Biomedical subjects
D M Meyer
Publications and source records attributed to D M Meyer.
Assessment of the human health risks posed by exposure to chromium-contaminated soils.
Millions of tons of chromite-ore processing residue have been used as fill in various locations in northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is a human carcinogen following inhalation of high concentrations. It can also cause allergic contact dermatitis. This evaluation addresses a residential site where the arithmetic mean (x) and geometric mean (gm) concentrations of Cr(III) in soil were 2879 and 1212 mg/kg (ppm). The mean and geometric mean concentrations of Cr(VI) were 180 and 4 mg/kg, respectively. The uptake (absorbed dose) of Cr(III) via soil ingestion, consumption of homegrown vegetables, and ingestion of inspired particles was determined. The uptake of Cr(VI) via dermal absorption from contact with surface soil and building wall surfaces, as well as inhalation, was also evaluated. The techniques used in this assessment are applicable for evaluating the human health risks posed by any residential site having contaminated soil. The potential for both sensitized and unsensitized persons to develop allergic contact dermatitis due to exposure to soil contaminated at these levels was found to be negligible. The estimated average daily dose (ADD) via ingestion and dermal absorption for the maximally exposed individual (MEI) was about 1500- and 40-fold below the EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. It was shown that for residential sites, the most important route of exposure to Cr(III) was incidental soil ingestion. Although not relevant to these sites specifically, if garden vegetables could be successfully grown in these soils, then they would probably be the predominant source of uptake of Cr(III). Since inhalation of Cr(VI)-contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the doses and associated risks were assessed. The estimated cancer risks for the MEI and most likely exposed individual (MLEI) were approximately 5 x 10(-9) and 2 x 10(-9), respectively. These levels of risk have always been considered well below those that warrant regulatory concern. For persons living on residential properties, the cancer risk due to inhaling suspended particles is likely to be less than 1 in 1,000,000 if Cr(VI) levels in soil are less than 180 mg/kg (ppm). Based on this analysis, the levels of Cr(III) and Cr(VI) at this and similar sites do not pose a health hazard following acute or chronic exposure.
An assessment and quantitative uncertainty analysis of the health risks to workers exposed to chromium contaminated soils.
Millions of tons of chromite-ore processing residue have been used as fill in various locations in Northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is considered a inhalation human carcinogen at high concentrations. Approximately 40 commercial and industrial properties in Northern New Jersey have been identified as containing chromite ore processing residue in the soil. One site, a partially-paved trucking terminal, was evaluated in this assessment. The arithmetic mean and geometric mean concentrations of total chromium in soil were 977 and 359 mg/kg, respectively. The data were log-normal distributed. The arithmetic mean and geometric mean concentrations of Cr(VI) in surface soil were 37.6 and 3.1 mg/kg, respectively. The data could not be fit to a standard distribution, likely due to the large number of samples with concentrations below the method detection limit (65%). Dose was calculated for each exposure route using a Monte Carlo statistical simulation. Probability distributions of most exposure parameters were incorporated into the analyses to predict the range and probability of uptake for persons in the exposed population. The exposure parameter distributions included in this assessment are: the concentrations of Cr(VI) and total chromium in air and soil, fraction of the year when suspension of airborne soil particulates is likely to occur due to weather conditions, fraction of Cr(VI) in air which is respirable (less than 10 microns), soil loading rate on skin, occupational tenure, and body weight. The techniques used in this assessment are applicable for evaluating the human health risks posed by most industrial sites having contaminated soil. The estimated average daily dose (ADD) via ingestion and dermal absorption for the individual exposed at the 95th percentile was about 48,000- and 91-fold below the U.S. EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. Since inhalation of Cr(VI) contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the lifetime average daily doses (LADDs) associated with exposure at the 50th and 95th percentile were calculated to be 9.8 x 10(-8) and 1.3 x 10(-6), respectively. Based on this analysis, industrial sites having soil concentrations of Cr(VI) below 230 ppm do not pose a significant noncarcinogenic or carcinogenic health hazard following acute or chronic exposure. These risks would be even smaller if the sites were paved.
The evaluation of blunt abdominal trauma: computed tomography scan, lavage, or sonography?
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Effect of different degrees of hypothermia on myocardium in treatment of hemorrhagic shock.
The use of hypothermia in cardiac and neurologic surgery is well established, but its use in treating hemorrhagic shock is controversial. Using a modified Wiggers hemorrhagic shock model, we examined the effects of hypothermia (group 1, 33 degrees C, N = 7; group 2, 28 degrees C, N = 12) after inducing hemorrhagic shock. In group 3, N = 6, dogs were maintained at body temperature in hemorrhagic shock and throughout resuscitation (normothermic shock). Sixty minutes after resuscitation (shed blood and lactated Ringer's solution, 50 ml/kg body wt), all hypothermic dogs were rewarmed and studied for an additional 120 min. Comparison of moderately hypothermic, severely hypothermic, and normothermic dogs showed a lower heart rate (80.6 +/- 3.3, 62.5 +/- 4.1, and 136.7 +/- 4.2 beats/min, P less than 0.05), reduced rate of left ventricular pressure fall (938 +/- 125, 700 +/- 75, and 1550 +/- 275 mm Hg/sec, P less than 0.05), a lower arterial pH (7.15 +/- 0.02, 7.10 +/- 0.03, and 7.24 +/- 0.02, P less than 0.05), a lower respiratory rate (18 +/- 1, 14 +/- 1, and 24 +/- 2 breaths/min, P less than 0.05), and a higher arterial pCO2 (36.6 +/- 1.6, 46.9 +/- 4.6, and 20.3 +/- 2.0 mm Hg, P less than 0.05). Left ventricular end-diastolic pressure was lower in the severely hypothermic dogs while stroke volume was higher in this group. Rewarming ablated all differences in cardiovascular performance and acid-base balance. Our data show that moderate hypothermia during hemorrhagic shock increased coronary perfusion, enhanced cardiac contractile performance, and significantly reduced myocardial oxygen requirements.(ABSTRACT TRUNCATED AT 250 WORDS)
Multiple nonatherosclerotic aneurysms unrelated to a clinical syndrome.
Two cases of multiple inflammatory aneurysms in young patients without evidence of autoimmune disease or an aneurysmal syndrome are presented. Neither case showed any clinical or histologic characteristics typical of Ehlers-Danlos syndrome, Marfan's syndrome, Takayasu's arteritis, or other aneurysmal syndromes. Pathologic findings showed adventitial and medical destruction in both patients; although the first case displayed more adventitial involvement, the second showed greater destruction of the medial elastic laminae. The decision to repair an aneurysm should be tempered by its location, the amount of involvement of the artery with multiple lesions, and the risk to the end-organ if repair is unsuccessful.
Carbon dioxide elimination in anaesthetized children.
Carbon dioxide elimination (VCO2) was measured in 186 anaesthetized, spontaneously breathing infants and children with body weights ranging from 2.8 to 26.5 kg. They all underwent minor paediatric surgical procedures. The influence on VCO2 of age, operation, premedication, caudal anaesthesia, and different volatile anaesthetic agents was investigated. The volume of exhaled gas, during three- to five-minute collection periods, was measured and the fraction of exhaled CO2 was determined by a CO2 meter. Under basal anaesthetic conditions, the average output before operation followed the equation: VCO2 (ml.min-1) = -1.25X + 13.0X2, in which X = lne (body weight, kg). Expressed on a weight basis, the youngest infants (weighing less than 5 kg) had the lowest VCO2. Higher values were measured up to a body weight of 10 kg above which a negative correlation occurred between VCO2 (ml.min-1.kg-1) and body weight. The use of premedication resulted in a more variable VCO2 during operations than when opioid premedication was not used. The combination of a general anaesthetic and caudal anaesthesia stabilized VCO2. Also, children anaesthetized with halothane had a higher VCO2 than those who were anaesthetized with enflurane or isoflurane (P less than 0.05). The variable VCO2 emphasizes the need for increased monitoring of VCO2 during routine anaesthesia and operation in infants and children.
Evaluation of computed tomography and diagnostic peritoneal lavage in blunt abdominal trauma.
Three hundred one hemodynamically stable patients with equivocal abdominal examinations following blunt abdominal trauma had a CT scan followed by DPL. Both studies were negative in 194 patients (71.6%) and positive in 51 patients (27.1%). Seven of the 51 patients (13.7%) had an additional significant injury at operation that was not seen on the CT scan. Nineteen patients had a negative CT scan, a positive DPL, and a significant injury confirmed at celiotomy. In this group of 19 patients, the CT failed to identify seven splenic, three hepatic, and three small bowel injuries. There were two complications attributed to DPL. Three patients had a false negative DPL. Diagnostic peritoneal lavage continues to be a reliable study (sensitivity--95.9%, specificity--99%, accuracy--98.2%). The CT scan is not as sensitive (sensitivity--74.3%, p less than 0.001; specificity--99.5%, accuracy--92.6%). It is concluded that selective use of both procedures is appropriate as long as one recognizes the inherent limitations of each.
The role of abdominal CT in the evaluation of stab wounds to the back.
Two hundred five patients with stab wounds to the back were evaluated with CT scans using both oral and IV contrast material. One hundred sixty-nine patients had a negative scan. Thirty (17.8%) of the 169 patients were operated upon because of clinical concern. Injuries were found in two of these patients: a diaphragmatic injury in one and a combined diaphragmatic and liver injury in the other. None of the 139 patients observed developed any sequelae. Twenty of the 33 patients with a positive CT were taken to the operating room where 16 were found to have a significant injury. Seven of these 16 patients had additional injuries not identified on CT. There were four false positive scans. Thirteen patients with a positive scan and two patients with an equivocal scan were observed based upon clinical judgment. Ten of these 15 patients had minor isolated renal or hepatic injuries seen on scan. None of these developed complications. It is concluded that abdominal computed tomography, with a sensitivity of 89%, specificity of 98%, and accuracy of 97% is a reliable study in the evaluation of patients with stab wounds to the back.
Assessment of spontaneous ventilation in anesthetized children with use of a pediatric circle or a Jackson-Rees system.
To compare respiratory workloads, inspiratory efforts were evaluated in 11 children anesthetized with halothane while breathing through a pediatric circle or a Jackson-Rees system. All underwent urogenital surgery and received caudal analgesia after tracheal intubation. Anesthesia was maintained with O2/air at an end-tidal halothane concentration of 0.8%. A pediatric circle system at a fresh gas flow (FGF) of 0.5 and 1.5 x min ventilation (VE) (C0.5 and C1.5, respectively) and a Jackson-Rees system at FGF of 1.5 and 3.0 x VE (JR1.5 and JR3.0, respectively) were used in each patient in a random order. Tidal volume (VT), mean inspiratory flow (VT divided by the duration of inspiration TI, VT/TI), and the initial fast slopes of the airway occlusion pressure phase (delta P degrees/delta t FAST) were significantly lower (P less than 0.05) with the Jackson-Rees than with the circle system, indicating greater impedence to spontaneous breathing with the Jackson-Rees system. The Jackson-Rees system also required a greater peak transpulmonary pressure (PtpMAXe) than did the circle system to achieve the same peak expiratory flows (VMAXe, P less than 0.05), again suggesting an increased resistance with the Jackson-Rees system. These results are most likely explained by the difference in elastic loads (two to three times more with the Jackson-Rees systems) between the two systems. The pediatric circle system appears to be a reliable alternative to the Jackson-Rees system.
Effect of moderate hypothermia in the treatment of canine hemorrhagic shock.
This study evaluated a possible protective and therapeutic effect of moderate hypothermia in the treatment of severe hemorrhagic shock. A modified Wiggers shock preparation was used. Normothermic dogs (Group I, N = 6) were maintained at normal body temperature throughout hemorrhagic shock and resuscitation. In Group II, hypothermia was initiated after 15 minutes of hemorrhagic shock (N = 12) and maintained for 60 minutes after fluid resuscitation. Animals were then rewarmed with Group IIA (N = 7) receiving sodium bicarbonate to correct acidosis, while Group IIB (N = 5) did not; all dogs were studied for an additional 120 minutes. During shock heart rate was lower in both hypothermic groups (IIA and IIB) compared to normothermic dogs (85.0 +/- 3.9, 77.7 +/- 4.6 vs. 136.7 +/- 4.2, respectively, p less than 0.05), while +dP/dt (mmHg/s) remained stable in all dogs. Furthermore, pH was lower in the hypothermic (Groups IIA and IIB) compared to normothermic animals at this time period (Group IIA: 7.19 +/- 0.02, Group IIB: 7.13 +/- 0.02 vs. Group I: 7.24 +/- 0.02). Arterial pCO2 was higher in the hypothermic hemorrhagic shock Groups IIA and IIB compared to normothermic group (34.5 +/- 2.2, 37.4 +/- 2.2 vs. 20.3 +/- 20,3 +/- 2.0, p less than 0.05) due to hypothermia-depressed respiration. A higher myocardial O2 consumption and a negative myocardial lactate balance occurred in the normothermic animals during hemorrhagic shock. After resuscitation and rewarming, stroke volume (mL/beat) and cardiac output (L/min) were lower in hypothermic animals with persistent acid-base derangements (12.6 +/- 2.5, 1.3 +/- 3.0, respectively) compared to hypothermic dogs with acid-base correction (20.1 +/- 3.3, 2.2 +/- 0.3) and normothermic dogs (24.6 +/- 3.0, 3.0 +/- 0.3, p less than 0.05), while myocardial O2 extraction and myocardial lactate production were higher. Results suggest hypothermia decreases the metabolic needs and maintains myocardial contractile function in hemorrhagic shock. Hypothermia may have a beneficial effect and, with normalization of acid-base balance, a therapeutic role in hemorrhagic shock.
Assembly and remodelling of myofibrils and intercalated discs in cultured neonatal rat heart cells.
The reorganization of myofibrils and the re-formation of intercalated discs was examined in neonatal rat cardiac muscle cells during the first 72 h of culture. Rhodamine phalloidin was used to monitor the organizational state of the myofibrils and antibodies to desmoplakin and vinculin were used as markers for the presence of desmosomes and fasciae adherentes, respectively. Tiny punctate desmosomes were observed between muscle cells after 24 h and apparently increased in number and/or size between 24 and 48 h in culture. Fasciae adherentes were not detectable with antibodies to vinculin until after 48 h in culture. Well-defined sarcomeres were restored after 48 h in culture. Once formed the sarcomeric organization of the myofibrils was found to be stable provided they were attached to the sarcolemma via intercalated discs. However, if the myofibrils attached to regions of the membrane that lacked intercalated discs the sarcomeres appeared to break down gradually centripetally. When myofibrils attached to the membrane at the free edges of cells that were not in contact with other muscle cells, the striations stopped abruptly at a considerable distance before the myofibril attached to the membrane. These non-striated terminals elongated between 48 and 72 h and were associated with focal contacts that contained vinculin. Overall the results suggest that cell-cell contact may be critical for the stabilization of normal myofibrillar structure in the heart.
Isolation and characterization of 1-O-alpha-2-acetamido-2-deoxy-D-galactopyranosyl-myo-inositol from pregnancy urine.
A new neutral glycoside of myo-inositol was isolated from the pregnancy urine of a single donor. Its structure was investigated by 1H-NMR spectroscopy and mass spectroscopy. It was identified as 1-O-alpha-2-acetamido-2-deoxy-D-galactopyranosyl-myo-inositol. No such structure or sequence has previously been reported in either myo-inositol or glucose glycosides.
Characterization of a new oligosaccharide containing myo-inositol found in pregnancy urine.
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Human liver neuraminidase.
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A collaborative effort to study methods of teaching physical examination skills.
A collaborative study was conducted between two medical schools to evaluate critically the teaching of physical examination skills to first-year medical students, assess the effect of different instructional methods on student performance, and improve teaching programs at both schools. Students at the two schools were videotaped performing a physical examination on a paid model at the completion of their physical diagnosis courses. The videotapes were sent to a third school for independent evaluation based on criteria agreed upon by all three schools. Students participating in a highly structured course and utilizing a very specific behavioral checklist as both a teaching and evaluating instrument tended to perform more complete physical examinations than students from a less structured course and employing a more generalized checklist. Both medical schools benefited from participation in the study.
Differentiation of human mycoplasma using gas chromatography.
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[Isolation and structure of an acetylpeptide of orosomucoid].
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