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Biomedical subjects

P A Baron

Publications and source records attributed to P A Baron.

At least 19 recordsLinked to original sources
PubMed2001

Variation of human immunodeficiency virus type 1 viral RNA levels in the female genital tract: implications for applying measurements to individual women.

The short-term detection and variability of human immunodeficiency virus type 1 (HIV-1) RNA level was assessed in the blood plasma and genital tracts of 55 HIV-1-infected women. Specimens were collected weekly for 8 weeks from the endocervical canal with wicks and cytobrushes and from the ectocervix and vagina with cervicovaginal lavage. In all, 48 women (87.3%) had detectable genital tract HIV-1 RNA at > or =1 collection times. HIV-1 RNA levels varied least in specimens from endocervical canal wick and most in cervicovaginal lavage samples. The within-subject variation for genital-tract virus level was greater than that for blood. Overall, the odds for viral RNA detection in the genital tract approximately tripled for each 10-fold increase in plasma viral RNA concentration (P<.001) or with concomitant genital tract infection (P=.003). Endocervical canal wicks should be considered as an adjunct to cervicovaginal lavage, to improve the sensitivity and precision of HIV-1 RNA detection.

Cervix Uteri↗
PubMed2001

Measurement of airborne fibers: a review.

Current fiber measurement techniques arose primarily due to health concerns over asbestos exposure. Fiber toxicity appears to be primarily a function of fiber concentration, dimensions and durability in the lungs. There are two basic approaches to fiber measurement. Fibers can be collected on filters and counted or analyzed by light or electron microscopy; alternatively, fibers can be detected directly using a combination of fiber alignment and light scattering techniques. All of these measurement approaches work best when the fibers are simple rod-shaped particles. However, most fibers can exist as curved rods, complex bundles of fibrils, and agglomerates of fibers and compact particles. These non-ideal shapes contribute to measurement bias and variability.

Air↗
PubMed2000

Effect of menstrual cycle on HIV-1 levels in the peripheral blood and genital tract. WHS 001 Study Team.

OBJECTIVE: To assess the variation in HIV-1 over the menstrual cycle, including RNA levels in the female genital tract, plasma HIV-1-RNA levels, CD4 cell counts, and culturable virus. DESIGN: A prospective analysis of 55 HIV-1-infected women. METHODS: Blood and genital tract specimens were collected weekly over 8 weeks, spanning two complete menstrual cycles. Applying repeated-measures models that used menses as the reference level, the variation in viral RNA levels was compared in endocervical canal fluid and cells (collected by Sno-strips and cytobrush, respectively) and ectocervicovaginal lavage (CVL) fluid. Repeated-measures models were also used to assess the variation in plasma CD4 cell counts and viral load. RESULTS: Shedding patterns differed among the three sampling methods, independent of genital tract co-infections. Genital tract HIV-1-RNA levels from CVL fluid and endocervical canal cytobrush specimens were highest during menses and lowest immediately thereafter (P = 0.001 and P = 0.04). The HIV-1-RNA level in endocervical canal fluid was highest in the week preceding menses (P = 0.003). The menstrual cycle had no effect on blood levels of RNA (P = 0.62), culturable virus (P = 0.34), or CD4 cell counts (P = 0.55). HIV-1-RNA levels were higher in endocervical canal fluid than in peripheral blood plasma during the late luteal phase (P = 0.03). CONCLUSION: HIV-1-RNA levels vary with the menstrual cycle in the female genital tract but not the blood compartment. HIV-1-RNA levels are higher in endocervical canal fluid than in blood plasma. These findings may have important implications for sex-specific pathogenesis, heterosexual transmission, and contraceptive hormone interventions in HIV-1-infected women.

Adult↗
PubMed2000

Particulate penetration of porous foam used as a low flow rate respirable dust size classifier.

Porous foam has been used as a material for classification of particulate matter into various size fractions. The penetration characteristics of a nominal 90 pores per inch porous foam were studied at various flow rates, face velocities, and foam plug diameters and compared to the aerosol penetration of a 10 mm Dorr Oliver cyclone operated at 1.7 L/min. Poly-dispersed triethanolamine spheres were classified through porous foam plugs and the resulting penetration was determined using an aerodynamic particle sizer. Results showed that for a given plug diameter, as face velocity increased from 26 to 39 cm/sec, the 50 percent cut point decreased from 4.5 to 3.8 microns. Furthermore, as the diameter of the plug increased from 4 to 12 mm, the 50 percent cut points were similar to other plug diameters at equivalent face velocities. The best match to the 1.7 L/min cyclone penetration characteristics occurred at a flow rate of 250 ml/min through a 25 mm by 4 mm diameter section of 90 pore per inch foam. Because of the need to provide short-term or real-time estimates of worker respirable dust exposure, porous foam may be a viable classification media for a low flow rate, disposable respirable dust sampler for use in the coal mining industry.

Aerosols↗
PubMed1999

Ultrasonic extraction and portable anodic stripping voltammetric measurement of lead in paint, dust wipes, soil, and air: an interlaboratory evaluation.

Recent studies have demonstrated the utility of ultrasonic extraction (UE), followed by portable anodic stripping voltammetry (ASV), for the on-site determination of lead in environmental and industrial hygiene samples. The aim of this work was to conduct an interlaboratory evaluation of the UE-ASV procedure, with a goal of establishing estimates of method performance based on results from collaborative interlaboratory analysis. In this investigation, performance evaluation materials (PEMs) with characterized lead concentrations were used for interlaboratory testing of the UE-ASV procedure. The UE-ASV protocol examined has been promulgated in the form of two separate national voluntary consensus standards (one for UE and another for electroanalysis, which includes ASV). The PEMs consisted of characterized and homogenized paints, soils, and dusts (the last of which were spiked onto wipes meeting national voluntary consensus standard specifications), and air filter samples (mixed cellulose ester membrane) generated using characterized paints within an aerosol chamber. The lead concentrations within the PEMs were chosen so as to bracket pertinent action levels for lead in the various sample matrices. The interlaboratory evaluation was conducted so as to comply with an applicable national voluntary consensus standard that can be used to estimate the interlaboratory precision of a given analytical test method. Based on the analytical results reported by the participating laboratories, relative standard deviations (RSDs) for repeatability and reproducibility were computed for three different lead contents of the four PEMs. RSDs for repeatability were 0.019-0.100 for paints; 0.030-0.151 for soils; 0.085-0.134 for dust wipes; and 0.095-0.137 for air filters. RSDs for reproducibility were 0.127-0.213 for paints; 0.062-0.162 for soils; 0.085-0.134 for dust wipes; and 0.114-0.220 for air filters. With the exception of one of the air filter samples and one of the paint samples, the precision estimates were within the +/- 20% precision requirement specified in the US Environmental Protection Agency National Lead Laboratory Accreditation Program (NLLAP). The results of this investigation illustrate that the UE-ASV procedure is an effective method for the quantitative measurement of lead in the matrices evaluated in this study.

Air Pollution, Indoor↗
PubMed1996

Application of the thoracic sampling definition to fiber measurement.

As part of a consideration of the sampling method for refractory ceramic fibers, calculations were carried out at the National Institute for Occupational Safety and Health to evaluate different approaches to fiber measurement. The most common technique for estimating fibers that can reach the lungs is to use an upper diameter limit of 3 microns in the phase contrast optical microscope counting rules. Calculations were carried out to estimate the aerodynamic diameter of fibers in several lognormal size distributions likely to occur in workplaces. Using these size distributions, the use of a 3 microns fiber diameter upper limit in the counting rules was compared with results expected from a sampler designed to collect fibers according to the thoracic definition, which is based on the aerodynamic diameter of compact particles. The other limits in the optical courting procedure, i.e., counting only fibers longer than 5 microns and thicker than 0.25 micron, were included in the calculations. The calculations indicate that the 3 microns upper diameter counting rule agrees with the thoracic definition within about +/- 25% for a wide range of possible fiber size distributions. The advantages of using a sampler designed to collect the thoracic fiber size fraction include reducing analyst decision making (all fibers collected would be counted) and reducing the nonthoracic particles on the sample, making the sample easier to analyze. Until thoracic samplers are available for fibrous aerosols, incorporating the 3 microns upper diameter limit as part of the criteria for counting fibers may serve as a surrogate for thoracic sampling.

Aerosols↗
PubMed1994

Direct-reading instruments for aerosols. A review.

Direct-reading instruments for aerosols have not had the popularity within the industrial hygiene community that similar instruments for gases and vapours have enjoyed. There are several reasons for this: aerosols have complex properties that are difficult to characterize with a single measurement, commercial instruments often do not provide an accurate measure of a useful aerosol property and aerosol instruments are relatively expensive for industrial hygiene use. A variety of instruments are commercially available and are briefly reviewed. Two general classes of instruments used for industrial hygiene measurements are covered: field instruments and research instruments. The International Symposium on Air Sampling Instrument Performance held in Research Triangle Park, NC, USA, in October, 1991 included a workshop on direct-reading aerosol instruments that produced several recommendations to advance the state of the art. The two primary recommendations approved by the symposium attendees were to develop voluntary consensus standards for aerosol mass measuring instruments and optical particle counters and to develop an accurate, portable, direct-reading aerosol mass monitor. Some progress is being made on the latter recommendation through a project supported by the US Bureau of Mines. Other instruments have found specific application in industrial hygiene measurements. A miniaturized condensation nucleus counter is being used to estimate fit factors for respirators. A fibre monitor is used for monitoring asbestos, especially in asbestos abatement operations. Optical particle counters are used for low-concentration aerosols, especially in clean rooms. Aerosol research instruments are being used to evaluate and improve field instrumentation, such as respirable, thoracic and inhalable samplers and cascade impactors.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1994

Nonuniform air flow in inlets: the effect on filter deposits in the fiber sampling cassette.

Smoke stream studies were combined with a new technique for visualizing a filter deposit from samples used to monitor asbestos or other fibers. Results clearly show the effect of secondary flow vortices within the sampler under anisoaxial sampling conditions. The vortices observed at low wind velocities occur when the inlet axis is situated at angles between 45 degrees and 180 degrees to the motion of the surrounding air. It is demonstrated that the vortices can create a complex nonuniform pattern in the filter deposit, especially when combined with particle settling or electrostatic interactions between the particles and the sampler. Inertial effects also may play a role in the deposit nonuniformity, as well as causing deposition on the cowl surfaces. Changes in the sampler, such as its placement, may reduce these biases. The effects noted are not likely to occur in all sampling situations, but may explain some reports of high variability on asbestos fiber filter samples. The flow patterns observed in this study are applicable to straight, thin-walled inlets. Although only compact particles were used, the air flow patterns and forces involved will have similar effects on fibers of the same aerodynamic diameter.

Aerosols↗
PubMed1994

Relationship between plasma concentrations of 3'-deoxy-3'-fluorothymidine (alovudine) and antiretroviral activity in two concentration-controlled trials.

Two concentration-controlled trials (CCTs) defined the relationship between plasma concentrations of 3'-deoxy-3'-fluorothymidine (alovudine) and changes in surrogate markers of antiretroviral activity. In an initial open-label CCT involving 14 subjects infected with human immunodeficiency virus (HIV), unacceptable hematologic toxicity occurred when the area under the concentration-time curve during a 12-h dosing interval (AUC12) was > or = 300 ng*h/mL. Consequently, 46 subjects were assigned to AUC12s of 50, 100, or 200 ng*h/mL for up to 16 weeks in a prospective, randomized, double-blind CCT. Alovudine caused a concentration-dependent reduction in p24 antigen and peripheral blood mononuclear cell HIV titers within 4 weeks of start of treatment. The AUC12 producing a 50% reduction in p24 (108 ng*h/mL) had a trough concentration identical to the reported IC50 of alovudine in HIV-infected H9 cells. It may be possible to predict the antiretroviral activity of certain nucleoside analogues as a function of plasma drug concentration.

Adult↗
PubMed1992

An approach to evaluating and correcting aerodynamic particle sizer measurements for phantom particle count creation.

An aerodynamic particle sizer (APS) can be used to make real-time measurements of the aerodynamic particle size distribution over the range of 0.5 to 32 microns. This instrument is very useful in conducting health-related aerosol measurements involving aerosol generation, respirator efficiency, and particulate sampling efficiency. One of the two signal processors within the APS can create spurious or phantom particle counts that can significantly affect relative measurements and calculated mass distributions. In the APS, particle size measurement is based upon a particle's transit time between two laser beams that are perpendicular to an accelerating airflow. The signal processors measure each particle's transit from the time between the two pulses of scattered light that are generated as the particle passes through the two laser beams. When only a single pulse from a particle is detected, another pulse can cause the recording of a randomly sized phantom particle. The small particle processor (SPP), which measures particle transit from the times in digital increments of 4 nanoseconds, can create phantom particles; the large particle processor (LPP), which measures particle transit times in digital increments of 66.67 nanoseconds, is designed to prevent the creation of phantom particles. These two processors overlap in the range of 5.2 to 15.4 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1992

An investigation of dust generation by free falling powders.

To identify the dust generation processes, aluminum oxide powder was dropped as a free falling slug in a test chamber. The effect of the slug's mass, diameter, and drop height upon the aerosol concentration and size distribution was measured with an aerodynamic particle sizer. To differentiate between aerosol generated during the free fall and at the end of the fall, the slug was dropped either onto a flat surface or into a container of water that suppressed dust generation associated with the impact at the end of the fall. Aerosol generation occurred during the slug's free fall as well as at the end of the fall. The falling solid induced an airflow that followed the falling solid to the end of the fall. This induced airflow contained the aerosol generated during the free fall. At the end of the free fall, the induced airflow, combined with air jets created on impact, dispersed the aerosol throughout the test chamber. Additional measurements were made by using "neutral buoyancy" helium-filled bubbles to visualize the airflow in the test chamber. The airflow and ensuing turbulence were sufficient to keep large, inspirable particles suspended throughout the test chamber for periods greater than 10 min. During experimental work, the effect of drop height, mass, and slug diameter upon aerosol generation by a single slug of powder was studied. The results indicated that the manner in which a powder is handled may be as important as material dustiness as measured by a dustiness tester. Aerosol generation can be reduced by minimizing the contact between the falling powder and the air.

Aerosols↗
PubMed1992

Three-drug synergistic inhibition of HIV-1 replication in vitro by 3'-fluoro-3'-deoxythymidine, recombinant soluble CD4, and recombinant interferon-alpha.

3'-Fluoro-3'deoxythymidine (FLT), recombinant soluble CD4 (CD4), and recombinant interferon-alpha (IFN alpha) were evaluated in two- and three-drug regimens against HIV-1 replication in vitro. Peripheral blood mononuclear cells were studied using p24 antigen production as the virologic endpoints. FLT showed 2.5-fold higher efficacy and a similar selectivity index to zidovudine. Drug interactions were evaluated by the median effect principle and the isobologram technique. FLT, CD4, and interferon alpha at noncytotoxic concentrations inhibited HIV-1 synergistically in two- and three-drug combinations with a combination index smaller than one and dose reduction index greater than one. The three-drug regimen provided greater virus suppression than the two-drug regimen. These results suggest that FLT is an alternative agent to AZT for the treatment of HIV infection either as a single agent or in combination with CD4 and/or interferon-alpha.

Antiviral Agents↗
PubMed1990

Electrostatic effects in asbestos sampling. I: Experimental measurements.

Electrostatic charge can cause errors during sampling of airborne asbestos fibers and other particles. The change in particle trajectories caused by charge effects during sampling can result in nonuniform deposits on the collecting filter surface and net loss of sample. The degree of these electrostatic effects depends on particle charge, sampler charge, sampler conductivity, and sampling flow rate and direction. The purpose of this research was to evaluate the dependence of sampling efficiency and sample uniformity on these variables. Humidity has been postulated as a primary determinant of particle charge during aerosol generation. Measurements of particle charge and concentration were made as a function of relative humidity with chrysotile fibers generated from a fluidized bed. A strong increase in charge and a decrease in concentration of fibers was noted as the relative humidity was decreased below 15%. The effects of conductive versus nonconductive samplers and sampling flow rate were measured as a function of particle and sampler charge levels. Nonconductive samplers can carry a large and variable charge distribution on their surfaces. This can result in a biased and highly variable particle deposit on the filter when sampling charged particles. Conductive cowls spread any acquired charge over the entire surface and produce a more symmetrical and less biased charged particle deposit. Increasing the sampling flow rate will improve sampling efficiency and decrease deposit variability because the charged particle has less time to interact with the field produced by the sampler. These results suggest that sampling problems caused by electrostatic charge interactions are most likely to occur under low humidity conditions of dust generation, that sampling should be done at as high a flow rate as possible to reduce these effects, and that analysts should select fields toward the center of the filter to minimize bias and variability.

Aerosols↗
PubMed1990

Electrostatic effects in asbestos sampling. II: Comparison of theory and experiment.

A series of calculations was conducted to estimate the degree and type of electrostatic interactions that might occur with electrically charged asbestos samplers collecting charged particles. Relatively simple theoretical models were constructed assuming only charge-charge electrostatic interactions between a charged particle and a charged sampler. The results of these calculations were compared with some experimental measurements and the agreement between the two allowed some confidence in predicting behavior trends. Under conditions where both the particles and the sampler are charged, the nonconductive sampler exhibits increased particle loss, especially near the filter edge, and increased variability of the particle deposit. The variability of the deposit also tends to be greatest near the filter edge. Under similar conditions, conductive cowled samplers also can be expected to exhibit losses in particle deposit, especially near the filter edge. The variability over the filter surface, however, is less than for the nonconductive cowl. Particle collection onto the sampler filter generally is expected to be greatest for isokinetic, isoaxial sampling conditions. Particle collection on the filter decreases with lower sampling flow rates, lower air velocities near the sampler inlet, and increased turbulence near the inlet.

Air Pollutants↗
PubMed1990

Sampling and interpretation errors in aerosol monitoring.

The aerosol recorded by simple filter collection or by sophisticated instrument aerosol monitoring may differ considerably from the original, unsampled aerosol. Through use of particle-sizing instruments and computer modeling, the potential biases in sampling, display, and interpretation are demonstrated. The aerosol-size distribution and, therefore, the reported number or mass concentration may be affected by the characteristics of the sampling inlet, the transport to the sensor and the sensor itself. The particle count in specific size ranges determines the precision of the registered particle-size distribution, depending on the weighting chosen. The type of display, by histograms or cumulative plot, focuses on different aspects of the size distribution, and the calibration of the aerosol monitor may modify it further. Particle-size classification to simulate a specific region of the human respiratory system may be achieved through inertial classification or the sensitivity characteristics of the aerosol sensor. Aerosol monitors using passive sampling register the same aerosol-size distribution as active ones, if the aerosol is transported to the sensor with the same efficiency as in the active mode. The sources of various types of errors are presented using computer simulations of typical aerosol-size distributions, often combined with measurements found in the literature. Presentation of these errors in graphical format allows the health professional to estimate more accurately the health implications of aerosol measurements.

Aerosols↗
PubMed1989

Inactivation of human immunodeficiency virus in vitro by gossypol.

Gossypol, a polyphenolic aldehyde extracted from cottonseed, is a male anti-fertility agent which has been reported to have anti-viral activity. In this paper we report that gossypol inactivates human immunodeficiency virus (HIV) in an in vitro system. Following exposure of cell-free incubates of HIV to 100 uM gossypol, ultracentrifugation and inoculation of the washed pellet onto H9 cells, there is no evidence of elevated reverse transcriptase activity over 21 days. Treatment with lower concentrations of gossypol reduces the peak and lengthens the time to maximal reverse transcriptase activity compared with control cultures. These observations suggest that gossypol could be used as a vaginal spermicidal/virucidal agent. The mechanism of the in vitro anti-viral action as well as the effect of orally administered gossypol on the infectivity of semen of HIV-seropositive men warrant further study.

Cell Line↗