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Biomedical subjects

R Mayer

Publications and source records attributed to R Mayer.

At least 55 records · Page 3Linked to original sources
PubMed1998

CT-simulator based brachytherapy planner: seed localization and incorporation of biological considerations.

Radiation dose prescription, interpretation, and planning can be problematic for brachytherapy due to high spatial heterogeneity, varying and various dose rates, absence of superimposed calculated isodose distributions onto affected tissues, and lack of dose volume histograms. A new treatment planner has been developed to reduce these limitations in brachytherapy planning. The PC-based planning system uses a CT-simulator to sequentially scan the patient to generate orthogonal images (to localize seed positions) and subsequently axially scan the patient. This sequential scanning procedure avoids using multiple independent patient scans, templates, external frames, or fiducial markers to register the reconstructed seed positions with patient contours. Dose is computed after assigning activity to (low dose rate) Ir192, linear Cs137, or I125 seeds or dwell times (high dose rate) to the Ir192 source. The planar isodose distribution is superimposed onto axial, coronal, or sagittal views of the tissues following image reconstruction. The treatment plan computes (1) direct and cumulative volume dose histograms for individual tissues, (2) the average, standard deviation, and coefficient of skewness of the dose distribution within individual tissues, (3) an average (over all tissue pixels) survival probability (S) and average survival dose DASD for a given radiation treatment, (4) normal tissue complication probability (NTCP) delivered to a given tissue. All four computed quantities account for dose heterogeneity. These estimates of the biological response to radiation from laboratory-based studies may help guide the evaluation of the prescribed low- or high-dose rate therapy in retrospective and prospective clinical studies at a number of treatment sites.

Brachytherapy↗
PubMed1998

CT number distribution and its association with local control and as a marker of lung tumor response to radiation.

An early noninvasive indicator of tumor response to therapy and the ability to predict clinical outcome may potentially enhance disease management. Currently, however, tumor response to therapy is often delayed, potentially compromising disease management. We examined the computed tomography (CT) number or Hounsfield unit distribution to follow lung tumor response to radiation treatment. To help interpret the results, we examined whether the CT number distribution follows a simple two-component model. The CT number distribution was derived from a CT-simulator for 11 patients with lung cancer before and after the initial radiation treatment (1-1.5 months, average 3,407 cGy). Clinical outcomes were followed in 8 patients who received 5,580-6,660 cGy. All patients were scanned serially, using identical radiation imaging parameters (voltage, current, scan time, and slice thickness) in a CT-simulator. The lung tumors were digitally contoured, and software windows were applied to avoid inclusion of lung tissue in the analysis. Histograms and statistical analysis of the CT numbers for the tumor were generated. Radiation-induced CT number or Hounsfield unit (HU) shifts exceeding a threshold (13 HU) in lung tumors were associated with (P=0.04) local control (> or = 10 months). Initial lung tumor size (below 100 cm3) was less well-associated with local control (P=0.26). The change in standard deviation of the CT numbers (derived from the more careful contouring and using software windows) induced by radiation treatment correlated with the change in average CT number (R2=0.71). The change in standard deviation did not correlate with a change in tumor volume (R2=0.02). Radiation treatments reduced the average CT number (P < 0.001). In summary, radiation reduces the CT number and this reduction may be associated with local control at 10 months. A two-component model is consistent with lung tumor number distribution and its response to radiation.

Adult↗
PubMed1998

[The photon therapy of subfoveal choroidal neovascularization in age-dependent macular degeneration. The results of a prospective study in 40 patients].

AIM: To determine the effect of external beam radiotherapy on subfoveal choroidal neovascularization in age-related macular degeneration. PATIENTS AND METHODS: Between September 1995 and July 1996, 40 patients (9 males and 31 females; mean age 74 years, range 61 to 83 years) were included in a prospective study. Eight patients had classic, well-defined neovascularisations, 32 patients had occult lesions. Complete ophthalmic investigations included visual acuity contrast sensitivity as well as fluorescein and indocyanine green angiographic examinations prior to treatment and 1, 3, 6, and 12 months after radiotherapy. External beam radiotherapy (8-MV photons) was delivered with a total dose of 14.4 Gy in 8 fractions of 1.8 Gy per day (Figures 1 and 2). The field size averaged 5.5 x 4.5 cm. RESULTS: No treatment related morbidity during or after treatment was obtained. After 6 months follow-up the visual acuity was improved in 2 (5%) patients and maintained at pretreatment level in 17 (42%) patients. However, 12 months post treatment a stable situation was found in 6 (15%) patients and a decrease in visual acuity in 34 (85%) patients (Table 1). The central visual fields deteriorated significantly from 16.5 decibel (dB) to 12.4 dB. The enlargement of exudates and neovascular membranes increased 5- to 7-fold. At 12 months after treatment, 3 (7.5%) patients stated that they had improved vision subjectively, 12 (30%) patients had no change and 25 (62.5%) patients suffered from subjective decrease in visual acuity. CONCLUSIONS: Using a total dose of 14.4 Gy/1.8 Gy no difference concerning visual acuity and exudative changes in comparison to the natural history on age-related macular degeneration was obtained after 12 months. However, the results of multicenter studies are to be awaited.

Aged↗
PubMed1998

[A totally implantable hearing aid for inner ear deafness: TICA LZ 3001].

Recently, Zenner et al. implanted the first totally implantable electronic hearing devices in patients with SNHL (HNO 46 [1998] 844-852). In the present report, technical and audiological features of the implant TICA are published. The development of the piezoelectric transducer and the microphone for implantation in the posterior wall of the auditory canal as components for the present fully implantable hearing system has already been described (HNO 45, 1997, 792-880). Here we report about our experience with the electronic main module that completes the TICA LZ 3001 system. This module is suited for implantation in the mastoid bone and contains the signal-processing electronics and an integrated battery that can be recharged transcutaneously with a portable charger. The recharging time is around 2 h for an implant operating time of 50 h. The microphone and transducer connectors allow for easy replacement of the main module when the battery lifetime is reached. This lifetime is around 3-5 years. A small wireless remote control allows volume adjustment, contains an on/off switch, and permits selection of four different individual hearing programs. The basic audiological features are provided by a flexible, digitally programmable 3-channel-AGC-system with a peak clipping function. The total bandwidth is around 10 kHz. To our knowledge this is the first fully implantable hearing system that has been in implanted in humans.

Ear Canal↗
PubMed1998

Transrectal color Doppler sonography of the A. uterina in cyclic mares.

Color Doppler ultrasound was used transrectally in 6 mares to locate both the left and right Aa. uterinae and to obtain flow velocity waveforms at defined times (Days 0, 5, 10, 15 and 20) during 4 estrous cycles. Blood flow reflected by the resistance index (RI) was determined for both arteries on 120 occasions. As there was no significant difference and a high correlation in the RI values between the left and right arteries (paired Student's t-test, correlation coefficient r > 0.94; P < 0.05), the average RI value was used for subsequent analyses. There were correlations between RI values, mares and day of estrous cycle (P < 0.0001). The mean RI was higher (P < 0.05) in the 2 multiparous mares (age, 12 to 13 yr) than in the 4 younger maiden mares (age, 6 to 10 yr). During the estrous cycle mean RI values on Day 0 (day of ovulation) and Day 10 were higher (P < 0.05) than on Days 5, 15 and 20, whereas between estrous cycles within mares no differences (P > 0.05) could be measured. The results suggest that transrectal Color Doppler sonography is a noninvasive method for examining differences in impedance to uterine blood flow between different mares and cycle periods.

Animals↗
PubMed1998

Glycotargeting: the preparation of glyco-amino acids and derivatives from unprotected reducing sugars.

Lectins are present on the surface of many cells. Many lectins actively recycle from membrane to endosomes and efficiently take up glycoconjugates in a sugar-dependent manner. On this basis, glycoconjugates, specially those obtained by chemical means, are good candidates as carriers of drugs, oligonucleotides or genes. In this paper, we present a panel of methods suitable to transform unprotected reducing oligosaccharides into glycosynthons designed to be easily linked to therapeutic agents. All the glycosynthons presented here are glycosylamines or derivatives, mainly glyco-amino acids or glycopeptides. Glycosylamines are easy to obtain, but they are very labile in slightly acidic or neutral medium; they must be stabilized, by acylation for instance. The coupling efficiency of a reducing sugar with ammonia as well as an alkylamine or an arylamine is higher at high temperature, however, because of the Amadori rearrangement, special conditions have to be selected to prepare the expected glycosylamine derivative with a high yield. Glycosylamines are easily acylated by N-protected amino acids, or by halogeno acids which can then be transformed into amino acids. Alternatively, unprotected reducing oligosaccharides may very efficiently be transformed into N-glycosyl-amino acids and then protected by N-acylation. With a glutamyl derivative having both the alpha-amino and the gamma-carboxylic groups free, the coupling and the acylation, which is intramolecular, are roughly quantitative. N-oligosaccharyl-amino acid derivatives are interesting glycosynthons, because their sugar moiety bears the specificity towards membrane lectins while the amino acid part has the capacity to easily substitute a therapeutic agent.

Amines↗
PubMed1998

Three cdg operons control cellular turnover of cyclic di-GMP in Acetobacter xylinum: genetic organization and occurrence of conserved domains in isoenzymes.

Cyclic di-GMP (c-di-GMP) is the specific nucleotide regulator of beta-1,4-glucan (cellulose) synthase in Acetobacter xylinum. The enzymes controlling turnover of c-di-GMP are diguanylate cyclase (DGC), which catalyzes its formation, and phosphodiesterase A (PDEA), which catalyzes its degradation. Following biochemical purification of DGC and PDEA, genes encoding isoforms of these enzymes have been isolated and found to be located on three distinct yet highly homologous operons for cyclic diguanylate, cdg1, cdg2, and cdg3. Within each cdg operon, a pdeA gene lies upstream of a dgc gene. cdg1 contains two additional flanking genes, cdg1a and cdg1d. cdg1a encodes a putative transcriptional activator, similar to AadR of Rhodopseudomonas palustris and FixK proteins of rhizobia. The deduced DGC and PDEA proteins have an identical motif structure of two lengthy domains in their C-terminal regions. These domains are also present in numerous bacterial proteins of undefined function. The N termini of the DGC and PDEA deduced proteins contain putative oxygen-sensing domains, based on similarity to domains on bacterial NifL and FixL proteins, respectively. Genetic disruption analyses demonstrated a physiological hierarchy among the cdg operons, such that cdg1 contributes 80% of cellular DGC and PDEA activities and cdg2 and cdg3 contribute 15 and 5%, respectively. Disruption of dgc genes markedly reduced in vivo cellulose production, demonstrating that c-di-GMP controls this process.

Amino Acid Sequence↗
PubMed1998

Energy requirement for eating in cattle.

We determined the energy requirement for the activity associated with eating in an experiment with four adult Hinterwälder steers weighing 640+/-25 kg BW (mean+/-SD), using indirect calorimetry in respiration chambers. Heat production was measured during 3 h with and 3 h without ad libitum access to wheat straw, and the energy cost of eating was calculated as the difference, which was on average 27+/-13 J/(min x kg BW) (mean+/-SD). Straw intake, the time spent for eating, and the number of jaw movements were recorded. Values for the energy cost of eating reported in the literature are similar to those in this study, and values for ruminating amount to approximately 27% of those for eating. The energy cost of eating (literature values) varies greatly between feeds and feed treatments, when related to the amount of feed ingested, but it was relatively constant when related to time spent eating and was similar for cattle, sheep, and horses, when related to BW or metabolic BW (35 J/[min x kg BW] or 124 J/ [min x kg BW.75]). Calculations indicated that in high-quality roughage 10% of the ME and in untreated straw approximately 30% of the ME provided by the feed are used for eating and ruminating. This might be the main reason for the lower efficiency of ME utilization in roughages. The energy requirement for eating and ruminating should therefore be considered as a distinct proportion of the total ME requirement.

Animal Feed↗
PubMed1998

Immigration and health: the Italian situation. Italian National Focal Point (NFP) of the AIDS & Mobility Project.

This report is a description of the situation of migrant populations in Italy. It was written as part of the European project "AIDS & Mobility", which is being co-ordinated by the Netherlands Institute for Health Promotion and Disease Prevention and financed by the European Union (EU). The report was written by the Italian National Focal Point (NFP) of the AIDS & Mobility Project, which consists of a committed team of experts from public institutions, non-governmental organizations, volunteer associations, and researchers from the Telefono Verde AIDS (National AIDS Help-line of Italy) of the Centro Operativo AIDS (COA, National AIDS Unit of Italy) of the Istituto Superiore di Sanità. The report illustrates the phenomenon of immigration in Italy, with demographic data (updated at 31 December 1997) on the presence of non-Italians and a review of the current laws pertinent to this phenomenon, with particular reference to health care laws. Moreover, epidemiological data on HIV/AIDS and on sexually transmitted diseases are provided, particularly as they relate to drug addiction and prostitution. Finally, following an accurate analysis of the situation and in light of the experience gained, the report includes proposals for identifying needs, objectives to pursue, and strategies to adopt, with respect to confronting the issue of immigration.

Emigration and Immigration↗
PubMed1997

Allergenic sesquiterpene lactones from Eupatorium cannabinum L. and Kaunia rufescens (Lund ex de Candolle).

From Eupatorium cannabinum L., a hitherto unknown alpha-methylene-gamma-butyrolactone, 3 beta-peroxyeucannabinolide, was isolated. This compound and eupatoriopicrin from the same plant showed a weak sensitizing capacity in guinea pigs. 2-oxoludartin and dehydroleucodin, isolated from Kaunia rufescens (syn. Eupatorium rufescens), were strong sensitizers in the same sensitizarian procedure.

Allergens↗
PubMed1997

Short and long-term immunosuppressive effects of clozapine and haloperidol.

In line with the autoimmune hypothesis of schizophrenia we have tested in this study whether the commonly used neuroleptics, clozapine and haloperidol can also act as systemic immunosuppressants. Twenty one hospitalized chronic schizophrenic patients participated in the study. Five were free of neuroleptic treatment while the other 16 were under chronic treatment with either clozapine (n = 8), or haloperidol (n = 8). Fourteen age matched normal subjects served as the control group. Conventional in vitro mitogenic stimulation of peripheral blood lymphocytes with phytohaemagglutinin (PHA) indicated a clear suppression of responsiveness of approximately 50% in all treated patients. The PHA response of the untreated patients was virtually identical to that of the control group. The in vitro effect of haloperidol and clozapine on PHA stimulation of lymphocytes from normal subjects was determined by 3H-thymidine uptake and secretion of interleukin-2, interleukin-4 and interferon-gamma. Both clozapine and haloperidol suppressed thymidine incorporation and cytokine secretion at a drug concentration of above 1 microM, reaching full suppression at 50 microM. Similar suppressive effects of clozapine and haloperidol were also observed in mixed lymphocyte reaction of mouse lymphocytes. Assays with radioactive ligands indicated that clozapine is not incorporated into the lymphocytes but presumably exerts its action by binding to specific surface sites. The long term immune suppression induced by neuroleptic treatment may inhibit putative autoimmune responses against neurological sites and could thus act synergistically with the direct antagonistic action on brain receptors for the overt amelioration of psychotic behaviour.

Adult↗
PubMed1997

Thresholds for fetal hemorrhages produced by a piezoelectric lithotripter.

Hemorrhage to fetal tissues occurred when late-term pregnant mice were exposed to lithotripter fields of relatively low amplitude. These hemorrhages were always observed in tissues near developing bone or cartilaginous structures such as the head, limbs and ribs, while soft tissues distant from bone were relatively free of hemorrhage. Thresholds for hemorrhage in the fetus were determined for exposures of pregnant mice on the 18th day of gestation to 200 pulses from a piezoelectric lithotripter. Animals were exposed to axial peak positive pressures of either 0 (sham), 1, 2, 3, 5 or 10 MPa. Thresholds for hemorrhage to the head, limbs, ribs and lung were all < 1 MPa.

Animals↗
PubMed1997

The influence of contrast agents on hemorrhage produced by lithotripter fields.

Ultrasonic contrast agents greatly increase the side effects of low-amplitude lithotripter fields in mice. Using a piezoelectric lithotripter, adult mice were exposed to 200 lithotripter pulses with a peak positive pressure amplitude of 2 MPa. During the exposure period, mice were injected with approximately 0.1 mL of the ultrasonic contrast agent Albunex. For comparison, another group of mice experienced the same lithotripter exposures, but were not injected with contrast agent. Following exposures, animals were sacrificed and observed for hemorrhage in various organs and tissues. Mice exposed to the lithotripter field alone had minimal hemorrhage only in the intestine and lung. In comparison, mice injected with Albunex during exposure exhibited extensive hemorrhage in the intestine, kidney, muscle, mesentery, stomach, bladder, seminal vesicle and fat.

Albumins↗