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Biomedical subjects

J Schaefer

Publications and source records attributed to J Schaefer.

At least 73 records · Page 4Linked to original sources
PubMed1991

Turbinate hypertrophy in habitual snorers and patients with obstructive sleep apnea: findings of acoustic rhinometry.

Forty-five habitual snorers (mean respiratory disturbance index = 6) and 22 patients with obstructive sleep apnea syndrome (mean respiratory disturbance index = 36) were examined by polysomnography, radiocephalometry, rhinomanometry, nasopharyngeal videoendoscopy, and acoustic rhinometry. In 97% of these patients, hypertrophy of the inferior nasal turbinates was found by acoustic rhinometry, while increased nasal resistance of various degrees was measured in 93% of all patients by active anterior rhinomanometry. Acoustic rhinometry demonstrated that the most resistive segment was located in the anterior parts of the nasal cavity and was built up by two compartments: the region of the isthmus nasi and the region of the head of the inferior turbinate. In our snoring patients, the cross-sectional areas at the head of the inferior turbinate were always smaller than the cross-sectional areas in the isthmus nasi, which in normal controls presented the minimal cross-sectional values of the whole nasal cavity. While rhino-manometry can only measure the amount of nasal resistance, acoustic rhinometry can clearly determine the exact size and location of the different stenoses in the nasal cavity that contribute to the increased nasal resistance.

Acoustics↗
PubMed1991

Functional evaluation following microvascular oromandibular reconstruction of the oral cancer patient: a comparative study of reconstructed and nonreconstructed patients.

Over the past decade, the use of free flap transfers in head and neck surgery has led to remarkable advances in the reliability and the ultimate results of oromandibular reconstruction. Stable and retentive dental restorations have been achieved using enosseous implants placed directly into the vascularized bone flaps. However, the functional assessment of patients who underwent primary mandibular reconstruction with these techniques has not been previously reported. A group of 10 reconstructed and 10 nonreconstructed segmental hemimandibulectomy patients were compared using a battery of tests to assess their overall well-being, cosmesis, deglutition, oral competence, speech, length of hospitalization, and dental rehabilitation. In addition, objective measures of the masticatory apparatus (interincisal opening, bite force, chewing performance, and chewing stroke) were used to compare these two groups as well as normal healthy subjects and edentulous patients restored with conventional and implant-borne dentures. The results show a clear advantage for the reconstructed patients in almost all categories. Persistent problems and future directions in oromandibular reconstruction are discussed.

Adult↗
PubMed1990

Neurophysiological abnormalities in adolescents with type I Crigler-Najjar syndrome.

We report neurophysiological abnormalities in two adolescents with type I Crigler-Najjar syndrome, an autosomal recessive disorder characterized by severe unconjugated hyperbilirubinemia. Electroencephalograms (EEGs) demonstrated frequent generalized single and polyspikes, and background slowing. Normal pattern reversal evoked responses (PRVERs) and normal central brain-stem auditory evoked responses (BAERs) were recorded in both patients. These findings differ from the EEG triphasic wave pattern seen in the EEG in hepatic encephalopathy and the central BAER abnormalities seen in many infants with kernicterus. Thus these findings most likely result from complex multifactorial processes and are not simply the result of the hyperbilirubinemia which is common to all 3 conditions.

Acoustic Stimulation↗
PubMed1990

Clinical significance of biliary sludge.

Although biliary sludge has been considered to be a benign condition associated with factors promoting bile stasis, its clinical significance and whether it contributes to biliary tract symptoms are uncertain. We conducted a retrospective review of patients with ultrasonographic diagnosis of biliary tract sludge during the 6-year period from 1979 to 1985. Of the 87 patients with gallbladder sludge alone, 11 (13%) had definite clinical findings and evolving laboratory abnormalities consistent with acute biliary tract disease. Four of these 11 patients proved to have gallstones at the time of surgery, while three had sludge alone as the apparent cause of their biliary tract symptoms. The clinical illness in four remaining patients resolved with medical therapy. We conclude that gallbladder sludge, as defined by ultrasound, may be associated with acute biliary tract disease.

Acute Disease↗
PubMed1990

Hemodynamic dependence of myocardial oxygen consumption indexes.

We tested the afterload and contractile state dependency of three indexes of myocardial oxygen consumption (MVO2): total energy requirement (Et), pressure work index (PWI), and pressure-volume area (PVA). MVO2 was measured in seven isolated canine hearts at four or five different end-diastolic volumes at each of three settings of afterload resistance and with the hearts contracting isovolumically. In several hearts, contractility was also varied by dobutamine infusion. Measured MVO2 (MMVO2) was compared with values predicted (PMVO2) by each index. There was always a high degree of correlation between MMVO2 and PMVO2 for each of the indexes. However, there was a large degree of variability in the coefficients of the MMVO2-PMVO2 relation from one heart to another. We also observed a statistically significant influence of both afterload and contractile state on the predictive power of each of the indexes. Thus each index that we tested had shortcomings in being able to predict MVO2 accurately over a wide range of hemodynamic conditions.

Animals↗
PubMed1989

Protein dynamics from chemical shift and dipolar rotational spin-echo 15N NMR.

The partial collapse of dipolar and chemical shift tensors for peptide NH and for the amide NH at cross-link sites in cell wall peptidoglycan, of intact lyophilized cells of Aerococcus viridans, indicates NH vector root-mean-square fluctuations of 23 degrees. This result is consistent with the local mobility calculated in typical picosecond regime computer simulations of protein dynamics in the solid state. The experimental root-mean-square angular fluctuations for both types of NH vectors increase to 37 degrees for viable wet cells at 10 degrees C. The similarity in mobilities for both general protein and cell wall peptidoglycan suggests that one additional motion in wet cells involves cooperative fluctuations of segments of cell walls, attached proteins, and associated cytoplasmic proteins.

Bacterial Proteins↗
PubMed1988

Solid-state NMR observation of cysteine and lysine Michael adducts of inactivated estradiol dehydrogenase.

The inactivation of estradiol dehydrogenase by enzyme-generated 3-hydroxy-14,15-secoestra-1,3,5(10)-trien-15-yn-17-one is accompanied by the formation of a lysine enaminone. The experiments leading to this conclusion involved degradation of the inactivated enzyme with Pronase and subsequent analysis by solution-state 13C NMR. The present paper reports solid-state 13C NMR experiments on lyophilized intact inactivated enzyme which are free from problems due to Pronase digestion. These experiments combine conventional cross-polarization and magic-angle spinning with selective irradiation of resonances arising from a 13C double label in the steroid. Magnetization transfer between neighboring 13C nuclei is used to simplify the spectra and to identify peaks due to label. The formation of cysteine and lysine Michael adducts of the enzyme is established by comparisons with chemical shifts of solid model adducts.

17-Hydroxysteroid Dehydrogenases↗
PubMed1988

In vitro studies of isolated supported human hearts.

We developed methods to revive human hearts, obtained at the time of cardiac transplantation, and study them in the physiology laboratory. The hearts were arrested with cardioplegic solution at the time of explanation and transported to the laboratory at 4 degrees C. The hearts were perfused with a human blood based solution whose flow rate, temperature, and ionic concentration were controlled. Six hearts with various endstage cardiomyopathies were revived in this manner. Once perfusion was started, the hearts maintained a steady contractile state for approximately 30 min during which time data could be collected. Within this time period we could measure end-systolic and end-diastolic pressure-volume relations, the time courses of contraction and relaxation, and the influence of heart rate and premature stimulation on contractile state. The results suggest that evidence of specific cellular abnormalities in human heart disease might be obtained from measurements of global ventricular performance. Furthermore, the type of abnormality identified, namely sarcoplasmic reticulum dysfunction, in several forms of cardiomyopathy was in concordance with results obtained in muscle bath studies of similarly diseased human and animal myocardium.

Cardiomyopathy, Dilated↗
PubMed1988

Metabolism of glyphosate in Pseudomonas sp. strain LBr.

Metabolism of glyphosate (N-phosphonomethylglycine) by Pseudomonas sp. strain LBr, a bacterium isolated from a glyphosate process waste stream, was examined by a combination of solid-state 13C nuclear magnetic resonance experiments and analysis of the phosphonate composition of the growth medium. Pseudomonas sp. strain LBr was capable of eliminating 20 mM glyphosate from the growth medium, an amount approximately 20-fold greater than that reported for any other microorganism to date. The bacterium degraded high levels of glyphosate, primarily by converting it to aminomethylphosphonate, followed by release into the growth medium. Only a small amount of aminomethylphosphonate (about 0.5 to 0.7 mM), which is needed to supply phosphorus for growth, could be metabolized by the microorganism. Solid-state 13C nuclear magnetic resonance analysis of strain LBr grown on 1 mM [2-13C,15N]glyphosate showed that about 5% of the glyphosate was degraded by a separate pathway involving breakdown of glyphosate to glycine, a pathway first observed in Pseudomonas sp. strain PG2982. Thus, Pseudomonas sp. strain LBr appears to possess two distinct routes for glyphosate detoxification.

Biodegradation, Environmental↗
PubMed1988

Cycle length dependence of human action potential duration in vivo. Effects of single extrastimuli, sudden sustained rate acceleration and deceleration, and different steady-state frequencies.

Using a new method for long-term recording of monophasic action potentials from the human heart, we studied in 17 patients the effects on ventricular action potential duration (APD) of three clinically pertinent cycle length perturbations: (1) single extrastimuli, (2) abrupt sustained rate acceleration and deceleration, and (3) different steady-state cycle lengths. Results were: (a) APD after single extrastimuli at progressively longer cycle lengths were related to the extrastimulus cycle length with a biphasic electrical restitution curve which after an initial steep rise and a subsequent transient descent rose again more gradually to a plateau at cycle lengths above 800-1,000 ms. (b) After a sustained step decrease in cycle length, the first APD shortened abruptly while final steady-state adaptation required up to several minutes. The transition between the rapid and slow phase of APD change was characterized by a variable alternans of APD which correlated inversely with the preceding diastolic interval. (c) In the steady state, APD correlated linearly with cycle length, increasing an average of 23 ms per 100 ms cycle length increase (r = 0.995). The divergence between steady-state and non-steady-state APD, and the slowness of steady-state adaptation, are important factors to be considered in clinical electrophysiologic studies and in rate correction algorithms of APD or QT intervals, respectively.

Action Potentials↗
PubMed1988

Effect of nisoldipine on coronary resistance, contractility and oxygen consumption of the isolated blood-perfused canine left ventricle.

Nisoldipine reportedly has little direct myocardial effect. However, because of interactions between the heart and vascular load, the effects on myocardial contractility and left ventricular oxygen consumption (LVO2) have not been established. The authors performed experiments on six isolated, blood-perfused canine left ventricles that were isovolumically contracting and paced at constant rate. Coronary arterial pressure (CAP) and coronary blood flow were measured for evaluation of coronary vascular resistance, and coronary arteriovenous oxygen difference was measured for determination of LVO2. Intracoronary injection of 1 and 10 micrograms of nisoldipine decreased coronary vascular resistance by 16.9 and 36.8% (CAP approximately 40 mm Hg), respectively, and by 21.5 and 47.7% (CAP approximately 80 mm Hg). At both doses, nisoldipine caused no decrease in peak systolic pressure as long as CAP was kept constant at 80 mm Hg. However, when CAP was decreased to 40 mm Hg, peak systolic pressure was significantly decreased even without nisoldipine. This impaired contractile state was associated with a decreased coronary blood flow and a slight decrease in LVO2, whereas 10 micrograms of nisoldipine at CAP approximately 80 mm Hg increased LVO2 significantly. Using the end-systolic pressure-volume relationship as an index of contractility, the authors found nisoldipine not to change the contractile state at CAP approximately 80 mm Hg. They conclude that nisoldipine decreases coronary vascular resistance over a wide range of CAP. It neither depresses the contractile state nor decreases LVO2 in the canine left ventricle. Nisoldipine might effectively counteract anginal attacks by dilating the coronary vessels without depressing myocardial contractility as found in this study on normal ventricle.

Animals↗
PubMed1987

Metabolism of glyphosate in an Arthrobacter sp. GLP-1.

The metabolism of glyphosate [N-(phosphonomethyl)glycine] in a bacterium tentatively identified as an Arthrobacter sp., capable of growth on this herbicide as its sole phosphorus source, has been investigated using solid-state NMR techniques as well as radiotracer analysis. The pathway involves the conversion of glyphosate to glycine, a C1 unit and phosphate. The phosphonomethyl carbon is specifically incorporated into the amino acids serine, cysteine, methionine, and histidine, as well as into purine bases and thymine, indicating the involvement of tetrahydrofolate in single-carbon transfer reactions. Glycine derived from glyphosate is utilized in purine and protein biosynthesis. This pathway for glyphosate degradation in a gram-positive bacterium is similar to that previously reported for Pseudomonas sp. PG2982 [Jacob et al. (1985) J. Biol. Chem. 260, 5899-5905] and is distinct from that reported for soil metabolism of glyphosate where aminomethylphosphonic acid has been shown to be a major metabolite. Preliminary evidence is presented which indicates that the conversion of glyphosate to glycine and the C1 unit involves the intermediate formation of sarcosine. Thus, the primary event in glyphosate degradation by Arthrobacter sp. GLP-1 is the cleavage of its C-P bound. This report constitutes the first demonstration of the metabolism of glyphosate in a gram-positive bacterium.

Arthrobacter↗
PubMed1987

Aromatic cross-links in insect cuticle: detection by solid-state 13C and 15N NMR.

Cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy has been used to determine insect cuticle composition and cross-link structure during sclerotization or tanning. Unsclerotized cuticle from newly ecdysed pupae of the tobacco hornworm, Manduca sexta L., had a high protein content with lesser amounts of lipid and chitin. Concentrations of chitin, protein, and catechol increased substantially as dehydration and sclerotization progressed. Analysis of intact cuticle specifically labeled with carbon-13 and nitrogen-15 revealed direct covalent linkages between ring nitrogens of protein histidyl residues and ring carbons derived from the catecholamine dopamine. This carbon-nitrogen adduct was present in chitin isolated from cuticle by alkaline extraction and is probably bound covalently to chitin. These data support the hypothesis that the stiffening of insect cuticle during sclerotization results primarily from the deposition of protein and chitin polymers and their crosslinking by quinonoid derivatives of catecholamines.

Animals↗
PubMed1987

Solid-state NMR studies of regulation of N-(phosphonomethyl)glycine and glycine metabolism in Pseudomonas sp. strain PG2982.

Lyophilized samples of Pseudomonas sp. PG2982 grown on 13C- and 15N-labeled glyphosate have been analyzed by single and double cross-polarization 13C NMR. Both the carbon and nitrogen metabolism of glyphosate are significantly influenced by the nitrogen source used for the growth of the organism. When ammonium sulfate is the source of nitrogen, the glycyl moiety of glyphosate is utilized intact for the biosynthesis of purines and proteins. But when the organism is grown on glycine as the source of nitrogen, the carbons and nitrogen of glyphosate are scrambled, consistent with incorporation into serine and pyruvate, and hence participation in general metabolism. When both ammonium and glycine are present in the growth medium, regulation of the metabolic fluxes along each of the two major pathways appears to be determined by the intracellular glycine concentration.

Ammonia↗
PubMed1987

Solid-state NMR studies of Klebsiella pneumoniae grown under nitrogen-fixing conditions.

The carbon and nitrogen metabolism of Klebsiella pneumoniae M5a1 has been characterized using 13C and 15N labeling with detection by cross-polarization magic-angle spinning solid-state NMR. Cells grown on ammonium typically require some 20 h to derepress fully for nitrogenase when transferred to medium devoid of any source of fixed nitrogen. We have established that during this period some cellular proteins are catabolized with the liberated nitrogen being used for the synthesis of purines needed for formation of ribosomal RNA. The 20-h derepression period can be shortened to 6 h by the introduction of fixed nitrogen in certain specific forms. Serine is the most successful agent we have examined for shortening the derepression period and glycine among the least successful. We attribute this difference to the advantage of serine over glycine in providing both specific and nonspecific carbon and nitrogen sources for complete purine synthesis. These determinations were made by tracing the metabolism of 13C- and 15N-labeled chemical bonds from the 2 amino acids during derepression.

Bacterial Proteins↗
PubMed1987

Influence of ventricular contractility on non-work-related myocardial oxygen consumption.

The relationship between myocardial oxygen consumption (MVO2) and the total pressure-volume area (PVA), which represents the total mechanical work performed during a cardiac cycle, has been shown to be linear and independent of loading conditions: MVO2 = aPVA + b. When inotropic state is enhanced, the MVO2-PVA relation shifts upward (increase in b), and when inotropic state is depressed the relation shifts downward (decrease in b). However, the quantitative relationship between contractility and b (the non-work-related myocardial oxygen consumption) determined over a wide range of contractilities is not known. In seven isolated blood perfused canine hearts, left ventricular (LV) contractility was increased by dobutamine and decreased with nifedipine or reduction of coronary blood flow. At each level of contractility, the end-systolic pressure-volume relationship (ESPVR) and the MVO2-PVA relation were determined. For each heart, the resulting values of b (ml O2/beat) were plotted as a function of Emax (mmHg/ml), an index of contractility defined as the slope of the ESPVR. There was a linear relation between Emax and b over a wide range of contractilities; on average, b (ml O2/beat) = 0.0036 Emax (mmHg/ml) + 0.0101 [r = 0.929-0.978 (95% confidence interval)], when Emax was varied over an average range of 2.8-9.6 mmHg/ml. These results suggest a common underlying determinant of contractility and non-work-related oxygen consumption.

Animals↗