Search PubMed⌕ Search

Biomedical subjects

J H Nelson

Publications and source records attributed to J H Nelson.

At least 19 recordsLinked to original sources
PubMed1992

Breakthrough time and adsorption capacity of respirator cartridges.

A model developed in previous studies was applied to investigate the respirator cartridge contaminant breakthrough of 121 different chemical compounds. Included in this set of 121 contaminants are representative examples of various types of organic compounds, (e.g., acetates, ketones, aromatics, alcohols, amines, alkanes, chlorinated hydrocarbons). Intrinsic to the model are two important parameters, k' (a rate constant) and tau (50% breakthrough time). Values of the two parameters pertinent to an assault concentration of 1000 ppm were determined for each of the 121 organic compounds. These values were used to calculate the breakthrough time at specified fractional breakthrough as well as the respirator cartridge loading capacity under various conditions. An approach was presented that permits the determination of contaminant loading capacity (on carbon) as a function of breakthrough time at a specified assault concentration. The effect of contaminant assault concentration on the saturation capacity was investigated for various combinations of nine different compounds and three different types of respirator cartridges. Calculated saturation capacity data derived from application of the model compare favorably (+/- 5%) with corresponding experimental data. Saturation capacities calculated by using the model addressed in this study were compared with corresponding results previously calculated by others using the Dubinin adsorption isotherm.

Acetates↗
PubMed1992

A theoretical model for respirator cartridge service life for binary systems: application to acetone/styrene mixtures.

A theoretical model, developed previously to assess respirator cartridge service life, was applied to various acetone/styrene binary assault systems. Experimental data, collected for several binary mixtures differing only with respect to the concentration of each of the two compounds, were interpreted in terms of the model. Styrene concentrations varied from 228 to 1578 ppm; the range of acetone concentrations was 92-985 ppm. The specific influence of the compound assault concentrations on respirator cartridge service life was carefully characterized, as break-through curves were generated for both acetone and styrene for each of several different binary systems. Specifically, experimental data for each system were used to determine values of the following theoretical parameters: k'1, tau 1, k'2, tau 2, and Am. These parameters were employed with the theory to generate complete theoretical breakthrough curves and to determine the time-dependence of the weight of each compound adsorbed by the respirator cartridge carbon bed. An interesting phenomenon observed for the acetone/styrene systems was the displacement (from the carbon) of previously adsorbed acetone molecules by styrene molecules. Acetone breakthrough was observed first in each of the systems studied. Following the onset of this breakthrough, the acetone breakthrough concentration was enhanced by the displacement of acetone from the carbon bed by the adsorption of styrene. The theoretical model accurately predicts both this enhancement and the associated breakthrough characteristics of styrene. In addition, the theory is capable of predicting the ratio of the number of displaced acetone molecules to the corresponding number of displacing styrene molecules. For these studies, this ratio ranged from 0.3 to 0.7. The service life of respirator cartridges exposed to acetone/styrene mixtures depends on the assault concentration of each compound and is significantly influenced (shortened) by the displacement phenomenon.

Acetone↗
PubMed1991

Comparing the medical school curricula followed by students in an independent study program and a traditional one.

This 1988 retrospective study examined the medical school curricula followed by students from two classes using two curricular styles at one medical school. By consulting school records, the authors ascertained the courses actually taken, the number of weeks that students actually devoted to them, and the sequence of courses, both for those students following an independent-study curriculum and for those following a traditional one. These data were compared with the corresponding data concerning the traditional curriculum requirements to determine whether the curricula the students actually followed, in either style, showed any marked difference from the required curriculum. The findings showed that the curricula followed by the independent-study students deviated considerably from both the requirements of the traditional curriculum and also the actual curricula followed by the students using the traditional curriculum, who almost never chose to deviate from the requirements. The independent-study students showed considerable intragroup variation in the ways they organized their curricula, most commonly in eliminating selected formal clerkship or specialty medicine courses, or altering the duration of clerkships. Elective coursework was substituted for formal clerkship experiences in the majority of cases where clerkship courses were eliminated.

Clinical Clerkship↗
PubMed1990

Effects of humidity and contaminant concentration on respirator cartridge breakthrough.

A model described previously was developed further to examine the effect of both test humidity and contaminant assault concentration on respirator cartridge service life. The model emphasized the characterization of cartridge performance in the range of 0% to 50% breakthrough. This study specifically addressed a contaminant concentration range of 250-2000 ppm and test humidities ranging from 0% to 80%. The preconditioning humidity was fixed at 50%. The compounds studied were benzene and methyl chloroform. Two parameters, k' and tau, were described and values of these parameters were determined for each of several different sets of experimental conditions. The determined values of k' and tau were applied using derived expressions to generate each of several complete breakthrough curves for benzene and for methyl chloroform at specified contaminant assault concentrations and test humidities. The effect of humidity on the value of an additional theoretical parameter, a, was investigated. Values of this parameter and the parameters, k and K", were determined for specific test conditions. These values were substituted into pertinent expressions to produce a complete set of breakthrough curves (each curve corresponding to a particular contaminant assault concentration) for a given compound at a fixed test humidity. Several examples of breakthrough curves were generated for methyl chloroform. The results derived from the study agreed with corresponding experimental data.

Equipment Failure↗
PubMed1990

Contaminant breakthrough: a theoretical study of charcoal sampling tubes.

A previously developed theoretical model was applied to investigate contaminant breakthrough on charcoal sampling tubes. Associated with the model are two important theoretical parameters. These parameters are k' (a rate constant) and tau (the time required for 50% contaminant breakthrough). In this study, values of K' and tau were determined for n-heptane at five different concentration levels in air: 98, 117, 234, 330, and 988 ppm. These values were used along with pertinent theoretical considerations to calculate the entire (0-100%) breakthrough curve (plot of percent breakthrough versus time) regarding the adsorbance of n-heptane on charcoal sampling tubes. In addition, available experimental data for perchloroethylene, isobutyl acetate, ethyl acetate, and dichloromethane were used in conjunction with the theory to generate theoretical breakthrough curves over the entire range of 0 to 100%. In each case, calculated theoretical breakthrough curves are in remarkable agreement with corresponding experimental data. With the use of an additional theoretical parameter, a, the theory was extended to calculate the weight of contaminant collected on a single element (section) of a charcoal sampling tube at 10% breakthrough and at each of several different contaminant assault concentrations.

Acetates↗
PubMed1990

Arsenic levels in fingernails as a biological indicator of exposure to arsenic.

The analysis of urine, blood, and hair has been used previously to monitor occupational exposure to arsenic (As). Although arsenic is normally present in human fingernails (usually as a result of dietary factors), this study evaluated the potential use of levels of arsenic in fingernails as a biological indicator of occupational exposure to this element. Air samples and fingernail clippings were obtained from individuals with no exposure and high, medium, and low exposure. A washing technique, previously developed to remove exogenous arsenic from hair, was modified to wash the fingernail samples collected in this study. It was demonstrated that 98% of exogenous arsenic was removed from these nails. A high correlation coefficient (r = 0.89) was observed in a comparison of the mean air arsenic concentrations of each exposure group with corresponding arsenic levels in fingernails. From the data collected, an equation was derived to estimate the air arsenic exposure level for a worker from the arsenic content of fingernails: air arsenic concentration (micrograms As/m3) = 1.79 x fingernail arsenic level (micrograms As/g nail)-5.9.

Air Pollutants, Occupational↗
PubMed1989

Bleeding patterns with low-dose, monophasic oral contraceptives.

Cycle control over 12 months with low-dose oral contraceptives (OCs) was analyzed using calendars of bleeding on pill-taking days 1 through 21 (intermenstrual bleeding; IMB). One preparation contained 0.5 mg norethindrone and 0.035 mg ethinyl estradiol (NET + EE), the other 0.3 mg norgestrel and 0.03 mg ethinyl estradiol (Ng + EE). Half the subjects had previously used OCs containing greater than or equal to 0.05 mg estrogen (switch-over); the others had not previously used OCs for 2 months or more (fresh). Fresh subjects reported more IMB than switch-over subjects, especially during the first three cycles; IMB decreased over time for both groups. Ng + EE subjects had fewer IMB episodes during the early cycles than NET + EE subjects. Daily incidence of IMB formed a characteristic W-shaped curve in the NET + EE subjects that was most apparent in early cycles.

Adolescent↗
PubMed1989

ESWL treatment of urinary calculi.

A total of 711 patients with symptomatic upper and lower urinary tract calculi underwent extracorporeal shock-wave lithotripsy (ESWL) at the Ohio Kidney Stone Center during the first six months. At follow-up 84 percent of the first 180 patients are stone-free. Retreatment was required for 2.8 percent of the patients with residual stone material. Thirty-seven percent of the treatments required cystoscopy with ureteral stent placement for manipulation of stones or delineation of distal ureteral anatomy to facilitate ESWL. Complications were minimal at less than 3 percent.

Female↗
PubMed1988

Electrochemistry of flavonoids. Relationships between redox potentials, inhibition of mitochondrial respiration, and production of oxygen radicals by flavonoids.

We have investigated the redox behavior of a series of structurally related flavonoids employing cyclic voltammetry under physiological conditions. The flavonoids that auto-oxidized and produced oxygen radicals had oxidation potentials (E 1/2) significantly lower [-30 to +60 mV vs (SCE)] than those that did not undergo auto-oxidation (+130 to +340 mV vs SCE). The range of E 1/2 values for the auto-oxidizable flavonoids was comparable to the E 1/2 range reported for the optimum quinone induced production of superoxide (O2 pi) in mitochondrial NADH-CoQ reductase (complex I). The most potent flavonoid inhibitors of mitochondrial succinate-CoQ reductase (complex II) possessed hydroxyl configurations capable of supporting redox reactions. For a series of 3,5,7-trihydroxyflavones that differed by b-ring hydroxylation it was found that decreasing E 1/2 of the flavonoids was associated with decreasing I50 values towards succinoxidase. These findings suggest that the electrochemical properties of the flavonoids may contribute to their biological activity.

Animals↗
PubMed1988

Effects of screen materials on droplet size frequency distribution of aerosols entering sentinel mosquito exposure tubes.

Aerosol filtration effects of three types of mesh screen used for mosquito cages were evaluated with aerosolized water, mineral oil and chlorpyrifos. The screen materials were two nylon tulles (3 x 4 and 8 x 11 repeats per cm2) and corrosion-resistant steel (7 x 7 repeats per cm2). Open areas of these three mesh materials were, respectively, 94%, 79% and 88%. Aerosol droplet size frequency distributions were altered when passed through test screens of these materials fitted to standard tubes from World Health Organization test-kits for exposure of adult mosquitoes. The alterations included reductions in total droplets and volume median diameter (VmD). Nylon screen with fewer repeats of the mesh altered droplet VmD and frequency distribution the least, allowing the greatest number of droplets to enter sentinel mosquito cages for bioassays of mortality-rates. The greater filtration effect of screens with less open area, giving rise to selective deposition of particular droplet sizes on the screen material, could result in anomalous exposures of test mosquitoes to contact with insecticide filtrate on the screen substrate. This might help to explain the poor correlation often observed between insecticide aerosol impact on wild target mosquito populations as compared with sentinel caged mosquitoes. In addition to other standard test procedures, the need for standardization of materials used for construction of sentinel cages employed for aerosol bioassays is emphasized.

Aerosols↗
PubMed1987

Stented versus nonstented transverse colon conduits: a comparative report.

Postoperative urinary tract complications were evaluated in 75 women who underwent urinary diversion with formation of a transverse colon conduit after radiation for gynecologic cancer. Urinary stents were placed at the ureterocolonic junction in 37 women, while no stents were used in 38 women. Leaks or fistulae developed in 18% of the nonstented group but in only 3% of the stented group (P less than 0.05). Ureteral strictures developed in 18% of the nonstented but in only 8% of the stented group. Pyelonephritis developed in 13% of the nonstented and in 8% of the stented patients. Overall, urinary tract complications developed in 50% of the nonstented and in 16% of the stented group (P less than 0.01). Leaks or strictures developed in 11% of the 75 renal units in the nonstented group but in only 1% of the 72 renal units in the stented group (P less than 0.02). Postoperative leaks or fistulae were associated with further serious complications. Results indicate a significant advantage in employing stents at the ureterocolonic junction in the formation of a transverse colon conduit.

Colon↗
PubMed1987

Health promotion for children. Key to a lifetime of health.

Evidence indicates that preventive healthcare in childhood reduces healthcare costs and enhances health. Physicians can assume a leadership role in promoting children's health by incorporating health promotion measures into their everyday practice, serving as resource persons or leaders in community and school efforts in health promotion, and lobbying for legislation aimed at preventive care. The goals of these efforts are to achieve a healthy childhood, provide a foundation for a healthy adulthood, and develop in children positive values about personal health responsibility and use of healthcare services.

Adolescent↗
PubMed1987

The development and evaluation of a hydrobromic acid-coated sampling tube for measuring occupational exposures to ethylene oxide.

A new sampling method has been developed for the measurement of ethylene oxide (EtO) exposures in the workplace. This sampling method uses a hydrobromic acid-coated charcoal tube to collect EtO as its 2-bromoethanol reaction product. Because 2-bromoethanol is less volatile and less reactive than EtO, improved sampling capacity and sample stability are observed with this method over the collection of EtO on untreated charcoal. Sample analysis is performed by gas chromatography with electron capture detection (GC/ECD) following desorption with dimethylformamide (DMF) and derivatization of the 2-bromoethanol reaction product with heptafluorobutyrylimidazole (HFBI). The direct analysis of 2-bromoethanol by GC/ECD was not reproducible and this effect was attributed to the presence of excess hydrobromic acid (HBr) in the sample. This matrix effect was eliminated by the formation of the heptafluorobutyrate ester, a water-insoluble derivative of 2-bromoethanol, which was extracted into iso-octane for analysis. This analytical scheme is very sensitive and was used to monitor test atmospheres of EtO at the 0.1 ppm level. An average recovery of 96% was obtained for short-term samples (15 minutes) collected from a 5-ppm test atmosphere at 23 degrees C and 80% relative humidity. Similar high recoveries were obtained for 4-hr samples collected at a sampling rate of 0.1 L/min from test atmospheres in the concentration range of 0.1 to 16 ppm EtO at high humidity (80%) and ambient temperature (22 degrees C to 25 degrees C). Samples collected under these same conditions and stored for a minimum of 2 weeks resulted in average recoveries that ranged from 84% to 101%. Average recoveries of 97% were obtained for 2-ppm air samples collected at low humidity with no storage; however, storage of these samples at 22 degrees C to 25 degrees C resulted in an approximate loss of 5% per week. A field comparison study of samples, that was obtained from a hospital sterilization facility, used the test method and the Qazi-Ketchum sample method and resulted in a correlation for paired samples of 0.99 over a concentration range of 0.3 to 7.0 ppm EtO. These results indicate that this sampling and analytical method is a convenient, accurate and reliable means of monitoring EtO exposures in the workplace.

Acids↗
PubMed1987

A new type of collapsible insect-surveillance light trap for sampling Diptera.

The newly designed Army Collapsible Insect Surveillance trap for nocturnal collection of flying Diptera that are attracted by light is described. A polyvinyl chloride construction increases durability, while the capability to collapse from a height of 92.1 cm to 24.1 cm facilitates transportation and storage.

Animals↗
PubMed1986

Management of high-grade stage I adenocarcinoma of the endometrium: hysterectomy following low dose external beam pelvic irradiation.

Sixty-eight patients with FIGO stage I, grade 2 or 3 adenocarcinoma of the endometrium were treated according to a protocol involving 10 Gy external pelvic irradiation, prompt hysterectomy with surgical staging, and postoperative therapy individualized according to surgical-pathologic findings. Five-year survival for the entire group was 78%, 87% for those with grade 2 disease, and 59% for those with grade 3 disease. For patients whose disease was found to be confined to the uterus, surgical stage I, the 5-year survival was 98%. Patients with surgical stage I, grades 2 and 3 disease had 97 and 100% probabilities of surviving 5 years, respectively. Five-year disease-free probability was 96% for all patients with surgical stage I carcinoma, 97% for patients with grade 2 disease, and 94% for patients with grade 3 disease. Myometrial penetration influenced survival; no patient with less than 50% myometrial penetration died or suffered a relapse, while only 40% of patients with deeper penetration survived 5 years. Twenty-three percent of patients with surgically confirmed disease spread beyond the corpus survived 5 years; 29% remained disease-free at this interval. Ten of the 68 patients developed recurrences, none has had a known pelvic recurrence. Two major complications, one requiring surgery, were seen, both in patients receiving postoperative external beam irradiation. The rationale behind low-dose, preoperative external pelvic irradiation is described, and an approach to high-grade, FIGO stage I adenocarcinoma of the endometrium is outlined.

Adenocarcinoma↗
PubMed1986

Production of vinylidene chloride from the thermal decomposition of methyl chloroform.

This study investigated the extent to which methyl chloroform undergoes thermal decomposition to form vinylidene chloride. The experiment was conducted under laboratory conditions that approximate those found in industrial environments. Methyl chloroform vapors at approximately the TLV concentration of 1910 mg/m3 were passed through a heated quartz tube packed with glass or copper beads. In the presence of glass, the decomposition reaction began at 350 degrees C and was essentially complete at 605 degrees C. Vinylidene chloride was detected in nearly stoichiometric amounts. In the presence of copper, the reaction occurred initially at 180 degrees C. At 442 degrees C no methyl chloroform was detected. Once again, the conversion to vinylidene chloride was nearly complete. Two major conclusions have been derived from this study. First, under these experimental conditions, methyl chloroform undergoes thermal decomposition to yield substantial quantities of vinylidene chloride. Second, the dehydrohalogenation reaction proceeds at much lower temperatures in the presence of copper.

Chemical Phenomena↗