Biomedical subjects

J Majewski

Publications and source records attributed to J Majewski.

At least 37 records · Page 2Linked to original sources

PubMed2001

[The effect of changes in stroke volume on QT dispersion during long-term DDD and VVI pacing].

UNLABELLED: The aim of this study was to evaluate the alterations of stroke volume (SV) on the QT dispersion (QTD) as a result of different pacing modes (DDD, VVI) and programmed AV delays (AVD). MATERIAL AND METHODS: We studied 60 patients (pts) (22 F, 38 M) in mean age 67.5 +/- 7.5 yrs in whom DDD pacemakers were implanted due to complete atrioventricular block (AVB III degree). 10 pts had coronary artery disease (CAD)--"CAD" subgroup, 14 pts arterial hypertension (AH)--"AH" subgroup, 27 pts CAD and AH--"AH + CAD" subgroup. The control group consisted of 9 pts without structural heart disease, but with AVB III degree, paced in DDD mode. Previous myocardial infarction was recognised in 7 patients in "CAD" subgroup and in 7 patients in "AH + CAD" subgroup. Left ventricular hypertrophy was detected in 4 men in "AH" subgroup and in 8 patients in "AH + CAD" subgroup. In all cases basic rate of the pacemaker was programmed at 70/min. Resting ECG showed all atrial and ventricular complexes captured. AVD optimization was based on the measurements of SV by Doppler echocardiography. QT intervals (QT) were measured from 12-lead ECG at 50 mm/sec. speed. QTD was calculated as the difference between maximal and minimal QT. It was measured at optimal AVD (with highest SV--opt. DDD) and "unoptimal" AVD (unopt. DDD) programmed AV intervals and then in VVI mode (with lowest SV) after 24 hrs following reprogramming of the pacemaker. RESULTS: In the whole population, in DDD mode, we found a strong correlation between SV and QTD (r = -0.655; p < 0.01). In VVI mode SV was significantly lower than in unopt. DDD (78.7 ml vs 90.0 ml, p < 0.001) and QTD was significantly greater (74.3 ms vs 69.2 ms, p < 0.05). The modifications in AVD and conversion of pacing mode (VVI to DDD) leading to maximal SV resulted in decreased QT dispersion. The highest SV (128.9 ml at opt. DDD) and the lowest QTD (48.3 ms at opt. DDD) were seen in the controls, but changes in dispersion were the least and insignificant during different pacing modes. In CAD; AH + CAD pts, we observed the lowest SV (61.7 ml; 74.9 ml at VVI respectively) and the highest QTD (77.8 ms; 80.9 ms at VVI respectively). In these pts, the modifications of AVD and conversion of pacing mode (VVI to opt. DDD) leading to maximal SV (106.8 ml; 115.9 ml in CAD and AH + CAD pts, respectively) resulted in decreased QTD (53.9 ms; 56.6 ms, respectively). During DDD pacing there was significant correlation of QTD to SV (r = -0.680; r = -0.656, respectively). In CAD pts with myocardial infarction or in AH pts with LV hypertrophy the correlation of SV to QTD was stronger (r = -0.937, r = -0.886, p < 0.025, respectively). We didn't find the correlation in the control group (r = -0.318). CONCLUSIONS: Programming of different AVD and pacing modes significantly influences QTD in CAD and/or AH pts. QTD reflects hemodynamic status of these paced pts.

Adult↗

PubMed2001

[QT dispersion in DDD and VVI paced patients after myocardial infarction or with left ventricular hypertrophy].

The aim of this study was to assess the alterations of stroke volume (SV) on the QT dispersion (QTD) as a result of different pacing modes and programmed AV delays in patients (pts) after myocardial infarction (MI) or with left ventricular hypertrophy (LVH). We studied 14 MI pts (9 M, 5 F) in mean age 72.3 +/- 3.7 yrs (Group I) and 12 pts with LVH (7 M, 5 F) in mean age 67.3 +/- 5.9 yrs (Group II), in whom DDD pacemakers were implanted due to complete atrioventricular block. The control group (Group III) consisted of 9 pts without MI or LVH. In all cases basic rate of the pacemaker was programmed at 70/min. Resting ECG showed all atrial and ventricular complexes captured. AV delay optimization was based on the measurements of SV by Doppler echocardiography. QT intervals (QTi) were measured from 12-lead ECG at 50 mm/s speed. QTD was calculated as the difference between maximal and minimal QTi. It was measured at optimal (opt. DDD, with highest SV) and "unoptimal" (unopt. DDD) programmed AV intervals and then in VVI mode (with lowest SV) after following reprogramming of the pacemaker. In Group I and II, a strong correlation between SV and QTD was found (R = 0.816 and -0.897, respectively). In control group, it was insignificant (R = -0.339). In VVI mode SV was significantly lower than in unopt. DDD (in Mi pts: 56.1 ml vs 71.1 ml, respectively, p < 0.01; in LVH pts: 64.1 ml vs 96.7 ml, respectively, p < 0.005) and QTD was significantly greater (74.8 ms vs 66.8 ms, respectively, p < 0.005 and 70.0 ms vs 53.5 ms, respectively, p < 0.005). In LVH pts or MI pts programming of different AV intervals and pacing modes significantly influences QTD.

Aged↗

PubMed2001

[Successful RF ablation in a patient with paroxysmal atrial fibrillation induces by atrioventricular nodal reentrant tachycardia].

We describe a case of 47-year old patient with frequent episodes of paroxysmal atrial fibrillation (PAF) with fast ventricular rate. During electrophysiological study an atrioventricular nodal reentrant tachycardia (AVNRT) was diagnosed with rapid degeneration into atrial fibrillation. Successful RF ablation of slow pathway was performed. There were no PAF recurrences during six months follow-up.

Atrial Fibrillation↗

PubMed2000

Familial juvenile hyperuricemic nephropathy: localization of the gene on chromosome 16p11.2-and evidence for genetic heterogeneity.

Familial juvenile hyperuricemic nephropathy (FJHN), is an autosomal dominant renal disease characterized by juvenile onset of hyperuricemia, gouty arthritis, and progressive renal failure at an early age. Using a genomewide linkage analysis in three Czech affected families, we have identified, on chromosome 16p11.2, a locus for FJHN and have found evidence for genetic heterogeneity and reduced penetrance of the disease. The maximum two-point LOD score calculated with allowance for heterogeneity (HLOD) was 4.70, obtained at recombination fraction 0, with marker D16S3036; multipoint linkage analysis yielded a maximum HLOD score of 4.76 at the same location. Haplotype analysis defined a 10-cM candidate region between flanking markers D16S501 and D16S3113, exhibiting crossover events with the disease locus. The candidate interval contains several genes expressed in the kidney, two of which-uromodulin and NADP-regulated thyroid-hormone-binding protein-represent promising candidates for further analysis.

Adolescent↗

PubMed2000

X-ray and neutron surface scattering for studying lipid/polymer assemblies at the air-liquid and solid-liquid interfaces.

Simple mono- and bilayers, built of amphiphilic molecules and prepared at air-liquid or solid-liquid interfaces, can be used as models to study such effects as water penetration, hydrocarbon chain packing, and structural changes due to head group modification. In the paper, we will discuss neutron and X-ray reflectometry and grazing incidence X-ray diffraction techniques used to explore structures of such ultra-thin organic films in different environments. We will illustrate the use of these methods to characterize the morphologies of the following systems: (i) polyethylene glycol-modified distearoylphosphatidylethanolamine monolayers at air-liquid and solid-liquid interfaces; and (ii) assemblies of branched polyethyleneimine polymer and dimyristoylphophatidylcholine lipid at solid-liquid interfaces.

Adsorption↗

PubMed2000

GT repeats are associated with recombination on human chromosome 22.

The rate of meiotic recombination is not a constant function of physical distance across chromosomes. This variation is manifested by recombination hot spots and cold spots, observed in all organisms ranging from bacteria to humans. It is generally believed that factors such as primary and secondary DNA sequence, as well as chromatin structure and associated proteins, influence the frequency of recombination within a specific region. Several such factors, for example repetitive sequences, gene promoters, or regions with the ability to adopt Z-DNA conformation, have been hypothesized to enhance recombination. However, apart from specific examples, no general trends of association between recombination rates and particular DNA sequence motifs have been reported. In this paper, we analyze the complete sequence data from human chromosome 22 and compare microsatellite repeat distributions with mitotic recombination patterns available from earlier genetic studies. We show significant correlation between long tandem GT repeats, which are known to form Z-DNA and interact with several components of the recombination machinery, and recombination hot spots on human chromosome 22.

Chromosomes, Human, Pair 22↗

PubMed2000

Barriers to genetic exchange between bacterial species: Streptococcus pneumoniae transformation.

Interspecies genetic exchange is an important evolutionary mechanism in bacteria. It allows rapid acquisition of novel functions by transmission of adaptive genes between related species. However, the frequency of homologous recombination between bacterial species decreases sharply with the extent of DNA sequence divergence between the donor and the recipient. In Bacillus and Escherichia, this sexual isolation has been shown to be an exponential function of sequence divergence. Here we demonstrate that sexual isolation in transformation between Streptococcus pneumoniae recipient strains and donor DNA from related strains and species follows the described exponential relationship. We show that the Hex mismatch repair system poses a significant barrier to recombination over the entire range of sequence divergence (0.6 to 27%) investigated. Although mismatch repair becomes partially saturated, it is responsible for 34% of the observed sexual isolation. This is greater than the role of mismatch repair in Bacillus but less than that in Escherichia. The remaining non-Hex-mediated barrier to recombination can be provided by a variety of mechanisms. We discuss the possible additional mechanisms of sexual isolation, in view of earlier findings from Bacillus, Escherichia, and Streptococcus.

Base Pair Mismatch↗

PubMed2000

[Multi-site pace making for dilated cardiomyopathy].

Dual chamber pacing (DDD) has been reported to be effective in patients with dilated cardiomyopathy (DCM). Other works, however, show contradictory results. Deleterious effects resulting from desynchronization of the right and left ventricular contraction have been suggested. In patients with end-stage DCM and severe congestive heart failure multisite pacing may be associated with fast and sustained hemodynamic improvement.

Cardiac Pacing, Artificial↗

PubMed2000

[Quality of life in patients after implantation of pacemaker type DDD].

The aim of this study was to evaluate quality of life in pts with DDD pacemakers. The study group consisted of 343 pts (181 F, 162 M), mean age 66.7 +/- 2.5 y (19-92) in whom DDD pacemakers were implanted in the years 1992-1998 due to sick sinus syndrome (213 pts) or AV block (130 pts). Follow-up period was 111-2574 days, mean 924.58 +/- 550 days. The QOL assessment was based on the questionnaire prepared at our Center. The questionnaires were mailed to the pts. The significant improvement in overall well-being (p < 0.001), physical capacity (p < 0.005) and concentration (p < 0.025) was found as compared to the time before implantation. The incidence of syncopy decreased after implantation (p < 0.001). The pts complained of: limitation of arm moving (50.1%), anxiety for disturbances of PM function (41.4%), resignation from job (17.2%), restriction of sport activity (15.7%), necessity for follow-up visits (15.7%) and limitation of sex activity (10.2%). There were not significant differences in QOL between pts paced due to SSS or AV block. We found significant improvement in QOL after implantation of DDD pacemakers. The questionnaire-based assessment of QOL may be useful in management of DDD-paced pts.

Adult↗

PubMed2000

[Incidence of atrial fibrillation in paced patients with complete atrioventricular block].

The aim of the study was to evaluate the incidence of chronic AF in patients paced due to complete AV block. The study group consisted of 130 pts (70 F, 60 M), mean age 68.6 +/- 14.3 y in whom pacemakers were implanted in the years 1990-1998 due to III degree AV block. There were 76 pts with VVI, 24 DDD and 30 VDD modes of pacing. Follow-up period was mean. 47.6 +/- 25.9 m (7-110). Chronic AF developed in 25 pts (19.2%). In the VVI group the incidence of AF was significantly higher than in DDD and VDD groups--30.3% vs. 4.17% and 3.33% respectively, p < 0.01. Ventriculo-atrial conduction (VAC) was found in 19 pts (14.6%), but did not correlate with the development of AF. Stroke occurred in 2 pts with VVI pacing and chronic AF. In conclusion, in pts with complete AV block VDD and DDD pacing significantly reduce the incidence of chronic AF as compared to VVI.

Adolescent↗

PubMed2000

[The new cemetery in Katyn: a permanent monument to the murder of Polish officers, including pharmacists. The authors' own report].

Polish army officers were called up in 1939, due to German aggression against Poland. Those who were in eastern Poland which had been occupied but the Soviet Union since September 17th 1939, were captured by the Red Army and committed to the NKVD. They were imprisoned in several camps and murdered (nearly 25.000 persons) in April and May 1940. The prisoners from the camp in Kozelsk (over 4.400 persons) were shot in Katyn forest near Smolensk. The authors went there on April 19, 2000 and were attracted by the commemorative plaques to over 60 murdered pharmacists.

History, 20th Century↗

PubMed1999

Polymer-cushioned bilayers. I. A structural study of various preparation methods using neutron reflectometry.

This neutron reflectometry study evaluates the structures resulting from different methods of preparing polymer-cushioned lipid bilayers. Four different techniques to deposit a dimyristoylphosphatidylcholine (DMPC) bilayer onto a polyethylenimine (PEI)-coated quartz substrate were examined: 1) vesicle adsorption onto a previously dried polymer layer; 2) vesicle adsorption onto a bare substrate, followed by polymer adsorption; and 3, 4) Langmuir-Blodgett vertical deposition of a lipid monolayer spread over a polymer-containing subphase to form a polymer-supported lipid monolayer, followed by formation of the outer lipid monolayer by either 3) horizontal deposition of the lipid monolayer or 4) vesicle adsorption. We show that the initial conditions of the polymer layer are a critical factor for the successful formation of our desired structure, i.e., a continuous bilayer atop a hydrated PEI layer. Our desired structure was found for all methods investigated except the horizontal deposition. The interaction forces between these polymer-supported bilayers are investigated in a separate paper (Wong, J. Y., C. K. Park, M. Seitz, and J. Israelachvili. 1999. Biophys. J. 77:1458-1468), which indicate that the presence of the polymer cushion significantly alters the interaction potential. These polymer-supported bilayers could serve as model systems for the study of transmembrane proteins under conditions more closely mimicking real cellular membrane environments.

Adsorption↗

PubMed1999

Adapt globally, act locally: the effect of selective sweeps on bacterial sequence diversity.

Previous studies have shown that genetic exchange in bacteria is too rare to prevent neutral sequence divergence between ecological populations. That is, despite genetic exchange, each population should diverge into its own DNA sequence-similarity cluster. In those studies, each selective sweep was limited to acting within a single ecological population. Here we postulate the existence of globally adaptive mutations, which may confer a selective advantage to all ecological populations constituting a metapopulation. Such adaptations cause global selective sweeps, which purge the divergence both within and between populations. We found that the effect of recurrent global selective sweeps on neutral sequence divergence is highly dependent on the mechanism of genetic exchange. Global selective sweeps can prevent populations from reaching high levels of neutral sequence divergence, but they cannot cause two populations to become identical in neutral sequence characters. The model supports the earlier conclusion that each ecological population of bacteria should form its own distinct DNA sequence-similarity cluster.

Adaptation, Physiological↗

PubMed1999

DNA sequence similarity requirements for interspecific recombination in Bacillus.

Gene transfer in bacteria is notoriously promiscuous. Genetic material is known to be transferred between groups as distantly related as the Gram positives and Gram negatives. However, the frequency of homologous recombination decreases sharply with the level of relatedness between the donor and recipient. Several studies show that this sexual isolation is an exponential function of DNA sequence divergence between recombining substrates. The two major factors implicated in producing the recombinational barrier are the mismatch repair system and the requirement for a short region of sequence identity to initiate strand exchange. Here we demonstrate that sexual isolation in Bacillus transformation results almost exclusively from the need for regions of identity at both the 5' and 3' ends of the donor DNA strand. We show that, by providing the essential identity, we can effectively eliminate sexual isolation between highly divergent sequences. We also present evidence that the potential of a donor sequence to act as a recombinogenic, invasive end is determined by the stability (melting point) of the donor-recipient complex. These results explain the exponential relationship between sexual isolation and sequence divergence observed in bacteria. They also suggest a model for rapid spread of novel adaptations, such as antibiotic resistance genes, among related species.

Bacillus↗

PubMed1999

[Hereditary long QT syndrome: our own experience].

We report the case of 16-year old girl who was admitted to our Department after the episode of ventricular fibrillation. We diagnosed the hereditary long QT syndrome. The patient's family was investigated and complex therapy was started in affected individuals including cardioselective beta-blocker (atenolol) and permanent cardiac pacing (VVIR and DDDR). This therapy is effective in prevention of life-threatening cardiac arrhythmias in our patients.

Adolescent↗

PubMed1998

A neutron reflectivity study of polymer-modified phospholipid monolayers at the solid-solution interface: polyethylene glycol-lipids on silane-modified substrates.

The structure of polymer-decorated phospholipid monolayers at the solid-solution interface was investigated using neutron reflectometry. The monolayers were composed of distearoylphosphatidylethanolamine (DSPE) matrixed with varying amounts of DSPE-PEG (DSPE with polyethylene glycol covalently grafted to its headgroup). Mixed lipid monolayers were Langmuir-Blodgett deposited onto hydrophobic quartz or silicon substrates, previously hydrophobized by chemically grafting a robust monolayer of octadecyltrichlorosilane (OTS). We show that this method results in homogeneous and continuous phospholipid monolayers on the silanated substrates and determine that the grafted PEG chains extend away from the monolayers into the solvent phase as a function of their density, as expected from scaling theories. In addition, ligands were coupled to the end of the PEG chains and selective binding was demonstrated using fluorescence microscopy. Our results demonstrate that these constructs are ideal for further characterization and studies with well-defined monomolecular films.

Adsorption↗

PubMed1998

Structural studies of polymer-cushioned lipid bilayers.

The structure of softly supported polymer-cushioned lipid bilayers, prepared in two different ways at the quartz-solution interface, were determined using neutron reflectometry. The polymer cushion consisted of a thin layer of branched, cationic polyethyleneimine (PEI), and the bilayers were formed by adsorption of small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles. When vesicles were first allowed to adsorb to a bare quartz substrate, an almost perfect bilayer formed. When the polymer was then added to the aqueous solution, it appeared to diffuse beneath this bilayer, effectively lifting it from the substrate. In contrast, if the polymer layer is adsorbed first to the bare quartz substrate followed by addition of vesicles to the solution, there is very little interaction of the vesicles with the polymer layer, and the result is a complex structure most likely consisting of patchy multilayers or adsorbed vesicles.

Adsorption↗

PubMed1998

The effect of mismatch repair and heteroduplex formation on sexual isolation in Bacillus.

In Bacillus transformation, sexual isolation is known to be an exponential function of the sequence divergence between donor and recipient. Here, we have investigated the mechanism under which sequence divergence results in sexual isolation. We tested the effect of mismatch repair by comparing a wild-type strain and an isogenic mismatch-repair mutant for the relationship between sexual isolation and sequence divergence. Mismatch repair was shown to contribute to sexual isolation but was responsible for only a small fraction of the sexual isolation observed. Another possible mechanism of sexual isolation is that more divergent recipient and donor DNA strands have greater difficulty forming a heteroduplex because a region of perfect identity between donor and recipient is required for initiation of the heteroduplex. A mathematical model showed that this heteroduplex-resistance mechanism yields an exponential relationship between sexual isolation and sequence divergence. Moreover, this model yields an estimate of the size of the region of perfect identity that is comparable to independent estimates for Escherichia coli. For these reasons, and because all other mechanisms of sexual isolation may be ruled out, we conclude that resistance to heteroduplex formation is predominantly responsible for the exponential relationship between sexual isolation and sequence divergence in Bacillus transformation.

Bacillus↗