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Biomedical subjects

A Roos

Publications and source records attributed to A Roos.

At least 55 records · Page 3Linked to original sources
PubMed1995

The light-flash-evoked response as a possible indicator of increased intracranial pressure in hydrocephalus.

Surgical treatment of infantile hydrocephalus by shunt implantation may result in suboptimal intracranial pressure. Major neurological impairments and death are usually prevented by shunt treatment, but minor sequelae may persist or develop. The introduction of adjustable shunts has improved the possibilities of optimizing shunt function and minimizing the risk of such impairments. However, it is still impossible to determine the intracranial pressure without invasive measurements. Clinical findings and procedures such as computed tomography (CT) are not always enough to allow a conclusion as to whether a child's signs and symptoms are the result of suboptimal intracranial pressure (shunt dysfunction) or are of another etiology. With the aim of reducing the number of invasive pressure measurements and CT scans, we investigated the effect of increased intracranial pressure on the visual evoked response (VER). Binocular light flash stimuli of supramaximal intensity were used and VER recordings were performed from Oz and Cz. The VER results from a group of 31 infants and children with hydrocephalus and 2 children with pseudotumor cerebri were compared with responses from a control group of 35 healthy children. The results show that a subpotential, P' (P-prime), usually just preceding P1 (P100), had an increased latency ( > 96 ms) in all hydrocephalic children before surgery. The P' latency in this group was usually even above 110 ms. The latencies of other VER potentials were also increased but not as consistently as P'. After surgical intervention the VER latencies decreased and usually normalized. The P' latency in four children in the control group was just above the borderline latency, but was less than 110 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Active site labeling with dansyl-glutamyl-glycyl-arginyl chloromethyl ketone demonstrates the full activity of the refolded and purified tissue-type plasminogen activator variant BM 06.022.

BM 06.022 is a tissue-type plasminogen activator deletion variant that is comprised of the kringle 2 and the protease domain of the native molecule. BM 06.022 is expressed as inactive inclusion bodies in E. coli and transferred into the active enzyme by an in vitro folding process. Active site labeling with dansyl-glutamyl-glycyl-arginyl chloromethyl ketone provides evidence that the purified BM 06.022 is fully active and that misfolded species are completely removed by affinity chromatography on ETI-Sepharose. The comparison of the kinetics of the inhibition of BM 06.022 with that of CHO-t-PA indicates that the active centers of both enzymes are rather similar. The further evaluation of the site of interaction of BM 06.022 and DnsEGRck by mass spectroscopy and amino acid sequence analysis revealed that the inhibitor is bound selectively to His322, which is part of the catalytic triad of this serine protease.

Amino Acid Chloromethyl Ketones↗
PubMed1994

Cytomegalovirus in liver biopsies of marrow transplant recipients: detection methods, clinical, histological and immunohistological features.

In a retrospective analysis liver biopsy specimens obtained from 44 marrow transplant recipients were studied to evaluate the frequency of local presence of human cytomegalovirus (CMV) and graft-versus-host disease (GvHD)-like histological and immunohistological alterations in patients with and without liver dysfunction following bone marrow transplantation (BMT). In 22 of 28 patients with marked liver dysfunction after BMT and histopathological alterations described as typical for acute GvHD CMV could be detected in the liver biopsy specimen. The polymerase chain reaction (PCR) technique revealed the highest sensitivity for CMV detection in liver biopsy samples, but in 20 of 22 PCR-positive specimens CMV infection could be confirmed by at least one additional technique. All the liver biopsies obtained from 16 patients with normal liver function lacking histopathological signs of GvHD were CMV negative. In all 3 patients with CMV-positive liver biopsy started on antiviral therapy liver function improved and no generalized CMV disease occurred. All the 4 patients without local presence of CMV started on severe immunosuppressive therapy showed an improvement of liver dysfunction without occurrence of CMV infection. Local CMV infection of the liver could not be differentiated from hepatic GvHD by clinical and histopathological features, nor by immunohistological analysis of the bile duct epithelium. In contrast, only in liver biopsy with local viral presence could an increase in HLA class II- and ICAM-1 expression be demonstrated on hepatocytes. Thus, especially the high negative predictive value of the PCR technique helps to manage the patient with liver dysfunction after BMT.

Adolescent↗
PubMed1994

Transforming growth factor-beta and the glomerular extracellular matrix in renal pathology.

Transforming growth factor-beta (TGF-beta) is a multifunctionally acting peptide with a broad spectrum of cellular targets. The biologic function of this peptide is currently widely studied. These studies reveal remarkable effects on proliferation, differentiation, migration, and production of many cell types. Among these effects, the regulatory function of TGF-beta in extracellular matrix homeostasis is thought to represent a major part of its action, mediating various other effects. Because disturbance of the regulation of extracellular matrix production is involved in various diseases, TGF-beta was expected to play a role in pathologic accumulation of extracellular matrix. By now, involvement of TGF-beta in the development of pathologic matrix production is most clear in experimental glomerular diseases. In this review, various lines of evidence for such an involvement are presented. After a general introduction about the molecular structure of TGF-beta and its biologic function, the regulation of extracellular matrix production by TGF-beta is discussed, with special emphasis on the glomerulus. Finally, the involvement of TGF-beta in the development of glomerulosclerosis is considered. Because in vivo inhibition of TGF-beta action in animal models seems to prevent pathologic matrix accumulation, the possible role of TGF-beta as an important mediator in the development of glomerulosclerosis may have important implications for prevention of glomerulosclerosis in human renal disease. Extensive study of the in vivo regulation of TGF-beta activity, both in animal models and human diseases, will be necessary for further elucidation of pathogenetic mechanisms and possibilities for therapeutic intervention.

Animals↗
PubMed1993

In vivo behavior of a high performance duplex stainless steel.

An in vivo investigation of a new high molybdenum and nitrogen duplex stainless steel (25Cr--7Ni--4Mo--0.3N) has been performed. Cylindrical pins and specially developed devices, to test in static conditions the in vivo localized corrosion resistance, made of this new duplex steel and of a common austenitic stainless steel were implanted in rabbit's femurs for 6 and 12 months. After sacrifice, SEM observations and EDS microanalyses to detect metallic ion release were carried out on the femur sections surrounding the pins. Morphologic observations with stereoscope and SEM were performed on the metallic surfaces of the special devices in order to detect the presence of localized corrosion. Both ion release and localized corrosion were observed for the specimens made of austenitic stainless steel, but not for those made of 25Cr--7Ni--4Mo--0.3N duplex stainless steel.

Animals↗
PubMed1993

Lumbar radiculopathy caused by a lost silverclip.

The case of an adult patient with lumbar radiculopathy (L:4) caused by a migrated silverclip, which was probably lost during the successful extirpation of a cerebellar tumor many years before is presented. The clip was removed surgically and the nerve root was submitted to a partial neurolysis. Increased tension in the root due to corrosion of the clip and scar formation is the proposed pathophysiological mechanism in this case.

Astrocytoma↗
PubMed1993

Management of a giant intracranial aneurysm using surface-heparinized extracorporeal circulation and controlled deep hypothermic low flow perfusion. A case report.

Extracorporeal circulation with controlled hypothermic low flow perfusion was introduced during the surgical treatment of a patient with a giant intracranial aneurysm of the anterior communicating artery. Heparin-coated equipment (Carmeda Bio-Active Surface; CBAS) was utilized, thus reducing the need for systemic heparinization. Direct cannulation of the right atrium and aorta was established through thoracotomy. Blood flow through the circuit was kept at 4.5 l/min during normothermia. Core cooling, in combination with external surface cooling, was performed for 30 min to a temperature of 18 degrees C (nasopharynx). During a period of 25 min, the time for surgical repair of the aneurysm, blood flow was minimized to 0.4 l.min-1, equilibrating central and peripheral blood pressures to approximately 5-10 mmHg (0.65-1.3 kPa). Reperfusion was started immediately after the low flow period concomitantly with rewarming, aiming at a temperature of 36 degrees C following 150 min. The patient could be weaned off the extracorporeal circulation with minimal inotropic support. The postoperative course was uneventful apart from a left-sided hemiparesis, probably due to an infarction in the area of the right pericallosal artery (A2). The patient was weaned off the ventilator after 6 days. He recovered and the hemiparesis regressed slowly.

Aged↗
PubMed1993

IgA anti-dsDNA antibodies in systemic lupus erythematosus: occurrence, incidence and association with clinical and laboratory variables of disease activity.

The relationship between IgA anti-dsDNA antibodies and systemic lupus erythematosus (SLE) disease activity was investigated. IgA anti-dsDNA antibodies were measured using ELISA techniques. Elevated serum levels of IgA anti-dsDNA antibodies were detected in 51% of the patients with SLE (n = 57) and 8% of the diseased controls (n = 214). The presence of IgA anti-dsDNA antibodies was associated with kidney and joint abnormalities, with hypocomplementemia and with circulating immune complexes. We conclude that increased levels of IgA anti-dsDNA antibodies are associated with disease activity in patients with SLE.

Adult↗
PubMed1992

Evaluation of cerebrospinal fluid shunt function in hydrocephalic children using 99mTc-DTPA.

The increasing numbers and survival of children with shunt-treated hydrocephalus make it mandatory to refine the methods for cerebrospinal fluid (CSF) shunt function evaluation. Radionuclide shuntography with 99mTc-DTPA, which has proved to be a safe and effective method, was performed in eight children with suspected CSF-shunt dysfunction. Characteristic shuntography patterns were found for proximal and distal CSF-shunt catheter obstruction as well as for overdrainage and normal CSF-shunt function. Shuntography contributed to the explanation of suspected CSF-shunt dysfunction in all children investigated.

Adolescent↗
PubMed1992

pH regulation in adult rat carotid body glomus cells. Importance of extracellular pH, sodium, and potassium.

The course of intracellular pH (pHi) was followed in superfused (36 degrees C) single glomus (type I) cells of the freshly dissociated adult rat carotid body. The cells had been loaded with the pH-sensitive fluorescent dye 2',7'-(2-carboxyethyl)-5 (and -6)-carboxyfluorescein. The high K(+)-nigericin method was used for calibration. The pHi of the glomus cell at pHo 7.40, without CO2, was 7.23 +/- 0.02 (n = 70); in 5% CO2/25 mM HCO3-, pHi was 7.18 +/- 0.08 (n = 9). The pHi was very sensitive to changes in pHo. Without CO2, delta pHi/delta pHo was 0.85 (pHo 6.20-8.00; 32 cells), while in CO2/HCO3- this ratio was 0.82 irrespective of whether pHo (6.80-7.40; 14 cells) was changed at constant PCO2 or at constant [HCO3-]o. The great pHi sensitivity of the glomus cell to pHo is matched only by that of the human red cell. An active Na+/H+ exchanger (apparent Km = 58 +/- 6 mM) is present in glomus cells: Na+ removal or addition of the amiloride derivative 5-(N,N-hexamethylene)-amiloride induced pHi to fall by as much as 0.9. The membrane of these cells also contains a K+/H+ exchanger. Raising [K+]o from 4.7 to 25, 50, or 140 mM reversibly raised pHi by 0.2, 0.3, and 0.6, respectively. Rb+ had no effect, but in corresponding concentrations of Tl+ alkalinization was much faster than in K+. Reducing [K+]o to 1.5 mM lowered pHi by 0.1. These pHi changes were shown not to be due to changes in membrane voltage, and were even more striking in the absence of Na+. Intrinsic buffering power (amount of strong base required to produce, in the nominal absence of CO2, a small pHi rise) increased from 3 to approximately 21 mM as pHi was lowered, but remained nearly unchanged below pHi 6.60. The fitted expression assumed the presence of one "equivalent" intracellular buffer (pK 6.41, 41 mM). The exceptional pHi sensitivity to pHo suggests that the pHi of the glomus cell is a link in the chemoreceptor's response to external acidity.

Acid-Base Equilibrium↗
PubMed1991

Flashed pattern-induced activity in the visual system: I. The short latency evoked response recorded from the cat visual cortex.

Previous methods for estimating visual acuity have used the visual evoked response conventionally the late visual evoked response components or the steady-state potential. The present experiments were undertaken to evaluate the possible use of short latency flashed pattern evoked responses in estimating pattern dependent activity in the cat visual system. Recordings were made from the skull bone and the dura above the primary visual cortex and intracortically. The visual evoked responses to patterned (checks) and non-patterned light flashes of high intensity and short duration were recorded. The visual evoked response activity recorded from the cortical surface had an onset latency of 14-15 ms. The initial positive-negative potential sequences of the responses were similar for patterned and non-patterned stimuli, however a difference was recorded from 35-40 ms after stimulus. The smallest check size which separated a pattern from a non-pattern VER was in the order of 10 min of arc. The results indicate that the short-latency cortical VER may be used to estimate visual resolution.

Animals↗
PubMed1991

Which value for the first dissociation constant of carbonic acid should be used in biological work?

The apparent first dissociation constant of carbonic acid has been defined in different ways in the literature. Harned and co-workers (8-10) have defined it in terms of molalities of the participating species, including H ions: Ks = mHmHCO3/mCO2. In contrast, Hastings and Sendroy have defined an apparent constant in which acidity is expressed as H ion activity: K'1 = aHmHCO3/mCO2. These constants differ by a factor gamma H, the activity coefficient of H ions at the prevailing ionic strength. Therefore, pK'1 is greater than pKs by an amount equal to -log gamma H, which, at mu = 0.16 M, is approximately 0.1. It is important that the correct value for the apparent dissociation constant or its logarithmic form be entered in the mass action expression or in the Henderson-Hasselbalch equation in order to prevent significant errors in the computation by means of these equations of quantities that cannot be directly measured. Specifically, for the derivation of bicarbonate concentration from PCO2 and pH (-log aH), pK'1 is to be used and not an uncorrected pKs.

Carbon Dioxide↗
PubMed1990

Changes in intracellular pH caused by high K in normal and acidified frog muscle. Relation to metabolic changes.

We examined the effect of depolarization on intracellular pH (pHi) of normal (pHi approximately 7.37) and acidified (pHi 5.90-6.70) frog semitendinosus muscle using microelectrodes. A small bundle was superfused with a Na(+)-free buffered solution (10 mM HEPES, 100% O2, pH 7.35) containing either 2.5 or 25 mM K+. An NH4Cl prepulse was used to lower pHi. At normal pHi, depolarization usually produced a slight (0.04) alkalinization, followed by a fall in pHi of approximately 0.2. In contrast, in all 25 acidified bundles pHi rose by 0.1-0.7. The rise was greater the lower the initial pHi. It could be imitated by caffeine and blocked by tetracaine and thus was, most likely, initiated by release of calcium. We ascribed the alkalinization to hydrolysis of phosphocreatine (PCr); 2,4-dinitrofluorobenzene abolished it. Biochemical analysis on fibers at the peak of alkalinization showed PCr to be reduced by one-half, while PCr in normal fibers that had been depolarized for the same period (4-6 min) showed no change. We postulated that low pHi slows glycolysis with its associated ATP formation by reducing glycogenolysis and particularly by reducing conversion of fructose-6-phosphate to fructose-1,6-diphosphate through inhibition of phosphofructokinase (PFK), an enzyme which is known to be highly pH sensitive. Thus PCr hydrolysis would be required to replace much of the hydrolyzed ATP. This postulated effect on PFK is in agreement with the finding that glucose-6-phosphate (in near-equilibrium with fructose-6-phosphate) was increased nearly fivefold in the depolarized acid fibers, but not in the depolarized normal fibers. However, fructose-1,6-diphosphate also increased significantly; 3-phosphoglycerate was not affected. This suggests an additional acid-induced bottleneck between the latter two substrates. We measured the intrinsic buffering power, beta, of frog semitendinosus muscle with small pulses of NH4Cl. It was found to vary with pHi according to beta = 144.6 - 17.2 (pHi).

Adenosine Triphosphate↗
PubMed1989

Duplex stainless steels for osteosynthesis devices.

The austenitic stainless steels used today for the manufacture of osteosynthesis devices are sensitive to crevice corrosion. In this study the corrosion properties of some duplex stainless steels were evaluated and compared to traditional austenitic stainless steels. According to our results the following ranking was established: 23Cr-4Ni less than AISI 316L less than ASTM F138 less than 22Cr-5Ni-3Mo less than 27Cr-31Ni-3.5Mo less than 25Cr-7Ni-4Mo-N. In particular the results showed that the high-performance 25Cr-7Ni-4Mo-N duplex stainless steel, with high molybdenum and nitrogen contents, can be considered not susceptible to crevice corrosion in the human body. The duplex stainless steels have also better mechanical properties at the same degree of cold working compared with austenitic stainless steels. Hence the 25Cr-7Ni-4Mo-N duplex stainless steel can be considered a convenient substitute of ASTM F138 for orthopedic and osteosynthesis devices.

Biocompatible Materials↗