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Biomedical subjects

D T Allen

Publications and source records attributed to D T Allen.

At least 19 recordsLinked to original sources
PubMed2001

Accounting for spatial variation of ozone productivity in NOx emission trading.

The potential air quality benefits of NO(x) emission-trading programs were compared to the air quality benefits of across-the-board NO(x) reductions for point sources in eastern Texas. The comparison was performed by first determining, using the Comprehensive Air Quality Model with extensions (CAMx), the changes in ozone concentrations associated with NO(x) reductions at more than 50 individual facilities in eastern Texas. These facility-specific changes in ozone concentrations due to NO(x) reductions were then converted into a variety of indices representing ozone reduction benefits. Trading scenarios were then evaluated through Monte Carlo simulations. The results indicate that approximately 20% of all trading scenarios result in ozone reduction benefits that deviate by 25% or more from the ozone reduction benefits achieved by across-the-board reductions. This result was independent of the index used to calculate ozone reduction benefit. This variability in the benefits associated with trading scenarios was comparable to the variability in benefits associated with changes in meteorological conditions over the days that were modeled. Additional Monte Carlo simulations indicated that the average benefit associated with NO(x) trading could be improved and that the variability in benefit was reduced by creating a trading program where a small group of high impact facilities are allowed to sell but may not buy NO(x) allowances.

Air Pollutants↗
PubMed2001

A central giant cell granuloma in a patient seeking orthodontic treatment.

BACKGROUND: This case report illustrates the need to consider central giant cell granuloma, or CGCG, in the differential diagnosis in cases of greatly displaced teeth and facial deformity. The authors review the literature regarding CGCG and emphasize the importance of early diagnosis and treatment. CASE DESCRIPTION: A 9-year-old boy was seen in an orthodontic office with the chief complaint of overlapping front teeth. On radiographic examination, the authors noted a large maxillary midline radiolucency. The child was referred to an oral and maxillofacial surgeon for definitive diagnosis and treatment. CLINICAL IMPLICATIONS: Patients may come to dental offices for treatment of malaligned teeth. The dentist needs to be aware of possible oral pathology when malaligned teeth are present. CGCG should be included in the differential diagnosis for patients with greatly displaced teeth and facial deformity.

Child↗
PubMed2000

Painful chewing and blindness: signs and symptoms of temporal arteritis.

BACKGROUND: This case report illustrates the need to consider temporal arteritis in the differential diagnosis of jaw or tooth pain. This disease affects the cranial arteries, more frequently in women and usually in those older than age 60 years, causing jaw pain, visual symptoms, headache, scalp pain and sometimes blindness. CASE DESCRIPTION: A 71-year-old man had jaw pain that increased with chewing and speaking, scalp tenderness and dimming vision. A temporal artery biopsy confirmed the diagnosis of temporal arteritis. Treatment with decreasing amounts of oral steroids over 23 months was successful in relieving his signs and symptoms and in saving his vision. CLINICAL IMPLICATIONS: Patients with this disease may seek care from their dentist first. Jaw or tooth pain is the most reliable clinical symptom in the diagnosis of temporal arteritis. Diagnosis and timely referral for treatment with oral steroids can prevent blindness.

Aged↗
PubMed1994

Permeation of proteins from the blood into peripheral nerves and ganglia.

We have attempted to resolve apparently conflicting observations of previous investigators regarding the penetration of proteins into peripheral ganglia and nerves of the rat. Horseradish peroxidase, which is largely cleared from the blood and extracellular fluids in less than 30 min, entered all the extracellular spaces of ganglia, including the clefts between glial cells and neurons, but it did not enter the endoneurium. Rhodamine B-conjugated bovine albumin quickly entered sensory and sympathetic ganglia, but its penetration into avascular enteric nervous tissue was arrested at the outer margin of each myenteric and submucosal ganglion. If injected daily for a week, this fluorescent protein was seen also in the endoneurium, but it was still absent from enteric ganglia. The failure to enter enteric ganglia may have been due to the entrapment of aggregates of dye-labelled albumin molecules in the basal lamina that encloses the enteric nervous system. Extracellular endogenous albumin immunoreactivity was seen in all parts of peripheral nerves and in all types of ganglion. Some neuronal perikarya contained albumin-immunoreactive material; the strongest staining was in enteric neurons. Albumin may reach these cell bodies by retrograde axonal transport from peripheral terminals. We conclude that all the extracellular spaces of the rat's peripheral nervous system are accessible to plasma proteins, though diffusion occurs more slowly into the endoneurium than into ganglia.

Animals↗
PubMed1992

Flow rates and compositions of incinerated waste streams in the United States.

The quantity and composition of RCRA hazardous wastes incinerated during 1986 were examined using the National Hazardous Waste Survey. This Survey, collected for U.S. EPA by the Research Triangle Institute, is the most extensive examination of hazardous waste generation and management available. The survey data show that although a wide variety of hazardous wastes were treated by incineration, more than 75 percent of incinerated waste streams were from chemical manufacturing. The survey data also show that more than 90 percent of the incinerated wastes were treated by incinerators located at the facility generating the waste. Despite the predominance of a single industrial sector in generating incinerated hazardous wastes, the compositional profile of the wastes is far from uniform. To illustrate this variability, the metals and chlorine content of the wastes are reported along with the sources of the metal and chlorine loadings.

Air Pollution↗
PubMed1992

Excluded babies.

Explore the source record for details and available documents.

Adolescent↗
PubMed1990

A circulating exogenous protein can enter enteric nervous tissue in the rat.

Previous studies of the permeation of circulating protein tracers yielded conflicting results in the enteric nervous system. We show that within 5 min of intravenous injection, horseradish peroxidase (HRP) enters all the extracellular spaces of the ganglia and connecting strands of the submucous and myenteric plexuses of the rat's small intestine, including the clefts between neuroglial cells and neurons. The tracer is still there after 10 min, but is nearly all gone 30 min after injection. Enteric neurons, like others with somata in peripheral ganglia, are therefore probably accessible to plasma proteins and to substances with smaller molecules that are protein-bound when circulating in the blood.

Animals↗
PubMed1990

Flow characteristics of bioprosthetic heart valves.

A review of the in vivo and in vitro fluid dynamic performance of three bioprosthetic heart valves is presented. Data on Hancock porcine valves (standard models 242 aortic and 342 mitral and modified orifice model 250 aortic), Carpentier-Edwards porcine valves (model 2625 aortic and 6625 mitral), and the Ionescu-Shiley pericardial valve are reviewed. These valves were chosen because of their past or present popularity in clinical use and because of the variation in fluid dynamic performance reported by different investigators. The flow parameters that are reported include in vivo and in vitro mean pressure drop, cardiac output or cardiac index, regurgitant volume, effective orifice area, and performance index. These data provide a framework for differentiation of normal and abnormal bioprosthetic valve function.

Animals↗
PubMed1990

A multifocal outbreak of hepatitis A traced to commercially distributed lettuce.

From February 1 through March 20, 1988, 202 cases of hepatitis A were reported in and around Jefferson County, Kentucky. The epidemic curve indicated a common-source exposure. However, there was no apparent single source of exposure from a restaurant, or community gathering; nor was there a geographic clustering by residence. Cases were mainly adults 20-59 years old (89 percent); 51 percent were female. A case-control study using neighborhood controls found that factors associated with hepatitis A were: having eaten downtown (odds ratio [OR] = 4.0) and having dined at any one of three restaurants (OR = 21.0). Case-control studies of patrons of two of these restaurants found that eating green salad was strongly associated with acquiring hepatitis A: OR = 11.6 and OR = 4.4. The three implicated restaurants accounted for 71 percent of the cases. All three restaurants were supplied by the same fresh produce distributor; however, investigation suggested that contamination most likely occurred prior to local distribution. This outbreak of hepatitis A is the first in the United States apparently associated with fresh produce contaminated before distribution to restaurants, and raises important public health issues regarding the regulation of fresh produce.

Adult↗
PubMed1989

In vitro flow dynamics of four prosthetic aortic valves: a comparative analysis.

The velocity fields downstream of four prosthetic heart valves were mapped in vitro over the entire cross-section of a model aortic root using laser Doppler anemometry. THe Björk-Shiley 60 degrees convexo-concave tilting disc valve, the Smeloff-Cutter caged ball valve, the St. Jude Medical bileaflet valve, and the Ionescu-Shiley standard bioprosthesis were examined under both steady and pulsatile flows. Velocity profiles under steady flow conditions were a good approximation for pulsatile profiles only during midsystole. The pulsatile flow characteristics of the four valves showed variation in large scale flow structures. Comparison of the valves according to pressure drop, shear stress and maximum velocities are also provided.

Aortic Valve↗
PubMed1988

An emergency physician's guide to prosthetic heart valves: identification and hemodynamic function.

We describe methods for identifying the type and size of seven commonly used prosthetic heart valves and how these features influence the hemodynamics of flow through the valve. The four mechanical heart valves reviewed are Starr-Edwards silicone rubber ball valves (Models 1200/1260 aortic and 6120 mitral valves), Bjork-Shiley tilting disc valves (60 degrees standard spherical model and the 60 degrees convexo-concave model), Medtronic-Hall (Hall-Kaster) tilting disc valve, and St Jude Medical bileaflet valve. The three bioprostheses reviewed are Hancock porcine valve, Carpentier-Edwards porcine valve, and Ionescu-Shiley bovine pericardial valve. These valves were chosen because of their past or present popularity and therefore are the ones most apt to be implanted in patients seen in the emergency department.

Bioprosthesis↗
PubMed1988

An emergency physician's guide to prosthetic heart valves: valve-related complications.

Serious valve-related complications that occur in patients with prosthetic valves have been discussed. The emergency physician's role primarily is to recognize the high probability that one of these serious complications exists and hospitalize the patient so that rapid definitive diagnoses and therapeutic decisions are not delayed.

Anemia, Hemolytic↗
PubMed1987

Cervical cancer.

This conference concerns economic, psychosocial, preventive, and medical aspects of the care of an indigent, unemployed, 22-year-old mother of three who died of an invasive, large cell, nonkeratinizing cervical cancer 35 months after her last Pap smear, 19 months after the onset of vaginal discharge, 12 months after consulting a physician, 10 months after an exploratory laparotomy, nine months after initiation of radiation therapy, five months after performance of a colostomy, four months after initiation of chemotherapy, and three months after treatment of small bowel obstruction with hyperalimentation and resection. We discuss the cost effectiveness of preventive programs.

Adolescent↗
PubMed1986

Flow characteristics of four commonly used mechanical heart valves.

The in vivo and in vitro fluid dynamic performance of 4 mechanical heart valves was reviewed: Starr-Edwards silicon-rubber ball valves (models 1200/1260 aortic and 6120 mitral valves), Björk-Shiley tilting disc valves (standard spherical model, modified and unmodified convexo-concave [60 degrees and 70 degrees C-C] models), the Medtronic-Hall (Hall-Kaster) tilting disc valve and the St. Jude Medical bileaflet valve. These valves were chosen because of their past or present popularity in clinical use and because they encompass most of the basic mechanical valve designs used during the past 2 decades. The flow measurements reported include in vivo and in vitro mean pressure drop, cardiac output or cardiac index, regurgitant volume, effective orifice area and performance index.

Cardiac Output↗
PubMed1986

Comparison of the effects of 3-ethoxycarbonyl-1,4-dihydro-2,4-dimethylpyridine and 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine on ferrochelatase activity and heme biosynthesis in chick embryo liver cells in culture.

3-Ethoxycarbonyl-1,4-dihydro-2,4-dimethylpyridine (EDP) was shown to lack the ferrochelatase-lowering activity of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) in chick embryo liver cells in culture. This was attributed to the inability of EDP to cause destruction of the heme moiety of cytochrome P-450 with concomitant formation of N-methylprotoporphyrin IX. EDP was less potent as a porphyrinogenic agent than DDC and caused the accumulation of uroporphyrin, heptacarboxylic porphyrin, and coproporphyrin in contrast with DDC which caused primarily protoporphyrin to accumulate. The inactivity of EDP as a ferrochelatase-lowering agent and its low porphyrinogenic potency was explained, at least in part, by its rapid transformation in aqueous solution to other nondihydropyridine products. The two ethoxycarbonyl substituents of DDC are therefore essential for N-methylprotoporphyrin formation, ferrochelatase-lowering activity, and optimal porphyrin-inducing activity.

Animals↗
PubMed1985

Neonatal outcome in planned v unplanned out-of-hospital births in Kentucky.

We conducted a survey of 1,064 out-of-hospital Kentucky births during 1981 to 1983 in order to classify each by planning status (planned or unplanned to occur out of hospital) and attendant. Among the 809 births for which we obtained information, 575 (71.1%) were planned. We examined birth outcome by low birth weight (LBW) and neonatal mortality (NM). Compared with planned births, unplanned births were associated with increased risk of LBW (odds ratio = 6.6; 95% confidence limits [CL], 3.9 to 11.2, adjusted for maternal age). Furthermore, after adjusting for maternal age and parity, LBW births occurred at less than expected frequency among planned births (observed to expected [O:E] ratio = 0.48; 95% CL, 0.29 to 0.73), but at greater than expected frequency among unplanned births (O:E ratio = 2.9; 95% CL, 2.2 to 3.8). A similar, but nonsignificant, trend was seen for NM and NM was much greater in the unplanned group (72.7 per 1,000 live births) than in the planned group (3.5 per 1,000).

Adolescent↗
PubMed1985

Suicidal destruction of cytochrome P-450 and reduction of ferrochelatase activity by 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine and its analogues in chick embryo liver cells.

The ferrochelatase-reducing activity and cytochrome P-450- and heme-destructive effects of a variety of analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) were studied in chick embryo liver cells. A group of DDC analogues was found in which an inability to reduce ferrochelatase activity corresponded with an inability to cause cytochrome P-450 and heme destruction. In a second group of DDC analogues, the ability to reduce ferrochelatase activity corresponded with the ability to cause cytochrome P-450 and heme destruction. These observations support the idea that the protoporphyrin IX moiety of N-alkylprotoporphyrin IX originates from the heme moiety of cytochrome P-450. A third group of DDC analogues caused cytochrome P-450 and heme destruction despite an inability to reduce ferrochelatase activity. With this third group of DDC analogues, the heme moiety of cytochrome P-450 is likely degraded to products other than N-alkylporphyrins. The inability of several lipophilic DDC analogues [4-benzyl, 4-isopropyl, 4-cyclohexyl, 4-(3-cyclohexenyl)] to reduce hepatic ferrochelatase activity may explain their low porphyrinogenicity. The pattern of porphyrin accumulation produced in response to two DDC analogues that did not inhibit ferrochelatase was investigated using high performance liquid chromatography. Coproporphyrin was the major porphyrin to accumulate in response to the 4-isopropyl analogue and uro- and heptacarboxylic acid porphyrins in response to the 4-benzyl analogue. These patterns of porphyrin accumulation are consistent with the inability of these analogues to inhibit ferrochelatase.

Animals↗