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Biomedical subjects

D Thomas

Publications and source records attributed to D Thomas.

At least 1,009 records · Page 56Linked to original sources
PubMed1976

Mitral valve replacement: a 10-year follow-up of non-cloth-covered vs. cloth-covered caged-ball prostheses.

The timing of operation and the selection of prosthesis depend upon the evaluation of long-term results at 5 years and beyond. From 1965 to 1975, 290 patients had isolated mitral valve replacement with currently used prostheses, resulting in a 6.6% operative mortality and 64% relative survival at 10 years. In considering mortality, the results obtained with both series of valves were combined and a search made for significant differences in preoperative variables between the operative deaths and operative survivors. The significant variables for operative mortality were valve model, preoperative functional class, pump time, and the presence or absence of right ventricular hypertrophy on electrocardiography. There were significant differences in long-term survival only with regard to preoperative functional class, pulmonary vascular resistance, and pump time. Exponential curves were fitted to the event-free rates, and long-term results were then extrapolated. The 10-year projection of the percentage of patients alive and free of embolus (disregarding transient ischemic attacks) for the Model 6310-6320 (50%) was similar to that actually observed for the Model 6120 (46%). Although further experience may show one prosthesis more effective than the other, statistical extrapolations suggest continued comparable performance.

Female↗
PubMed1975

Magnetic enzyme membranes as active elements of electrochemical sensors: specific amino acid enzyme elctrodes.

The basic principle of the described magnetic enzyme electrodes is a kinetic accumulation of CO2 at the active layer electrode interface. The local pCO2 level is linked to three simultaneous phenomena: substrate diffusion in, enzyme reaction CO2 diffusion out. After a transient state there is a stationary state between the quantity of CO2 produced by the enzyme reaction and the CO2 diffusing from the active membrane to the bulk solution. Continuous determination of free amino acids in biological media is useful in biological processing, fermentation, medicine, pharmaceutical industries and biological research. No methods are presently available for any specific continuous measurement of lysine which is of nutritional importance in protein industrial syntheses; of phenylalanine and tyrosine which have to be monitored in several inborn diseases (phenylketonuria being the most important of them); of arginine and histidine which play a still imperfectly understood part in neurochemistry. The use of decarboxylase bearing membranes as sensors in such measurements could offer several novel advantages: (a) a simple device made of a currently manufactured electrode slightly modified by the use of an enzyme membrane; (b) The absence of any enzymic consumption due to the immobilization and the negligible consumption of substrate during the measurements; (c) The sensitivity which can be sharpened by a systematic study of the membrane parameters; (d) the continuous response of the electrode as long as it is in contact with the substrate solution; (e) the further feasibility as a miniature sensor. The magnetic device introduced allows obviously a convenient use of the enzyme electrode, the active part can be removed and replaced without disturbance for the pCO2 electrode itself. The enzyme electrodes are not only useful at the applied point of view but also at the fundamental point of view by allowing a direct measurement of an intra membrane concentration. The influence of simple structures on enzyme kinetics was studied with enzyme electrodes by our group, in the case of memory and oscillations obtained with enzyme systems.

Amino Acids↗
PubMed1975

Magnetic enzyme membranes as active elements of electrochemical sensors. Lactose, saccharose, maltose bienzyme electrodes.

The direct monitoring of sugars such as lactose, maltose, saccharose is not only useful at the applied point of view but also at the fundamental point of view for studying enzymology, especially in microbiology and fermentation. Benzyme systems were extensively used in solution for analytical applications in industry and medicine. The progress in the field of immobilization of bienzyme systems [1-3], especially within membranes [4-5], makes possible the production of new analytical devices. From the studies dealing with concentration profiles in artificial enzyme membranes [14], evidence was obtained for a well defined relationship between the local concentration of a metabolite and concentration of the first substrate in the bulk solution. In the described systems a substrate is transformed into glucose within a membrane, the glucose is then transformed in gluconic acid with a local oxygen consumption. The local pO2 level is linked to the glucose oxidase velocity, which is only linked to the glucose production, that is to say to the concentration of the first substrate. The enzyme electrode is based on the transformation of kinetic phenomena (reaction rates) into absolute values (local concentrations) through the diffusion-reaction coupling process. The manufacture of magnetic enzyme electrodes [6] allows convenient use of the active sensors. The pO2 electrode has some adventages, namely the specificity based on the selectivity of the gas permeable membrane and the linear relationship between the oxygen and the output of the electrode. pCO2, pH, ion electrodes give a logarithmic response as a function of the concentration. The grafting of a multienzyme system on a sensor allows a study of sequential systems in a defined context with a measurement of the local concentration of the metabolites. The tool is useful for both kinetics [4] and regulation studies [5].

Disaccharides↗
PubMed1975

The kinetic behavior of an artificial bienzyme membrane.

Artificial membranes bearing immobilized enzymes can be used to study some effects of membrane structure on enzyme kinetic behavior. The bienzyme system described is a mixture of beta-glucosidase and glucose oxidase. Gluconolactone, the product of thesecond enzyme, is an inhibitor of the first one. The resulting feedback effect has been compared using a mixed two-enzyme membrane, two separated one-enzyme membranes, and astirred bienzyme solution. The feedback effect is quicker and more efficient in the two-enzyme membrane than in solution; it is slower and less efficient in the case of the separated one-enzyme membranes. Effects of enzyme proximity in the structure are discussed. Conclusions are drawn concerning the efficiency of feedback mechanisms when enzymes are embedded within a single structure.

Anaerobiosis↗
PubMed1975

Kinetic studies dealing with an immobilized bienzyme system.

The binding of enzymes into artificial membranes makes possible a study of the interaction between membrane structure and enzyme kinetics within a simple context. Artificial protein membranes bearing a bienzyme system (xanthine oxidase, uricase) are produced by using a co-crosslinking method. The inhibition of uricase was shown to be dependent not only on the concentration of inhibitor in the bulk solution, but also on the kinetic properties of the membrane-bound enzymes. In the presence of xanthine oxidase inside the structure the uricase inhibition by xanthine is less important than in solution. Under defined conditions the activity was found to be higher in the presence of inhibitor than in its absence. Due to diffusion limitations this specific bienzyme system is more efficient when immobilized inside a membrane than when in solution.

Binding, Competitive↗
PubMed1975

The effects of differential prenatal and postnatal social enviroments on sexual maturation of young prairie deermice (Peromyscus maniculatus bairdii).

We compared the influence of different social enviroments on sexual maturation of young prairie deermice. Between 12 and 48 hr after parturition, one-half of a litter from a population was exchanged with one-half of a litter from a bisexual pair. In each situation the remaining half-litter served as controls for the exchange procedure. The testes and vesicular weights of population-reared males were significantly larger than those of males reared by bisexual pairs, irrespective of prenatal enviroment. Generally, population-reared females also had larger reproductive organs than those reared by bisexual pairs, although these differences were not statistically significant. There were no significant differences in the adrenal weights of males or females, but females reared by bisexual pairs had larger absolute and relative adrenals than females reared in populations.

Adrenal Glands↗
PubMed1975

Studies on the stability of antilymphocyte globulins.

An account is given of the effect of storage under various conditions on the physical and immunosuppressive properties of antilymphocyte globulins. No loss of in vivo immunosuppressive potency was shown by horse antimouse lymphocyte globulin when stored for up to 2 years in a liquid, frozen, or lyophilised state. Similar studies on horse antihuman lymphocyte globulin showed no loss of in vitro activity, as measured by an immunofluorescence test. Ultracentrifugal analyses showed no increase in aggregate when antilymphocyte globulin was stored liquid or freeze-dried at 4 degrees C. Storage experiments at abnormally high temperatures demonstrated that under these conditions freeze-dried horse antihuman lymphocyte globulin was stabilised by the presence of glucose (4.6%w/v). Antilymphocyte globulin lyophilised in the presence of glucose showed improved solubility properties as compared with material dried from saline.

Animals↗
PubMed1975

[Partial 11q monosomy and trigonocephaly. A new syndrome].

Partial monosomy 11q occurring de novo and concerning the 11q231 leads to qter region, is reported in a 2-month-old boy. This observation together with three others from the literature allows the individualization of a syndrome characterized by: severe growth retardation: more or less pronounced mental retardation; trigonocephaly; facial dysmorphia.

Chromosome Deletion↗
PubMed1975

Radiological changes over 20 years in relation to chrysotile exposure in Quebec.

Radiological changes in 267 male Quebec chrysotile mine and mill workers, each with five chest films spanning an average of 20 years, were related to age, smoking habit, mining area, duration of employment and average dust concentration before and between films. (1) Abnormality in the earliest film was related mainly to the time since first employment. (2) In 45 (30%) of the 150 men completely normal at earliest film, some radiological abnormality developed during the period of observation: incidence was weakly related to age; in Asbestos, the risk of developing small opacities was lower in smokers than in non-smokers. (3) There was an irregular pattern of correlation, more evident in Thetford Mines than in Asbestos, between radiological progression and various stimulus variables. That associations between radiological responses and measures of asbestos exposure were, as always, weak, despite powerful methodology, indicates that effects are obscured by other factors (including susceptibility) uncorrelated with exposure.

Adult↗