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Biomedical subjects

I Janssen

Publications and source records attributed to I Janssen.

65 records · Page 4Linked to original sources
PubMed1994

Patterns of cerebrovascular reactivity in patients with unilateral asymptomatic carotid artery stenosis.

BACKGROUND AND PURPOSE: Intracranial hemodynamic status varies in patients with unilateral significant carotid artery stenosis. It ranges from normal, because of sufficient collaterals, to poor, because of a severely reduced blood supply that puts the patient at an increased risk of stroke or cerebral ischemia. The present study examined patterns of abnormal cerebrovascular hemodynamics in patients with asymptomatic carotid artery stenosis. METHODS: The CO2 reactivity of the cerebral resistance index (CRi) and of mean blood flow velocity (vmean) was determined via transcranial Doppler sonography in 91 patients with unilateral high-grade to threadlike carotid artery stenosis and in 37 control subjects. The interhemispheric asymmetry of CRi reactivity of the control group was used to differentiate between normal and abnormal findings. RESULTS: We found that 64.8% of the patients demonstrated normal CRi asymmetry with comparable CRi reactivity (ipsilateral, 4.42 +/- 0.44 %CRi/vol%CO2; contralateral, 4.51 +/- 0.39 %CRi/vol%CO2) and vmean reactivity (ipsilateral, 0.080 +/- 0.004 m/s per vol%CO2; contralateral, 0.079 +/- 0.005 m/s per vol%CO2) at both hemispheres. In 16.5% of the patients, CRi reactivity was supranormal at the affected hemisphere. This phenomenon was due to an exaggerated dilatory response of the ipsilateral hemisphere and was combined with an absent CRi reactivity of the contralateral hemisphere (ipsilateral, 6.63 +/- 1.03 %CRi/vol%CO2; contralateral, -1.16 +/- 1.78 %CRi/vol%CO2). In contrast, hemispheric vmean reactivities were comparable (ipsilateral, 0.078 +/- 0.008 m/s per vol%CO2; contralateral, 0.077 +/- 0.008 m/s per vol%CO2). The remaining 18.7% showed severely diminished ipsilateral CRi reactivity (ipsilateral, 1.91 +/- 0.83 %CRi/vol%CO2; contralateral, 8.48 +/- 1.00 %CRi/vol%CO2) and vmean reactivity (ipsilateral, 0.073 +/- 0.007 m/s per vol%CO2; contralateral, 0.108 +/- 0.012 m/s per vol%CO2; P < .01), compatible with a significantly reduced perfusion pressure at the poststenotic hemisphere. CONCLUSIONS: Most asymptomatic patients do not suffer from severely abnormal hemodynamics at the poststenotic hemisphere. One small subgroup of patients presented with severely disturbed ipsilateral hemodynamics; another small subgroup demonstrated a steal phenomenon with secondary dilation of large cerebral vessels at the contralateral hemisphere. These subgroups require specific evaluation of proper treatment.

Aged↗
PubMed1993

Baculovirus immediate early gene promoter based expression vectors for transient and stable transformation of insect cells.

A recombinant plasmid vector was constructed in which the bacterial LacZ gene was placed under the control of a Bombyx mori baculovirus early promoter. The vector proved to be active in transfected cultured dipteran and lepidopteran cells. Co-transfection carried out with this recombinant plasmid vector and a plasmid containing the hygromycin phosphotransferase gene followed by selection with the antibiotic hygromycin B, resulted in stable transformation of cultured Drosophila melanogaster Schneider 2 cells. Southern blot analysis of the host cell's genomic DNA in combination with chromosomal in situ hybridization demonstrated that multiple copies of both plasmids were integrated in the host cell's genome.

Animals↗
PubMed1992

Gamma distribution and house 222Rn measurements.

The statistical distribution of 222Rn measurements from basements and first floors of homes in northeastern Pennsylvania was investigated. The gamma distribution was statistically significantly superior to the normal distribution (p less than 0.005) in describing the frequency distribution of the logarithm of observed 222Rn levels. The fit to the data was closer both in the central portion and in the upper tail. The gamma distribution has certain characteristics that make it generally useful in the study of environmental toxic agents where several different exposures over a lifetime occur and must be combined, as for risk assessment or for statistical power calculations for epidemiologic studies.

Air Pollution, Indoor↗
PubMed1991

Prediction of 222Rn from topography in Pennsylvania.

The relationships of Rn levels in basements and first floors of homes to topographic location in a northeastern ridge and valley section of Pennsylvania were investigated. Topographic variables relating to elevation and slope were quantified and related to house Rn levels using both conventional and classification and regression tree (CART) analyses. The original interest was in using topographic correlates to estimate missing values in epidemiologic studies. In this area, Rn levels are usefully predicted by relative and absolute elevations and nearness to hills and ridges. Three- to fourfold differences in geometric mean Rn levels can be obtained for categories representing significant portions of the population of houses. The relationship of first-floor to basement Rn levels was found to be curvilinear and modestly affected by topography.

Air Pollutants, Radioactive↗
PubMed1990

The cyanelle genome of Cyanophora paradoxa, unlike the chloroplast genome, codes for the ribosomal L3 protein.

We describe a 1132 bp sequence of the cyanelle genome of Cyanophora paradoxa containing the rpl3 gene. This gene, which is not chloroplast encoded in plants, is the first of a long cyanelle ribosomal operon whose organization resembles that of the S10 operon of E. coli. We have shown that the rpl3 gene is transcribed in cyanelles as a 7500 nucleotide precursor and that the 5'-end of the mRNA starts approximately 90 nucleotides upstream from the initiation codon. However, no typical procaryotic promoter could be found for this gene. We have detected, using anti E. coli L3 antibodies, the cyanelle L3 protein in cyanelle extracts and in E. coli cells transformed with the cyanelle rpl3 gene.

Amino Acid Sequence↗
PubMed1990

[Transcranial Doppler curve analysis. On the pathophysiology of unilateral carotid stenoses].

Vascular reactivity to changes in arterial CO2 content can be measured by analysis of Doppler curves in the middle cerebral artery (MCA). Vascular reactivity indicates the capability of the cerebrum of controlling peripheral resistance. In patients with threatening cerebrovascular disease (CVD) vascular autoregulation may be reduced. The circle of Willis plays a central role in the pathophysiology of unilateral high-grade ICA-stenosis. Previous classification of the degree of stenosis or of the clinical stage does not allow to describe the actual pathophysiology or prognosis of CVD sufficiently.

Adult↗
PubMed1989

Evolutionary relationship of psbA genes from cyanobacteria, cyanelles and plastids.

The psbA gene is part of the reaction center of photosystem II in cyanobacteria and the plastids of higher plants. Its primary sequence is highly conserved among all species investigated so far and its sequence shows homologies with the L and M subunits of the reaction center of photosynthetic bacteria. We have analyzed the psbA homolog from a eukaryotic alga, Cyanophora paradoxa, where the gene is encoded on cyanelle DNA. These cyanelles are surrounded by a murein sacculus and resemble cyanobacteria in many other characteristics, although they are genuine organelles that functionally replace plastids. Analysis of the gene revealed a psbA protein identical in length (360 codons) with the cyanobacterial counterpart. The overall sequence identity is, however, more pronounced between cyanelle psbA and the shorter (353 amino acids) psbA product found in higher plants. These data strongly support the postulated bridge position of cyanelles between chloroplasts and free-living cyanobacteria.

Amino Acid Sequence↗
PubMed1987

A stochastic repair--misrepair model for the effects of radiation on cells.

The purpose of this paper is to present a stochastic model for effects of radiation on cells. The model includes provisions for lethal effects and for transformation to malignant status. Empirical findings indicate the presence of some repair mechanism in the cells, and a way to incorporate this idea into the model is discussed. Comparisons of the derived survival and transformation probabilities with actual data are favorable. The interpretation of the estimated values leads to questions to be investigated by the experimenters.

Animals↗
PubMedDate not supplied

Comparison of three methods for recording tibial H reflex: a clinical note.

Recording the tibial H reflex from the calf is routine in clinical electromyography. Two widely used methods are Hugon's and Braddom and Johnson's. Both methods produce an H wave with an initial positive deflection. Another method, the "half and half" method, generates an H wave with an initial negative deflection. To compare these methods, H-reflex responses were recorded in the right calf of 20 normal adults with each method using identical amplifier and stimulator settings. Stimulus current was increased by increments of 0.5-1.0 mA until the H reflex and motor (M) wave responses reached maximum amplitudes (Hmax, Mmax). H wave to M wave (H/M) amplitude ratios were calculated. The half-and-half method produced greatest Hmax, Mmax, and H/M ratio. Wave form configuration for the half-and-half method was biphasic with an initial negative deflection; it was triphasic with an initial positive deflection with the other methods. The shapes of M and H waves were similar in two methods but dissimilar in one. Because of the greater amplitude and the initial negative deflection, the H wave may be easier to detect with the half-and-half method and may present a latency that is more easily determined. For these reasons, the half-and-half method is recommended for measuring amplitude and latency in clinical settings.

Adult↗
PubMedDate not supplied

Linking age-related changes in skeletal muscle mass and composition with metabolism and disease.

Skeletal muscle (SM) plays a central role in many biological functions, such as movement and metabolism, and alterations in SM mass and composition can have a marked influence on health and disease. The purpose of this review was to examine and characterize age-related changes in SM mass and composition and to link these changes to corresponding changes in metabolism and disease. It can be concluded from several studies that SM mass decreases with advancing age in both men and women. The age-related reduction in SM, also known as sarcopenia, is related to a corresponding reduction in SM strength, and if left untreated, sarcopenia may lead to functional impairment and physical disability. An emerging body of evidence also suggests that age-related changes in the composition of SM, particularly the accumulation of lipids within SM fibers, may lead to metabolic disorders such as insulin resistance.

Activities of Daily Living↗