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Biomedical subjects

P Schultz

Publications and source records attributed to P Schultz.

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

Are some chondrule rims formed by impact processes? Observations and experiments.

Observations and experimental evidence are presented to support the hypothesis that high-speed impact into a parent body regolith can best explain certain textures and compositions observed for rims on some chondrules. A study of 19 interclastic rimmed chondrules in the Weston (H 3/4) ordinary chondrite shows that two main rim types are present on porphyritic olivine-pyroxene (POP) and porphyritic pyroxene (PP) chondrules: granular and opaque rims. Granular rims are composed of welded, fine-grained host chondrule fragments. Bulk compositions of granular rims vary among chondrules, but each rim is compositionally dependent on that of the host chondrule. Opaque rims contain mineral and glass compositions distinctly different from those of the host, partially reacted chondrule mantle components, and some matrix grains. Opaque rims are greatly enriched in FeO (up to 63 wt%). The original chondrule pyroxene compositional zonation patterns and euhedral grain outlines are discontinuous at the chondrule/rim interface. Opaque rims are dominated by fayalitic olivine (Fa92-56), with high Al2O3 content (0.78-3.15%), which makes them distinctly different from primary olivine, but similar to Fe-olivine in chondrule rims of other meteorites. Thin zones of chondrule minerals adjacent to the present rims are intermediate in FeO content between the Mg-rich interior and the Fe-rich rim, which indicates a reaction relationship. Regardless of conclusions drawn regarding other types of rims, granular and opaque rim characteristics appear to be inconsistent with nebular condensation, in that host and matrix fragments are included within the rim. We have initiated a series of experiments, using the Ames two-stage light gas gun, to investigate the hypothesis that the Weston chondrule rims are the result of thermal and mechanical alteration upon impact into a low-density medium. Clusters of approximately 200-micron-sized silicate particles were fired into aerogel (density = 0.1 g cm-3) at velocities of 5.6, 4.7, and 2.2 km sec-1. Recovered grains show characteristics that range from fragmented projectile grains mixed with melted aerogel that nearly rim the grains to grains that have melted aerogel clumps mixed with partially melted projectile. These experimental results demonstrate that rim-like thermal and mechanical alteration of projectiles can result from a high-velocity encounter with a low-density target. Therefore, experiments using appropriately chosen projectile and target materials can provide a test of the hypothesis that chondrule rims common to Weston and possibly other ordinary chondrites were formed by such a process.

Astronomical Phenomena↗
PubMed1991

Subhypnotic doses of thiopentone and propofol cause analgesia to experimentally induced acute pain.

Subhypnotic doses of thiopentone are considered to have a hyperalgesic effect, while propofol has a hypoalgesic effect. We investigated the effect of these drugs on the nociceptive system by measuring the pain threshold to laser stimulation and the pain evoked potential (power and latency). Nineteen patients (ASA group I) participated. Twelve patients received thiopentone 0.5 mg kg-1 and propofol 0.25 mg kg-1 in random order separated by an interval of 14 h, and seven patients received saline. Immediately after the injection of both agents, the pain threshold was increased significantly (P less than 0.001) and the amplitude of the evoked potential was reduced significantly (P less than 0.05), while the latency of the evoked potential remained constant. It is concluded that, in subhypnotic doses, both thiopentone and propofol decrease the acute pain evoked by argon laser stimulation.

Acute Disease↗
PubMed1991

Postoperative pulmonary complications and lung function in high-risk patients: a comparison of three physiotherapy regimens after upper abdominal surgery in general anesthesia.

The effect of three postoperative regimens of respiratory therapy on pulmonary complications and lung function was compared in high-risk patients. Fifty-one patients were randomized to: 1) conventional chest physiotherapy alone (PHYS), 2) chest physiotherapy and positive expiratory pressure (PEP), or 3) chest physiotherapy with both positive expiratory pressure and inspiratory resistance (RMT). Treatments were given twice daily by a physiotherapist and self-administered. The incidence of postoperative pulmonary complications (PPC) was respectively, 71%, 76% and 65% in the PHYS-, PEP- and RMT-groups. The incidence of PPC requiring treatment with antibiotic, bronchodilator or supplementary oxygen according to the existing clinical practice was 47%, 47% and 29%. The incidence of atelectasis was 65%, 64% and 60% and of pneumonia 29%, 35% and 6%. There was no difference between the groups, except for a tendency to a lower frequency of pneumonia in the RMT-group. Postoperatively forced vital capacity (FVC) decreased to mean 54%, forced expired volume in 1 s to 48% and functional residual capacity to 76% of preoperative values. Arterial oxygen tension (PaO2) declined to mean 8.1 kPa and arterial saturation (SaO2) to 89%. There was no difference between the groups except for FVC, PaO2 and SaO2 (P = 0.008, P = 0.008 and P = 0.002), which showed the least decrease in the RMT-group. None of the regimens could be considered as satisfactory concerning the prevention of PPC, but RMT seemed to be the most efficient. Insufficient self-administration of treatment was probably one of the causes of the overall high incidence of PPC in this study.

Abdomen↗
PubMed1991

Variation in spinal analgesia with plain bupivacaine 0.5% when repeated in the same patient.

The study was done to see if it was possible to predict the level of analgesia in repeated spinal blocks with our routine technique where the patient is seated during injection of plain 0.5% bupivacaine 3.5 ml at the L3-L4 interspace and placed in the lithotomy position after 0.5 min. Thirty patients with tumour of the bladder had two spinal blocks during a 13-month period. The segmental spread of sensory loss was tested with the pin-prick technique. A wide range of height of blocks was found, increasing with age. Regression analysis on maximum cephalad spread of the second spinal analgesia against the first had a slope of 0.48 (P less than 0.01 for the hypothesis that the slope is zero). A significant correlation between the time for maximal cephalad spread was found, while the correlation between duration of thoracal analgesia was non-significant.

Aged↗
PubMed1991

Postoperative pulmonary complications.

This discussion presented the most common causes of postoperative pulmonary complications. The categories of obstruction, hypoxemia, and hypoventilation were used for structure, with the most common causes of each identified. Problems and patients at risk for these problems have been identified along with treatment priorities. The reader is reminded that the categories of obstruction, hypoxemia, and hypoventilation cannot be taken as absolute. The existence of one usually suggests the presence of another.

Humans↗
PubMed1990

Structural study of the yeast RNA polymerase A. Electron microscopy of lipid-bound molecules and two-dimensional crystals.

Two-dimensional crystals of yeast RNA polymerase A (I) were obtained by interaction with positively charged lipid layers. The analysis of single molecular images of lipid-bound RNA polymerases showed that the enzyme was preferentially oriented by the lipid phase, which probably facilitated crystallization. Electron micrographs of the crystals revealed a rectangular unit cell 25.8 nm by 45.6 nm in size containing four RNA polymerase dimers related by P22(1)2(1) symmetry. The projection map showed, at about 2.5 nm resolution, two different views of the enzyme characterized by two bent arms, which appeared to cross at one end. These arms are likely to contain the A190 and A135 subunits and delimit a 3 to 4 nm wide groove. Additional structural features were observed and compared to the Escherichia coli enzyme.

Lipid Bilayers↗
PubMed1990

Chromatin reconstitution on small DNA rings. III. Histone H5 dependence of DNA supercoiling in the nucleosome.

Mononucleosomes were reconstituted on small DNA rings in the presence of histone H5 and relaxed to an equilibrium using calf thymus topoisomerase I. DNA products, when compared to the equilibria observed with the same minicircles in the absence of histones, showed that a linking number reduction of 1.6 to 1.7 was associated with this reconstitution, in contrast with the 1.1 to 1.2 figure reported in our recent study of the H5-free nucleosome. Gel electrophoretic properties and electron microscopic visualization of the nucleosomes suggest a correlation between this increase and a further wrapping of the DNA around the histone core from less than 1.5 turns of the superhelix in the absence of H5, to close to two turns in its presence. Implications for DNA topology in chromatin are discussed.

Animals↗
PubMed1990

Two-dimensional crystallization of DNA gyrase B subunit on specifically designed lipid monolayers.

The B subunit of DNA gyrase formed two-dimensional crystals when bound to a specifically recognized phospholipid spread into a monolayer at the air/water interface. The especially designed lipids consisted of novobiocin coupled through the 3' or 2" hydroxyl group and a hydrophilous linker of a given length to dioleoylphosphatidic acid. Two-dimensional crystals of the gyrase B subunit are formed under physiological conditions of pH and ionic strength, with no precipitant added to the solution. Crystal diffraction extended to a 2.7 nm resolution in negative stain, with unit cell parameters a = 6.1 nm, b = 7.6 nm and gamma = 64 degrees.

Bacteria↗
PubMed1990

[Inguinal paravascular block (3-in-1 block)].

The three main nerves from the lumbar plexus may be blocked by injection of local anesthetic into the facial envelope of the femoral nerve ("three-in-one block"). The femoral nerve may be localized by obtaining paresthesia, by employing a nerve stimulator or by the loss of resistance technique. We prefer the use of a nerve stimulator. The "three-in-one block" may be employed for immediately pain relief of pain and for treatment of postoperative pain from fractures in the hip, femur and knee. Introduction of a catheter into the femoral nerve sheath is recommended to provide continuous block of the lumbar plexus for relief of postoperative pain.

Anesthesia, Local↗
PubMed1990

Electron microscopic study of yeast RNA polymerase A: analysis of single molecular images.

The structural features of the yeast DNA-dependent RNA polymerase A (I) were examined by Scanning Transmission Electron Microscopy. The enzyme was absorbed in its monomeric form and negatively stained prior to digital image acquisition at low dose. The signal to noise ratio of single particle images was improved through averaging of a large number of previously aligned and partitioned images. Six classes of images were obtained reproducibly which corresponded to different projections of the enzyme. The enzyme structure was characterized by its presence of two curved arms which defined a longitudinal cleft. By analogy with the Escherichia coli enzyme, these arms could correspond to the two large subunits A135 and A190.

Chemical Phenomena↗
PubMed1990

Spinal anaesthesia in young patients using a 29-gauge needle: technical considerations and an evaluation of postoperative complaints compared with general anaesthesia.

One hundred patients aged 18-49 yr, undergoing elective arthroscopy of the knee joint, were allocated randomly to either spinal anaesthesia using a 29-gauge spinal needle or general anaesthesia. Dural puncture was considered difficult in 18% of the patients receiving spinal anaesthesia. In three patients (6%) it was necessary to supplement the spinal anaesthetic with general anaesthesia. Spinal and general anaesthesia were otherwise uneventful in all patients. The incidence of postoperative headache was similar in the two groups. One patient developed post dural puncture headache following spinal anaesthesia. This headache was of short duration and disappeared without treatment. Spinal anaesthesia caused more backache than general anaesthesia, otherwise the frequency of postoperative complaints was the same or lower. Ninety-six percent of the patients receiving spinal anaesthesia would prefer the same anaesthetic for a similar procedure in the future.

Adolescent↗
PubMed1990

Continuous blockade of the lumbar plexus after knee surgery: a comparison of the plasma concentrations and analgesic effect of bupivacaine 0.250% and 0.125%.

In 20 patients a continuous block of the lumbar plexus was administered after knee-joint surgery, and the analgesic effect of two different concentrations of bupivacaine was compared. The same volume of bupivacaine was given to both groups of patients: a bolus dose of 0.4 ml/kg, 0.5% or 0.25%, followed by infusion of 0.14 ml/kg/h, 0.25% or 0.125%, respectively, via a catheter placed in the neurovascular fascial sheath of the femoral nerve according to the "3-in-1 block" technique. The median morphine consumption during the first 16 h postoperatively was 6.0 mg when bupivacaine 0.5/0.25% was used and 9.5 mg when 0.25/0.125% was used. This difference is not significant. The visual analogue pain scores were also similar in the two groups (P greater than 0.05). All plasma concentrations were below 4 micrograms/ml, the highest concentration measured being 3.6 micrograms/ml. It is concluded that when used for a continuous block of the lumbar plexus after knee-joint surgery, bupivacaine in a concentration of 0.125% offers the same pain relief as a concentration of 0.25%, and the risk of toxic reactions is reduced.

Adult↗
PubMed1990

A clinically homogeneous group of families with facioscapulohumeral (Landouzy-Déjérine) muscular dystrophy: linkage analysis of six autosomes.

Facioscapulohumeral muscular dystrophy (FSHMD) is a neuromuscular disorder characterized by autosomal dominant inheritance and clinical onset in the muscles of the face and shoulder girdle. Using a set of RFLP markers spaced at approximately 20 centimorgans, we have begun a systematic search for markers linked to the disease. A total of 81 RFLP loci on six autosomes (1, 2, 5, 7, 10, and 16) have been examined for linkage to FSHMD in 13 families. With the computer program CRI-MAP, two-point and multipoint analyses have not resulted in any LOD score indicative of linkage to FSHMD. However, these analyses have allowed us to exclude 909 centimorgans (sex average) of our genetic maps in intervals where the LOD score is less than -2.0. We estimate our data have excluded 23% of the human genome.

Blotting, Southern↗
PubMed1990

Clinicopathologic and flow cytometric DNA study of medullary thyroid carcinoma.

Sixty-one patients with medullary thyroid carcinoma were investigated to establish relationships between the neoplasm's DNA content, other clinicopathologic factors, and patient survival (at least 5 years' follow-up). There were 26 (42.6%) familial and 35 (57.4%) sporadic carcinomas. Forty-two neoplasms (68.8%) were diploid and 19 (31.2%) were aneuploid by flow cytometric assessment. In univariate analysis, age, hereditary background, DNA content, calcitonin immunoreactivity, and type of surgery were strong predictors of clinical outcomes. In multivariate regression analysis, none of these factors was an independent prognosticator. Patients' gender, clinical stage, histologic subtype, and amyloid content of the tumor did not influence survival.

Adolescent↗
PubMed1989

The two DNA-binding domains of yeast transcription factor tau as observed by scanning transmission electron microscopy.

Yeast transcription factor tau interacts with the intragenic promoter of tRNA genes, binding to both the A and B block elements. Affinity-purified tau factor and tau-tDNA complexes were examined by scanning transmission electron microscopy to analyze the structural features of free and DNA bound factor. The free factor appeared as two tightly associated globular domains of roughly similar size (10 nm in diameter) and mass (approximately 300 kd). A combination of these two domains results in a mass for the factor of 510-670 kd. When tau was allowed to interact with recombinant tRNA(3Leu) genes with variable A block-B block spacing, different structures were observed. With short genes, the two globular domains were not resolved and tau appeared as a large particle covering the A and B block region. On the other hand, with genes having a larger A-B distance (53 or 74 bp), mostly dumb-bell-shaped complexes were formed with individualized factor domains bound separately to the A and B blocks. A smaller proportion of the complexes appeared to consist of a large particle bound at only one site, essentially on the B block. Mapping of the binding domains in the DNA showed a good correlation with the respective positions of the A and B promoter elements. Factor binding did not induce a noticeable DNA bending, although with extended genes apparent DNA shortening and cases of DNA looping were observed. Upon cleavage of the tRNA(3Leu) gene between the A and B blocks after or prior to complex formation, the two factor domains remained attached to the same DNA fragment (mostly the B-DNA fragment). In addition, images of protein-linked, reconstituted full-length genes were also observed. These different conformational states of the tau-tDNA complexes probably reflect the dynamic aspect of the interaction of the factor with its DNA target.

DNA Polymerase III↗
PubMed1989

The mobilization of ferritin iron by liver cytosol. A comparison of xanthine and NADH as reducing substrates.

Considerable evidence suggests that the release of iron from ferritin is a reductive process. A role in this process has been proposed for two hepatic enzymes, namely xanthine oxidoreductase and an NADH oxidoreductase. The abilities of xanthine and NADH to serve as a source of reducing power for the enzyme-mediated release of ferritin iron (ferrireductase activity) were compared with turkey liver and rat liver homogenates. The maximal velocity (Vmax.) for the reaction with NADH was 50 times greater than with xanthine; however, the substrate concentration required to achieve half-maximal velocity (Km) was 1000 times less with xanthine than with NADH. NADPH could be substituted for NADH with little loss in activity. Dicoumarol did not inhibit the reaction with NADH or NADPH, demonstrating that the ferrireductase activity with those substrates was not the result of the liver enzyme 'DT-diaphorase' [NAD(P)H dehydrogenase (quinone)]. A flavin nucleotide was required for ferrireductase activity with rat and turkey liver cytosol when xanthine, NADH or NADPH was used as the reducing substrate. FMN yielded twice the activity with NADH or NADPH, whereas FAD was twice as effective with xanthine as substrate. Kinetic comparisons, differences in lability and partial chromatographic resolution of the ferrireductase activities with the two types of reducing substrates strongly indicate that the ferrireductase activities with xanthine and NADH are catalysed by separate enzyme systems contained in liver cytosol. Complete inhibition by allopurinol of the ferrireductase activity endogenous to undialysed liver cytosol preparations and the ability of xanthine to restore equivalent activity to dialysed preparations indicate that the source of reducing power for the endogenous activity is xanthine. These studies suggest that xanthine, NADH or NADPH can serve as a source of reducing power for the enzyme-mediated reduction of ferritin iron, with a flavin nucleotide serving as the shuttle of electrons from the enzymes to the ferritin iron.

Animals↗
PubMed1989

Lung function and postural changes during pregnancy.

The aim of this study was to determine the effects of postural changes on lung function in pregnant women during the first, second, third trimester and post partum. A significant decrease in FRC, PEF and FEV1 was observed as a result of the postural changes. Arterial oxygenation, MVV and DLCO remained largely the same.

Adult↗