Search PubMed⌕ Search

Biomedical subjects

E Michel

Publications and source records attributed to E Michel.

At least 73 records · Page 4Linked to original sources
PubMed1994

Cerebral autoregulation of preterm neonates--a non-linear control system?

The low frequency cerebral blood flow velocity (CBFV) oscillations in neonates are commonly attributed to an under-dampened immature linear type cerebral autoregulation, and the 'instability' is regarded as causative for peri-intraventricular haemorrhage/periventricular leukomalacia. In contrast, oscillations susceptible to frequency entrainment are a fundamental part of the stable function of non-linear control systems. To classify the autoregulation an observational study was done on the relationship between CBFV oscillations, heart rate variability, and artificial ventilation. In 10 preterm neonates (gestational age 26 to 35 weeks) we serially Doppler traced arterial CBFV continuously for 12 minutes between days 1 and 49 of life. The individual time series of CBFV and heart rate were subjected to spectral analysis. Forty six of 47 tracings showed significant low frequency CBFV oscillations. Low frequency heart rate oscillations were not a prerequisite thereof. All patients with < 30% of total power in the low frequency band of CBFV oscillations were on the ventilator. Three of them demonstrated a shift of spectral power from low frequency to a frequency equal or harmonic to the ventilator rate indicating entrainment. The findings of CBFV oscillations combined with entrainment classify the autoregulation as a non-linear system. It is suggested that entrainment by periodic high amplitude stimuli might challenge the regulatory capacity to its limits thus increasing the risk for cerebral damage.

Blood Flow Velocity↗
PubMed1993

Adaptive multipurpose probe fixation device for use on newborns.

Detailed information on the construction and assembly of a noncommercial hood-like multipurpose probe fixation device is given. A vacuum technique is used to individually mold the device to the skull of newborn infants and to attach sensors firmly with minimum pressure. By design, in the range of 22 to 38 cm head circumference for transfontanellar Doppler monitoring, no more than four different sizes of the hood are required to match individual positions of the anterior fontanelle. A ball-and-socket joint facility is integrated. The flexibility of the design allows for an easy adaptation of the device to different probe requirements. This provides the opportunity to investigate cerebral circulation by using various methods simultaneously.

Blood Flow Velocity↗
PubMed1993

Induction of phagocytic behaviour in human epithelial cells by Escherichia coli cytotoxic necrotizing factor type 1.

Cytotoxic necrotizing factor type 1 (CNF1) from strains of pathogenic Escherichia coli induces in human epithelial HEp-2 cells, a profound reorganization of the actin cytoskeleton into prominent stress fibres and membrane ruffles. We report here that this process is associated with induction of phagocytic-like activity. CNF1-treated cells acquired the ability to ingest latex beads as well as non-invasive bacteria such as Listeria innocua, which were taken as a model system. Uptake of bacteria was similar to pathogen-induced phagocytosis, since L. innocua transformed with DNA coding for the pore-forming toxin listeriolysin O behaved, with respect to intracellular growth, like the invasive, pathogenic species L. monocytogenes. Our results raise the possibility that, in vivo, pathogenic CNF1-producing E. coli may invade epithelia by this novel induced phagocytic-like mechanism.

Actin Cytoskeleton↗
PubMed1993

Resuscitation of the very immature infant: cerebral Doppler flow velocities in the first 20 minutes of life.

Blood flow velocity of the anterior cerebral artery was investigated by Doppler ultrasonography in five time intervals up to 20 min after birth in 16 non-asphyxiated very immature infants (median birth weight 1,058 g, range 720-1,930 g; median gestational age 30 weeks, range 27-32 weeks) delivered by caesarean section and intubated after birth. Heart frequency, oscillometric mean arterial blood pressure and blood gases were recorded as well. There was a transitory increase in both systolic and end-diastolic velocities (from 29 to 35 and from 1 to 10 cm/s) during the first 5 min after birth which occurred together with an increase in heart frequency. The overall incidence of intracranial haemorrhage was low (3/16, 19%). This observation study shows a transitory increase in cerebral blood flow velocity with a peak at about 5 min after birth in preterm infants < 33 weeks of gestation undergoing standard resuscitation.

Birth Weight↗
PubMed1993

Simultaneous influence of blood pressure, PCO2, and PO2 on cerebral blood flow velocity in preterm infants of less than 33 weeks' gestation.

In extremely preterm infants, the protective capacity for cerebral blood flow (CBF) autoregulation may be impaired or absent, which increases the risk for developing cerebral lesions. The purpose of this study was to quantify the simultaneous influence of several vital parameters, such as mean arterial blood pressure (MABP), PCO2, and PO2, on cerebral blood flow velocity (CBFv), which is used as a measure for CBF. In 16 mechanically ventilated infants of < 33 wk gestation, the CBFv in the internal carotid artery was measured every minute for 1 h by a computer-controlled pulsed Doppler device. MABP and transcutaneous PCO2 and PO2 were recorded as well. A multiple linear regression analysis was performed in each patient to determine the individual MABP, PCO2, and PO2 reactivities as a measure for CBF autoregulation. The medians (and ranges) of the whole group were an MABP reactivity of 7.5% (-12.5 to 20.1%) rise in CBFv/1 kPa rise in MABP, a PCO2 reactivity of 32.7% (-8.1 to 79.5%) rise in CBFv/1 kPa rise in PCO2, and a PO2 reactivity of -3.1% (-14.2 to 7.9%) fall in CBFv/1 kPa rise in PO2. In preterm infants, the individual's capacity for MABP-, PCO2-, and PO2-dependent CBF autoregulation can be estimated by means of the present method, even if the vital parameters change simultaneously.

Blood Flow Velocity↗
PubMed1992

Menstrual cycle exhibits no effect on postprandial lipemia.

Menstrual cycle effects on postprandial lipemia were investigated in 13 healthy women. They were monitored (dietary intake, basal body temperature) for a period of one cycle. Statistically significant follicular-luteal differences were neither observed between fasting triglyceride serum levels nor between areas under triglyceride response curves after a standardized oral fat load.

Adult↗
PubMed1992

Physical map of the Listeria monocytogenes chromosome.

The circular physical map of the pathogenic bacterium Listeria monocytogenes LO28 (serovar 1/2c) was established by using pulsed-field gel electrophoresis. The L. monocytogenes chromosome contains eight NotI fragments of 1,100, 940, 400, 335, 280, 45, 30, and 20 kb in size and eight Sse8387I fragments of 860, 680, 680, 370, 335, 130, 70, and 25 kb. Therefore, the total length of the genome is 3,150 kb. To order the NotI fragments on the chromosome, we used a strategy which can be of general use. We first cloned chromosomal HindIII or EcoRI fragments in pBR322. DNA extracted from the total libraries was digested by NotI and ligated to a NotI-kanamycin resistance cassette obtained by cutting Tn5 with NotI. After transformation in Escherichia coli, kanamycin-resistant clones originating from NotI-containing EcoRI or HindIII fragments were isolated. The two EcoRI-NotI or HindIII-NotI fragments of each recombinant plasmid were isolated and used as probes on Southern blot hybridizations to identify and link the corresponding NotI fragments. Seven NotI fragments were ordered in this way. The last junction was demonstrated by partial digest analysis. All L. monocytogenes genes identified so far as well as the six rRNA operons were localized on the NotI map. Regions homologous to genes from closely related bacteria were also detected and localized. Southern blot analysis of simple Sse8387I digests or double Sse8387I-NotI digests probed with the various NotI probes allowed us to align the Sse8387I fragments and localize the single SfiI site, resulting in the establishment of the first genetic and physical map of the L. monocytogenes chromosome.

Base Sequence↗
PubMed1992

[Trends in mortality characteristics in Aids in France 1983-1990].

From 1983 to 1990, the number of AIDS deaths in France (8119 deaths overall), increased substnatially but the annual rate of progression has fallen since 1987 (+35% in 1990). The socio-demographic characteristics of the deaths remained quite steady with the exception of the proportion of subjects living in Paris which decreased. The proportion of AIDS deaths out of all deaths is still low for the entire population (5 deaths out of 1000 in 1990) but appears important in some sub-groups. In 1990, AIDS represents for the 25-34 years old group, 12 deaths out of 100 for males and 7 deaths out of 100 for females and for the 25-44 years old group, 15 deaths out of 100 for nonmarried males and 4 deaths out of 10 for males working in an information or artistic profession. Furthermore, it accounts, in 1989, for the third of the deaths of males between 25 and 44 years living in Paris. The analyse tends to show that there is not an important under-declaration of AIDS deaths in France.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Attenuated mutants of the intracellular bacterium Listeria monocytogenes obtained by single amino acid substitutions in listeriolysin O.

Listeriolysin O (LLO), a major virulence factor of the intracellular bacterium Listeria monocytogenes, shares with other known 'thiol-activated toxins' a conserved undecapeptide, ECTGLAWEWWR, located in the C-terminal region of the protein and containing the unique cysteine of the molecule. Single amino acid substitutions were created in this region to study the role of cysteine and tryptophan residues in the lytic activity of LLO as well as in the virulence of the bacterium. Transformation of a transposon-induced non-haemolytic mutant with plasmids carrying the mutated genes allowed allele exchange and transfer of mutations on to the chromosome by in vivo recombination. The mutant strains secreted a full-length 59 kilodalton LLO. A decrease of 25% in the haemolytic activity in culture supernatants was observed in the case of mutation Cys-484 to Ala and of 80% for mutation Cys-484 to Ser. Mutations Trp-491 and Trp-492 to Ala decreased activity by, respectively, 95% and 99.9%. LLOs produced by the mutants, as the wild type, were active at low pH, inhibited by cholesterol, and able to bind to cell membranes. A close relationship was found between virulence of mutants in the mouse model and haemolytic activity in their culture supernatants. These results demonstrate that the thiol group of Cys-484 is not essential for either haemolytic activity in vitro or virulence in vivo. In contrast, Trp-492 appears to be required for both haemolytic activity and virulence. The finding that the nearly non-haemolytic mutant Trp-492-Ala persisted in the spleen for several days after inoculation indicates that mutagenesis of a virulence determinant can attenuate virulence and provides a novel approach to the development of live vaccine strains.

Alleles↗
PubMed1990

Histochemical and immunocytochemical localization of prolactin receptors on Nb2 lymphoma cells: applications of confocal microscopy.

We studied prolactin (PRL) binding sites on Nb2 lymphoma cells using two different light microscopic methods. First, histochemical detection was accomplished by using an aminomethyl coumarin-acetic acid-conjugated ovine prolactin molecule (AMCA-oPRL) on both glutaraldehyde-fixed and unfixed Nb2 lymphoma cells. Binding of AMCA-oPRL was studied after UV illumination and appeared as punctate fluorescence associated with many but not all cells. Binding was abolished when tissue sections were treated with excess unlabeled lactogenic hormones and was unchanged when a non-lactogenic hormone was used for displacement. Counting revealed significant differences between the number of labeled cells in populations known to exhibit up- or down-regulated PRL receptors. Second, indirect immunocytochemistry of Nb2 PRL receptors was accomplished by immunological detection of exogenously added ovine PRL using two antisera directed against ovine PRL. Visualization of the ligand-antibody complexes was accomplished by confocal laser scanning microscopy. Staining was restricted to a subpopulation of cells. The morphological results presented here add to the previous physiological and biochemical data on the presence of lactogenic hormone receptors on Nb2 lymphoma cells.

Animals↗
PubMed1990

[The phagocytic activity of the blood neutrophilic granulocytes in patients with marginal periodontitis].

The ingestion of opsonized zymosan particles by neutrophil blood granulocytes and the chemiluminescence in samples of whole blood, induced by zymosan, Streptococcus mutans as well as phorbol myristate acetate, as a measure of the generation of reactive oxygene species were studied in patients with various forms of marginal periodontitis. Compared to a control group the phagocytic activity was found to be enhanced in progressive adult periodontitis and diminished in juvenile periodontitis whereas no differences to controls were found in chronic nonprogressive or postjuvenile periodontitis. With respect to the height of the chemiluminescence signals increased values were only measured in chronic nonprogressive periodontitis after stimulation by phorbol myristate acetate. The results indicate that impairment of blood granulocyte functions may be a pathogenetic factor for the development and the progression of marginal periodontitis.

Adolescent↗
PubMed1989

Acute and protracted effects of intratracheal surfactant application on internal carotid blood flow velocity, blood pressure and carbondioxide tension in very low birth weight infants.

As a part of a multicentre clinical trial of prophylactic treatment with bovine surfactant (SF-RI 1) given to immature infants below 31 gestational weeks, short term and protracted effects on cerebral haemodynamics were assessed by Dopplersonographic measurements of the right internal carotid artery. Measurements were performed every 10 min for 1 h after intratracheal application of the surfactant in ten treated infants. The results of additional measurements every 12 h up to the age of 100 h were compared with a control group. In single cases there were changes of time averaged mean maximum velocity (Vmax) of as much as 100% immediately after intratracheal surfactant application, although the mean short term and protracted variability of Vmax was the same as the protracted variability in the control group. Variability of mean arterial blood pressure and transcutaneous carbondioxide tension (tcpCO2) was even less. With proper adjustment of ventilatory settings intratracheal treatment with surfactant does not affect variability or absolute values of internal carotid Vmax, mean arterial blood pressure and transcutaneous pCO2 in low birth weight infants within 100 h after application.

Blood Flow Velocity↗
PubMed1989

Postneonatal mortality, sudden infant death syndrome: factors preventing the decline of infant mortality in France from 1979 to 1985.

The sudden infant death syndrome (SIDS) is known to be associated with a peak in mortality rates at 3 months of age, and a seasonal peak in winter. The aim of this study was to analyse the relationship between the month of death, month of birth and age at death for cohorts of monthly births in France between 1979 and 1985. Statistics concerning the causes of death were collected and used to calculate life-tables firstly from SIDS and secondly from all other causes. They show that the specific age distribution at death was not the same for babies born in late summer or autumn as for other newborns. Total infant death rates were higher for cohorts born in the autumn, because of the peak in deaths from SIDS at about three months of age.

Actuarial Analysis↗
PubMed1989

Histochemical demonstration of prolactin binding sites.

We have developed a new probe for histochemical demonstration of prolactin binding sites. Ovine prolactin (oPRL) was conjugated with the N-hydroxy-succinimide ester derivative of the fluorochrome 7-amino-4-methylcoumarin-3-acetic acid. Under mild reaction conditions the ester derivative reacted with available NH2 groups of the prolactin molecule to form stable bonds. The coupling reaction yielded products that co-migrated with oPRL but had slightly decreased isoelectric points. The receptor binding and bioactivity of the flurochrome-hormone derivatives were decreased essentially proportional to the extent of conjugation. The derivatives were further tested for their ability to label PRL binding sites, using frozen sections of mammary gland and brain tissue of lactating rats. The results presented in this report describe the validation of this probe with regard to labeling of PRL binding sites at the light microscopic level in known target organs (mammary gland and choroid plexus). In addition, this fluorescent probe was used to demonstrate the presence of PRL binding sites at a novel site, the ependymal lining of the third ventricle.

Animals↗
PubMed1989

[Cellular chemiluminescence of activated phagocytes of whole blood].

Both, the phagocytic process and the activation of phagocytes with soluble stimuli are accompanied by increased production of reactive oxygen species (ROS). Chemiluminescence (CL) measurement is a simple and sensitive method for the detection of ROS generation. Phagocytes (mainly polymorphonuclear leukocytes, PMNL) were stimulated with soluble stimulus or via phagocytosis in diluted whole blood, and the generation of Luminol-enhanced CL was registered. The time dependence of CL, determined in whole blood, corresponds to the CL from isolated leukocytes. A relationship between peak CL and the number of leukocytes as well as of PMNL was observed. The specific CL, i.e. the CL response related to a defined PMNL number, increases with the age of investigated healthy individuals. No correlations were found between CL and the capacity of PMNL to ingest zymosan particles. Relations between CL and spontaneous platelet aggregation suggest, that reactivity of blood platelets may be a contributing factor to the kinetics of the CL signal in our test system. The inhibition of CL by the sulphydryl reagents diamide and fever few extract indicate the role of cellular sulphydryl groups for phagocyte function. Measurement of CL in whole blood is proved to be a simple assay for assessment of PMNL function and allows measurements in very small blood samples (greater than or equal to 10 ul).

Cell Separation↗
PubMed1989

N-(2-mercaptopropionyl)-glycine inhibits chemiluminescence and accelerates phagocytosis in human polymorphonuclear leukocytes.

Treatment of polymorphonuclear leukocytes with the soluble and cell penetrating thiol N-(2-mercaptopropionyl)-glycine (2-MPG) inhibits luminol-enhanced chemiluminescence induced by opsonized zymosan, which is believed to be a measure for the generation of reactive oxygen species, and accelerates the rate of phagocytosis measured as ingestion of zymosan particles. It is discussed that 2-MPG protects the phagocyting cells from oxidative damage by reactive oxygen species that are formed during particle ingestion.

Humans↗