Biomedical subjects

David L Johnson

Publications and source records attributed to David L Johnson.

At least 19 recordsLinked to original sources

PubMed2007

Intramammary infections in heifers during early lactation following intramammary infusion of pirlimycin hydrochloride or penicillin-novobiocin at the first milking after parturition.

A study was conducted to determine whether intramammary antibiotic treatment of heifer mammary glands following the first milking after calving was effective for reducing the percentage of mammary quarters infected during early lactation. Jersey and Holstein heifers from two research herds were assigned to one of three treatment groups: (1) no intramammary infusion following the first milking after parturition, (2) intramammary infusion of all quarters with pirlimycin hydrochloride following the first milking after parturition and (3) intramammary infusion of all quarters with novobiocin sodium plus penicillin G procaine following the first milking after parturition. Almost 93% of Jersey heifers (40/43) and 73.1% of quarters (125/171) were infected at the first milking. Almost 77% of quarters (33/43) were cured following treatment with pirlimycin, 61.8% (21/34) were cured following treatment with penicillin-novobiocin and 39.6% (19/48) of infections were eliminated spontaneously in the untreated control group. Significantly fewer infections were observed in pirlimycin or penicillin-novobiocin treated mammary glands of Jersey heifers during early lactation than in untreated control mammary glands. Almost 89% of Holstein heifers (32/36) and 52.8% of quarters (76/144) were infected at the first milking. About 57% (12/21) of quarters were cured following treatment with pirlimycin, 41.4% (12/29) were cured following treatment with penicillin-novobiocin and 23.1% (6/26) of infections were eliminated spontaneously in the untreated negative control group. Significantly fewer infections were observed in pirlimycin treated mammary glands of Holstein heifers during early lactation than in untreated control mammary glands. However, no significant differences were observed following penicillin-novobiocin treatment of Holstein heifers after the first milking of lactation compared with untreated control quarters. Coagulase-negative staphylococci, Streptococcus uberis and Streptococcus dysgalactiae subsp dysgalactiae were isolated most frequently in heifers from both herds.

Animals↗

PubMed2006

Mass transfer of soil indoors by track-in on footwear.

Inadvertent soil ingestion, especially by young children, can be an important route of exposure for many environmental contaminants. The introduction of exterior soil into the interior environment is a significant element of the exposure pathway. The unintentional collection of outside soil on footwear followed by subsequent deposition indoors is a principal route of soil ingress. Here we have investigated likely rates of dry and wet soil deposition on indoor hard surface flooring as a result of mass transfer from soiled footwear. In this pilot study, testing involved both single track-in events (with deposition resulting from a single progression of transfer steps) and multiple tracking actions (with deposition and dispersion resulting from repeated transfer steps). Based on soil mass recovery from the floor surface it was found that any contamination introduced by one-time track-in events was of limited spatial extent. In contrast, under repeated tracking conditions, with multiple soil incursions, widespread floor surface contamination was possible. Soil mass recovery was accomplished by brushing, by vacuum cleaner removal and by wet wiping. All the clean-up methods operated imperfectly and failed to remove all initially deposited soil. The level of floor surface soiling that resulted from the track-in tests, and the incomplete clean-up strongly suggest that under unrestricted transfer conditions rapid accumulation and dispersal of soil on indoor flooring is likely.

Dust↗

PubMed2006

Role of sooty mold fungi in accumulation of fine-particle-associated PAHs and metals on deciduous leaves.

The focus of this research was on elucidation of the role of deciduous tree ecosystems in accumulation of fine-particle-associated polycyclic aromatic hydrocarbons (PAHs) and heavy metals on leaves of deciduous trees. The studied species were Tilia x euchlora (frequently infested by sooty mold fungi) and Pyrus calleryana (unaffected by sooty mold fungi). The selected species have similar leaf morphology and were exposed to identical environmental conditions. Intra-species comparison showed that moldy linden leaves accumulate significantly higher amounts of PAHs and metals than unaffected linden leaves. Inter-species comparison revealed that in the absence of sooty mold fungi, physico-chemical properties of epicuticular waxes, rather than the amounts of waxes, might play an important role in accumulation of particulate matter on leaves. The accumulation and/or degradation of a number of high-molecular-weight (HMW) PAHs on leaves was temperature dependent. The results show that the presence of sooty mold fungi on deciduous leaves alters either the accumulation modes and/or degradation pathways of PAHs on deciduous leaves.

Air Pollutants↗

PubMed2005

Granular dynamics in compaction and stress relaxation.

Elastic and dissipative properties of granular assemblies under uniaxial compression are studied both experimentally and by numerical simulations. Following a novel compaction procedure at varying oscillatory pressures, the stress response to a step strain reveals an exponential relaxation followed by a slow logarithmic decay. Simulations indicate that the latter arises from the coupling between damping and collective grain motion predominantly through sliding. We characterize an analogous "glass transition" for packed grains, below which the system shows aging in time-dependent sliding correlation functions.

Journal Article↗

PubMed2005

Are public health workers aware of what they don't know?

OBJECTIVES: Training of public health workers is an important part of preparedness. Self-assessment is often used to measure how well workers are trained and whether they are ready to respond to an emergency event. The current study assessed how well self-assessment predicts actual knowledge. METHODS: Public health workers at a Public Health Ready pilot site self-assessed their general level of confidence, answered objective knowledge items about their local response plan, and self-assessed whether they were correct on the objective knowledge items. Correlational analysis was used to assess how well workers could assess what they knew and did not know. RESULTS: In the first analysis, for 15 objective knowledge items, the median correlation between self-assessment and actual performance was 0.18. When the average self-assessment on the core competencies was correlated with the number of correct answers to the objective knowledge items, the correlation was 0.34. CONCLUSIONS: The modest sizes of the correlations suggest that workers are weak judges of what they know and do not know. To prepare public workers for emergency events, it is suggested that two steps are important: (1) using the core competencies, develop a local response plan, and (2) develop an objective knowledge test to assess workers' knowledge of the local response plan.

Attitude of Health Personnel↗

PubMed2005

Partnering for preparedness: the project public health ready experience.

Effective partnerships between local and state public health agencies and schools of public health have tremendous potential to improve the health of communities nationwide. This article highlights successful collaboration between local public health agencies (LPHA), state health departments, and Academic Centers for Public Health Preparedness (ACPHP) in schools of public health developed through participation in Project Public Health Ready, a program to recognize LPHA emergency preparedness. The project's pilot phase illustrated that LPHAs, state health departments, and ACPHP can effectively work together to improve individual public health worker competency and organizational response capacity in local public health agencies nationwide.

Community Health Centers↗

PubMed2005

Seasonality and children's blood lead levels: developing a predictive model using climatic variables and blood lead data from Indianapolis, Indiana, Syracuse, New York, and New Orleans, Louisiana (USA).

On a community basis, urban soil contains a potentially large reservoir of accumulated lead. This study was undertaken to explore the temporal relationship between pediatric blood lead (BPb), weather, soil moisture, and dust in Indianapolis, Indiana; Syracuse, New York; and New Orleans, Louisiana. The Indianapolis, Syracuse, and New Orleans pediatric BPb data were obtained from databases of 15,969, 14,467, and 2,295 screenings, respectively, collected between December 1999 and November 2002, January 1994 and March 1998, and January 1998 and May 2003, respectively. These average monthly child BPb levels were regressed against several independent variables: average monthly soil moisture, particulate matter < 10 microm in diameter (PM10), wind speed, and temperature. Of temporal variation in urban children's BPb, 87% in Indianapolis (R2 = 0.87, p = 0.0004), 61% in Syracuse (R2 = 0.61, p = 0.0012), and 59% in New Orleans (R2 = 0.59, p = 0.0000078) are explained by these variables. A conceptual model of urban Pb poisoning is suggested: When temperature is high and evapotranspiration maximized, soil moisture decreases and soil dust is deposited. Under these combined weather conditions, Pb-enriched PM10 dust disperses in the urban environment and causes elevated Pb dust loading. Thus, seasonal variation of children's Pb exposure is probably caused by inhalation and ingestion of Pb brought about by the effect of weather on soils and the resulting fluctuation in Pb loading.

Child, Preschool↗

PubMed2005

Suitability of caspofungin for aerosol delivery: physicochemical profiling and nebulizer choice.

BACKGROUND: Aerosolized antifungal therapy is a promising route of drug delivery for pulmonary aspergillosis due to attainment of high localized concentrations. Caspofungin, a new antifungal agent with proven efficacy against invasive aspergillosis, has ideal potential for aerosolization. STUDY OBJECTIVE: To examine in vitro the suitability of caspofungin for aerosol administration by characterizing factors that influence efficacy and airway tolerance of aerosol delivery: physicochemical properties, aerodynamics of drug particles, and efficiency of nebulizing systems. DESIGN: Physicochemical characteristics of caspofungin solutions (10 mg/mL and 30 mg/mL) were analyzed: osmolality, pH, viscosity, and surface tension. A time-of-flight aerosol spectrometer API Aerosizer was used to determine aerosol particle size and distribution. Drug output was quantified by high-performance liquid chromatography assay. Nebulizer efficiency was measured by drug output and respirable fraction (percentage of aerosolized particles with a 1 to 5 mum aerodynamic diameter) and compared among three jet nebulizer/compressor systems: device 1, Micromist (Hudson RCI; Temecula, CA)/Pulmo-Aide (model 5650D; DeVilbiss; Somerset, PA); device 2, Sidestream MS 2400/Envoy model IRC 1192 (Invacare; Elyria, OH); and device 3, Pari LC Star/Proneb Ultra (Pari Respiratory Equipment; Midlothian, VA). MEASUREMENTS AND RESULTS: Caspofungin requires 0.9% NaCl rather than sterile water as the diluent and addition of 0.3N NaOH buffer to adjust acidity of solutions (pH 6.17 to 6.26) in order to achieve optimal physicochemical properties for airway tolerability (osmolality, 150 to 550 milliosmol per kilogram; chloride ion, 31 to 300 mmol/L; and pH 7.4). The drug output rate increased with higher concentrations of drug solution: device 1, 4.0 mg/min vs 12.5 mg/min; device 2, 5.4 mg/min vs 14.7 mg/min; and device 3, 2.3 mg/min vs 12 mg/min, respectively. The percentage of particles within the respirable range varies depending on device and concentration of drug solutions (10 mg/mL vs 30 mg/mL): device 1, 85% vs 38%; device 2, 44% vs 57%; and device 3, 83% vs 93%, respectively. CONCLUSION: Caspofungin solution with adjustments appears to have physicochemical and aerodynamic characteristics suitable for aerosolization when used with either the Pari LC Star/Proneb Ultra or Micromist/Pulmo-Aide devices. Further in vivo testing is warranted.

Antifungal Agents↗

PubMed2005

Is running performance enhanced with creatine serum ingestion?

Runners Advantage (RA) creatine (Cr) serum has been marketed to increase running performance. To test this claim, cross-country runners completed baseline testing (BASE), an outdoor 5,000-m run followed by treadmill Vo(2)max testing on the same day. Subjects repeated testing after ingesting 5 ml of RA (n = 13) containing 2.5 g of Cr or placebo (n = 11). Heart rate (HR), rating of perceived exertion (RPE), and run time were recorded. With RA (56.48 +/- 8.93 ml.kg(-1.)min(-1)), Vo(2)max was higher (p = 0.01) vs. BASE (54.07 +/- 9.36 ml.kg(-1.)min(-1)), yet the magnitude of the increase was within the coefficient of variation of Vo(2)max. No effect of RA on maximal HR was exhibited, yet Vco(2)max and duration of incremental exercise were significantly higher (p < 0.025) vs. BASE. Vo(2)max was similar in PL (58.85 +/- 6.67 ml.kg(-1).min(-1)) and BASE (57.28 +/- 7.22 ml.kg(-1.)min(-1)). With RA, the 5,000-m time was unchanged, and RPE was lower (p < 0.025) vs. BASE. These data do not support the ergogenic claims of RA in its current form and dose.

Adult↗

PubMed2005

Cadaver testing to validate design criteria of an adult intraosseous infusion system.

INTRODUCTION: The FAST 1 intraosseous (IO) infusion system was designed to deliver fluids and medications into the adult sternum in the prehospital and battlefield environments. OBJECTIVE: To test the prototype in 106 cadavers and excised sterna and compare it with other IO devices. RESULTS: The insertion force was similar to that of other IO devices (mean, 8.5 kg; range, 2.3-19.6 kg). In 39 of 39 trials, the depth-control mechanism inserted the portal within 1.0 mm of a predetermined distance below the anterior surface of the cortical bone. If misplaced, underpenetration was more likely than overpenetration (mean displacement, -0.3 mm; SD, 0.5 mm). After release, the portal could not be advanced further into the manubrium. Marrow was accessed in 75 of 77 trials. Mean flow rates were 109 mL/min for normal saline solution and 102 mL/min for hypertonic saline/dextran, similar to the Cook Sur-Fast device. CONCLUSION: The cadaver and bench tests demonstrated the reliability and safety of the FAST 1 system at the design/prototype stage.

Aged↗

PubMed2004

Granular packings: nonlinear elasticity, sound propagation, and collective relaxation dynamics.

Experiments on isotropic compression of a granular assembly of spheres show that the shear and bulk moduli vary with the confining pressure faster than the 1/3 power law predicted by Hertz-Mindlin effective medium theories of contact elasticity. Moreover, the ratio between the moduli is found to be larger than the prediction of the elastic theory by a constant value. The understanding of these discrepancies has been a long-standing question in the field of granular matter. Here we perform a test of the applicability of elasticity theory to granular materials. We perform sound propagation experiments, numerical simulations, and theoretical studies to understand the elastic response of a deforming granular assembly of soft spheres under isotropic loading. Our results for the behavior of the elastic moduli of the system agree very well with experiments. We show that the elasticity partially describes the experimental and numerical results for a system under compressional loads. However, it drastically fails for systems under shear perturbations, particularly for packings without tangential forces and friction. Our work indicates that a correct treatment should include not only the purely elastic response but also collective relaxation mechanisms related to structural disorder and nonaffine motion of grains.

Journal Article↗

PubMed2004

An evaluation of portable high-efficiency particulate air filtration for expedient patient isolation in epidemic and emergency response.

Extraordinary incidents resulting in airborne infectious disease outbreaks could produce patient isolation requirements that exceed most hospitals' capacity. This article investigates expedient methods to establish airborne infection isolation areas using a commercially available portable filtration unit and common hardware supplies. The study was conducted within a conventional, nonisolation hospital room, and researchers evaluated several airborne isolation configurations that did not require building ventilation or structural modifications. A portable high-efficiency particulate air filtration unit and full-length plastic curtains established a "zone-within-zone" protective environment using local capture and directional airflows. The cost of constructing the expedient configurations was less than US2,300 dollars and required fewer than 3 person-hours to construct. A medical nebulizer aerosolized polystyrene latex microspheres to generate respirable condensation nuclei. Aerosol spectrometers sized and counted respirable particles at the source patient and health care worker positions and in areas outside the inner zone. The best-performing designs showed no measurable source migration out of the inner isolation zone and mean respirable particle counts up to 87% lower at the health care worker position(s) than those observed directly near the source patient location. Investigators conclude that with careful implementation under emergency circumstances in which engineered isolation rooms are unavailable, expedient methods can provide affordable and effective patient isolation while reducing exposure risks and potential disease transmission to health care workers, other patients, and visitors.

Bioterrorism↗

PubMed2003

The effectiveness of handheld ventilated sanders in reducing inhalable dust concentrations.

Ventilated sanders are commonly used during aircraft surface abrasion but there is limited data on their effectiveness in reducing worker exposures. This study compared two handheld ventilated sander brands, DCM and Dynabrade, in a laboratory glovebox. Both sanders collect particulates by drawing air through holes in the sanding pads; the dust subsequently passes into a vacuum collection system. Aluminum panels coated with aircraft epoxy primer and polyurethane paint were abraded and inhalable dust concentrations were measured inside the glovebox with IOM samplers. The results indicate that both sanders effectively control inhalable dust, with the DCM sander reducing mass concentrations by 93 percent, and the Dynabrade by 98 percent, when the ventilation system is used. The Dynabrade unit, however, was more aggressive and produced over four times as much dust per unit time as the DCM unit. In spite of this, the Dynabrade sander adequately collected this additional dust. Varying abrasive grit size did not significantly affect dust generation, although the differences between the grit sizes used (180 and 240 grit) were not great and may have influenced the results.

Air Pollutants, Occupational↗

PubMed2003

Efficacy of extended pirlimycin therapy for treatment of experimentally induced Streptococcus uberis intramammary infections in lactating dairy cattle.

Streptococcus uberis is an important cause of mastitis in dairy cows throughout the world, particularly during the dry period, around the time of calving, and during early lactation. Strategies for controlling S. uberis mastitis have not received adequate research attention and are therefore poorly defined and inadequate. Objectives of the present study were to evaluate the efficacy of extended therapy regimens with pirlimycin for treatment of experimentally induced S. uberis intramammary infections in lactating dairy cows during early lactation and to evaluate the usefulness of the S. uberis experimental infection model for evaluating antimicrobial efficacy in dairy cows. The efficacy of extended pirlimycin intramammary therapy regimens was investigated in 103 mammary glands of 68 dairy cows that became infected following experimental challenge with S. uberis during early lactation. Cows infected with S. uberis in one or both experimentally challenged mammary glands were randomly allocated to three groups, representing three different treatment regimens with pirlimycin, including 2-day (n = 21 cows, 31 mammary quarters), 5-day (n = 21 cows, 32 quarters), and 8-day (n = 26 cows, 40 quarters). For all groups, pirlimycin was administered at a rate of 50 mg of pirlimycin hydrochloride via intramammary infusion. A cure was defined as an experimentally infected mammary gland that was treated with pirlimycin and was bacteriologically negative for the presence of S. uberis at 7, 14, 21, and 28 days after treatment. Experimental S. uberis intramammary infections were eliminated in 58.1% of the infected quarters treated with the pirlimycin 2-day regimen, 68.8% for the 5-day regimen, and 80.0% for the 8-day regimen. Significant differences (P <.05) in efficacy were observed between the 2-day and 8-day treatment regimens. The number of somatic cells in milk decreased significantly following therapy in quarters for which treatment was successful in eliminating S. uberis. However, there was no evidence to suggest that extended therapy with pirlimycin resulted in a greater reduction in somatic cell counts in milk than the 2-day treatment. The S. uberis experimental infection model was a rapid and effective means of evaluating antimicrobial efficacy during early lactation at a time when mammary glands are highly susceptible to S. uberis intramammary infection.

Animals↗

PubMed2002

The relationship of particle size to olfactory nerve uptake of a non-soluble form of manganese into brain.

The essential element, manganese, can produce chronic neuromotor impairment related to basal ganglia (BG) damage when it is presented in excessive quantities. The uptake and elimination patterns of manganese following ingestion have been well studied and, under normal conditions, excretion appears to keep manganese levels under tight control. Less is known about inhalation exposure, but it has been proposed that the lung might serve as a long-term reservoir for manganese transport into blood. Recent data suggest that a third route of exposure, transport by the olfactory nerve directly to the brain, might have importance in toxicology since such a route would bypass liver uptake and biliary excretion of manganese. In this study, we sought to determine how particle size and the use of a poorly soluble form of manganese might influence net systemic absorption of manganese dust and the potential role of the olfactory nerve in transport of manganese dioxide. Rats were exposed in nose-only exposure chambers to manganese dioxide (MnO2) aerosols of 1.3 and 18 microm mass median aerodynamic diameter (MMAD). The concentration of aerosols was kept constant at 3 mg/m3 as Mn. Following 15 days of exposure (five times per week for 3 weeks), rats were euthanized and tissues harvested for manganese determination carried out by graphite furnace atomic absorption spectroscopy. Small-particle MnO2 exposure resulted in an elevation in olfactory bulb manganese concentration, presumably through uptake by the olfactory nerve, but the effect was highly variable. While small increases in cortical and neostriatal manganese levels were also observed in these rats, they did not reach statistical significance. By contrast, there was no evidence of olfactory nerve MnO2 uptake in rats receiving the large-particle exposure.

Administration, Inhalation↗

PubMed2002

Differences in accumulation of PAHs and metals on the leaves of Tiliaxeuchlora and Pyrus calleryana.

The accumulation of substances associated with PM2.5 [polycyclic aromatic hydrocarbons (PAHs) and metals] on leaves of Pyrus calleryana (pear) and Tiliaxeuchlora (linden) along an urban road was investigated. These species have similar leaf morphology and were exposed to the identical environmental conditions. The accumulation of both PAHs and metals per leaf area was significantly higher on linden leaves than on pear leaves.

Air Pollutants↗

PubMed2002

Potentiation of noise-induced hearing loss by low concentrations of hydrogen cyanide in rats.

Noise-induced hearing loss is the most prevalent occupational injury in the United States despite the adoption of clear permissible exposure limits and protocols for hearing conservation. This study identifies low-level chemical asphyxiant exposure as a risk factor capable of potentiating noise-induced hearing loss. Rats were exposed to 10, 30, and 50 ppm hydrogen cyanide (HCN) alone for 3.5 h (n = 28) or in combination with 2 h octave band noise exposure (100 dB(lin); n = 28). Additional groups received noise exposure alone (n = 16) and no treatment other than placement in an inhalation chamber with clean air and quiet (n = 16). Pure tone compound action potential (CAP) thresholds were determined 4 weeks following the exposure in order to assess pure tone auditory sensitivity and permanent threshold impairment. Cochleae from an additional 13 subjects were processed for light microscopy to permit assessment of hair cell loss. The results demonstrate that the noise exposure alone impaired CAP threshold by about 10 dB, averaged between 12-40 kHz, and produced a 5% loss of outer hair cells at the base of the cochlea, but no inner hair cell loss. The combined exposure to noise and HCN caused a cyanide dose-dependent CAP threshold impairment that exceeds the noise exposure alone. This effect reached statistical significance at a HCN level of 30 ppm. Combined exposure also produced more outer hair cell loss than noise alone. HCN alone did not cause significant hearing loss or hair cell loss. A risk assessment analysis was conducted for the auditory threshold data using benchmark dose software published by the U. S. EPA (BMDS version 1.3). A continuous model showed that the data could be described by a linear function. For a benchmark response corresponding to a 5 dB increase in auditory threshold above the effect of noise alone, the lower bound on the 95% confidence interval for the benchmark dose was 9 ppm. The benchmark dose that impaired auditory threshold 10% above the effect of noise alone had a lower bound of 2 ppm. The lower bound to the HCN dose that produced a 1 SD elevation in noise-induced hearing loss was 16 ppm. These exposure levels provide a range of concentrations below to slightly above the short-term exposure limit for HCN. However, if these levels are adjusted for an 8 h time-weighted average (TWA), the resulting levels are below the permissible exposure level (PEL) for HCN.

Animals↗

PubMed2002

Handguns and ammunitions indicators extracted from the GSR analysis.

The computer automated scanning electron microscope. X-ray microanalysis of Firearms Discharge Residue (FDR) can reveal substantial information about the circumstances of their generation beyond the presence of characteristic gunshot residue (GSR). Indicators of the type of weapon and ammunition used can he obtained from the distribution of GSR particle shapes and from the multi-element analysis of the FDR sample. This is demonstrated for a large database of GSR samples from nine different handguns and over 60 different ammunitions. An example classification scheme is presented for the supporting particles generally found present in FDR. When particle type area concentration ratios are normalized to the iron (Fe) particle type, results show it is possible to distinguish much about the metal used in the weapon manufacture, whether it was of large or small caliber, whether the bullets were jacketed or plated, and whether the cartridge cases were of aluminum, brass, or nickel-plated brass. Standardization of such analytical schemes would be advantageous.

Journal Article↗