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Biomedical subjects

D Petit

Publications and source records attributed to D Petit.

82 records · Page 5Linked to original sources
PubMedDate not supplied

Regional spectral analysis of the REM sleep EEG in mild to moderate Alzheimer's disease.

Regional spectral analyses of the EEG during wakefulness and REM sleep was performed in eight patients with mild to moderate Alzheimer's disease and compared to that of healthy age-matched controls. Alzheimer patients presented some EEG slowing in frontal, parieto-occipital and temporal regions in the waking state. However, this EEG slowing was much better revealed in REM sleep, whether expressed by the ratio of slow to fast frequencies or by changes in each of the frequency bands. Moreover, regional differences in EEG slowing, relatively nonexistent in the awake EEG, were a prominent feature of the REM sleep EEG. Importance of cholinergic basal forebrain in the desynchronization of the REM sleep EEG might explain these results because this structure is affected in early Alzheimer's disease.

Aged↗
PubMedDate not supplied

What is the surface specific area of porous cement-based material? A nuclear magnetic relaxation dispersion approach.

We propose a new NMR method to measure and follow the evolution of the surface specific area, Sp, of a porous cement-based material. This method, that does not require any preliminary drying process, uses nuclear magnetic relaxation dispersion (NMRD), the measurement of spin-lattice relaxation rate as a function of magnetic field strength or nuclear Larmor frequency. The method is applied for three different mortars samples prepared by mixing cement, sand, silica fume, water and superplasticizer with a water to cement ratio w/c=0.25, 0.38 and 0.65, respectively. The evolution of Sp grows linearly with the degree of advancement of chemical reactions measured by thermal heating and we evidence two relaxation processes independent of the w/c ratio.

Construction Materials↗
PubMedDate not supplied

Micropore size analysis by NMR in hydrated cement.

The understanding of the microstructure of cement remains incomplete. Especially, the progressive setting of the material is still unclear. Micropore size distribution (microstructure) has been investigated by both standard proton nuclear magnetic relaxation (1H-NMR) and field-cycling relaxation in C3S hydrated paste. The non-exponential decay was interpreted as a distribution of discrete relaxation rates. The attribution of T1 is supported by both a spectral and a dispersion curve analyses. These experiments allow us to follow the structuration of the material during setting.

Calcium Compounds↗
PubMedDate not supplied

Analysis of microporosity and setting of reactive powder concrete by proton nuclear relaxation.

The proton spin-lattice relaxation measured at several frequencies leads to a resolved distribution of four Tli for reactive powder concrete (RPC). The typical Tli frequency dependences are quantitatively interpreted by a biphasic fast exchange model and a proton nuclear relaxation of hydrated paramagnetic ions at the surface of the pores. This leads to an estimation of the pore sizes. We present the first application of this nuclear relaxation method to follow in situ the kinetics of the hydration and setting of such material.

Cementation↗
PubMedDate not supplied

Sleep in menopause: differential effects of two forms of hormone replacement therapy.

OBJECTIVES: The aim of the present study was to evaluate differences between two regimens of estrogen/progestogen replacement therapy on nocturnal sleep in postmenopausal women. METHODS: Twenty-one (21) postmenopausal women were studied. They were randomized into two treatment groups: (1) estrogen (Premarin 0.625 mg) and medroxyprogesterone acetate (Provera 5 mg) (n = 11) or (2) estrogen (Premarin 0.625 mg) and oral micronized progesterone (Prometrium 200 mg) (n = 10). Postmenopausal women were recorded for two consecutive nights in the sleep laboratory at baseline and again after 6 months of treatment in a randomized trial. The women also had to fill out evening and morning sleep and vigilance questionnaires for 7 days before baseline recordings and for 23 days before month 6 recordings. RESULTS: Sleep efficiency was found to be significantly improved in the micronized progesterone group. It increased by 8% (p = 0.014) with no such increase observed in the medroxyprogesterone acetate group. Time spent awake after sleep onset was also significantly improved in the micronized progesterone group but not in the medroxyprogesterone acetate group. On the other hand, menopausal symptoms and subjective measures of sleep (questionnaires) improved in both groups after treatment. CONCLUSION: This study suggests that medroxyprogesterone acetate and micronized progesterone are both effective for treating menopausal symptoms but that the latter might better improve the quality of sleep in postmenopausal women taking estrogen.

Estrogen Replacement Therapy↗