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Biomedical subjects

M Michaud

Publications and source records attributed to M Michaud.

At least 19 recordsLinked to original sources
PubMed2007

Electron photoemission from charged films: absolute cross section for trapping 0-5 eV electrons in condensed CO2.

The electron trapping or attachment cross section of carbon dioxide (CO2) condensed as thin films on a spacer of Ar is obtained using a simple model for electron trapping in a molecular film and then charge releasing from the same film by photon absorption. The measurements are presented for different electron exposures and impact energies, film thicknesses, and probing photon energies. The cross section for trapping an electron of incident energy between 0 and 5 eV reveals three different attachment processes characterized by a maximum at about 0.75 eV, a structured feature around 2.25 eV, and a shoulder around 3.75 eV. From the measurement of their dependence with the probing photon energy, the two lowest processes produce traps having a vertical electron binding energy of approximately 3.5 eV, whereas the highest one yields a slightly higher value of approximately 3.7 eV. The 0.75 eV maximum corresponds to the formation of vibrational Feshbach resonances in (CO2)n- anion clusters. The 2.25 eV feature is attributed to the formation of a vibrationally excited 2Piu anion in (CO2)n- clusters, followed by fast decay into its vibrational ground state without undergoing autodetachment. Finally, 3.75 eV shoulder is assigned to the well-known dissociative electron attachment process from 2Piu anion state producing the O- anion in the gas phase and the (CO2)nO- anions in clusters.

Carbon Dioxide↗
PubMed2006

[Acute pancreatitis due to hypercalcemia revealing adult T-cell leukemia].

INTRODUCTION: Hypercalcemia frequently occurs in the course of Adult T-cell leukemia/lymphoma (ATLL). We report the first case of acute pancreatitis revealing ATLL. EXEGESIS: A 41-year-old woman, without medical history, presented with acute pancreatitis. Physical examination found recent loss of weight, hepatosplenomegaly and generalised lymphoadenopathy. Biochemical tests showed severe hypercalcemia and the peripheral white blood cell count revealed an atypical lymphocytosis. ATLL was diagnosed by immunophenotypic and morphological analysis of circulating lymphocytes, bone marrow and lymphatic node biopsy. Level of serum parathyroid hormone-related protein was not increased. We discuss the mechanism of hypercalcemia in this context. CONCLUSION: In spite of the high prevalence of hypercalcemia in ATLL, acute pancreatitis revealing this pathology is an exceptional condition.

Acute Disease↗
PubMed2006

Assessing whole brain perfusion changes in patients with REM sleep behavior disorder.

OBJECTIVE: To investigate the regional cerebral perfusion in patients with idiopathic REM behavior disorder (RBD) in order to establish the topography of networks involved. METHODS: We performed cerebral blood flow evaluation using (99m)Tc-Ethylene Cysteinate Dimer (ECD) SPECT on eight patients with polysomnographically confirmed RBD and nine age-matched controls. Comparisons were made using SPM2. RESULTS: We found increased perfusion in the pons and putamen bilaterally and in the right hippocampus. In addition, we observed a decreased perfusion in frontal (Brodmann area [BA] 4, 6, 10, 43, 44, 47 bilaterally and left BA 9, 46) and temporo-parietal (BA 13, 22, 43 bilaterally and left BA 7, 19, 20, 21, 39, 40, 41, 42) cortices. CONCLUSION: Perfusional abnormalities in patients with REM behavior disorder were located in the brainstem, striatum, and cortex. These abnormalities are consistent with the anatomic metabolic profile of Parkinson disease.

Aged↗
PubMed2006

Long-term treatment with pramipexole in restless legs syndrome.

The aim of the present study was to look at the long-term efficacy and side effects profiles of pramipexole in a large cohort of drug naïve patients with regard to dopaminergic medications. In all, 195 consecutive restless legs syndrome (RLS) patients who were prescribed pramipexole more than 1 year previously, agreed to undergo a telephone interview to assess both the efficacy and side effects of pramipexole. Forty-three patients had discontinued pramipexole: 20 because of side effects, six because of a lack of efficacy, six for both and 11 for other reasons. Patients who continued pramipexole for more than 1 year (n = 152) reported a mean decrease in RLS symptoms severity of 80.9% (SD = 19.6%). At the onset of treatment, the most common side effects were nausea (30%), tiredness (9%), dizziness (8%), headache (4%), insomnia (3%), dry mouth (2%), difficulty to concentrate (1.3%) and sleepiness (0.7%), At 30 months, most patients (n = 124/152; 81.6%) reported an absence of side effects of pramipexole. None of the adverse effects occurred in more than 5% of patients at follow-up. The present study confirms, in a large cohort of unselected patients, that pramipexole is effective and safe in the long-term treatment of RLS.

Adult↗
PubMed2005

Absolute electronic excitation cross sections for low-energy electron (5-12 eV) scattering from condensed thymine.

The absolute cross sections for electronic excitations of thymine by electron impact between 5 and 12 eV are determined by means of electron-energy loss (EEL) spectroscopy for the molecule deposited at submonolayer coverage on an inert Ar substrate. The lowest EEL features at 3.7 and 4.0 eV are attributed to the excitation of the triplet 1 3A'(pi --> pi*) and 1 3A''(n --> pi*) valence states of the molecule. The higher EEL features located at 4.9, 6.3, 7.3, and 9 eV with a weak shoulder around 6 eV are ascribed mostly to triplet valence (pi --> pi*) excitation manifold of the molecule. The energy dependence of the cross section for both the lowest triplet valence excitations shows essentially a peak at about 5 eV reaching a value of 2.9 x 10(-17) cm2. The cross sections for the higher EEL features are generally characterized by a common broad maximum around 8 eV. The latter reaches a value of 1.36 x 10(-16) cm2 for the combined 6 and 6.3 eV excitation region. The maxima in the present cross sections are found to correspond to the resonances that have been reported at about the same energies in the O- yield from electron impact on thymine in the gas phase.

Models, Chemical↗
PubMed2005

Absolute vibrational and electronic cross sections for low-energy electron (2-12 eV) scattering from condensed pyrimidine.

Low-energy vibrational and electronic electron-energy-loss (EEL) spectra of pyrimidine condensed on a thin film of solid argon held at 18 K are reported for the incident-energy range of 2-12 eV. Sensitivity to symmetry and spin forbidden transitions as well as correlations to the triplet states of benzene make it possible to ascribe the main features, below 7 eV in the electronic part of the EEL spectrum, to triplet transitions. The lowest EEL feature with an energy onset at 3.5 eV is attributed to a transition to the (3)B(1)(n-->pi(*)) valence electronic state and the next triplet n-->pi(*) transition to a (3)A(2) state located around 4.5 eV. The remaining EEL features at 4.3, 5.2, 5.8, and 6.5 eV are all assigned to pi-->pi(*) transitions to states of symmetry (3)B(2), (3)A(1), (3)B(2), and (3)B(2)+(3)A(1), respectively. The most intense maximum at 7.6 eV is found to correspond to both (1)B(2) and (1)A(1) transitions, as in the vacuum ultraviolet spectra. Absolute inelastic cross sections per scatterer are derived from a single collision treatment described herein. Their values are found to lie within the 10(-17) cm(2) range for both the electronic and the vibrational excitations. Features in the energy dependence of the cross sections are discussed, whenever possible, by comparison with data and mechanisms found in the gas phase. A maximum over the 4-5 eV range is attributed to a B (2)B(1) shape resonance and another one observed in the 6-7 eV range is ascribed to either or both sigma(*) shape resonances of (2)A(1) and (2)B(2) symmetries.

Journal Article↗
PubMed2005

[Multidrug resistance in uveal melanoma].

In spite of important progress in the local treatment of uveal melanoma, the most frequent primitive intraocular tumor, 15%-30% of patients still die because of tumor metastasis. This tumor is characterized by constitutive chemoresistance, thwarting any attempt to control it using the usual chemotherapy protocols. The chemoresistance of uveal melanoma is mainly due to the typical multidrug resistance phenotype (MDR), which is linked to overexpression of membrane proteins that actively extrude anticancer drugs from the cell. Typical MDR is particularly complex in this tumor since several chemoresistance-related proteins are simultaneously produced. The negative prognostic significance of the overexpression of P-glycoprotein, the main representative among the typical MDR-related proteins, was shown in uveal melanoma. The atypical MDR phenotype, which refers to other chemoresistance mechanisms such as resistance to apoptosis also contributes to the chemoresistance of uveal melanoma. Thanks to the recent progress in molecular biology, the chemosensitization strategies of gene therapy approaches, which aim at weakening the pathological activity of MDR genes in cancer cells, are currently on the rise. This approach will disrupt current therapeutic strategies and necessarily improve and standardize the methods used to characterize the chemoresistance profile of this cancer. Indeed, we will have to know the genes to be targeted for each melanoma in order to induce cell chemosensitivity.

Antineoplastic Agents↗
PubMed2004

Vibrational and electronic excitations of H(2)O on thymine films induced by low-energy electrons.

We investigated vibrational and electronic excitations of 0.1-layer up to 2.4-layer film of H(2)O deposited on a 1.4-layer film of thymine condensed on Ar at a temperature of 18 K using high-resolution electron-energy loss (EEL) spectroscopy at the incident energy of 12 eV. The spectral contribution originating essentially from the H(2)O overlayer is obtained by separating the measured contribution from the underlying film of thymine, considering the electron beam attenuation in the H(2)O overlayer. The vibrational EEL spectrum of submonolayer amount of H(2)O on thymine, which excepts for small energy shift of the vibrational bands, is found to compare in intensity to that of the same amount of H(2)O deposited directly on the argon. The electronic energy-loss intensity near 8.6 eV, which is attributed to the excitation of (3,1)B(1) states of H(2)O in condensed phase, is observed to decrease by a factor of about 3 by the presence of the underlying film of thymine. This indicates that the corresponding cross section for excitation the (3,1)B(1) states of H(2)O by the electron impact is reduced significantly by the close proximity of the thymine molecules.

Biophysics↗
PubMed2004

Damage induced by low-energy electrons in solid films of tetrahydrofuran.

We report on the low-energy electron-induced production of aldehydes within thin solid films of tetrahydrofuran (THF) condensed on a solid Kr substrate. The aldehyde fragments, which remain trapped within the bulk of the THF film, are detected in situ via their 3,1(n-->pi*) and 3(pi-->pi*) electronic transitions and vibrational excitations in the ground state using high-resolution electron-energy-loss spectroscopy. The production of aldehyde is studied as a function of the electron exposure, film thickness, and incident electron energy between 1 and 18.5 eV. The aldehyde production is calibrated in terms of an electron scattering cross section, which is found to be typically 6-7 x 10(-17) cm(2) between 11 and 19 eV. Its energy dependence is characterized by a small feature around 3 eV, a strong rise from 6 eV up to a maximum at 12.5 eV, followed by two structures centered around 15 and 18 eV. The aldehyde production is discussed in terms of the formation of electron resonances or transient anion states, which may lead to the fragmentation of the molecule and explain the structures seen in the energy dependence of the measured cross section.

Journal Article↗
PubMed2004

Low-energy electron scattering cross section for the production of CO within solid films of carbon dioxide.

We report absolute electron scattering cross sections sigma(p) for the production of CO within thin solid film of carbon dioxide (CO(2)) condensed on a solid Ar substrate. The CO fragments, which remain trapped within the bulk of the carbon dioxide film, are detected in situ by recording energy losses to their lowest triplet electronic state a (3)Pi using high-resolution electron-energy-loss spectroscopy. The production of CO is studied as a function of the electron exposure, film thickness, and incident electron energy between 2 and 30 eV, a range within which most of the secondary electrons are created in systems irradiated by high-energy particles. The energy dependence is characterized by a feature around 4 eV with sigma(p)=(7.0+/-4.0)x10(-18) cm(2), a minimum around 7 eV, a strong rise up to a large and broad maximum around 15 eV with sigma(p)=(5.4+/-2.5)x10(-17) cm(2), a decrease to a minimum around 18.5 eV, and finally a monotonous increase up to 30 eV. The CO production is discussed in terms of the formation of electron resonances or transient anion states, which may lead directly to the fragmentation of the molecule via dissociative electron attachment or indirectly by decaying into an entirely repulsive part of the corresponding excited neutral and positive ion states.

Journal Article↗
PubMed2003

Age and gender effects on heart rate activation associated with periodic leg movements in patients with restless legs syndrome.

OBJECTIVE: Periodic leg movements during sleep (PLMS) are often associated with electroencephalographic (EEG) changes, such as microarousals (MA), and with heart rate (HR) variations. The aim of the present study was to evaluate the effects of age and gender on HR changes associated with PLMS in restless legs syndrome (RLS) patients. METHODS: Forty-two RLS patients underwent one night of polysomnographic recordings. They were divided into 3 groups of 14 subjects (7 women and 7 men) according to age, i.e. young (25-40 years), middle-aged (41-55 years) and elderly (56-71 years) patients. The RR interval was calculated for 5 intervals before and 15 intervals after the onset of 50 PLMS in each patient. RESULTS: PLMS were associated with HR changes characterized by a tachycardia followed by a bradycardia. However, a reduction in the tachycardia and the bradycardia was observed with age. Moreover, women showed a higher amplitude in the bradycardia than men. No age or gender difference was found for MA index and duration. CONCLUSIONS: This study showed age and gender differences in the magnitude of the HR changes associated with PLMS. The knowledge of HR variations during sleep, including rapid HR changes associated with sleep events such as PLMS or MA, may be helpful in understanding the potential mechanisms involved in the increased cardiac risk observed in elderly.

Adult↗
PubMed2003

Optimal growth strategies of larval helminths in their intermediate hosts.

We consider optimal growth of larval stages in complex parasite life cycles where there is no constraint because of host immune responses. Our model predicts an individual's asymptotic size in its intermediate host, with and without competition from conspecific larvae. We match observed variations in larval growth patterns in pseudophyllid cestodes with theoretical predictions of our model. If survival of the host is vital for transmission, larvae should reduce asymptotic size as intensity increases, to avoid killing the host. The life history strategy (LHS) model predicts a size reduction <1/intensity, thus increasing the parasite burden on the host. We discuss whether body size of competing parasites is an evolved LHS or simply reflects resource constraints (RC) on growth fixed by the host, leading to a constant total burden with intensity. Growth under competition appears comparable with "the tragedy of the commons", much analysed in social sciences. Our LHS prediction suggests that evolution generates a solution that seems cooperative but is actually selfish.

Animals↗
PubMed2003

Cross sections for low-energy (1-100 eV) electron elastic and inelastic scattering in amorphous ice.

We report the integral cross sections per scatterer (i.e. elastic collision, phonon excitations, vibrational excitations, electronic excitations and ionization) for 1-100 eV electron scattering in an amorphous film of ice condensed at a temperature of 14 K. The integral cross sections are determined relative to the total from a two-stream multiple-scattering analysis of the electron energy distribution backscattered from the film. Their energy dependence is obtained from both the analysis of the elastic electron reflectivity as a function of the film thickness and the vibrational electron energy-loss spectra measured for several incident energies and large film thickness. The magnitude and various features found in the energy dependence of the cross sections are discussed, whenever possible, by comparison with data and with scattering mechanisms available in the gas phase. Microcospic effects, which are implicitly included in cross sections determined in this way, are discussed in terms of interference and coherent multiple-scattering contributions among the scattering sites as well as interactions of the scattering sites with their neighbors in the condensed phase.

Elasticity↗
PubMed2002

Periodic leg movements in REM sleep behavior disorder and related autonomic and EEG activation.

OBJECTIVE: To assess the frequency of periodic leg movements (PLM) in idiopathic REM sleep behavior disorder (RBD) and to analyze their polysomnographic characteristics and associated autonomic and cortical activation. BACKGROUND: PLM during sleep (PLMS) and wakefulness (PLMW) are typical features of restless legs syndrome (RLS), but are also frequently observed in patients with RBD. METHODS: Forty patients with idiopathic RBD underwent one night of polysomnographic recording to assess PLMS frequency. PLM features, PLMS-related cardiac activation during stage 2 sleep, and EEG changes were analyzed in 15 of these patients with RBD. Results were compared with similar data obtained in 15 sex- and age-matched patients with primary RLS. RESULTS: Twenty-eight (70%) of 40 patients with RBD showed a PLMS index greater than 10. No between-group differences were found in sleep architecture or indexes of PLMW and PLMS during non-REM sleep, but a trend for a higher PLMS index during REM sleep was found in patients with RBD. PLM mean duration and interval in the two conditions were similar. A transient tachycardia followed by a bradycardia was observed in close association with every PLMS in both groups, but the amplitude of the cardiac activation was significantly reduced in patients with RBD. In addition, significantly fewer PLMS were associated with microarousal in this condition. CONCLUSIONS: Periodic leg movements are very common in idiopathic RBD, occurring in all stages of sleep, especially during REM sleep. In idiopathic RBD, the reduction of cardiac and EEG activation associated with PLMS suggests the presence of an impaired autonomic and cortical reactivity to internal stimuli.

Aged↗
PubMed2002

Age difference in heart rate changes associated with micro-arousals in humans.

OBJECTIVES: Heart rate (HR) is known to change in association to micro-arousals (MA) during sleep. The aim of the present study was to evaluate the effect of age on HR variations associated with MA. METHODS: Thirty-two healthy subjects underwent one night of polysomnographic recording. They were divided into two groups of 16 subjects according to age i.e. young (20-35 years) and middle-aged (50-65 years). The R-R intervals were calculated for 11 heart beats (10 intervals) before and 15 heart beats after the onset of MA. RESULTS: HR changes associated with MA were characterized by a tachycardia followed by a bradycardia in both young- and middle-aged subjects. However, middle-aged subjects showed a significant reduction in the amplitude of both tachycardia and bradycardia as compared to young subjects. CONCLUSIONS: This study revealed an age-related reduction in the amplitude of the HR changes associated with MA. These results may reflect a decline in parasympathetic functions and a higher risk of cardiovascular diseases with advancing age.

Adult↗
PubMed2001

Dopaminergic neurotransmission and restless legs syndrome: a genetic association analysis.

In order to examine the genetic substrate of the dopamine hypothesis in restless legs syndrome, we analyzed eight genes coding for receptors and enzymes related to dopaminergic transmission, using a population of 92 patients with restless legs syndrome and 182 controls matched for ethnic background. No significant differences were found in the genotypic or allelic distributions between groups. Furthermore, no effect of the loci examined was observed with stratification using clinical parameters such as age at onset or periodic leg movements during sleep index.

Adult↗