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Biomedical subjects

K Karcher

Publications and source records attributed to K Karcher.

11 recordsLinked to original sources
PubMed2003

Determination of dose coefficients and urinary excretion function for inhalation of carbon-14-labelled benzene.

Based on existing pharmacokinetic models for benzene, the distribution and retention of activity after inhalation of 14C-labelled benzene in humans were studied. Six different benzene concentrations from 0.1 to 10,000 ppm (corresponding to activity concentrations between 9.6 x 10(6) and 9.6 x 10(11) Bq m(-3)) and five exposure times from 0.1 to 1000 min were considered. The cumulated activities in the different organs and tissues and the urinary excretion rates were observed to depend non-linearly on the activity intake. The fraction of activity removed via urine varies between 52 and 10% of the intake. Nevertheless, for times that are long compared to the exposure duration the urinary excretion rate is determined by the activity clearance from adipose tissue and thus decreases at a constant rate. This decrease is common for all exposure conditions examined and thus allowed determining a mean urinary excretion rate and corresponding dose coefficients for committed equivalent doses as well as for the effective dose. The uncertainty of the dose coefficients is estimated to be about 50% for the exposure range covered. A 14-day interval for the incorporation monitoring by urine activity counting seems to be reasonable.

Administration, Inhalation↗
PubMed2003

Is radiation protection for the unborn child guaranteed by radiation protection for female workers?

ICRP Publication 88 recommends doses to the embryo and fetus from intakes of radionuclides by the mother for various intake scenarios. Mainly by answering the question 'Is radiation protection for the unborn child guaranteed by radiation protection for female workers?' it has been assessed if the intake scenarios given in ICRP Publication 88 are adequate for radiation protection purposes. This is generally the case, but the consideration of an additional chronic intake scenario for early pregnancy would be helpful. It is demonstrated that following chronic intake by inhalation, for most radionuclides radiation protection for (female) workers is also adequate for protection of the unborn child, considered as a member of the public. However, there are a number of radionuclides for which possible intakes in routine operations should be more restricted (up to 1% of the annual limits on intake for workers in the case of nickel isotopes) to ensure radiation protection for the unborn child.

Computer Simulation↗
PubMed1999

Onset and duration of action of levocabastine nasal spray in atopic patients under nasal challenge conditions.

BACKGROUND: Although prior studies have documented the rapid onset of action of topical intranasal levocabastine (LEV), little is known about its duration of action under nasal challenge conditions. OBJECTIVES: We sought to assess the onset and duration of action of escalating doses of LEV nasal spray by using a nasal allergen challenge (NAC) model. METHODS: Eighteen asymptomatic subjects with histories of seasonal allergic rhinitis were enrolled into a randomized, single-blind, placebo-controlled, dose-ranging crossover study. Each patient was randomly assigned to receive single doses of placebo and intranasal LEV 0.1, 0.2, and 0.4 mg during 2 parts of the study. In part 1 (onset of action), NAC consisted of a single dose of allergen administered 5 minutes after study drug treatment. In part 2 (duration of action), NAC consisted of increasing doses of allergen administered 0.5, 6, 12, and 24 hours on separate days after study drug treatment. Nasal symptom scores (NSSs) and nasal peak expiratory flow rates were measured after NAC in both phases of the study. Blood samples for plasma LEV concentrations were drawn after each NAC. RESULTS: In part 1, NSSs were significantly lower after the administration of LEV 0.1, 0.2, and 0.4 mg compared with placebo (P <.05). In part 2, NSSs were significantly lower after LEV doses of 0.2 and 0.4 mg compared with placebo at 0.5, 6, 12, and 24 hours after treatment (P <.05). The mean provocative dose of allergen required to elicit a positive nasal reaction was increased after LEV doses of 0.2 and 0.4 mg at 0.5, 6, and 12 hours after treatment. Nasal peak expiratory flow rates demonstrated no significant differences between LEV and placebo for any doses at any time points. Mean plasma LEV concentrations were low (range, 0 to 3. 7 ng/mL) after all doses and did not correlate with drug efficacy. CONCLUSIONS: Single intranasal LEV doses of 0.1, 0.2, and 0.4 mg significantly reduced the severity of the immediate nasal response to allergen when administered 5 minutes before NAC. This protective effect against NAC continued to be present 24 hours after administration of LEV doses of 0.2 and 0.4 mg. Efficacy in blocking the reaction to NAC did not correlate with plasma LEV levels, suggesting that the inhibitory effect was due largely to topical rather than systemic effects.

Administration, Intranasal↗
PubMed1999

Studies on an immunologically induced synovitis model in pigs and sheep.

Chronic synovitis was induced in seven sheep and nine pigs to investigate the potential applicability of laser treatment in arthroscopic synovectomy. Systemic sensitization was accomplished using chicken egg or turkey egg albumin antigens with Freund's incomplete adjuvant, enriched with killed and dried Mycobacterium tuberculosis. Ten days after the second immunizing dose, skin sensitization testing was undertaken. After a satisfactory systemic reaction had been observed, the respective antigen was injected once or twice into the left knee of each animal at 2-week intervals. After chicken egg albumin sensitization at varying systemic immunization and joint injection doses, sheep (five of five) showed neither strong morphologic nor continuous synovitis, despite a positive systemic reaction. In pigs (three of three) the inflammatory signs also were unsatisfactory for the manifestation and characterization of a synovitis model. In contrast, the application of turkey egg albumin to pigs (six of six) during the 4-month study provided a persistent, clearly manifested synovitis that developed visible villi formation and an amber to gray synovial fluid and microscopically showed follicular aggregations of lymphocytes and plasma cells. In similarly immunized sheep (two of two), only a light synovitis developed with occasional perivascular inflammatory foci.

Animals↗
PubMed1994

[Holmium laser versus mechanical cartilage resection. Comparative studies in the rabbit arthrosis model].

The aim of this work was to investigate and evaluate the tissue reactions after sham operation and after mechanical and holmium laser chondral debridement in a rabbit model at different postoperative intervals. In 27 rabbits an arthrosis was induced by implantation of a piece of polyethylene sheeting in one knee joint. After 5 months, distinct arthritic changes had developed. Nine animals each were randomized for sham operation, mechanical debridement, and holmium laser chondral debridement. At 1 day, 1 month, and 3 months postoperatively, three animals in each group were sacrificed and their joints examined grossly and microscopically. At 3 months after mechanical debridement the articular surface was relatively smooth, and tears and defects were filled with fibrous repair tissue. After holmium laser debridement chondral necroses were regularly found, occasionally with damage to the subchondral bone and distinct inflammation in the marrow space. The articular surface remained rough and uneven. These preliminary results suggest that use of the holmium laser is not superior to mechanical methods for remodelling and smoothing of fairly large chondral areas.

Animals↗
PubMed1993

[Comparative experimental studies of mechanical and holmium laser synovectomy].

The goal of this study was to evaluate tissue reactions in rabbit knees following laser synovectomy using a holmium:YAG laser (wavelength: 2.1 microns) and to compare these results with those found after conventional mechanical abrasion treatment. Chronic arthritis was immunologically induced in one knee joint each of 48 rabbits. Twelve served as controls, 12 were sham-operated, 12 were exposed to laser radiation, and 12 others were treated according to conventional methods. In the laser group, a pulse length of 1 ms at a repetition rate of 3 Hz resulted in a pulse energy of 600 mJ. After periods of 1 day, 1 week and 1 and 3 months, respectively, three animals from each group were sacrificed and the synovialis was examined macroscopically and histologically using light and electron microscopy. Edema, acute inflammation, and coagulation necrosis occurred immediately following laser therapy. After 1 week, the synovial layer showed slight fibrosis, which was comparable to that found in the controls. One month later the surface appeared to be smooth. The mechanical abrasion caused hemorrhage and necrosis. Fibrosis was pronounced in all capsular layers, and after 3 months the surface appeared coarse and villous in this group. Based on these preliminary findings, holmium-laser synovectomy may offer an alternative to existing therapeutic techniques in the treatment of rheumatoid arthritis. The arthroscopic approach could prevent additional capsular fibrosis associated with mechanical irritation.

Animals↗
PubMed1987

Changes in lymphocyte subsets after treatment with cyclophosphamide and during the development of contact sensitivity in the guinea pig.

Changes in lymphocyte subpopulations were investigated in guinea pig lymph nodes during the development of contact sensitivity to 2,4-dinitrofluorobenzene (DNFB) and following the injection of cyclophosphamide (CY; 300 mg/kg) using a panel of monoclonal antibodies against guinea pig lymphocyte surface markers. Application of a sensitizing dose of DNFB to the ear resulted in a significant increase in the number of cells recovered from the draining auricular and cervical lymph nodes, 4 and 6 days post sensitization. A significant increase in the number of cells in the contralateral cervical node was found at day 6 but not at day 4. At 4 days postsensitization the proportions of Ia positive lymphocytes were higher than those of immunoglobulin positive B cells in the draining auricular and cervical node and the contralateral cervical lymph nodes suggesting T-cell "activation". Four and six days after sensitization there were no significant changes in the proportions of Pan T and T suppressor/cytotoxic (Ts/c) positive lymphocytes in the draining auricular and cervical lymph nodes. Although contact sensitivity is "classically" a T-cell mediated phenomenon there was a significant increase in the proportion of B cells found in the draining auricular node 4 days after sensitization as compared to the "normal" auricular node. 1, 2, 3 and 7 days after injection of CY there was a significant depletion in the proportion of B-lymphocytes in the cervical lymph node. This effect was maximal between 2 and 3 days after CY and was paralleled by an increase in the proportion of Pan T positive cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Coherent active methods for applications in room acoustics.

An adjustment of reverberation time in rooms is often desired, even for low frequencies where passive absorbers fail. Among the active (electroacoustic) systems, incoherent ones permit lengthening of reverberation time only, whereas coherent active methods will allow sound absorption as well. A coherent-active wall lining consists of loudspeakers with microphones in front and adjustable control electronics. The microphones pick up the incident sound and drive the speakers in such a way that the reflection coefficient takes on prescribed values. An experimental device for the one-dimensional case allows reflection coefficients between almost zero and about 1.5 to be realized below 1000 Hz. The extension to three dimensions presents problems, especially by nearfield effects. Experiments with a 3 X 3 loudspeaker array and computer simulations proved that the amplitude reflection coefficient can be adjusted between 10% and 200% for sinusoidal waves at normal and oblique incidence. Future developments have to make the system work with broadband excitation and in more diffuse sound fields. It is also planned to combine the active reverberation control with active diffusion control.

Facility Design and Construction↗
PubMedDate not supplied

Efficacy and safety of levocabastine nasal spray for seasonal allergic rhinitis.

This multicenter, double-blind, placebo-controlled trial evaluated the efficacy and safety of levocabastine nasal spray, a potent and selective H1-receptor antagonist, in the control of histamine-mediated symptoms of seasonal allergic rhinitis. Adults with > or = 2 year history of allergic rhinitis due to Mountain Cedar were randomized to treatment with levocabastine nasal spray (0.2 mg twice daily) or placebo for 28 days during the 1994-1995 Mountain Cedar allergy season. Patients assessed the severity of their rhinitis symptoms on a four-point scale twice daily. At the end of the trial, patients also performed a global evaluation of treatment efficacy on a five-point scale. Overall for the 4-week treatment period, levocabastine nasal spray significantly reduced major nasal (runny nose and sneezing) and primary rhinitis (runny nose, sneezing, and itchy/gritty eyes) symptoms compared with placebo on both repeated measures (p = 0.023; p = 0.01) and ANOVA (p = 0.003; p < 0.001) analyses. Global evaluations of treatment efficacy at the end of the trial significantly favored levocabastine over placebo (p = 0.002). Overall, the incidence of adverse events was similar for both treatment groups. In general, most adverse events were mild in intensity, with sinusitis (17% each group), headache (17% placebo, 14% levocabastine), and rhinitis (8% placebo, 2% levocabastine) most commonly reported. Levocabastine nasal spray 0.2 mg twice daily was significantly more effective than placebo in the relief of histamine-mediated symptoms in patients with seasonal allergic rhinitis and was well tolerated over the 28-day treatment period.

Administration, Intranasal↗