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Biomedical subjects

T Lehmann

Publications and source records attributed to T Lehmann.

At least 127 records · Page 7Linked to original sources
PubMed1993

Ectoparasites: direct impact on host fitness.

Despite being restricted to the host's first line of defence (the integument, away from vital organs), ectoparasite damage has a pronounced impact on host fitness. This generalization can be explained by the reduced dependence of most ectoparasites on their individual host, which minimizes the fitness loss linked to host death. This explanation implies that permanent ectoparasites evolve less 'aggressively' than do either nest or field ectoparasites. This, and other determinants of ectoparasitic virulence are discussed here by Tovi Lehmann.

Journal Article↗
PubMed1993

A hardware efficient cascadable chip set for ANN's with on-chip backpropagation.

In this paper, an analogue, cascadable, CMOS chip set for artificial neural networks is presented. The chip set (a synapse chip and a neuron chip) offer on-chip back-propagation learning in a fully parallel, layered, feedforward network of arbitrary size and topology. The learning scheme is implemented with no extra circuits at the synapse sites (compared to the system without the learning scheme) and extra circuits of a complexity only about the same as the neurons at the neuron sites. Also, no additional wiring is required by the learning scheme. Measurements on an experimental chip set are presented.

Algorithms↗
PubMed1993

Predictors of perioperative morbidity and mortality in repeat valve replacement: a seven-year experience.

Forty-nine consecutive repeat cardiac valve replacements in 46 patients were reviewed to define in-hospital morbidity, mortality, and determinants of risk. The overall operative mortality rate was 10.2%; it was 9% for the first reoperation and 25% for the second (four patients). The mortality rate was 12% at the mitral position (25 patients), 11% at the aortic position (18 patients), and 0% for repeat double valve replacement (four patients). Univariate and multivariate stepwise logistic regression models show that age over 70 years and the use of an intraaortic balloon pump preoperatively predict operative mortality, and age over 70, preoperative care in the coronary care unit, endocarditis, and the presence of an intraaortic balloon pump are determinants of perioperative morbidity in patients undergoing repeat valve replacement. Based on these data, close follow-up of patients with initial valve replacement is encouraged so that reoperation to correct prosthetic malfunction or periprosthetic leak can be done before hemodynamic collapse occurs. Furthermore, since age was the most significant factor affecting mortality (P < .01) and since most of the deaths (80%) in this study occurred in patients with torn bioprosthetic leaflets, the use of bioprostheses for initial valve replacement in patients under 70 years of age is discouraged.

Adult↗
PubMed1992

The probable conformation of substrates recognized by dipeptidyl-peptidase IV and some aspects of the catalytic mechanism derived from theoretical investigations.

By theoretical conformational investigations of substrates and nonsubstrates of the enzyme dipeptidyl-peptidase IV (DP IV) as well as dipeptide-esters using the ECEPP83 method we determined the structure of peptides recognized and cleaved by the enzyme. From a comparison of all possible structures for the substrates with conformations not possible in nonsubstrates we concluded that a single conformation explains substrate specificities of DP IV. This conformation is characterized by the following dihedral angles: psi 1 = 85 degrees, omega 1 = 180 degrees, phi 2 = -75 degrees, psi 2 = 80 degrees, and omega 2 = 180 degrees. The conclusions were supported by comparisons of molecular electrostatic potentials calculated with the molecular graphics program HAMOG.

Amino Acid Sequence↗
PubMed1992

Ectoparasite impacts on Gerbillus andersoni allenbyi under natural conditions.

To assess ectoparasite impact on individuals and populations of Gerbillus andersoni allenbyi under natural conditions, I addressed the following questions. Do ectoparasites affect their host fitness and, if so, how? Do ectoparasites affect host population level? Does this parasite-host interaction support the traditional concept of parasite evolution towards avirulence? For this purpose, host infestation, infection, survival, haematological indices, and physical condition were recorded. A field experiment which included manipulating host infestation while recording host survival was conducted to determine the causal relations between these variables. G. a. allenbyi was infested by 2 fleas (Synosternus cleopatrae and Stenoponia tripectinata), 5 mesostigmatid mites (Androlaelaps centrocarpus, A. hirsti, A. insculptus, A. marshalli and Hirstionyssus carticulatus), 1 tick (Rhipicephalus sanguineus), and 1 louse (polyplax gerbilli). Ectoparasite burden significantly reduced host survival and red blood cell indices (red cell concentration, haemoglobin concentration and haematocrit). Ectoparasite burden did not significantly affect white blood cell concentration. Gerbils were not infected by haemoparasites or gut helminths which potentially could cause anaemia. The causal relationship between S. cleopatrae burden and host survival was established by manipulation of host infestation. Both ectoparasite removal and initial level of infestation significantly affected host survival. Ectoparasites that caused anaemia were not associated with host physical condition (PC), measured as weight/length3. None of the red blood cell indices was correlated with host PC. These results suggest both that host PC was not affected by ectoparasite burden and that exsanguination leading to anaemia was the main effect of the ectoparasites. Ectoparasite pressure on the host population (based on the ectoparasite effects as estimated by statistical models, combined with dispersion of the infestation within the host population) changed seasonally and was greatest when host density was the highest. A large segment of the gerbil population was affected by ectoparasites during the entire year. An explanation for the evolution of parasite virulence, contrasting parasites that evolve towards increased virulence with parasites that evolve towards avirulence is presented. This classification is primarily based on whether parasite impact is equated with a higher efficiency of host exploitation, or whether it is a 'side effect' of parasite biology.

Animals↗
PubMed1992

Reproductive activity of Synosternus cleopatrae (Siphonaptera: Pulicidae) in relation to host factors.

Reproductive activity of Synosternus cleopatrae (Rothschild) infesting Gerbillus andersoni allenbyi Thomas was studied in a natural setting in Israel. Rodents were trapped and measured (weight and length), their sex was identified, and their reproductive status estimated. Their ectoparasites were removed, and fleas were dissected and their oocytes measured. Two indices of flea reproductive activity were analyzed: "reproductive status," which distinguished between gravid and nongravid females, and "reproductive intensity," which was estimated as the sum over the two largest oocytes of the products of oocyte length multiplied by oocyte width. Both indices showed that no reproduction took place between November and January, but reproduction was relatively stable during the rest of the year. Although flea reproductive activity differed significantly among individual hosts, only a small fraction of gerbils (10-15%) carried a significantly different proportion of reproductive fleas than their monthly sample proportion (based on all fleas regardless of hosts). All these hosts carried a lower proportion of reproductive fleas than their monthly sample proportion. The host's sex, but not reproductive status or age, had a significant effect on flea reproduction, expressed as a higher reproductive activity on male gerbils. Infestation burden expressed as ectoparasite counts was included in the statistical analysis. Only lice, Polyplax gerbilli Ferris, but not S. cleopatrae, Stenoponia tripectinata (Tiraboschi), and a total of five mesostigmatid Acari had a significantly negative association with S. cleopatrae reproductive activity. These relationships between S. cleopatrae reproductive activity and the host infestation burden do not support the hypothesis of modulation of S. cleopatrae reproduction by the infestation burden. However, differences in the reproductive activity of ectoparasites between their hosts may play a major role to generate the parasite clumped distribution. Thus, gerbil males probably carry more fleas than gerbil females because of the higher reproductive activity of S. cleopatrae on gerbil males.

Animals↗
PubMed1989

Immunochemical comparison of the glutamate dehydrogenase isoenzymes in yellow lupin root nodules.

Monospecific antisera against three glutamate dehydrogenase (GDH) subunits of lupin root nodules were obtained. The use of sensitive mixed rocket immunoelectrophoresis enabled detection of seven GDH forms at the early stage of nodule development, thus providing evidence for the earlier hypothesized (L. Ratajczak et al., 1986, Physiol. Plant., 67, 685-689) random association of subunits 2g and 2a to form the remaining five GDH forms. All seven forms were localized in mitochondria. Immunological similarity was found between form 1 and plastid GDH.

Fabaceae↗
PubMed1986

Lumbar disc herniation. A comparison of the results of chemonucleolysis and open discectomy after ten years.

Using data obtained by questionnaire in a retrospective review of patients with low-back and sciatic pain (eighty-five treated by injection of chymopapain and seventy-one, by open discectomy), the results at one and ten years after treatment were analyzed. For this analysis we used six measures of pain relief, six measures of the patients' course during the ten-year period since primary treatment, and four measures of the patients' history of employment or work since initial treatment. Validity studies demonstrated that the pain-outcome measures reflected the patients' condition adequately and that all six measures were significantly related to each other (Pearson's r, p less than 0.003). The chymopapain and discectomy groups were not distinguishable on the basis of the pain-outcome measures. However, body mass was directly related to the presence of pain ten years after discectomy but not after injection of chymopapain. Analysis of the progress measures (indicators of the course of the patients' pain during the ten-year period) showed that the rates of reoperation in the two treatment groups did not differ significantly, but the discectomy patients tended to have had a higher rate of reoperation at both one and ten years after initial treatment. These measures did not show unequivocal superiority of one treatment compared with the other. Using the work measures (assessments of the patients' history of employment since initial treatment), it was found that in both treatment groups the patients who returned to work six to twelve weeks after treatment despite persistent symptoms had significantly more pain at ten years (p less than 0.04). Also, the patients who returned to work less than six weeks after treatment, while still symptomatic, showed a similar trend. On the other hand, among the patients who were still symptomatic at twelve weeks, it made no difference in the final results whether they returned to work at twelve weeks or thereafter. These findings support the notion that after either discectomy or chemonucleolysis, patients should return to work only after complete symptomatic recovery or a minimum convalescence of twelve weeks.

Adult↗
PubMed1984

Effect of pelvic tilt on standing posture.

Low back dysfunction is associated in many cases with lumbar lordosis, and tilting the pelvis posteriorly is often recommended for therapeutic purposes. The influence of pelvic tilt on the spinal curves has not been studied. The purpose of this study was to use an objective noninvasive method to determine the effect of the pelvic tilt on the spinal curves in the sagittal plane. Thirty-two healthy subjects and 15 patients with chronic low back dysfunction (CLBD) were studied. Patients with CLBD and healthy subjects were instructed in performing active anterior and posterior pelvic tilt maneuvers, first in the supine and then in the standing position. Comparisons between the Patient Group and the Healthy Group were made for several variables representing the severity of spinal curves, pelvic orientation, hip orientation, and knee orientation. A computerized system, the Iowa Anatomical Position System, was used to obtain coordinates of external body surface landmarks from which pelvic tilt measurements were determined. The results showed that the voluntary pelvic tilt did not alter the thoracic spinal curve. For both the Healthy Group and the Patient Group, the lumbar curve was altered by the pelvic tilt: anterior tilt increased the depth of the lumbar curve and posterior tilt decreased the depth of the lumbar curve. The amount of pelvic tilt was the same whether knees were extended or flexed approximately 10 degrees. Pelvic tilt also tended to influence the orientation of the head and other parts of the body.

Adult↗
PubMed1983

Assessment of abdominal and back extensor function. A quantitative approach and results for chronic low-back patients.

A method was developed to obtain static and dynamic measures of trunk flexor and extensor strength and endurance. The method was evaluated using 32 normal subjects. Variables of trunk strength and endurance were used to compare 24 normals (12 men and 12 women) and 24 patients (16 men and eight women) with chronic low-back dysfunction. The Iowa Trunk Dynamometer is acceptably reliable and provides for assessment of isolated function of the abdominal and back muscles. For peak abdominal and back extensor strength, the range of superiority of men over women was 39-57%, and the range of superiority of normals over patients with chronic low-back dysfunction was 48-82%. Using time to percent decrement of peak strength as a criterion, the abdominals were more susceptible to fatigue than the back extensors, women demonstrated more endurance than men, and the endurance for normals was less than those patients who were able to perform dynamic reciprocal trunk movements.

Abdominal Muscles↗
PubMedDate not supplied

The polymer-supported phospholipid bilayer: tethering as a new approach to substrate-membrane stabilization.

We present a new molecular engineering approach in which a polymer-supported phospholipid bilayer is vertically stabilized by controlled covalent tethering at both the polymer-substrate and polymer-bilayer interfaces. This approach is based on lipopolymer molecules, which not only form a polymer cushion between the phospholipid bilayer and a solid glass substrate but also act as covalent connections (tethers) between the bilayer and cushion. Our approach involves Langmuir-Blodgett transfer of a phospholipid-lipopolymer monolayer followed by Schaefer transfer of a pure phospholipid monolayer and is capable of varying the tethering density between the polymer layer and the phospholipid bilayer in a very controlled manner. Further stabilization is achieved if the glass substrate is surface-functionalized with a benzophenone silane. In this case, a photocross-linking reaction between the polymer and benzophenone group allows for the covalent attachment of the polymer cushion to the glass substrate. This approach is similar to that recently reported by Wagner and Tamm in which double tethering is achieved via lipopolymer silanes (Wagner, M. L.; Tamm, L. K. Biophys. J. 2000, 79, 1400). To obtain a deeper understanding of how the covalent tethering affects the lateral mobility of the bilayer, we performed fluorescence recovery after photobleaching (FRAP) experiments on polymer-tethered bilayers at different tethering densities (lipopolymer/phospholipid molar ratios). The FRAP data clearly indicate that the hydrophobic lipopolymer moieties act as rather immobile obstacles within the phospholipid bilayer, thereby leading to hindered diffusion of phospholipids. Whereas the high lateral diffusion coefficient of D = 17.7 mum(2)/s measured at low tethering density (5 mol % lipopolymer) indicates rather unrestricted motion within the bilayer, corresponding values at moderate (10 mol % lipopolymer) and high (30 mol % lipopolymer) tethering densities of D = 9.7 mum(2)/s and D = 1.1 mum(2)/s, respectively, show significant hindered diffusion. These results are contrary to the recent findings on similar membrane systems reported by Wagner and Tamm in which no significant change in phospholipid diffusion was found between 0 and 10 mol % lipopolymer. Our experimental report leads to a deeper understanding of the complex problem of interlayer coupling and offers a path toward a compromise between stability of the whole system and lateral mobility within the bilayer. Furthermore, the FRAP measurements show that polymer-tethered membranes are very interesting model systems for studying problems of restricted diffusion within two-dimensional fluids.

Diffusion↗
PubMedDate not supplied

The Rift Valley complex as a barrier to gene flow for Anopheles gambiae in Kenya.

Recent studies of Anopheles gambiae, the principal mosquito vector of malaria in Africa, suggested that the eastern Rift Valley and its surrounding areas act as a barrier to gene flow. To quantify the unique effect of these areas on gene flow, we measured genetic variation within and between populations from each side of the Rift. Low differentiation was measured between populations on each side of the Rift (mean FST < 0.008, mean RST < 0.002). However, high differentiation was measured across the Rift (mean FST = 0.104; mean RST = 0.032). Genetic diversity within populations was lower in eastern populations, suggesting that the effective population sizes (Ne) of these populations were lower than those of western populations. We partitioned the overall differentiation across the Rift into three factors: variation in Ne between populations contributed 7-20%; distance contributed 10-30%, and the remainder, corresponding to the unique effect of the Rift was 50-80%. The Rift's effect was highly significant based on FST. The greater sensitivity of FST in measuring differentiation indicated that drift and not mutation generated the differences between populations. Restricted gene exchange across several hundred kilometers on the face of intense human transportation implies that active mosquito dispersal is the major form of migration, and that migration is a multistep process, where step length is relatively short.

Animals↗
PubMedDate not supplied

The Rift Valley complex as a barrier to gene flow for Anopheles gambiae in Kenya: the mtDNA perspective.

Descriptions of A. gambiae population structure based on microsatellite loci and mitochondrial DNA (mtDNA) were incongruent. High differentiation of populations was measured across the Rift Valley by microsatellites, but no differentiation was detected based on mtDNA. To resolve this conflict, we compared the old data to new mtDNA data using the same specimen previously genotyped in microsatellite loci. Analysis of a larger number of mtDNA sequences resulted in high and significant differentiation between populations across the Rift Valley. We developed a method to assess whether differentiation across the Rift Valley was generated by pure drift rather than mutation-drift, based on DNA sequence data. Applying this method to the mtDNA data suggested that pure drift was the primary force generating differentiation between the populations across the Rift, while mutation-drift generated differentiation across the continent. Given adequate sample size, mtDNA provided congruent results with microsatellite loci.

Animals↗
PubMedDate not supplied

Population Structure of Anopheles gambiae in Africa.

The population structure of Anopheles gambiae in Africa was studied using 11 microsatellite loci in 16 samples from 10 countries. All loci are located outside polymorphic inversions. Heterogeneity among loci was detected and two putative outlier loci were removed from analyses aimed at capturing genome-wide patterns. Two main divisions of the gene pool were separated by high differentiation (F(ST) > 0.1). The northwestern (NW) division included populations from Senegal, Ghana, Nigeria, Cameroon, Gabon, Democratic Republic of Congo (DRC), and western Kenya. The southeastern (SE) division included populations from eastern Kenya, Tanzania, Malawi, and Zambia. Inhospitable environments for A. gambiae along the Rift Valley partly separate these divisions. Reduced genetic diversity in the SE division and results of an analysis based on private alleles support the hypothesis that a recent bottleneck, followed by colonization from the NW populations shaped this structure. In the NW division, populations possessing the M rDNA genotype appeared to form a monophyletic clade. Although genetic distance increased with geographic distance, discontinuities were suggested between certain sets of populations. The absence of heterozygotes between sympatric M and S populations in the DRC and the high differentiation in locus 678 (F(ST)>0.28) contrasted with low differentiation in all other loci (-0.02<F(ST)<0.09) and with the persistence of departures from Hardy-Weinberg expectations within each form in the DRC. Neither recent reproductive isolation alone nor selection alone can explain these results, a situation that is compatible with incipient speciation. Because it is possible that the molecular forms play different roles in malaria transmission, future studies should treat them separately.

Africa South of the Sahara↗
PubMedDate not supplied

A novel method for quantifying shape deformation applied to biocompatibility testing.

Cytotoxicity tests are important for the screening and evaluation of biocompatibility of artificial organs. Morphologic changes of cells that were contacted biomaterials or biomaterial extracts indicate their toxicity. However, information on cytotoxic effects is still obtained by subjective visual inspection of microscopic samples. In this article, a novel computer assisted method is introduced. The automatic analysis of digitized micrographs is achieved in several stages: segmentation, separation, classification, and measurement. The segmentation of the image is provided by a new local adaptive thresholding technique, which adapts the threshold window sizes onto local gray level distribution and yields optimal window sizes. The actual threshold is obtained by maximizing interclass variances and minimizing intraclass variance. For the separation of connected cells, the binarized samples are cleaned from "false" markers by morphologic filtering. The subsequent separation is a two phase approach. Information levels are generated top-down by successively applying an enhanced erosion operator, which yields markers and filters noise usually evolving from multiple erosions. The converse bottom-up integration of the eroded markers is performed by successively applying an enhanced dilation operator, which reconstructs the cells and prevents merging of already separated objects. The subsequent measuring provides quantitative parameters of the distribution of size and compactness of the cells contained within the sample. The method was evaluated by L-929 fibroblasts that were in contact with 0%, 5%, and 10% concentrations of ethanol. For each concentration, 268 images of the cell populations were captured. The obtained quantitative parameters are highly correlated to the common verbal description of morphologic changes. Therefore, the proposed automatic method has several advantages compared with subjective examinations. The results allow an objective comparison of the quantification of phenomena; the subjective influence of the observer is eliminated; and the laboratory staff is relieved of time consuming routine work.

Animals↗