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Biomedical subjects

F Thomas

Publications and source records attributed to F Thomas.

At least 55 records · Page 3Linked to original sources
PubMed2001

Ferric chloride and lime conditioning of activated sludges: an electron microscopic study on resin-embedded samples.

Ferric chloride and lime conditioning of sewage sludge is usually interpreted in terms of enhanced aggregation of sludge components. In this study, transmission electron microscopy was used to investigate the conditioning mechanism at a submicronic scale. Samples were collected from two municipal wastewater treatment plants at different stages of the process, embedded in an epoxy resin, and sectioned with an ultramicrotome. Transmission electron microscopy examination of thin sections revealed that clumps of crystalloids develop on external surfaces of flocs after the application of both conditioners. This precipitate creates a rigid structure around the flocs which, upon mechanical dewatering, transmits the stresses applied to the inner parts of flocs. The porous structure of the precipitate may also participate to the withdrawal of water as a draining media. Energy dispersive X-ray spectroscopy revealed that Fe, P, and Ca are the dominant elements in the precipitate with Fe/P and Fe/Ca elemental ratios close to 2.8-3 and 1.1-3, respectively.

Calcium↗
PubMed2001

Should diastolic and systolic blood pressure be considered for cardiovascular risk evaluation: a study in middle-aged men and women.

OBJECTIVES: The goal of this study was to evaluate the role of diastolic blood pressure (DBP) in cardiovascular mortality for different systolic blood pressure (SBP) levels in middle-aged men and women. BACKGROUND: In middle-aged subjects it is unclear whether DBP, in addition to SBP, should be considered for risk evaluation. METHODS: Subjects (77,023 men; 48,480 women) aged 40 to 70 years old, had no major cardiovascular disease, no antihypertensive treatment and were examined at the Centre d'Investigations Preventives et Cliniques between 1972 and 1988. Mortality was assessed for an 8- to 12-year period. RESULTS: In both genders, cardiovascular mortality increased with the SBP level. In men and women with normal SBP levels, DBP did not influence cardiovascular mortality after adjustment for age and SBP. In men with systolic hypertension, a U-shaped curve relationship between cardiovascular mortality and DBP was observed, with the lowest mortality rates in the group with DBP 90 to 99 mm Hg. Compared with this group, age- and SBP-adjusted cardiovascular mortality was higher by 73% (p < 0.02) in the group with DBP <90 mm Hg and by 65% (p < 0.001) in the group with DBP > or =110 mm Hg. In women with systolic hypertension, however, DBP was positively correlated with cardiovascular mortality. CONCLUSIONS: In middle-aged subjects, classification of cardiovascular risk according to DBP levels should take into account gender, especially when SBP levels are elevated. Men with systolic hypertension are at higher risk when their DBP is "normal" than when they present a mild to moderate increase in DBP. In women of the same age, however, systolic-diastolic hypertension represents a higher risk than isolated systolic hypertension.

Adult↗
PubMed2001

Pulse pressure and heart rate: independent risk factors for cancer?

In the present study, the roles of heart rate (HR) and pulse pressure (PP) on cancer mortality, after taking into account physical activity, cigarette smoking, alcohol consumption and other confounding factors or underlying disease, were examined in men. The study included 125,513 men aged 20 to 95 years who had a health check-up at the IPC Center between 1978 and 1988. HR and PP were classified into three groups: < 60, 60-80, > 80 bpm for HR and < 50, 51-64, > or = 65 mmHg for PP. Adjusted risk ratios related to the increment from one class of HR or PP to the next for all cancer mortality were 1.4 (1.2-1.5) and 1.3 (1.1-1.4), respectively. This relationship was independent of several known risk and confounding factors, especially cigarette smoking and physical activity, and could not be explained by the presence of underlying disease.

Adult↗
PubMed2001

A tripartite anoikis-like mechanism causes early isolated islet apoptosis.

BACKGROUND: This study examines the mechanisms of early isolated islet apoptosis (II-APO) and loss of functional islet mass. METHODS: Rhesus islets were isolated for transplantation, and an aliquot was used for in vitro molecular studies of II-APO. These studies used Western blotting to examine caspase activation and perinuclear envelope protein cleavage that are associated with II-APO and used immunofluorescence analysis of Annexin V and mitochondrial permeability index to examine spontaneous and tripartite anoikis-like (TRAIL) mechanism--induced II-APO. RESULTS: Caspase 6 was prominently activated in association with spontaneous II-APO, which occurred after overnight culture. In contrast, caspase 7, 8, and 9 were not activated. Cleavage of focal adhesion kinase and Lamin, substrates of caspase 6, was also evident in spontaneous II-APO. II-APO was exaggerated by the addition of the TRAIL mechanism. The TRAIL mechanism--induced II-APO was blocked by the caspase 6 inhibitor, VEID, and by the soluble fusion proteins, DR4 or DR5, which act as decoy receptors. In vivo studies in diabetic severe combined immunodeficiency disease mice showed that rhesus islets were cytoprotected by either ex vivo gene transfer of Bcl-2 or treatment of the isolated islet with VEID. CONCLUSIONS: These studies suggest 3 major mechanisms involved in II-APO: caspase 6 activation, a TRAIL-induced apoptosis pathway, and the mitochondrial-associated apoptosis pathway. Inhibition of these II-APO pathways may improve isolated islet survival and reduce functional islet mass loss, which compromises the stable reversal of diabetes.

Animals↗
PubMed2001

Combined effects of heart rate and pulse pressure on cardiovascular mortality according to age.

OBJECTIVES: The aim of the study was to assess the combined effects of pulse pressure (PP) and heart rate (HR) on cardiovascular mortality in a large French population. DESIGN: The study population was composed of 125,513 men and 96,301 women aged 16-95 years who had a health check-up at the IPC Center between January 1978 and December 1988. Subjects taking antihypertensive treatment were excluded. Mortality was assessed for an 8-year period. HR and PP were classified into three groups. HR groups were: < 60, 60-79 and > or = 80 beats per minute (bpm). PP groups were: < 50, 50-64 and > or = 65 mmHg. RESULTS: In men, PP and HR were both positively associated with cardiovascular mortality risk. In women, mean arterial pressure (MAP) but not PP or HR was associated with cardiovascular mortality. In men, a combined elevation of PP and HR was associated with an important increase of cardiovascular mortality risk. The group with the highest PP and the highest HR had a 4.8-fold increase in cardiovascular mortality risk as compared to the reference group (PP < 50 mmHg and HR < 60 bpm). This effect was more pronounced in younger men (5.4-fold increase) than in older men (3.7-fold increase), as compared to the reference groups of the same age. In women, the combined effects of PP and HR on cardiovascular mortality were not significant. CONCLUSION: A combined elevation of the two components of pulsatile arterial stress is associated with an important increase in cardiovascular mortality in men, especially in younger men. In women, steady-state stress (evaluated primarily by MAP), but not pulsatile stress, is an important determinant of cardiovascular mortality.

Adolescent↗
PubMed2001

Disease diversity and human fertility.

The existence of parasitic constraints on the evolution of life-history traits in free-living organisms has been demonstrated in several plant and animal species. However, the association between different diseases and human traits is virtually unknown. We conducted a comparative analysis on a global scale to test whether the diversity of human diseases, some of them responsible for high incidences of morbidity and mortality, were associated with host life-history characteristics. After controlling for direct confounding effects exerted by historical, spatial, economic, and population patterns and their interactions, our findings show that human fertility increases with the diversity and structure of disease types. Thus, disease control may not only lower the costs associated with morbidity, but could also contribute directly or indirectly to reductions in human population growth.

Biological Evolution↗
PubMed2001

Effects of exposure to high temperature and feeding level on regional blood flow and oxidative capacity of tissues in piglets.

To determine to what extent exposure to high ambient temperature and feeding level affect tissue energy metabolism in piglets, regional blood flow and oxidative capacity of tissues were evaluated in sixteen 21.8 +/- 2.8 kg pigs. At 5 weeks of age, littermates were divided into three groups and acclimated to the treatment for 25 days. One group was reared at 33 degrees C and fed ad libitum (33AL, n = 6) while the other two groups were maintained at 23 degrees C and either pair-fed on the basis of the food consumption of their 33AL littermates (23PF, n = 5), or fed ad libitum (23AL, n = 5). Regional blood flow was determined in conscious pigs by injection of coloured microspheres, which were recovered in different tissues after slaughter. Activities of cytochrome oxidase and cytochrome aa(3) content were measured in tissue homogenates of heart, longissimus dorsi and rhomboideus muscles, liver and small intestine. There was decreased blood flow to internal adipose tissue (42 %) and increased blood flow to peripheral tissues (skin, 44 %) and tissues implicated in respiratory evaporative heat loss (diaphragm, 45 %, lungs, 59 %) at 33 degrees C compared to 23 degrees C, which can be viewed as an effective mechanism for increasing heat loss at high temperature. In addition, the concomitant decrease in blood flow (49 %) and slight reduction of oxidative capacities in both muscles at 33 degrees C might contribute to the reduction in thermogenesis, but these effects were also observed when the feeding level was reduced at thermal neutrality (23PF group). In the viscera (intestine, liver), blood flow was decreased in the two groups on a restricted food intake (about 50 % of 23AL), independently of environmental temperature. The results suggest that most of the mechanisms associated with the reduction in energy expenditure during warm acclimation are related to the adaptive reduction in food intake. Experimental Physiology (2001) 86.1, 83-91.

Acclimatization↗
PubMed2001

Continuous versus intermittent infusion of vancomycin in severe Staphylococcal infections: prospective multicenter randomized study.

A continuous infusion of vancomycin (CIV) may provide an alternative mode of infusion in severe hospital-acquired methicillin-resistant staphylococcal (MRS) infections. A multicenter, prospective, randomized study was designed to compare CIV (targeted plateau drug serum concentrations of 20 to 25 mg/liter) and intermittent infusions of vancomycin (IIV; targeted trough drug serum concentrations of 10 to 15 mg/liter) in 119 critically ill patients with MRS infections (bacteremic infections, 35%; pneumonia, 45%). Microbiological and clinical outcomes, safety, pharmacokinetics, ease of treatment adjustment, and cost were compared. Microbiological and clinical outcomes and safety were similar. CIV patients reached the targeted concentrations faster (36 +/- 31 versus 51 +/- 39 h, P = 0.029) and fewer samples were required for treatment monitoring than with IIV patients (7.7 +/- 2.2 versus 11.8 +/- 3.9 per treatment, P < 0.0001). The variability between patients in both the area under the serum concentration-time curve (AUC(24h)) and the daily dose given over 10 days of treatment was lower with CIV than with IIV (variances, 14,621 versus 53,975 mg(2)/liter(2)/h(2) [P = 0.026] and 414 versus 818 g(2) [P = 0.057], respectively). The 10-day treatment cost per patient was $454 +/- 137 in the IIV group and was 23% lower in the CIV group ($321 +/- 81: P < 0.0001). In summary, for comparable efficacy and tolerance, CIV may be a cost-effective alternative to IIV.

Adult↗
PubMed2001

Telomere length as an indicator of biological aging: the gender effect and relation with pulse pressure and pulse wave velocity.

Chronological age is the primary determinant of stiffness of central arteries. Increased stiffness is an independent indicator of cardiovascular risk. The aim of this study was to determine whether telomere length, a possible index of biological aging, provides a better account than chronological age for variation in arterial stiffness, evaluated by measuring pulse pressure and aortic pulse wave velocity. The study population included 193 French subjects (120 men, 73 women), with a mean age of 56+/-11 years, who were not on any antihypertensive medications. Telomere length was evaluated in white blood cells by measuring the mean length of the terminal restriction fragments. Age-adjusted telomere length was longer in women than in men (8.67+/-0.09 versus 8.37+/-0.07 kb; P=0.016). In both genders, telomere length was inversely correlated with age (P<0.01). Multivariate analysis showed that in men, but not in women, telomere length significantly contributed to pulse pressure and pulse wave velocity variations. In conclusion, telomere length provides an additional account to chronological age of variations in both pulse pressure and pulse wave velocity among men, such that men with shorter telomere length are more likely to exhibit high pulse pressure and pulse wave velocity, which are indices of large artery stiffness. The longer telomere length in women suggests that for a given chronological age, biological aging of men is more advanced than that of women.

Age Factors↗
PubMed2001

Cardiovascular mortality in hypertensive men according to presence of associated risk factors.

To evaluate the risk of cardiovascular disease (CVD) mortality in hypertensive men according to the presence of associated risk factors (ARFs). The population was composed of 29 640 normotensive men without ARFs (reference group) and 60 343 hypertensive men (with and without ARFs) who had a standard health checkup at the Centre d'Investigations Préventives et Cliniques between 1978 and 1988. Mortality data for a mean period of 14 years were analyzed. The following ARFs were considered: total cholesterol >/=2.5 g/L, personal history of diabetes, smoking (current smokers), body mass index >28 kg/m(2), and heart rate >80 bpm. CVD risk related to the presence of isolated hypertension (assessed in hypertensive subjects without ARFs versus the reference group) increased linearly from 15% at the age of 30 years to 134% at the age of 80 years. In hypertensive subjects, one additional ARF increased CVD risk by 56% (47% to 65%, P<0.01) in younger subjects but only by 4% (-8% to 17%, P=NS) in older subjects. The role of hypercholesterolemia and tobacco smoking in CVD mortality was significantly higher in hypertensive subjects aged <55 years than in hypertensive subjects aged >/=55 years (P<0.01), whereas the roles of tachycardia and obesity were not affected by age. In younger hypertensive subjects, evaluation of CVD risk and therapeutic strategies should target ARFS: In older subjects, the presence of high blood pressure levels seems to be the major determinant of CVD risk.

Adult↗
PubMed2001

Mechanical forces imposed on echinoid eggs during spawning: mitigation of forces by fibrous networks within egg extracellular layers.

Many echinoderms spawn large numbers of eggs in rapid spawning bouts directly into the water column. During spawning, the eggs pass from the gonad along a narrow oviduct and through a rigid gonopore before reaching the water. As the eggs traverse this pathway, they are exposed to shear stress induced by the development of a velocity gradient within the fluid formed by the eggs. In some species, the diameter of the eggs is larger than the diameter of the gonopore. In these cases, the eggs also experience strain resulting from compression of the egg as it passes through the relatively small gonopore. The magnitude of shear stress experienced by eggs differs among species depending upon the viscosity of the eggs. The degree of strain experienced by eggs differs among species depending upon the relative sizes of the egg and gonopore and also changes within species as they grow. Recent evidence suggests that these forces have the propensity to damage eggs, thereby reducing their fertilizability, or to destroy them. Experimental evidence shows that the jelly coat around the eggs can protect them from shear stresses and reduce the strain imposed on them under a compressive force. Echinoderm eggs are surrounded by a jelly coat that has a composite structure of irregularly arranged fibrous networks embedded in a jelly matrix. These fibrous networks have characteristics that are similar to those of engineered and biological materials that are known to reduce the transmission of mechanical forces to other structures. Given this similarity to other materials, three possible mechanisms for the action of the jelly coat may be identified. First, the apparent viscosity of the eggs of echinoids declines as the rate at which they are sheared during spawning increases. This reduction in viscosity with increasing shear rate (shear-thinning) may, in part, be due to the structure of the jelly coat and its resultant non-Newtonian nature. Second, experimental evidence indicates that the jelly coat preferentially deforms under a compressive load, reducing the transmission of that load to the egg. Third, the jelly (but not the fibers in the coating) may deform in a nearly viscous manner. In this case, the fibers may serve to provide an elastic 'backbone' to the layer and remain in place to stiffen the outer layer of the egg. The composite structure of the jelly coat and the morphology of the fibrous network are likely to be critical to all these mechanisms.

Animals↗
PubMed2001

International variability of ages at menarche and menopause: patterns and main determinants.

The purpose of this study was to review published studies on the variability of age at menarche and age at menopause throughout the world, and to identify the main causes for age variation in the timing of these events. We first present a summary table including mean (or median) values of the age at menarche in 67 countries, and of the age at menopause in 26 countries. General linear models showed that mean age at menarche was strongly linked to the mean female life expectancy, suggesting that one or several variables responsible for inequalities in longevity similarly influenced the onset of menarche. A closer examination of the data revealed that among several variables reflecting living conditions, the factors best explaining the variation in age at menarche were adult illiteracy rate and vegetable calorie consumption. Because adult illiteracy rate has some correlation with the age at which children are involved in physical activities that can be detrimental in terms of energy expenditure, our results suggest that age at menarche reflects more a trend in energy balance than merely nutritional status. In addition, we found the main determinant of age at menopause to be the mean fertility. This study thus suggests that, on a large scale, age at menarche is mainly determined by extrinsic factors such as living conditions, while age at menopause seems to be mainly influenced by intrinsic factors such as the reproductive history of individuals. Finally, these findings suggest that human patterns cannot be addressed solely by traditional, small-scale investigations on single populations. Rather, complementary research on a larger scale, such as this study, may be more appropriate in defining some interesting applications to the practical problems of human ecology.

Adolescent↗
PubMed2001

Trying to predict and explain the presence of African trypanosomes in tsetse flies.

Trypanosome infections identified by polymerase chain reaction on field-caught tsetse flies from various locations were analyzed with respect to factors intrinsic and extrinsic to the trypanosome-tsetse association. These factors were then simultaneously analyzed using artificial neural networks (ANNs) and the important factors were identified to predict and explain the presence of trypanosomes in tsetse. Among 4 trypanosome subgroups (Trypanosoma brucei s.l., T. congolense of the 'savannah' and of the 'riverine-forest' types, and T. simiae), the presence of the 2 types of T. congolense was predictable in more than 80% of cases, suggesting that the model incorporated some of the key variables. These 2 types of T. congolense were significantly associated in tsetse. Among all the examined factors, it was the presence of T. congolense savannah type that best explained the presence of T. congolense riverine forest type. One possible biological mechanism would be 'hitchhiking,' as previously suspected for other parasites. The model could be improved by adding other important variables to the trypanosome tsetse associations.

Africa, Western↗
PubMed2001

Interaction between Gammarinema gammari (Nematoda), Microphallus papillorobustus (Trematoda) and their common host Gammarus insensibilis (Amphipoda).

The influence of the nematode Gammarinema gammari on survival, mating success, and fecundity of its host Gammarus insensibilis (Amphipoda) was investigated. The prevalence and the mean intensity of G. gammari were significantly higher in males than in females. There was a positive and significant relationship between the mean number of G. gammari and male body size, suggesting that accumulation of this parasite had no significant effect on the survival of its host. Males that harbored the metacercariae of the trematode Microphallus papillorobustus had a lower number of nematodes than those that did not harbor the trematode. Fecundity was significantly reduced in infected females, and unpaired females tended to be more frequently infected by G. gammari than paired ones. However, we found no evidence for parasite-mediated reduction in male competitiveness because the mean number of G. gammari was not significantly different between paired and unpaired males.

Animals↗
PubMed2001

[Genetics of prostate cancer].

Genetic epidemiology studies have suggested the responsibility of genetic factors in prostate cancer susceptibility. The development of genomic and high throughput genetic studies has allowed the recent identification or localization of such susceptibility genes. Furthermore, these technologies have contributed to outstanding advances in somatic genetics of prostate cancer. The goal of the present review is to disclose contributing technologies to and results of genetic studies of prostate cancer.

Chromosome Aberrations↗
PubMed2000

Human fertility variation, size-related obstetrical performance and the evolution of sexual stature dimorphism.

In several animal species, change in sexual size dimorphism is a correlated response to selection on fecundity. In humans, different hypotheses have been proposed to explain the variation of sexual dimorphism in stature, but no consensus has yet emerged. In this paper, we evaluate from a theoretical and an empirical point of view the hypothesis that the extent of sexual dimorphism in human populations results from the interaction between fertility and size-related obstetric complications. We first developed an optimal evolutionary model based on extensive simulations and then we performed a comparative analysis for a total set of 38 countries worldwide. Our optimization modelling shows that size-related mortality factors do indeed have the potential to affect the extent of sexual stature dimorphism. Comparative analysis using generalized linear modelling supports the idea that maternal death caused by deliveries and complications of pregnancy (a variable known to be size related) could be a key determinant explaining variation in sexual stature dimorphism across populations. We discuss our results in relation to other hypotheses on the evolution of sexual stature dimorphism in humans.

Biological Evolution↗
PubMed2000

Somatosensory evoked fast optical intensity changes detected non-invasively in the adult human head.

This work is the first to report optical intensity changes (DeltaI/I approximately 0.05%) with a latency between 60 and 160ms after electrical median nerve stimulation at 5Hz detected non-invasively through the intact adult human skull in volunteers. The signal is localised and reproducible when measuring at the same position on successive examinations. Compared to previous reports of fast optical changes in the human adult by a single group (Psychophysiology, 32 (1995) 505) the here reported changes are much smaller. They are in line with results from a photon transport calculation on a head model employing data from exposed cortical tissue. The origin of the signal found here is still unclear, however, they might be the non-invasive equivalent to the scattering changes found in exposed cortical tissue studies (J. Neurophysiol., 78 (1997) 1707).

Adult↗