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Biomedical subjects

C Simon

Publications and source records attributed to C Simon.

At least 235 records · Page 13Linked to original sources
PubMed1988

Sexual partner selectiveness effects on homosexual HIV transmission dynamics.

Deterministic simulation models are used to show that HIV transmission dynamics in homosexual populations can be strongly affected by sexual partner selectiveness. The type of selectiveness or biased mixing examined is where individuals with similar new partnership formation rates are more likely to form a pair than would be expected by chance. The effect of such selectiveness could be strong even when the total number and distribution of new sexual partnerships and sex acts remains constant. This means that in order to predict the future course of HIV transmission and identify the populations at highest risk, we must have information not only on the frequency of new sexual partnerships and types of sex acts, but also on who has sex with whom. Given high sexual partner selectiveness, some groups of homosexuals with low rates of sex and new sex partners would take many decades before a single introduction would generate an epidemic. Epidemics in these groups can be markedly accelerated by only modest contact with higher risk groups. Even in very low activity groups, which if isolated would have no epidemic, an important proportion of their members can be infected when they are not selective. The relative risks of AIDS in groups making high numbers of new sexual partnerships compared to groups making low numbers are markedly affected by sexual partner selectiveness. The models developed were examined using information collected in 1984 from the Coping and Change Study in collaboration with the Chicago Multicenter AIDS Cohort Study. This population was divided into activity groups by the rate at which individuals established new sexual partnerships and then a structure of new sexual partnerships between these activity groups was defined consistent with available data. Even without introducing any behavior change in the models, the proportion of the homosexual population infected was seen to level off temporarily at around 50% after several years as a consequence of saturation in the high risk groups when lower risk groups were not yet being consumed by the epidemic process. Most sex in the study population is casual or anonymous. The sample selection procedures were biased toward individuals who engage in such sex. There is, however, a large group of individuals that avoids the casual and anonymous sex scene. Simulated epidemics indicated that under a variety of conditions, the population that does not engage in casual and anonymous sex could experience an epidemic of HIV infection quite some time after the epidemic in the population that does has waned.(ABSTRACT TRUNCATED AT 400 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1987

Night-day differences in the ultradian rhythmicity of plasma renin activity.

During night-sleep, plasma renin activity displays periodic oscillations which are closely related to the alternation of REM-NREM sleep. To see whether this nocturnal rhythm persisted during the day-time, plasma renin activity was measured every 10 min for 24 hours in 4 human volunteers and in 4 others over a 10-h day-time period. To avoid the influence of repeated food intake which stimulates renin release, the subjects were on continuous enteral nutrition. Spectral analyses of the data revealed clear differences between the nocturnal and the diurnal PRA patterns. In subjects on enteral nutrition, sustained 100-min oscillations with strong spectral densities persisted during the night. They were closely related to REM-NREM cycles. During the day-time, however, the fluctuations were damped and less regular, and power spectra were split into 2 or 3 peaks without any predominant period. These results demonstrate that regular 100-min PRA oscillations could only be detected during night-sleep. The clear night-day differences suggest that the underlying oscillatory mechanisms may be weaker during day-time or may be counteracted by other physiological processes.

Activity Cycles↗
PubMed1987

Postprandial oscillations of plasma glucose, insulin and C-peptide in man.

Postprandial plasma glucose, insulin and C-peptide profiles were studied in eight normal subjects, in the afternoon or in the evening. Two to five synchronous oscillations, with a mean period of 51 to 112 min were detected. The oscillations were highest after meals and were then damped, reverting to fasting levels after up to 340 min. Additional short-term oscillations, with periods of 20-30 min and 9-14 min, were observed. Cross-correlation studies of glucose and insulin and of insulin and C-peptide revealed a high correlation in the frequency bands considered. The synchronous oscillations of insulin and C-peptide suggest cyclic variations in pancreatic secretion rather than cyclic changes in insulin degradation.

Adult↗
PubMed1987

Bacterial and fungal infections after cardiac surgery in children.

Of 245 children operated on for congenital heart diseases in 1983-1984, bacterial and fungal infections occurred in 3.6% compared to 17.8% of 469 in 1968-1972. Staphylococcal infections decreased from 3.4%-0.8% and those by gram-negative bacteria from 6.9%-0%; Candida albicans infections increased from 0%-1.2%. Perioperative prophylaxis was performed with cefotaxime plus piperacillin in 1983-1984 versus oxacillin plus ampicillin in 1968-1972. It is argued that reduction of the infection rate is not only due to newer and more effective antibiotics but is mainly related to more advanced surgical techniques and improved hygiene in our intensive care units.

Adolescent↗
PubMed1987

Ultradian plasma corticotropin and cortisol rhythms: time-series analyses.

24-h plasma patterns of ACTH and cortisol were established in 6 subjects who had standard meals and in 4 subjects under continuous enteral nutrition. Temporal relationships between both hormones were analyzed. The individual assay data were subjected to time-series analyses to identify the periods of the oscillations in the plasma levels. The spontaneously occurring cortisol peaks were preceded by increases in ACTH levels, but z-score transformations clearly revealed that ACTH and cortisol were not quantitatively linked throughout the day. Individual subjects' power spectra gave evidence of a predominant periodicity in the oscillations of both hormones. These periodicities varied between individuals. They were 55-140 min for ACTH and 95-180 min for cortisol, indicating that, on occasion, a single cortisol peak may be initiated by two ACTH peaks. Cross spectral analysis of the individual data gave coherence spectra with a large peak which accounted for a substantial concordance of their period length, and cross variance spectra showed a consistent phase relationship between both hormones. These time series analyses applied to the data further support the concept that ACTH is the stimulating factor of cortisol release under basic conditions.

Activity Cycles↗
PubMed1987

Ultradian oscillations of plasma glucose, insulin, and C-peptide in man during continuous enteral nutrition.

The profiles of plasma glucose, insulin, and C-peptide were studied in normal men receiving continuous enteral nutrition. Large oscillations occurred with periods of 53-113 min. Their mean amplitudes, expressed as a percentage of the 24-h mean, were as high as 20% for glucose, 54% for insulin, and 56% for C-peptide. The oscillations of plasma insulin levels throughout the 24 h were concomitant with those of C-peptide. Rapid 8- to 14-min plasma insulin and glucose oscillations were smaller in magnitude and could only be detected in some segments of the longer period oscillations. These results indicate that in addition to the previously described 8- to 14-min oscillations, plasma glucose, insulin, and C-peptide oscillate at a mean 80-min periodicity in man during continuous enteral nutrition. These oscillations may reflect a pancreatic oscillatory mechanism and/or cyclic variations in gastrointestinal motility or peripheral glucose uptake.

Activity Cycles↗
PubMed1987

[Study of salivary cortisol using radioimmunological assay. Diagnostic value].

Salivary cortisol levels reflect the biologically active "free" fraction of blood cortisol. The authors describe the results obtained with the aim of a radio-immunoassay commercial serum cortisol kit, without prealable extraction in different physiological and pathological situations. Salivary cortisol determination appears performant both in nycthemeral studies and in stimulation or freination tests.

Adult↗
PubMed1987

[New tympanomastoid repair in open technics: Galea's flap].

After an anatomical review, the authors describe the method for obtaining the temporo-parietal facial flap and its particularities in the rehabilitation of the canal down technic. The main indications of this flap are: the rehabilitation of unstable cavities, a Palva's flap alternation, a solution to the filling up after petrectomy or enlarged canal down technic.

Ear, Middle↗
PubMed1987

CT diagnosis of hepatic adenoma.

Only few publication have so far been known on case histories in the context of CT-findings of hepatic adenoma (HA). An analysis was, therefore, made of the findings of ten patients with HA. Precontrast and postcontrast scans (dynamic CT), densitometric evaluations (gamma-fit) and "profile" determination were taken into consideration. Diagnostic relevance is attributed to two types of features (with and without tumour haemorrhage) as well as to complementary findings (capsule-like structure and fat-ring around the tumour, island-like areas).

Absorptiometry, Photon↗
PubMed1986

[Evaluation of malnutrition and immunity in alcoholic liver diseases].

Disorders of immunity and nutritional status are known to be present in alcohol-induced diseases of the liver, but their significance is still debated. Nutrition and immunity were evaluated at different stages of the disease in 58 alcoholic patients with steatosis (n = 20), alcoholic hepatitis (n = 14) or cirrhosis (n = 24). Most of the anthropometric data and biochemical values relating to nutrition were altered to the same degree in these 3 groups. Only patients with cirrhosis had significantly lower blood albumin and zinc levels (P less than 0.01). Humoral immunity was altered in cirrhosis only and cellular immunity in all 3 liver diseases. There was no correlation between immunity and nutrition (except for blood zinc and E rosettes; P less than 0.01) or between these and alcohol consumption. Like several nutritional parameters, blood lymphocyte values correlated negatively with a liver disease severity index. It is concluded that disorders of nutrition and immunity are broadly comparable in alcohol-induced liver diseases; there is no direct statistical correlation between these disorders which seem to be independent of the type of liver disease.

Adult↗