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Biomedical subjects

S Schuster

Publications and source records attributed to S Schuster.

At least 19 recordsLinked to original sources
PubMed1992

The definitions of metabolic control analysis revisited.

Various definitions of coefficients in metabolic control analysis are examined with respect to their theoretical consistency and practical applicability. We suggest agreement upon a definition for control coefficients which is clearly distinct from that for response coefficients, in such a way that the former describe inherent properties of the metabolic system while the latter refer to the influence of special parameters. Advantages and drawbacks of using normalized or non-normalized control coefficients are studied. It is shown that normalized control coefficients have the advantage of being invariant to a different rescaling of the particular fluxes. We demonstrate that some problems are easier to tackle if the consistency of time-independent control coefficients with their time-dependent counterparts is taken into account. It is shown that the matrix of flux control coefficients is an indempotent matrix. This allows an interpretation in terms of the transduction of the effect of parameter perturbations. Several aspects of the experimental measurement of control coefficients are discussed, with special reference to the different definitions.

Enzymes↗
PubMed1991

[Computer-assisted analysis of wall motion of the right ventricle in a normal patient sample and diagnosis of right heart infarction using transesophageal echocardiography].

Using 2D and M-Mode transesophageal short axis cross sections, right ventricular systolic wall motion was quantified in 15 normal patients. A further group of 39 patients with right ventricular infarction was investigated. In the normal group fractional shortening of the septum was -19.6% (-45 to 8%), that of the lateral wall 51.6% (37 to 73%), of the posterior wall 33.9% (5 to 50%) and of the anterior wall 42.7% (18 to 57%). Right ventricular infarction (RVI) was associated in 33 patients with posterior left ventricular infarction (85%) and in three patients with anterior infarction. In two cases only an isolated RVI was found. Right ventricular dilation occurred in 24 patients (61%). Hemodynamic criteria were fulfilled in eleven out of 21 patients (53%). RVI was confirmed in one patient by surgery and in ten patients by autopsy. Recognition of regional wall motion abnormalities by transesophageal echocardiography permits an accurate bedside identification of RVI. 2D and M-Mode registration of the short axis improves RVI assessment. Wall motion analyses offer the possibility to determine the extent of right ventricular infarction.

Adult↗
PubMed1991

Minimization of intermediate concentrations as a suggested optimality principle for biochemical networks. II. Time hierarchy, enzymatic rate laws, and erythrocyte metabolism.

The multiobjective problem of minimizing all intermediate concentrations is solved for a model of glycolysis, the pentose monophosphate shunt and the glutathione system in human erythrocytes. It turns out that one solution out of four obtained corresponds qualitatively to the real system. Furthermore, it is shown that for any reaction system, the mentioned optimality principle implies distinct time hierarchy in that some reactions are infinitely fast and subsist in quasi-equilibrium. Finally, the relationships to the standard method of deriving enzymatic rate laws are discussed.

Energy Metabolism↗
PubMed1991

Lingual vibrotactile threshold shift differences between stutterers and normal speakers during magnitude-estimation scaling.

The purpose of this study was to investigate differences in tactile sensory system function between stutterers and normal speakers. This task was accomplished by studying possible tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Ten normal speaking men (M age = 19.7 yr.) and 10 stutterers (M age = 25.9 yr.) participated. Analysis suggested that stutterers and normal speakers differ in terms of the responsiveness of the sensory mechanism for the lingual tactile threshold to vibratory stimulus intensities applied at suprathreshold levels. The stutterers and normal speakers performed similarly on all aspects of the magnitude-estimation scaling tasks, but the amount of threshold shift occurring during the scaling procedures was significantly greater for the stutterers at each suprathreshold intensity level employed.

Adolescent↗
PubMed1990

[Thrombolysis in resuscitated patients with pulmonary embolism].

A retrospective analysis is presented of data from 17 patients with proven pulmonary embolism (10 women, 7 men, mean age 50.8 [18-76] years) who had received short-term high dosage thrombolytic therapy shortly before or after (less than 24 h) undergoing mechanical resuscitation. The mean duration of resuscitation was 76 (20-160) minutes. Two patients had already been resuscitated half an hour and one hour, respectively, before the commencement of thrombolysis. In nine other patients thrombolysis was commenced during resuscitation. Hospital mortality in the latter group was amazingly low (four of nine patients died). In contrast, out of six patients who required resuscitation shortly after the commencement of thrombolysis, not one survived. Haemorrhagic complications occurred in four out of the 17 patients, but only in two were they directly attributable to the resuscitation: one female patient developed an extensive haematoma in the sternal region, and two days after resuscitation another female patient had a haemorrhage into the capsule of the liver during thrombolytic therapy which had been continued because of leg vein thrombosis. In the light of these results it seems justifiable, even on mere clinical suspicion of pulmonary embolism, to initiate short-term high dosage thrombolytic therapy during or after resuscitation.

Adolescent↗
PubMed1990

Dynamic exercise echocardiography of the left ventricle in physically trained children compared to untrained healthy children.

To evaluate the effect of physical training on left ventricular function, we investigated 52 children, aged 7 to 14 years, who had trained for endurance sports over a period of at least 1 year. The children (24 boys and 28 girls) were investigated echocardiographically during supine exercise on a bicycle at increasing work loads of 6, 9, 12 and 15 kpm/min/kg body weight. The parameters of left ventricular function (specifically fractional shortening and the velocity of circumferential fiber shortening; both these parameters corrected for heart rate) were evaluated before, during and after the test. The values obtained were compared to those in untrained children investigated in a previous study. Fractional shortening in trained children rose from 37 +/- 5% to 54 +/- 5%, and in untrained children from 37 +/- 4% to 46 +/- 4%. The velocity of fiber shortening in trained children rose from 1.27 to 3.15 circ/sec while in untrained children it increased from 1.25 to 2.53 circ/sec. Left ventricular contraction, therefore was significantly greater in trained than in untrained children during exercise. While untrained children increased their cardiac output in the first minutes of exercise mainly by elevating their heart rate, trained children increased simultaneously the stroke volume. There were no significant differences between boys and girls, or between stages of maturity. Thus, physical training causes quick adaptations of left ventricular function to exercise in children of all ages.

Adolescent↗
PubMed1990

Two distinct mutations at the same site in the PCCB gene in propionic acidemia.

Propionic acidemia is an inborn error of metabolism resulting from a deficiency of propionyl-CoA carboxylase activity. The alpha- and beta-subunits of the enzyme are encoded by the PCCA and PCCB genes, respectively. Using direct sequencing and restriction digests of amplified reverse transcripts and genomic DNA, we have identified two mutations of the PCCB gene in a propionic acidemia patient from the pccC complementation subgroup (the PCCB gene contains the major complementation group pccBC and subgroups pccB and pccC). One of the proband alleles contains an inframe 3-bp deletion inherited from the father which results in the deletion of an isoleucine residue in the beta-subunit of the enzyme. The other mutant allele, inherited from the mother, has a 14-bp deletion and an addition of 12 bp of new sequence at the same site as the father's allele. The inserted sequence is a partial duplication of a sequence just upstream of the mutation site. The net result of this mutation generates a frameshift and a downstream stop codon. Examination of fibroblast mRNA from the patient showed that it consists essentially of the father's sequence, making it effectively the only expressed allele for the beta-protein. A survey of additional patient cell lines revealed the insertion/deletion rearrangement in three additional patients, two from the pccBC group and one unclassified. The 3-bp deletion allele was unique to the proband. The identification of two distinct alleles occurring at the same site in the PCCB gene underscores the importance of this site in enzyme function or integrity.

Alleles↗
PubMed1990

Hemodynamics during PEEP ventilation in patients with severe left ventricular failure studied by transesophageal echocardiography.

The effects of mechanical ventilation with PEEP were investigated in five patients with normal cardiopulmonary function (group A) and in 11 patients with severe left ventricular failure (group B). Cross-sectional area of the right and left atrium (RA/LA), left ventricle (LV), and right ventricle (RV) was determined at EDA/ESA using transesophageal echocardiography. Hemodynamic parameters and transesophageal pressure were measured simultaneously at PEEP levels 0, 4, 8, 12, and 16 cm H2O. End-diastolic area of the right atrium decreased significantly in both groups. The RA pressure increased, while transmural pressure remained unaltered. The CI decreased in both groups. The decrease in cardiac output by PEEP ventilation was related to the decrease in RV filling volume by external compression. In patients with congestive heart failure, PEEP ventilation with 8 to 10 cm H2O did not worsen LV function.

Adult↗
PubMed1989

Fears of children and adolescents: a cross-sectional Australian study using the Revised-Fear Survey Schedule for Children.

The Revised-Fear Survey Schedule for Children was administered to over 3000 Australian youths, aged 8-16 yrs. Consistent with previous findings, there was a significant age-related decline in fears. Females reported significantly more fears than males. The most common fears were similar to those reported by children and adolescents in the U.S.A. Nuclear war was added to the stimulus items and found to be the most commonly endorsed fear. Thus the self-reports of fear showed a concern for physical danger and harm.

Adolescent↗
PubMed1989

[24-hour blood pressure behavior in patients with untreated and treated hypertension in comparison with normotensive patients].

Blood pressure was continuously monitored over 24 h in 201 patients with mild to moderate essential hypertension using a noninvasive method. Measurements were made both before and after 6 months of antihypertensive treatment and the data were compared to results from 100 normotensive patients. The frequency with which blood pressure values above 140/90 mm Hg occurred during the 24-h period proved to be the most reliable parameter for distinguishing between hypertensive and normotensive profiles. The blood pressures of all patients could be normalized (less than 140/90 mm Hg) on single or combined drug therapy as assessed by casual measurement. However, significant differences were observed between the 24-h profiles of the treated patients and the control group. The mean 24-h blood pressure, the mean day and nighttime blood pressures, the mean hourly pressure, and the frequency of increased blood pressure values were all significantly higher in the patients on medication as compared to the normotensive controls. This would suggest that normotension, as defined by the control group, cannot be attained with antihypertensive medication. In conclusion, 24-h continuous blood pressure monitoring allows a better evaluation of blood pressure profiles and consequently, will be of greater value in assessing cardiovascular risk than occasional random measurements.

Adult↗
PubMed1987

Time hierarchy in enzymatic reaction chains resulting from optimality principles.

Several optimality principles reasonable for the evolution of enzyme reaction chains are formulated, considering the kinetic parameters of the enzymes to be variables. The solutions of these parametric programming problems are studied for the case of linear kinetics and turn out to be not unique in every case. The investigations are confined to stationary states. The net flux through the chain is considered a fixed parameter. The optimality criteria concern the osmotic pressure caused by the intermediates, various relaxation times, largest time scale, and controllability. They all yield distinct time hierarchies. The influence of a constraint concerning the sum of intermediate concentrations is studied. Various combinations of the single criteria are treated as multiobjective programming problems.

Biological Evolution↗