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Biomedical subjects

M D Evans

Publications and source records attributed to M D Evans.

At least 91 records · Page 5Linked to original sources
PubMed1990

A comparison of the free radical chemistry of tobacco-burning cigarettes and cigarettes that only heat tobacco.

Cigarette smoke contains free radicals both in the particulate matter (tar) and in vapor-phase smoke. Vapor-phase smoke decreases the activity of alpha-1-proteinase inhibitor (alpha 1PI) in vitro. The free radical content of the tar and vapor-phase smoke from a cigarette that heats rather than burns tobacco has been compared with data on a standard 1R4F cigarette. No radicals were detected in the tar from the new cigarette and radicals in its vapor-phase smoke are lower by more than 99% relative to the 1R4F standard cigarettes. The vapor-phase smoke from the new cigarette causes essentially no reduction of alpha 1PI activity in vitro. These findings support our previously published mechanisms for the production of radicals in tar and in vapor-phase smoke.

Free Radicals↗
PubMed1990

How does cognitive therapy work? Cognitive change and symptom change in cognitive therapy and pharmacotherapy for depression.

The effects of changes in depression-relevant cognition were examined in relation to subsequent change in depressive symptoms for outpatients with major depressive disorder randomly assigned to cognitive therapy (CT; n = 32) versus those assigned to pharmacotherapy only (NoCT; n = 32). Depression severity scores were obtained at the beginning, middle, and end of the 12-week treatment period, as were scores on 4 measures of cognition: Attributional Styles Questionnaire (ASQ), Automatic Thoughts Questionnaire (ATQ), Dysfunctional Attitudes Scale (DAS), and the Hopelessness Scale (HS). Change from pretreatment to midtreatment on the ASQ, DAS, and HS predicted change in depression from midtreatment to posttreatment in the CT group, but not in the NoCT group. It is concluded that cognitive phenomena play mediational roles in cognitive therapy. However, data do not support their status as sufficient mediators.

Adolescent↗
PubMed1989

Alignment modification for pencil eye shields.

Accurate alignment of pencil beam eye shields to protect the lens of the eye may be made easier by means of a simple modification of existing apparatus. This involves drilling a small hole through the centre of the shield to isolate the rayline directed to the lens and fabricating a suitable plug for this hole.

Eye↗
PubMed1988

Standard compensators for ENT therapy fields.

Radiotherapy of the ENT region is frequently applied through two parallel-opposed, lateral fields covering a volume from the maxillary sinus to the base of the neck, with the isocentre close to the angle of the mandible. The large variation in separation throughout this volume, in both the transverse and the coronal planes, leads to field inhomogeneities which are often resolved by the use of custom designed, two-dimensional compensators. This paper presents an alternative method of compensation using a set of one-dimensional, standard compensators applied in the coronal plane which, in conjunction with a wedge in the transverse plane, yields a uniform distribution throughout the treatment volume for the majority of patient configurations. The advantages of this technique are the immediate availability of a computerised treatment plan incorporating the compensator, an increase in the dose homogeneity obtainable over that without compensation and the elimination of any delay which may be incurred by the design and fabrication of custom made compensators.

Head and Neck Neoplasms↗
PubMed1988

Rectal and oesophageal treatment by the Selectron High Dose Rate afterloader.

Rectal and oesophageal intracavitary treatments have been administered by the Selectron High Dose Rate afterloader. The treatment time is of the order of a few minutes which makes the use of a high dose rate advantageous as compared to medium and low dose rate procedures. Localizing techniques as well as dosimetry are discussed.

Brachytherapy↗
PubMed1987

Dose distributions around selectron applicators.

Measured and calculated dose distributions around selectron applicators, loaded with 60Co high dose rate pellets, are presented. The effect of the stopping screw, spacers, pellets themselves and the applicator wall on the dose distribution is discussed. The measured dose distribution is in almost perfect agreement with the calculated distribution in planes perpendicular to the applicator axis and containing a source. On the applicator axis directly below the applicator the measured dose amounts to about 75% of the calculated value, when only the stopping screw attenuates the beam from a pellet. When the beam is attenuated by spacers in addition to the stopping screw, the discrepancy between the calculated and measured dose may exceed 50%. Clinically relevant source geometries are also discussed. It is shown that for most regions around the applicator the method of a simple addition of dose contributions from individual point sources is an acceptable approximation for the calculation of dose distributions around the selectron applicators.

Brachytherapy↗
PubMed1987

An endocavitary rectal irradiation technique.

An alternative to standard short target-skin distance (TSD) rectal irradiation techniques is presented. The proctoscopic rectal cone is linked outside of the patient to a superficial X ray tube operated at 50 kVp and 25 mA. The cone is rigidly held in place by a hydraulic clamp and linked to the X ray tube with an electromagnetic lock. The X ray beam is filtered by 0.3 mm of aluminum, giving a half-value-layer of 0.27 mm of aluminum and an exposure rate of 720 R/min. (0.186 C/kg-min.) at the treatment TSD of 22 cm. The physical aspects of the technique are described in detail.

Brachytherapy↗
PubMed1986

Sources of immigrants' language proficiency: Australian results with comparisons to the Federal Republic of Germany and the United States of America.

Recent research on immigrants in the Federal Republic of Germany and the US suggests that their amount of education, the country in which they attained it, and their labor force experience both before and after migrating all have important effects on their skills in the language of the host country. This paper explores those influences on the English language proficiency of 4 groups of immigrants to Australia: 1) those from Northwestern Europe, 2) Eastern Europe, 3) the Mediterranean basin, and 4) the Third World. The data are drawn from the 1% public use sample of the 1981 Australian census. The models are flexible ordinary least squares specifications that permit a variety of curvilinear na interaction effects. The results generally parallel those for the Federal Republic of Germany and the US. 1 important difference from the US is that the harmful effect of foreign labor experience is greater than the beneficial effect of labor force experience in the host country.

Americas↗
PubMed1985

Changes in the survival curve shape of E. coli cells following irradiation in the presence of uncouplers of oxidative phosphorylation.

Four uncouplers of oxidative phosphorylation (UOP) (carbonyl cyanide m-chlorophenylhydrazone, 2,4-dinitrophenol, 4-hydroxybenzylidenemalonitrile and N-phenylanthranilic acid) have been found to alter the shape of the radiation survival curves of several cell lines of E. coli when present during irradiation in oxia. Incubation of cells with high concentrations of UOP for 30 min before irradiation induced an increase in extrapolation number (n) in cell lines AB 1157 (wild-type), AB 1886(uvrA-) and KMBL(polA-) but not GR 501(lig-)ts, AB 2463(recA-) and AB 2480(uvrA-recA-). In addition the UOP all effect a decrease in mean lethal dose (D0) even when tested at low concentrations or short contact times. Studies with wild-type cells correlate the increase in n with measured increased levels of ATP (above oxic control cells) produced upon incubation with UOP. The increased levels of ATP most likely arise from the UOP overstimulating glycolysis. The decrease in D0 cannot be associated with any of the repair pathways investigated and it is concluded that the highly lipophilic UOP directly or indirectly potentiate other target(s) to radiation damage as well as DNA under oxic conditions. Treatment of the cells with UOP did not result in the deleterious depletion of energy substrates, loss of non-protein thiols or the production of cytotoxins upon irradiation.

Adenosine Triphosphate↗
PubMedDate not supplied

Damage to human alpha-1-proteinase inhibitor by aqueous cigarette tar extracts and the formation of methionine sulfoxide.

The effects of aqueous extracts of cigarette tar (ACT) on human alpha-1-proteinase inhibitor (alpha 1PI) are examined by determining alterations in the elastase inhibitory capacity (EIC), amino acid residue content, and electrophoretic behavior of the protein. Hydrogen peroxide generated in ACT by autoxidative processes accounts for the major portion of the loss of EIC. This is indicated by several lines of evidence, including the fact that anaerobic incubations of ACT with alpha 1PI cause negligible loss of EIC. The hydrogen peroxide content of the ACT was estimated by measuring the ability of the extracts to oxidize methionine to methionine sulfoxide; hydrogen peroxide concentrations that model those in ACT cause a similar loss in EIC. Exposure of alpha 1PI to ACT leads to methionine sulfoxide as the only detectable amino acid residue modification and explains the loss of EIC. This is the first report to directly demonstrate methionine sulfoxide formation in alpha 1PI exposed to cigarette smoke components in vitro. Similar amounts of methionine sulfoxide are found in alpha 1PI exposed to hydrogen peroxide at the concentrations predicted to be formed in ACT. Nondenaturing PAGE reveals that alpha 1PI exposed to ACT, but not hydrogen peroxide, shows changes in electrophoretic behavior; the changes are nonoxidative in nature and are not related to the loss of EIC. Studies on the effect of chelators on ACT-mediated damage to alpha 1PI indicate some role for metal ions; however, none of the chelators completely protect alpha 1PI.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗