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Biomedical subjects

B Fischer

Publications and source records attributed to B Fischer.

At least 235 records · Page 13Linked to original sources
PubMed1993

Ultrastructural study on human lung in alveolitis versus pulmonary fibrosis.

Lung specimens of 21 patients with diffuse interstitial lung disease were examined. The present ultrastructural study outlines the topography and distribution of inflammatory changes in the interstitium, endothelium, and in pneumocytes and phagocytes. Alveolitis is characterized by marked regenerative activity of type II pneumocytes (cuboid metaplasia), intraluminal macrophage accumulation, endothelial swelling, multilamination of the endothelial basement membrane, pericapillary edema, and primarily by cellular infiltrates in the interstitial space. The most prominent feature of the interstitium in pulmonary fibrosis is the lack of immunoinflammatory cells. In some areas there is a marked absence of alveolar lumen while only a small number of macrophages are present in the remaining alveolar lumen. Most of the capillaries in the fibrous septum have been destroyed. Ultrastructural studies of lung biopsies in patients with diffuse interstitial lung disease allow the differentiation between alveolitis and pulmonary fibrosis and thus contribute to a therapeutic decision.

Adult↗
PubMed1993

Physiological consequence of expression of soluble and active hen egg white lysozyme in Escherichia coli.

Hen egg white lysozyme was expressed as a protein fusion with the OmpA signal sequence and an octapeptide linker in Escherichia coli. The expression yielded soluble and enzymatically active lysozyme. Lysozyme activity was detected in the periplasmic space, in the cytosol and in the insoluble cytosolic fraction of E. coli. The results indicate that the environmental conditions in both the cytosol and the periplasmic space of E. coli were sufficient for correct protein folding and disulphide bond formation of eukaryotic recombinant lysozyme. However, the expression of active enzyme in E. coli consequently led to bacterial cell lysis due to hydrolysis of the peptidoglucan.

Animals↗
PubMed1993

Context dependent amplitude modulations of express and regular saccades in man and monkey.

Saccadic reaction times and amplitudes were determined in four human subjects and two rhesus monkeys when they made saccades to visual targets appearing in different spatial or temporal contexts. Two stimuli were presented at different positions, either simultaneously (global condition) or in random order (range condition). Both the gap and the overlap paradigm were used. The characteristics of different groups of saccades defined by the separate peaks in the distribution of the saccadic reaction times as express and regular saccades, were analysed and compared. It is shown that, in man and monkey, the amplitudes of express saccades undergo the same or even stronger context-dependent changes as do those of regular saccades. Furthermore, the presence or absence of the fixation point also influences the saccadic amplitudes, at least for the express saccades. We conclude that the neural mechanisms that determine the amplitudes of the express saccades are more strictly under the control of the physical and physiological conditions of the stimulus situation, whereas regular saccades have greater--although not complete--dependence on the psychological context and, in particular, the subject's effort.

Adult↗
PubMed1993

The time of secondary saccades to primary targets.

When a first saccade is made in response to a single, suddenly appearing stimulus it often misses the target. The retinal error may be very large, in particular in those cases where the subject anticipates the target location and initiates a saccade to a wrong position. We have analyzed the time of the occurrence of the secondary saccades by which the subject corrects these errors. Using the gap task with random target locations we found that large errors after anticipatory saccades--especially those after direction errors--can be corrected very fast. The latencies of these corrective saccades (being measured from target onset, not from the end of the primary saccade) form bimodal distributions with a first peak at 100 ms. It is therefore concluded that large errors can be corrected by express secondary saccades.

Attention↗
PubMed1993

Separate populations of visually guided saccades in humans: reaction times and amplitudes.

The saccadic eye movements of 20 naive adults, 7 naive teenagers, 12 naive children, and 4 trained adult subjects were measured using two single target saccade tasks; the gap and the overlap task. In the gap task, the fixation point was switched off before the target occurred; in the overlap task it remained on until the end of each trial. The target position was randomly selected 4 degrees to the left or 4 degrees to the right of the fixation point. The subjects were instructed to look at the target when it appeared, not to react as fast as possible. They were not given any feedback about their performance. The results suggest that, in the gap task, most of the naive subjects exhibit at least two (the teenagers certainly three) clearly separated peaks in the distribution of the saccadic reaction times. The first peak occurs between 100 and 135 ms (express saccades), the second one between 140 and 180 ms (fast regular), and a third peak may follow at about 200 ms (slow regular). Other subjects did not show clear signs of two modes in the range of 100 to 180 ms, and still others did not produce any reaction times below 135 ms. In the overlap task as well three or even more peaks were obtained at about the same positions along the reaction time scale of many, but not all subjects. Group data as well as those of individual subjects were fitted by the superposition of three gaussian functions. Segregating the reaction time data into saccades that over- or undershoot the target indicated that express saccades almost never overshoot. The results are discussed in relation to the different neural processes preceding the initiation of visually-guided saccades.

Adolescent↗
PubMed1993

Saccadic eye movements of dyslexic adult subjects.

The characteristics of visually guided saccadic eye movements were compared in 12 normal adult subjects and 12 test subjects of normal intelligence, but with problems in reading and writing. All subjects were examined psychometrically for different cognitive abilities, and for their reading and writing capabilities. The anamnestic reports about their reading and writing problems earlier in their lives were analysed. Based on scores of the writing and reading tests, the test group was subdivided into two subgroups: A and B (group A reached medium, group B very low scores in both tests). Five different non-cognitive eye movement tasks were applied: two single tasks (gap and overlap) requiring single saccades from a fixation point to a peripherally appearing target and three sequential tasks (overlap, synchronous, and simultaneous) requiring sequences of saccades to four equally spaced targets presented sequentially to the right side from an initial fixation point. Many parameters of the subjects' eye movement performance were determined and their mean values were calculated for each subject. The Student t-test revealed that the eye movement data of the two test groups deviated differently from the data of the control group. Group B had the largest deviation of the eye movement parameter from the control group. The differentiating parameters were the consistency of target acquisition, the saccadic reaction time, and the number of anticipatory responses in the single target tasks. In the sequential tasks these differences were in the amplitude, the number of saccades, and the fixation durations. The incidence of regressive saccades did not discriminate between test subjects and controls. The possible underlying deficits in the attentional control over the saccadic system and their implications for reading are discussed.

Adult↗
PubMed1993

Oxygen tension in the oviduct and uterus of rhesus monkeys, hamsters and rabbits.

Oxygen tension was measured using flexible polarographic microelectrodes within the oviductal and uterine lumen in rhesus monkeys (n = 9), golden hamsters (n = 21) and rabbits (n = 6), during the reproductive cycle (monkey), during oestrus and pseudopregnancy (hamsters, rabbits) and during pregnancy (hamsters). In general, oxygen tensions in each species were much less than half of atmospheric O2, ranging from high values of about 60 mm Hg (8.7% O2) in the rabbit oviduct, rabbit and hamster uterus, to as low as 11 mm Hg (1.5% O2) in the monkey uterus. Oxygen tensions did not vary significantly between left and right sides of the reproductive tracts (all species), nor between pregnant and pseudopregnant states nor between oviduct and uterus (hamsters). Differences owing to reproductive stage were found in the monkey oviduct, hamster oviduct and uterus, and rabbit uterus. Oxygen tensions were consistently very low (11-14 mm Hg) in the monkey uterus throughout the menstrual cycle. In hamsters and rabbits, intrauterine O2 decreased significantly at about the normal time of blastocyst formation and implantation, to 37 mm Hg (5.3% O2) and 24 mm Hg (3.5% O2), respectively. This study indicates that embryos develop in vivo under low oxygen concentrations, especially during the peri-implantation period. The data have implications for investigations of embryo metabolism and for improving embryo development in vitro.

Animals↗
PubMed1993

[Ablation of junctional tachycardia by radiofrequency currents. Experience with 538 patients].

Junctional tachycardias may be related to intranodal reentry or to the existence of an accessory pathway. All are suitable for radical treatment by radiofrequency current applied either in the perinodal region or at the tricuspid or mitral atrioventricular rings respectively. 176 patients with intranodal reentry were treated by preferential modification of the rapid (8) or slow (167) anterograde pathway of the reentry circuit, with a 99% success rate (1 failure) and without significant complications, in particular atrioventricular block in the case of ablation of the slow pathway. 362 patients with one or more accessory pathways, patent or latent, were treated using the same type of energy. The ablation site was determined on the basis of indirect criteria and/or recording of the specific activity of the accessory pathway. The success rate here was 98%, once again without significant complications with the exception of those inherent to catheterisation procedures. Treatment duration time was 41 +/- 38 min in the treatment of intranodal reentry and 58 +/- 49 when one or more accessory pathways were responsible. X-ray exposure times were 14 +/- 14 min and 23 +/- 21 min respectively. Such results would justify the expectation of widened indications of the method.

Adolescent↗
PubMed1993

Pharmacologic hemostasis in laparoscopy: topical epinephrine facilitates cholecystectomy.

Bleeding may become a major impediment to accurate and safe dissection by laparoscopy. The traditional maneuvers of pressure, dumping, irrigation, and aspiration frequently applied during open procedures to maintain a clear field of dissection are cumbersome through laparoscopy. Several pharmacologic agents have been used topically or by local injection to stop bleeding or to prevent excessive blood loss during surgical procedures. They include calcium alginate, aluminum salts, silver nitrate, formalin, and coagulating agents like thrombin and collagens, all of which leave a layer of damaged tissue or foreign material on the surface. Epinephrine and vasopressin have been employed mostly by local injections. We report the use of topical epinephrine applied before and during the dissection of the cystic duct and artery area in the course of laparoscopic cholecystectomy. A 3/8-inch gauze sponge, impregnated with a 1:10,000 epinephrine solution, was used to blanch the tissues and to bluntly dissect the cystic duct and artery. It was also used to control minor bleeding in the gallbladder fossa. The prophylactic bleeding control with topical epinephrine proved to be an easy and safe maneuver, and greatly facilitated the dissection of the most critical areas during laparoscopic cholecystectomy. This technique may be applicable to laparoscopic dissection for other procedures.

Administration, Topical↗
PubMed1992

Analysis of catalytic properties of hen egg white lysozyme during renaturation from denatured and reduced material.

Catalytic properties of hen egg white lysozyme were analyzed during the renaturation of the enzyme from completely reduced and denatured material. The formation of intermediate folding products and the generation of native lysozyme was monitored by acetic acid/urea electrophoresis. The results showed that during the beginning of renaturation almost all reduced and denatured lysozyme is converted to forms possessing lower compactness than native lysozyme, probably as a result of formation of only one or two disulfide bonds. Kinetic analysis of lysozyme during renaturation showed that the generation of lysozyme with four disulfide bonds was not necessarily equivalent to the formation lysozyme with native-like catalytic properties. It appeared that the formation rate of the structures of the structures of the substrate binding site and of the catalytic site were limited by the generation of four disulfide bonds containing lysozyme. The catalytic properties of intermediate folding products made it evident that the final structures of the substrate binding site and of the catalytic site were formed after the generation of all disulfide bonds.

Animals↗
PubMed1992

Frequency of recurrent atrial fibrillation after catheter ablation of overt accessory pathways.

The effect of successful catheter ablation of overt accessory pathways on the incidence of atrial fibrillation (AF) was studied in 129 symptomatic patients with (n = 75) or without (n = 54) previous documented AF. Fourteen had had ventricular fibrillation. Factors predictive of recurrence were examined, including electrophysiologic parameters. Atrial vulnerability was defined as induction of sustained AF (greater than 1 minute) using single, then double, atrial extrastimuli at 2 basic pacing cycle lengths. When compared to patients with only reciprocating tachycardia, patients with clinical AF included more men (77 vs 54%, p = 0.008) and were older (35 +/- 12 vs 29 +/- 12 years, p = 0.01). They had a significantly shorter cycle length leading to anterograde accessory pathway block (252 +/- 42 vs 298 +/- 83 ms, p less than 0.001), greater incidences of atrial vulnerability (89 vs 24%, p less than 0.001) and subsequent need for cardioversion (51 vs 15%, p less than 0.001). After discharge, the follow-up period was 35 +/- 12 months (range 18 to 76); 7 patients with previous spontaneous AF (9%) had recurrence at a mean of 10 months after ablation. Age, presence of structural heart disease accessory pathway location, atrial refractory periods and accessory pathway anterograde conduction parameters were not predictive of AF recurrence. Persistence of atrial vulnerability after ablation was the only factor associated with further recurrence of AF. Atrial vulnerability was observed after ablation in only 56% of patients with previous AF versus 89% before ablation. It is concluded that successful catheter ablation of accessory pathways prevents further recurrence of AF in 91% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Characterization of human tissue-type plasminogen activator with monoclonal antibodies: mapping of epitopes and binding sites for fibrin and lysine.

The study defines interactions between human tissue-type plasminogen activator (t-PA) and 21 mouse monoclonal antibodies (mAb). Characterization includes epitope distribution, reactivity of different forms of t-PA with antibodies, and modification of t-PA function by antibody binding. Eighteen antibodies are directed against t-PA A-chain. These antibodies recognize four distinct epitopes (A, B, C, D) and one partially overlapping epitope (D'). The remaining three antibodies are directed against two different epitopes (E, F) on catalytically active t-PA B-chain. A-chain reactive antibodies do not bind to the reduced form of t-PA, while B-chain reactive antibodies bind to reduced and deglycosylated t-PA forms. The latter antibodies associate more tightly with sc t-PA than with tc t-PA and have a higher affinity for t-PA-PAI 1 complex as compared to free t-PA. The analysis of functional effects of antibodies reveals that antibodies directed against all above defined epitopes inhibit interactions between t-PA and fibrin: a) binding of t-PA to fibrin, b) fibrinolytic activity of t-PA, and c) fibrin activation of sc t-PA amidolytic activity. The observations support the assumption that several sites of t-PA are involved in fibrin binding and that fibrin-bound t-PA is closely surrounded by the fibrin mesh. Many antibodies quench also binding of t-PA to lysine-Sepharose. Experiments with free, non-fixed lysine confirm strong competition between lysine and mAb 16 and 18, directed against epitope A, and mAb 29, binding to epitope F.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1992

Oxygen tension in follicular fluid falls with follicle maturation.

The increase in follicular diameter during maturation is accompanied by an increase in vascular supply. The oxygen tension (PO2) in the follicular fluid of the growing follicle should therefore give an insight whether the oxygen delivery during this pertinent process is sufficient. Follicular fluid of 20 patients subjected to in vitro fertilization and embryo transfer were sampled in heparinized glass capillaries which were placed between the puncturing needle and the collecting reservoir. All patients were treated with human menopausal gonadotropin (HMG) and follicle-stimulating hormone (FSH). The PO2, PCO2 and pH of the follicular fluid were measured with an automatic gas analyser (Ciba Corning). Simultaneously, the same parameters were estimated in maternal capillary blood taken from the arterialized well perfused earlobe. Follicular size was measured by ultrasound. With growing follicular size (FS), the oxygen partial pressure (PO2) fell from 80 to 50-60 mmHg (PO2 = 114.4-3.3.FS; r = 0.79) while the carbondioxide partial pressure (PCO2) in the follicle increased from 35 to 50 mmHg (PCO2 = 15.1 +/- 1.9.FS; r = 0.71). In correlation to these results, the pH in follicular fluid fell from 7.40 to 7.30 (pH = 7.6-0.019.FS; r = 0.62). The correlation between the PCO2 and the pH demonstrates a deviation from the regression line if no metabolic alterations take place (delta log PCO2/delta pH = -0.69). The increase in ovarian blood flow during follicular maturation is obviously not sufficient to bridge the growing diffusion distance between the capillary network surrounding the follicle and its center.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Dioxide↗
PubMed1992

Characteristics of "anti" saccades in man.

Four subjects - all made large numbers of Express saccades in the normal gap task - were instructed to make saccades in the direction opposite to the side where a visual stimulus appeared ("anti" task). Gap and overlap trials were used. Saccadic reaction time (SRT), velocity and amplitude of the corresponding eye movements were analysed and compared to those of saccades made in the normal task. The velocity of "anti saccades" was found to be slightly (up to 15%) but significantly slower in two subjects. The distributions of SRTs in normal gap tasks show a small group of anticipatory saccades (with SRT below 80 ms and slower velocities) followed by a group of saccades with fast reaction times between 80 ms and 120 ms (Express saccades) followed by another large group ranging up to 180 ms (regular saccades). In the gap anti task there are anticipatory saccades and saccades with SRTs above 100 ms; Express saccades are missing. The distribution of SRTs obtained in the overlap anti task was unimodal with a mean value of 231 ms as compared to 216 ms in the normal task. The introduction of the gap therefore clearly decreases the reaction times of the anti saccades. Control experiments show that the delay of anti saccades is not due to an interhemispheric transfer time but must be attributed to the saccade generating system taking more time to program a saccade to a position where no visual stimulus appears. These data are discussed as providing further evidence for the existence of a reflex-like pathway connecting the retina to the oculomotor nuclei mediating the Express saccade.

Humans↗
PubMed1992

Dead zone for express saccades.

The saccadic eye movements of three humans and one non-human primate (a male rhesus monkey) have been measured for target eccentricities between 0.3 and 15 deg. With a gap task (fixation point offset precedes target onset by 200 ms) and a target at 4 deg, all subjects produced reasonable amounts of express saccades as indicated by a clear peak in the distribution of their saccadic reaction times (SRT): about 100 ms in human subjects and 70 ms in the monkey. This peak disappeared with decreasing target eccentricity below 2 deg, but saccades of longer (regular) reaction times were still present. Thus it was found that there exists a dead zone for express saccades. In addition, small saccades have a much stronger tendency to overshoot the target and their velocity falls above the main sequence as defined by the least square fit of an exponential v = vo(1-exp(-a/ao)) to the maximal velocity (v) versus amplitude (a) relationship (vo and ao are constants fitted). It is concluded that for small saccades the express way is blocked functionally or does not exist anatomically.

Animals↗
PubMed1992

Regulated inactivation of homologous gene expression in transgenic Nicotiana sylvestris plants containing a defense-related tobacco chitinase gene.

The class I chitinases are vacuolar proteins implicated in the defense of plants against pathogens. Leaves of transgenic Nicotiana sylvestris plants homozygous for a chimeric tobacco (Nicotiana tabacum) chitinase gene with Cauliflower Mosaic Virus (CaMV) 35S RNA expression signals usually accumulate high levels of chitinase relative to comparable leaves of non-transformed plants. Unexpectedly, some transgenic plants accumulated lower levels of chitinase than nontransformed plants. We call this phenomenon silencing. The incidence of silencing depends on the early rearing conditions of the plants. When grown to maturity in a greenhouse, approximately 25% of plants raised as seedlings in closed culture vessels were of the silent type; none of the plants raised from seed in a greenhouse showed this phenotype. Silencing is also developmentally regulated. Plants showed three patterns of chitinase expression: uniformly high levels of expression in different leaves, uniformly low levels of expression in different leaves, and position-dependent silencing in which expression was uniform within individual leaves but varied in different leaves on the same plant. Heritability of the silent phenotype was examined in plants homozygous for the transgene. Some direct descendants exhibited a high-silent-high sequence of activity phenotypes in successive sexual generations, which cannot be explained by simple Mendelian inheritance. Taken together, the results indicate that silencing results from stable but potentially reversible states of gene expression that are not meiotically transmitted. Gene-specific measurements of chitinase and chitinase mRNA showed that silencing results from co-suppression, i.e. the inactivation of both host and transgene expression in trans. The silent state was not correlated with cytosine methylation of the transgene at the five restriction sites investigated.

Base Sequence↗
PubMed1992

Ultrastructural and autoradiographic study of preimplantation rabbit embryos grown in conventional or uterine flushing-supplemented culture media.

Rabbit morulae and blastocysts were cultured in conventional culture media [Ham's F10 or BSM II supplemented with bovine serum albumin (BSA) or serum] or in Ham's medium supplemented with synchronous or asynchronous uterine flushings, mostly for 2 days, and afterwards investigated by light and electron microscopy and by autoradiography. Ultrastructure and cell proliferation differed considerably between cultured embryos and noncultured controls. Cultured embryos displayed more dead cells. They were developmentally retarded (predominance of smooth endoplasmic reticulum rather than the age-specific rough endoplasmic reticulum, mitochondria still round to ovoid shaped) and showed nonspecific signs of cells damage (swollen mitochondria and Golgi complex vesicles, increased number of lysosomes). All these features were also present in embryos grown in uterine flushing-supplemented media, but were less pronounced. Cell damage and impaired cell proliferation had affected trophoblast cells more than embryoblast cells. Endoderm could be differentiated only if culture had been started with blastocysts--not with morulae--and seems to require uterine secretions. No significant ultrastructural differences were observed between embryos cultured in synchronous or in asynchronous uterine flushings. Present results indicate that cultured preimplantation rabbit embryos deviate clearly from those grown in vivo and maintain, for some time, a better cellular structure--and probably function--in the presence of uterine flushings than in conventional culture media. Specific abnormal morphologic features related to a particular medium could not be identified.

Animals↗