theoretically possible, and recommendations to kill or inactivate HIV on environmental surfaces should be followed. Fortunately, HIV is easily inactivated in the environment. The cheapest and most convenient method is a 1:10 or 1:100 dilution of household bleach.(ABSTRACT TRUNCATED AT 250 WORDS)

Allied Health Personnel↗
PubMed1991

Regulatory implications of airborne respirable free silica variability in underground coal mines.

The respirable dust standard for respirable free crystalline silica in underground coal mines is expressed as milligrams per cubic meter (mg/m3) of respirable dust and is determined by the silica content of the dust. The Mine Safety and Health Administration (MSHA) regulates silica exposure by determining and enforcing compliance with the respirable dust standard for each active mine section. The MSHA strategy for regulation is examined in the context of respirable free crystalline silica and dust data. Deficiencies of the strategy include the same enforcement efforts regardless of compliance history, inappropriate treatment of data, and emphasis on short-term variability of silica content. These deficiencies result in inadequate enforcement in chronically dusty mines, "game playing" with optional samples, and an overall approach that does not focus on the long-term impact of silica exposure on lung health. Alternative approaches include enforcement efforts proportional to compliance history, use of a moving average silica content, and more statistically sound approaches to data interpretation.

Air Pollutants, Occupational↗
PubMed1991

Suggestions for the quantitative X-ray microanalysis of thin sections of frozen-dried and embedded biological tissues.

When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a 'tag' element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measureable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage.

Animals↗
PubMed1990

Evaluation of women with possible appendicitis using technetium-99m leukocyte scan.

The authors evaluated the use of technetium-99m albumin colloid white blood cell (TAC-WBC) scan in women with possible appendicitis. One hundred and nine women underwent 110 TAC-WBC scans. One woman had a second scan on a separate admission and was considered two individual patients in the analysis. Twenty-six women had appendicitis, 10 of whom had a perforated appendix at surgery. The TAC-WBC scan was indeterminate (abnormal but nondiagnostic for appendicitis) in 52 women (47%), nine of whom had appendicitis. Fifty-eight scans were read as positive or negative for appendiceal pathology. There were 16 true positives, 5 false positives, 36 true negatives, and 1 false negative. The predictive value of a positive scan was 76%, and the predictive value of a negative scan was 97%. The TAC-WBC scan was positive in 62% of patients with appendicitis and negative in 43% of the patients without appendicitis resulting in an overall accuracy of 47% in the 109 women. The main value of TAC-WBC scan in women with possible appendicitis is its high negative predictive value and the main problem with the TAC-WBC scan is its high indeterminate rate.

Abdominal Pain↗
PubMed1986

Optical transmission of normal and atheromatous arterial wall: a spectral analysis.

In laser angioplasty one of the factors influencing the immediate damage (and therefore the risk of acute arterial perforation) is the optical absorption characteristics of the target tissue. In an attempt to evaluate the differences in optical absorptive properties, the transmission spectrograms of samples of normal and atheromatous human postmortem aortic wall were measured over the visible spectrum. Optical transmission varied inversely with sample thickness and directly with wavelength through both normal and atheromatous samples. Over the whole visible spectrum atheromatous tissue transmitted less per unit thickness than normal tissue. This differential effect was, however, most pronounced at 500 nm, where atheromatous tissue transmitted light 5-10 times less strongly than normal aortic wall. Such wavelength dependent differential optical absorption could provide a means for the selective photovaporisation of atheroma in laser angioplasty.

Angioplasty, Balloon↗
PubMed1986

Properties of frozen sections relevant to quantitative microanalysis.

Difficulties in the quantitative X-ray microanalysis of frozen sections may conceivably arise from ice-crystal damage and from electron-beam damage. X-ray peak-to-continuum ratios are commonly taken as a quantitative index of elemental concentrations. But recent reports suggest that in dehydrated frozen sections such ratios vary greatly with the scale of ice-crystal formation existing prior to sublimation. The experiments in these reports are re-interpreted here; it is argued that peak intensities may be affected by ice-crystal scale but that ratios of peak to continuum should not be affected after corrections for exogenous continuum. The accuracy of the peak-to-continuum method is affected by beam-induced loss of mass from microvolumes during analysis. Mass loss can be reduced or slowed by a cold-stage. For example, the radiation sensitivity for loss of chlorine from PVC is reduced by a factor of 1000 or more with reduction of temperature from 300 to 100 K. For sections of soft tissue the effectiveness of cooling is not nearly so striking but at 100 K, analyses of 1 micron frozen-hydrated sections by the continuum method, with spatial resolution of the order of 1 micron, can be completed before substantial mass loss occurs. However, analysis of frozen-hydrated sections by the continuum method at much higher resolution, say 100 nm resolution in 100 nm sections, is precluded by mass loss. Measurements of local mass can be achieved with much lower dose by observation and calibration of the electron transmission or backscattering. But even with these methods, several problems remain in achieving quantitative X-ray analysis at very high resolution.

Electron Probe Microanalysis↗
PubMed1985

Electron probe X-ray microanalysis of the effects of Bacillus thuringiensis var kurstaki crystal protein insecticide on ions in an electrogenic K+-transporting epithelium of the larval midgut in the lepidopteran, Manduca sexta, in vitro.

An alkaline hydrolysate of Bacillus thuringiensis var kurstaki HD1 (Btk) parasporal crystals was administered at 25 micrograms ml-1 (f.c.) to isolated, short-circuited, midguts of tobacco hornworm (Manduca sexta) larvae. The short-circuit current (s.c.c.), a precise measure of K+ active transport, was inhibited by 78% in 10 min in Btk-treated midguts as compared to controls. The elemental concentrations of K, together with Na, Mg, P, S, Cl and Ca, as well as the water content, were determined by electron probe X-ray microanalysis (EPXMA) in the muscle cells, columnar cells and goblet cells, as well as in the extracellular goblet cavity and the bathing media. The average K concentration in the goblet cell cavity was 129 mmol/kg wet wt in control midguts but only 37 mmol/kg wet wt in Btk-treated midguts. The elemental concentrations, including that of K, in other cell compartments were much less affected by Btk, but a rise in total cell calcium is suggested. It has been previously suggested that in vitro Btk acts specifically on limited regions of the apical membrane of the midgut epithelial cells. The simplest interpretation of the EPXMA results would be that initially Btk interacts specifically with the goblet cell apical membrane, which bounds the goblet cavity and contains the K+ pump responsible for the s.c.c. and high transepithelial potential difference (p.d.). Such interaction results in a rapid disruption of K+ transport across the goblet cell apical membrane, leading to dissipation of the K+ gradient and loss of p.d. The histopathological changes previously reported by other workers would then be a consequence of K+ pump inhibition causing changes in the intracellular pH, Ca2+ etc. Some possible molecular bases for these specific interactions between Btk and cell membrane are discussed.

Animals↗
PubMed1984

X-ray microanalysis of elements in frozen-hydrated sections of an electrogenic K+ transport system: the posterior midgut of tobacco hornworm (Manduca sexta) in vivo and in vitro.

The lepidopteran midgut is a model for the oxygen-dependent, electrogenic K+ transport found in both alimentary and sensory tissues of many economically important insects. Structural and biochemical evidence places the K+ pump on the portasome-studded apical plasma membrane which borders the extracellular goblet cavity. However, electrochemical evidence implies that the goblet cell K+ concentration is less than 50 mM. We used electron probe X-ray microanalysis of frozen-hydrated cryosections to measure the concentration of Na, Mg, P, S, Cl, K, Ca and H2O in several subcellular sites in the larval midgut of Manduca sexta under several experimental regimes. Na is undetectable at any site. K is at least 100 mM in the cytoplasm of all cells. Typical in vivo values (mM) for K were: blood, 25; goblet and columnar cytoplasm, 120; goblet cavity, 190; and gut lumen, 180. The high K concentration in the apically located goblet cavity declined by 100 mM under anoxia. Both cavity and gut fluid are Cl deficient, but fixed negative charges may be present in the cavity. We conclude that the K+ pump is sited on the goblet cell apical membrane and that K+ follows a nonmixing pathway via only part of the goblet cell cytoplasm. The cavity appears to be electrically isolated in alimentary tissues, as it is in sensory sensilla, thereby allowing a PD exceeding 180 mV (lumen positive) to develop across the apical plasma membrane. This PD appears to couple K+ pump energy to nutrient absorption and pH regulation.

Animals↗