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Biomedical subjects

D W Johnson

Publications and source records attributed to D W Johnson.

At least 199 records · Page 11Linked to original sources
PubMed1986

Kinetics of the DFPase activity in Tetrahymena thermophila.

Crude homogenates of the ciliate protozoon, Tetrahymena thermophila, can hydrolyze the potent acetylcholinesterase inhibitors O,O-diisopropylphosphorofluoridate (DFP) and O-1,2,2-trimethylpropylmethylphosphonofluoride (soman). Characterization of the enzymatic activity of the homogenate has been performed. The DFPase operates over a pH range of 4 to 10 and an ionic range of 0-500 mM NaCl. Rate of reaction increases three- to four-fold from 25 degrees C to 40 degrees C and is still present at 55 degrees C. These results indicate that the enzymatic activity operates over a broad range of environmental conditions, making it an attractive material for use in the detoxification and detection of organofluorophosphates. DFPases may be important in the metabolism of naturally occurring organophosphates.

Animals↗
PubMed1986

Patient exposure trends in medical and dental radiography.

Patient exposure to medical and dental x rays has long been of interest to the radiological health community. With the cooperation of state and local agencies and professional groups, the Center for Devices and Radiological Health has conducted three major surveys of patient exposure to x rays. The latest of these surveys, the Nationwide Evaluation of X-ray Trends (NEXT), collected x-ray exposure data for each year starting in 1972. Two earlier studies, the 1964 and 1970 X-ray Exposure Studies collected x-ray data during the years these surveys were conducted. Exposure trends presented are based on results of all three studies. Major improvements in beam limitation are seen for medical and dental radiography. Since 1964, when the first nationwide survey was conducted, dental exposures have decreased about 75%. Decreases of up to one-third occurred in exposures for medical examinations. The current exposure data presented continue to show a wide variation in medical exposures. Also presented are organ doses for four organs (ovaries, testes, thyroid and active bone marrow).

Female↗
PubMed1985

Deuterium labelled steroid hormones: tracers for the measurement of androgen plasma clearance rates in women.

A method employing stable isotope-labelled tracers and gas chromatograph-mass spectrometry (GC-MS) analysis has been used to measure the plasma clearance rates (PCR's) of androstenedione (A) and testosterone (T) in normal women and women with androgen abnormalities including hirsutism and polycystic ovary syndrome. A solution of deuterium-labelled A and T is infused at a constant rate and blood samples taken at 2 and 2.25 h. Solvent extracts of the derived plasma samples, to which an internal standard has been added, are derivatized with pentafluoropropionic anhydride and the endogenous steroid and deuterated steroid are quantitated after an injection of the derivatization mixture into a capillary column GC-MS. The concentration of the deuterated steroid in the infusion mixture is measured and the PCR is calculated. In premenopausal normal women the PCRA is 1950 +/- 184 1/24 h (n = 5) and the PCRT is 484 +/- 82 1/24 h (n = 7).

Androgens↗
PubMed1985

Malignant obstructive jaundice: treatment with external-beam and intracavitary radiotherapy.

Eleven patients with obstructive jaundice from unresectable cholangiocarcinoma, metastatic porta hepatis adenopathy, or direct compression from a pancreatic malignancy were treated at the Stanford University Medical Center from 1978-1983 with an external drainage procedure followed by high-dose external-beam radiotherapy and by an intracavitary boost to the site of obstruction with Iridium192 (Ir192). A median dose of 5000 cGy was delivered with 4-6 Mv photons to the tumor bed and regional lymphatics in 9 patients, 1 patient received 2100 cGy to the liver in accelerated fractions because of extensive intrahepatic disease, and 1 patient received 7000 "equivalent" cGy to his pancreatic tumor bed and regional lymphatics with neon heavy particles. An Ir192 wire source later delivered a 3100-10,647 cGy boost to the site of biliary obstruction in each patient, for a mean combined dose of 10,202 cGy to a point 5 mm from the line source. Few acute complications were noted, but 3/11 patients (27%) subsequently developed upper gastrointestinal bleeding from duodenitis or frank duodenal ulceration 4 weeks, 4 months, and 7.5 months following treatment. Eight patients died--5 with local recurrence +/- distant metastasis, 2 with sepsis, and 1 with widespread systemic metastasis. Autopsies revealed no evidence of biliary tree obstruction in 3/3 patients. Mean survival time from initial laparotomy and bypass was 16.1 months, and from radiotherapy completion was 8.3 months. Evolution of radiation treatment techniques for biliary obstruction in the literature is reviewed. High-dose external-beam therapy followed by high-dose Ir192 intracavitary boost is well tolerated and provides significant palliation. Survival of these aggressively managed patients approaches that of patients with primarily resectable tumors.

Adenoma, Bile Duct↗
PubMed1985

Mainstreaming hearing-impaired students: the effect of effort in communicating on cooperation and interpersonal attraction.

Cooperative and individualistic learning experiences were compared in terms of their effects on interaction and relationships between hearing and hearing-impaired students. Two contradictory hypotheses were tested--one stating that the effort required for hearing and hearing-impaired students to communicate would lead to frustration, withdrawal, exclusion, and rejection; the other stating that cooperative learning experiences would lead to cross-handicap interpersonal attraction regardless of communication difficulties. Thirty 3rd-grade students (20 hearing and 10 hearing impaired) were assigned to conditions on a stratified, random basis controlling for handicap, sex, and ability level. They participated in the study for 55 min a day for 15 instructional days. The results indicate that subjects involved in cooperative learning experiences performed higher on measures of interaction and interpersonal attraction between hearing and hearing-impaired students than did subjects involved in individualistic learning experiences.

Achievement↗
PubMed1985

Oral interaction in cooperative learning groups: speaking, listening, and the nature of statements made by high-, medium-, and low-achieving students.

Oral interaction within cooperative learning groups was observed for high-, medium-, and low-achieving students. Initially, cooperative and individualistic learning situations were compared on achievement and attitudes. Forty-eight 4th-grade American students were assigned to learning situations on a stratified random basis controlling for ability and sex. They participated in the study for 55 min a day for 15 instructional days. Two observation schemes were used. The results for the cooperative situation were factor analyzed to determine the basic dimensions of oral interaction within cooperative learning groups. Five orthogonal factors were identified: Exchanging Task-Related Information, Elaborating on the Information, Encouraging Each Other to Learn, Disagreeing With Each Other's Conclusions, and Making Nontask Comments and Sharing Personal Feelings. The oral participation of students from different achievement levels was differentially related to achievement. Vocalizing was found to be more strongly related to achievement than was listening to other group members vocalize. Medium and low achievers especially benefited from cooperative learning experiences.

Achievement↗
PubMed1985

Virtues and vagaries of high-resolution CT air cisternography in the diagnosis of acoustic neuromas.

A series of 125 consecutive, bilateral, high-resolution, computerized tomographic (CT) air cisternograms was prospectively reviewed and analyzed. Emphasis was placed on identifying problems encountered in performing the study and potential sources of error in interpretation. In two patients there was difficulty in transporting the air bolus because spinal cord tumors coexisted with bilateral acoustic neuromas. Potential false-positive results were avoided in four patients by persistent efforts to fill the internal auditory canal. Later reexaminations were recommended for four patients whose examinations were suspicious or suggestive of tiny acoustic neuromas. Unilateral Mondini malformation was incidentally diagnosed in one patient. Six patients required therapy for persistent headache after lumbar puncture. High-resolution CT air cisternography is believed to be the method of choice for investigating the nonenhancing or small acoustic neuroma. However, this method is not without potential problems, some of which are discussed.

Humans↗
PubMed1985

Credentialing of diagnostic x-ray technologists: a question of public health impact.

This paper presents estimates of the number of diagnostic x-ray examinations performed in the United States, the population dose delivered, the percentage of that dose contributed by credentialed and noncredentialed operators, and one measure of performance: collimation of the x-ray beam. An estimated 82 per cent of medical x-ray examinations are performed by voluntarily certified (ARRT or ARCRT) operators. These procedures contribute 90 per cent of the radiation dose to the population. Data from the Nationwide Evaluation of X-Ray Trends (NEXT) program indicate that certified operators collimate the x-ray beam somewhat better than noncertified for chest examinations. They also indicate that differences in collimation practices may be attributed to the type of facility as well as to the credentials of the operators. One-third of the medical x-ray machines are in states presently requiring licensure of operators. It appears from these estimates that instituting operator licensure in the remaining states may reduce population dose by a maximum of one or two per cent.

Allied Health Personnel↗
PubMed1985

Effects of instrument type and orchestral position on hearing sensitivity for 0.25 to 20 kHz in the orchestral musician.

Minnesota Orchestra members (42 males, 18 females) aged 24 to 64 years, all asymptomatic for hearing problems or ear disease, were evaluated with a hearing history questionnaire, otolaryngologic examination, and pure tone audiometry for the conventional (0.25 to 8 kHz) and extended high frequency (9 to 20 kHz) ranges. Hearing sensitivity was examined with respect to musician instrument type, years of playing, and orchestral stage position. Type of instrument played and position on the orchestral stage had no significant correlation with hearing loss.

Adult↗
PubMed1985

Effect of maternal antibody upon vaccination with infectious bovine rhinotracheitis and bovine virus diarrhea vaccines.

This report presents the normal rate of decay of maternal antibody and the influence of maternal antibody on responses to a single vaccination with modified-live bovine virus diarrhea and infectious bovine rhinotracheitis virus vaccines at 196 days of age and on response to vaccinations with the same vaccines given twice at 84 and 196 days of age. Passive immunity decreased to near zero over the first six months of life for both bovine virus diarrhea and infectious bovine rhinotracheitis controls. All calves seroconverted to bovine virus diarrhea vaccine at 84 days of age, even though high levels (greater than 1:32) of maternal antibodies were present. These calves did not seroconvert to infectious bovine rhinotracheitis vaccine at 84 days of age when high levels (less than 1:16) of maternal antibodies were present. Calves responded well to bovine virus diarrhea and infectious bovine rhinotracheitis vaccines given only once at 196 days of age after passive immunity disappeared. Calves which were revaccinated with infectious bovine rhinotracheitis seroconverted showing a more rapid response than the single vaccinates. Those revaccinated with bovine virus diarrhea showed an immediate response of small magnitude.

Animals↗
PubMed1985

Adjuvant enhancement of humoral immune response to chemically inactivated bovine viral diarrhea virus.

Potentiation of the antibody response to inactivated bovine viral diarrhea virus by immunological adjuvants was studied in guinea pigs and cattle. The inactivated bovine viral diarrhea virus alone was demonstrated to be a weak immunogen. Addition of either 2 mg per mL diethylaminoethyl-dextran or 5% alhydrogel to inactivated bovine viral diarrhea virus did not or only slightly stimulated the antibody response; the combined adjuvants induced a significantly higher titer. A higher concentration (20 mg per mL) of diethylaminoethyl-dextran, on the contrary, suppressed the immune potentiation by the dual adjuvants. Combination of Bordetella bronchiseptica and alhydrogel adjuvants stimulated a high titer of antibody. The titer was further elevated upon revaccination and was significantly higher than that induced by alhydrogel alone. In cattle, alhydrogel enhanced the immune response and the additional inclusion of diethylaminoethyl-dextran did not cause a significant potentiation of the immunity. However, the antibody decay rate was significantly slower when stimulated by the combined adjuvants.

Adjuvants, Immunologic↗
PubMed1984

Air cisternography of the cerebellopontine angle using high-resolution computed tomography.

While high-resolution CT/air cisternography is considered the preferred method of investigating non-enhancing or small acoustic neuromas, it is not without pitfalls. Eighty such studies were reviewed, emphasizing procedural problems and sources of interpretive error. Two patients presented difficulty in transporting the air bolus due to a spinal cord tumor coexisting with bilateral acoustic neuromas; spinal cord decompression was required in one case. Three potential false positives were avoided by persistent efforts to fill the internal auditory canal. Of 4 patients thought to have a tiny acoustic neuroma, elective vestibular nerve section in 2 revealed no evidence of tumor. One unilateral Mondini malformation was diagnosed. Four patients required a blood patch for persistent headaches.

Cerebellopontine Angle↗