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Biomedical subjects

B Kahn

Publications and source records attributed to B Kahn.

At least 37 records · Page 2Linked to original sources
PubMed1988

Effect of postural changes, nitroglycerin and verapamil on diastolic ventricular function as determined by radionuclide angiography in normal subjects.

Whereas improvement in diastolic function indexes in response to therapeutic interventions has been attributed to a beneficial effect of the intervention, measurements of diastolic function appear to be influenced by changes in loading conditions, heart rate and sympathetic tone. To determine the effect of body position and short-term pharmacologic intervention on radionuclide angiographically determined left ventricular peak filling rate, high temporal resolution time-activity curves and absolute left ventricular volumes obtained by equilibrium-gated blood pool scans were evaluated in 12 normal subjects in the supine position at rest and in response to several postural and pharmacologic manipulations. This study confirmed the reproducibility of the technique and demonstrated that in normal subjects, peak filling rate varies in response to changes in body position and to short-term administration of sublingual nitroglycerin and intravenous verapamil. Peak filling rate ranged from 3.3 to 5.1 end-diastolic volumes (EDV)/s with a variability of 13.7% during five baseline supine measurements in the 12 subjects. Compared with values in the supine position (mean +/- SEM = 4.38 +/- 0.24 EDV/s), peak filling rate increased +16 +/- 6% to 4.75 +/- 0.27 EDV/s in the upright position (p less than 0.05) but did not change significantly with leg elevation. Peak filling rate at baseline and during postural changes correlated significantly with ejection fraction (r = +0.49), with stroke volume (r = +0.26) and inversely with end-systolic volume (r = -0.41), but did not correlate with heart rate or blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Use of environmental TLD data at a nuclear power station to estimate detection limits for radiation exposure due to station operation.

The environmental radiation monitoring network maintained by the Georgia Department of Natural Resources at the Hatch Nuclear Plant, Baxley, GA, was used to determine the variability in measured background exposures in order to estimate the detection limits for radiation due to station operation. Data were obtained from LiF thermoluminescent dosimeters (TLDs) exposed in sets of four at 46 locations for 16 consecutive quarters from 1982 to 1985. The average exposure for 695 values was 11.8 microC kg-1 y-1 (mR/quarter). At individual locations, the averages of quarterly exposures ranged from 9.3 to 14.3 microC kg-1 y-1 and had standard deviations from 0.8 to 2.2 microC kg-1 y-1 with a typical standard deviation of 1.5 microC kg-1 y-1. The standard deviation due to reading the TLDs and subtracting the transit plus storage exposure, estimated as 0.4 microC kg-1 y-1, contributed only a small fraction of the uncertainty of the mean background; the greater contribution is from temporal fluctuations. There is a spatial pattern of higher background along the Altamaha River but no distinct seasonal pattern. The observation that exposure values at most locations rose and fell in unison suggested a calculational model that adjusts the average exposure level at a location by an increment determined each quarter at control locations. This model reduced the standard deviation for a predicted quarterly background exposure to 0.9 microC kg-1 y-1, with a range of 0.5 to 1.3 microC kg-1 y-1. If the standard deviation of the net value is multiplied by an error probability constant of 3.3 (type I and II errors not greater than 5%), the detection limits range from 2 to 5 microC kg-1 y-1 at the individual locations, with an average of 3 microC kg-1 y-1. This approach or two similar ones described earlier are recommended for improving the detection limit where needed. The standard deviation, and hence the detection limit, can be further reduced by selecting a subset of indicator and control locations with more closely matched background exposure fluctuations. This was demonstrated with five indicator and five control locations, but further study is needed to determine selection guides.

Cesium Radioisotopes↗
PubMed1987

Bioaccumulation factor for 32P measured in bluegill, Lepomis macrochirus, and catfish, Ictalurus punctatus.

The ratio of the bioaccumulation factors for 32P and phosphorus was determined for edible tissue in two species of freshwater fish by measuring the specific activity (32P activity per milligram phosphorus) in muscle relative to feed. The 32P tracer was added to the feed at a uniform level throughout the study. Feeding was at two levels: ad libitum and at a lower but constant intake per body weight. In the main experiment, bluegill were maintained in a large flow-through tank and sacrificed at approximately weekly intervals for 51 d of 32P accumulation and 28 d of depuration to compare the specific activity with values predicted with a calculational model. In experiments performed in smaller aquaria, the specific activity in bluegill and catfish muscle was compared at two feeding levels and two temperatures. In addition, unfed fish were exposed to 32P in water at a known specific activity to determine the extent of phosphorus uptake directly from water. The pattern of specific activity increase and decrease in fish muscle during the accumulation/depuration experiment was consistent with a one-compartment model, so that specific activity ratios at steady state could be predicted from measurements during relatively brief exposures. On this basis, the ratio of the bioaccumulation factors of 32P and phosphorus in fish feeding ad libitum was 0.081 for bluegill and 0.17 for catfish. Hence, at a mean phosphorus bioaccumulation factor of 70,000, the factors for 32P are 6,000 and 12,000, respectively. The ratios were less at lower phosphorus intakes associated with lower feeding rates; moreover, the lesser value for bluegill occurred at a much lower phosphorus intake than by catfish. The bioaccumulation factor ratio was lower by an order of magnitude at a water temperature of 11 degrees C than at 16-27 degrees C, and was lower by two orders of magnitude when phosphorus uptake was from water by unfed fish.

Animals↗
PubMed1985

Radiological sampling and analytical methods for National Primary Drinking Water Regulations.

Radiological sampling and analysis performed under the National Interim Primary Drinking Water Regulations were evaluated for the U.S. Environmental Protection Agency (EPA) Office of Drinking Water to consider whether any changes should be recommended. The authors reviewed the analytical screening scheme; sample collection, storage and analysis procedures; selection of analytical methods; reliability of results; and possible future needs. The main problem in the program has been dependence on a screening scheme of gross alpha-particle activity measurement and 226Ra analysis for predicting elevated 228Ra levels to determine compliance with the maximum contaminant level (MCL) for Ra. In some aquifers, 228Ra levels have been found to be unrelated to 226Ra levels. Several alternatives are discussed to eliminate this problem. A secondary problem is that the measurement for assuring compliance with the MCL for gross alpha-particle activity minus Ra, Rn and U uses chemical U analysis and assumes equilibrium of 238U and 234U. Because some ground waters are known to be at disequilibrium, radiometric U analysis is needed for those gross alpha-particle activities and chemical U values that could result in an erroneous conclusion relative to the MCL. In addition, studies were recommended for determining analytical uncertainties and assuring reliable sampling and sample maintenance; improvements in the system for accepting methods were suggested; and methods were identified for several radionuclides not currently in the analytical program that may be needed to assure absence of elevated radiation doses and could be useful for identifying trace contaminants.

Alpha Particles↗
PubMed1984

Behavior of radionuclides in sanitary landfills.

his study was undertaken to evaluate the possibility of disposing low-level radioactive waste in sanitary landfills with leachate containment to prevent environmental releases. To meet this objective, two simulated landfills, each 200 l. in volume and containing 55 kg of municipal refuse, were operated in the laboratory with simulated rainfall additions for a 9-month period to observe the extent to which radio-cobalt, -cesium, -strontium and tritium were leached into the liquid phase. One of the units was operated with leachate recycle, the other as a single pass control. Liquid samples were analyzed weekly for 3H, 58Co, 85Sr and 134Cs tracers. Weekly analyses were also performed for approximately 30 parameters to define the degree of stabilization of the waste. Major parameters included BOD, COD, pH and concentrations of specific organics, metals and gases. Concentrations of stable cobalt, strontium and cesium were also measured periodically. Soluble radioactivity levels in both systems were reduced by factors of 50 for 58Co, 5 for 85Sr and 7 for 134Cs, taking radioactive decay and dilution into account. Some radionuclide removal from the liquid phase was associated with major chemical changes in the landfills that occurred within 80 days for the control system and within 130 days for the recycle unit. Observed acid, sulfide, and CO2 concentrations suggested mechanisms for removing some of the radionuclides from leachate. Detection of 3H in the off-gas indicated that less than 1% of tritiated waste became airborne. The waste in the leachate recycle unit was more completely stabilized than in the control unit.

Environmental Pollution↗
PubMed1984

The bioaccumulation factor for phosphorus-32 in edible fish tissue.

Information used to derive the bioaccumulation factor for 32P in edible portions of fish was reviewed to evaluate the currently recommended values of 100,000 in fresh water and 29,000 in sea water that are applied in calculating radiation doses to persons from nuclear-power reactor effluents. A generic phosphorus bioaccumulation factor of 70,000 was obtained for larger rivers and estuarine waters on the basis of geometric mean phosphorus concentrations of 2 mg/g wet weight in fish muscle and 0.03 mg/l dissolved in water. A 20-fold lower bioaccumulation factor was inferred for 32P because radioactive decay is much faster than phosphorus turnover. A phosphorus turnover rate in muscle of 0.2% per day was estimated as a long-term average for edible-size fish, although more rapid turnover has been observed for brief periods. Large deviations from the generic bioaccumulation factor will occur for different phosphorus concentrations in water and turnover rates in fish. Site-specific determinations are also needed because 32P is bioaccumulated at lower trophic levels in the food web, not in the fish. Hence, the availability of concentrating organisms determines the bioaccumulation factor. Several other conditions that affect the 32P bioaccumulation factor have not been quantified and are suggested for study.

Animals↗
PubMed1983

Radium and uranium concentrations in Georgia community water systems.

The first cycle of statewide radionuclide concentration measurements of public drinking water supplies was completed in accord with the Federal and Georgia Safe Drinking Water Acts. The recommended pattern of analysis is initial screening for gross alpha-particle activity, followed by measuring 226Ra if the gross alpha-particle activity is above 5 pCi/l. and then measuring 228Ra if the 226Ra concentration is above 3 pCi/l; and uranium analysis if the gross alpha-particle activity exceeds 15 pCi/l. Surface water supplies for more than 100,000 persons are analyzed for 3H and 90Sr and screened for gross beta-particle activity, with additional analytical requirements if the latter is above 50 pCi/l. Specified supplies downstream for nuclear facilities are analyzed for 3H, 90Sr and 131I, and further analyses are required if the gross beta-particle activity is above 15 pCi/l. More thorough screening was applied for 1400 public water supplies in Georgia, of which about 90% use groundwater. Radium concentrations exceeded the maximum contaminant level (MCL) of 5 pCi/l. in 24 groundwater supplies, mostly due to elevated 226Ra. The gross alpha-particle activity minus uranium concentrations exceeded the 15 pCi/l. MCL in 3 additional samples. No MCL was exceeded in surface water. The S.D.s of analytical results estimated from replicate analyses were approximately twice those based on counting statistics, suggesting that screening levels should be lowered to assure detection of 226Ra at MCL values.

Georgia↗
PubMed1983

Search for building materials as sources of elevated radiation dose.

A systematic approach to finding materials that cause elevated gamma radiation exposure rates or 222Rn progeny working levels in buildings was tested in the Atlanta area. With the proposed procedure, exposure rates in planned structures would be derived from a radiation survey of the material performed with a NaI(T1) detector. Working level values under specified conditions would be inferred from an additional measurement of 226Ra concentration in the material. To quantify the procedure, surveyed building materials were analyzed for radionuclide content and categorized according to an exposure rate index related both to the survey meter count rate and the radionuclide concentration. An available calculational model was used to predict from the index the exposure rate in a room totally enclosed by radioactive material. An additional model was developed for application to structures where the radioactive material is only in the floor or walls. 222Radon concentrations in an enclosed space were also predicted according to an available model. Exposure rates were measured in newly constructed buildings to test the approach. Measurements in older buildings found elevated gamma-ray emission from concrete blocks made with phosphate slag from a phosphorus producer in Alabama. Buildings with walls of these blocks were used to test the prediction of 222Rn concentrations in building air due to 226Ra in construction material. The calculational models predicted that the 226Ra concentration of approx. 20 pCi/g in these blocks would result in increases of the average exposure rates by 10 mu R/hr and of 222Rn concentrations by 0.2 pCi/l. under specified conditions. Observed levels were consistent with these predictions, but the major fraction of 222Rn in room air was attributed to inflow from the ground beneath the building.

Construction Materials↗
PubMed1982

Transportation of radioactive material in Georgia.

A 3-yr study of radioactive materials transportation examined the magnitude of radioactive materials shipments in terms of numbers of packages and motor vehicle trips and types of materials; compliance with regulations for packaging, labelling, handling, external radiation exposure, and surface contamination; and dose to workers as measured with personnel dosimeters. Much of the information was obtained at the Atlanta airport and its vicinity, a package distribution center for the southeastern U.S., and at the Barnwell, S.C. radioactive waste burial site, the destination of most shipments of radioactive waste from or through Georgia. Approximately 12,000 packages in radioactive material categories I, II and III were handled in Georgia each year. Motor vehicles made approximately 3300 trips per year. Some instances of noncompliance were observed, but few of them had the potential for elevated radiation exposure of persons. Several incidents associated with radioactive material transport are reported, of which one may have resulted in slightly elevated exposures to persons. Among drivers and handlers who worked with radioactive material shipments, dosimeters showed that less than one-half of them received radiation doses above background levels. The highest doses were found for drivers who transported large numbers of 99Mo generators.

Georgia↗
PubMed1982

Monitoring the critical radiation exposure pathways at a BWR nuclear power station.

Iodine-131 in milk and gamma radiation from radionuclides in air in the environment of a 3-unit nuclear power station were measured at the levels predicted for airborne effluent. These measurements were part of a modified environmental radiological monitoring program to confirm the population doses computed from radionuclide release rates and environmental transfer models. The limits of detection were lowered relative to conventional monitoring programs by analyzing 21 L samples of milk for 131I and by determining external gamma radiation with a system that combined use of thermoluminescent dosimeters, pressurized ionization chambers, and NaI(T1) survey meters. For monitoring periods slightly longer than 6 months, during a time when fallout from atmospheric nuclear tests contributed very little, the average measured 131I concentration in milk was 0.1 pCi/L for cows on a nearby pasture and 0.02 pCi/L for cows at a more distant control location, compared to predicted values of 0.07 and 0.02 pCi/L, respectively; the average radiation exposure from airborne radionuclides measured at 16 nearby dosimeter locations was 7 mR, compared to the average of predicted values of 4 mR.

Animals↗
PubMed1979

Superior gluteal artery laceration, a complication of iliac bone graft surgery.

In the 2 cases cited, laceration of the superior gluteal artery occurred when removing bone from the posterior ilium. A review of the anatomy shows how the superior gluteal artery, as it exists the sciatic notch, can be compressed locally and exposed for clipping or ligation. The internal iliac artery can be occluded by embolization of a Fogerty catheter. The bony origin of the gluteus maximus is a good landmark to help avoid entering the sciatic notch and a special retractor provides the necessary exposure.

Adult↗
PubMed1978

Foreign body (palm thorn) in knee joint.

A child who lives in a semitropical or tropical zone and has monarticular symptoms involving the knee joint and a history of playing in the vicinity of plams should be examined for the possibility of a palm thorn within the joint. The diagnosis, made after careful elimination of more common entities, can only be confirmed by surgical exploration.

California↗