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Biomedical subjects

S Levy

Publications and source records attributed to S Levy.

At least 127 records · Page 7Linked to original sources
PubMed1994

Numerical calculation of the potential distribution due to dipole sources in a spherical model of the head.

A three-dimensional spherical model of the head was investigated numerically. The model consists of four conductive layers representing the scalp, the skull, the cerebrospinal fluid, and the cortex with a dipole current source. The potential created by the dipole was calculated using quasistatic formulation and a linear medium. The volume conduction equation was discretized by the finite volume method to ensure the conservation of fluxes and efficient solution method. The large set of algebraic equations for the electric potential was solved iteratively by the successive over relaxation method. The new formulation of the volume conduction problem was validated by comparing the numerical results with two analytical solutions. The first test-case considers a homogeneous spherical model with a dipole in the center. The potential on the outer surface, as well as within the volume conductor, was calculated and very good agreement was obtained with the analytical solution. In the second test-case, the scalp potential due to a radially oriented eccentric dipole in a four concentric spheres model was compared with an analytic solution. It was found that a grid of 90 x 90 x 90 volume elements yielded accurate results on the scalp surface with errors on the order of 1%. The present numerical model can be extended to general cases with any volume conductor shape or with any distribution or orientation of the current dipoles. Compared to other numerical methods, this approach offers enhanced accuracy for given computational resources (both in CPU time and memory). The gain might be more than one order of magnitude, allowing simulation with considerably larger meshes.

Body Surface Area↗
PubMed1994

Evaluation of linked PCR-transcription amplification procedure for bean yellow mosaic virus detection in gladioli.

Bean yellow mosaic virus (BYMV) concentration in in-vitro cultured Gladiolus cormlets was low and impossible to detect by the commonly used diagnostic methods. The polymerase chain reaction (PCR) detected viral RNA in most infected cormlets but not in all. Additional amplification of the PCR products by transcription, using T7 RNA polymerase (PCR/T), resulted in virus detection in cases which otherwise went undetected. PCR products having a single polymerase promoter at one end served as a better template for T7 RNA polymerase, and yielded more transcripts of a particular orientation than a template containing promoters at both ends. Repeated cycles of PCR/T resulted in the production of a heterogeneous amplified material which correlated with a progressive decline in amplification rate. Therefore, only the first PCR/T cycle proved to be effective. The PCR/T procedure was shown to be better than other commonly used diagnostic methods including PCR.

Enzyme-Linked Immunosorbent Assay↗
PubMed1994

Predictive factors of hyperfibrinolytic activity during liver transplantation in cirrhotic patients.

Hyperfibrinolytic activity occurs frequently during liver transplantation in cirrhotic patients. In order to identify those patients at high risk for increased intraoperative blood loss before operation, we determined predictive indicators of hyperfibrinolysis. We studied 56 cirrhotic patients undergoing liver transplantation with the same anaesthetic procedure and transfusion regimen. The preoperative coagulation patterns of the 11 patients who experienced acute intraoperative hyperfibrinolytic activity were compared with those of the 45 patients who did not suffer this complication. Before surgery, patients with intraoperative hyperfibrinolysis had decreased prothrombin time (PT) and euglobulin lysis time (ELT), and increased thrombin time (TT) and fibrinogen degradation products (FDP), whereas alpha angle and maximum amplitude (MA) were reduced on thrombelastography. Stepwise multivariate analysis disclosed three components which were significantly linked with occurrence of hyperfibrinolysis: TT, FDP and MA. Their sensitivity, specificity, positive and negative predictive values demonstrated that patients with FDP > or = 48 mg litre-1 and MA < or = 35 mm before incision had 100% probability of developing hyperfibrinolytic activity during transplantation.

Adult↗
PubMed1994

Differentiating SVT from VT--a personal viewpoint.

There are two situations in which it may be difficult to differentiate supraventricular tachycardia from ventricular tachycardia via the surface 12 lead electrocardiogram: (1) when supraventricular tachycardia is conducted to the ventricles with aberration, and (2) when ventricular preexcitation is present. In both cases, the physician in faced with a tachycardia with wide (> = 0.12 s) QRS complexes. In order to avoid improper or delayed therapy the physician should keep in mind simple facts. Ventricular tachycardia is far more common than supraventricular with aberrant conduction, as it accounts for more than 80% of tachycardia with wide QRS complexes. The first step is to determine the tolerance of the tachycardia and therefore whether prompt termination is required. If the tachycardia is associated with syncope, cardiac arrest, severe hypotension or angina, DC cardioversion is necessary. Diagnosis should be delayed until after termination of the tachycardia. If tachycardia is well tolerated, the bedside diagnosis should take into account the clinical context: age of the patient, history or presence of heart disease and patient medications. In an adult patient with a history of myocardial infarction, the most likely diagnosis is ventricular tachycardia. The second step is to exclude or ascertain the presence of preexcitation. If this is suspected in young adults or children an ECG in sinus rhythm should indicate overt preexcitation. The physician should be aware of the various mechanisms of tachycardia with preexcited QRS complexes, all of which have a common denominator: anterograde conduction through the accessory pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Emergency department assessment of adolescent suicide attempters: factors related to short-term follow-up outcome.

Empirical data to help gauge risk for repeat suicide attempts and noncompliance with outpatient psychiatric care among adolescent suicide attempters discharged from emergency departments is scarce. In this study, 62 adolescent suicide attempters discharged from a regional trauma center serving an urban/suburban area with a broad range of social classes were followed up at three months after their attempts to assess treatment compliance and repeat attempts. Information regarding suicidal intent and characteristics of the attempt were collected by emergency physicians at the time of the attempt. Parental ratings of adolescent functioning were also collected. At three-month follow-up, none of the adolescents had completed suicide; 7% made a repeat suicide attempt, 16% never followed through with outpatient psychiatric appointments, 15% attended one session, and 21% went to only two appointments. A prior suicide attempt, alcohol use at the time of the attempt, and greater planning of the suicide attempt were associated with better compliance with outpatient psychiatric treatment. None of the variables predicted repeat attempts. Parental reports of an adolescent's physical fighting and health problems of a family member were related to referral failure. Clinical implications are discussed.

Adolescent↗
PubMed1994

Transient changes in intracellular calcium associated with a prolonged increase in excitability in neurons of Aplysia californica.

1. Transient stimulation of an afferent input to the bag cell neurons of Aplysia californica triggers a 30-min period of spontaneous firing termed the afterdischarge. Measurement of free calcium ion concentrations using calcium-sensitive electrodes revealed a biphasic pattern of elevation of intracellular calcium levels during the afterdischarge. Basal calcium levels at the soma were found to rise rapidly during afferent stimulation and then to decline before the onset of spontaneous firing. This early peak in intracellular calcium was followed by a slower, transient elevation of calcium levels during the period of rapid firing that occurs in the first few minutes of afterdischarge. Stimulation of clusters of bag cell neurons in a calcium-free external medium failed to trigger afterdischarge and produced no changes in basal intracellular calcium levels. 2. When calcium ions in the external medium were replaced by barium ions, stimulation of clusters of bag cell neurons triggered afterdischarges that were characterized by long-duration action potentials. Intracellular calcium levels during these afterdischarges rose slowly over the first few minutes of spontaneous firing. Because calcium-sensitive microelectrodes do not respond to barium ions, these data suggest that stimulation of afterdischarge triggers calcium release from an intracellular compartment. 3. During afterdischarges in barium-containing external media, each broadened action potential produced a discrete transient elevation of intracellular calcium levels. A similar effect was observed in isolated bag cell neurons in primary culture when action potentials were stimulated by depolarizing current pulses in a barium-containing medium. These data suggest that, under these conditions, individual action potentials trigger the release of intracellular calcium from some intracellular pool.

Afferent Pathways↗
PubMed1994

Efficacy of electroconvulsive therapy after propofol and methohexital anesthesia.

Fifty-eight patients with major depression were randomly assigned to receive a hypnotic dose of either propofol or methohexital for their complete treatment series of electroconvulsive therapy (ECT). As expected, seizure duration was significantly shorter with propofol than with methohexital anesthesia. Both groups recovered from their depression at the same rate. There was a significant improvement in the Hamilton Rating Scale for Depression scores between the first and last ECT session. However, this was independent of the choice of propofol or methohexital as the anesthetic. This study supports previous reports that seizure duration does not influence recovery from depression.

Adolescent↗
PubMed1994

Attitudes toward people with AIDS and implications for school-based youth AIDS education.

This study examines attitudes toward people with AIDS (PWAs) of a group of 853 7th, 8th, and 9th graders living in high-risk communities in the suburbs of a large Midwestern city. Females appear to be more tolerant than males, and whites appear to be more tolerant than other racial/ethnic groups with respect to attitudes toward PWAs. Although knowledge about actual modes of human immunodeficiency virus (HIV) transmission is not correlated with attitudes toward PWAs, students with greater knowledge about HIV transmission through casual contact, transmission of HIV through blood products, ways of preventing HIV infection, and myths about HIV prevention have more tolerant attitudes toward PWAs. Students who have ever had sexual intercourse are significantly less tolerant of PWAs. Implications of these findings for youth AIDS education are presented.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Effect of almitrine bismesylate on pulmonary vasoreactivity to hypoxia in chronic obstructive pulmonary disease.

The aim of this double-blind, placebo-controlled study was to determine whether acute administration of almitrine enhances hypoxic pulmonary vasoconstriction in patients with chronic obstructive pulmonary disease (COPD). Haemodynamics and blood gases were studied at various inspiratory fractional concentrations of oxygen (FIO2): 0.15, 0.21, 0.30 and 1.0, randomly administered for 20 min periods under constant infusion of either placebo or almitrine (8 micrograms.kg-1.min-1) in 20 patients with COPD. The almitrine group exhibited a significant increase in mean pulmonary artery pressure, pulmonary vascular resistance and arterial oxygen tension (PaO2) at FIO2 0.15, 0.21 and 0.30. During hypoxia, the increase in mean pulmonary pressure and pulmonary vascular resistance was three times greater in the almitrine group than the placebo group. No significant difference in cardiac output and systemic haemodynamics was found. These results suggest that almitrine at the dose used, enhances pulmonary vasoconstriction in COPD patients.

Almitrine↗
PubMed1993

The TAPA-1 molecule is associated on the surface of B cells with HLA-DR molecules.

TAPA-1 is a transmembrane protein that has been shown to be involved in cell growth and cellular adhesion. Our studies were aimed at determining the mechanisms of the biologic phenomena mediated by TAPA-1, which include the identification of proteins that are associated with it on the surface of lymphocytes. We and others have previously shown that Leu-13, a leukocyte Ag, is one such molecule and that in B cells TAPA-1 is associated with the CD19 Ag. Herein we identify an additional molecule, HLA-DR, that is noncovalently associated on the surface of B cells with TAPA-1. This association was first detected by immunoprecipitation by anti-TAPA-1 and by anti-HLA-DR antibodies in the presence of mild detergents. The initial observation was confirmed by 2-dimensional SDS-PAGE and by direct identification of TAPA-1 in anti-HLA-DR immunoprecipitates by Western blot analysis. The association of the two molecules on the surface of a human B cell line was shown by cocapping experiments. In addition, antibodies to both molecules can induce cellular adhesion and an antiproliferative effect. Because the tissue distribution of these two molecules only partially overlaps, with TAPA-1 being expressed on most cell types and MHC class II expressed on a more restricted group of tissue, it is possible that the TAPA-1 molecule provides a basic function that can augment a cell type specific activity. In B cells the association of TAPA-1 with CD19 and HLA-DR may increase cellular interaction and play a supporting role in the transmission of specific signals.

Antigens, CD↗
PubMed1993

Anti-TAPA-1 antibodies induce protein tyrosine phosphorylation that is prevented by increasing intracellular thiol levels.

We studied the signal induced by the anti-TAPA-1 antibody and compared it to the signal induced by anti-IgM antibodies in a human B cell line, OCl-LY8. We found that exposure of these cells to either antibody resulted in a rapid increase in protein tyrosine phosphorylation which was prevented by inhibitors of tyrosine kinases. Tyrosine phosphorylation was an early event in the cascase leading to the antiproliferative effect of the anti-TAPA-1 antibody. However, 2-ME, a reducing agent that is not an inhibitor of tyrosine kinases, prevented both tyrosine phosphorylation and the antiproliferative effect of the antibody. Cells grown in low concentrations of 2-ME did not exhibit an increase in tyrosine phosphorylation in response to the anti-TAPA-1 antibody and were insensitive to the antiproliferative effect of the antibody. In contrast, the same cells maintained in 2-ME were able to induce tyrosine phosphorylation in response to anti-IgM. The use of 2-ME resulted in an increase in intracellular thiols, mostly glutathione. Moreover, compounds that block glutathione synthesis rendered cells susceptible to the antibody, even in the presence of 2-ME. These experiments demonstrate that tyrosine kinases are involved in propagating the antiproliferative signal initiated by the anti-TAPA-1 antibody and suggest that this signal is dependent upon the level of intracellular thiols.

Antigens, CD↗
PubMed1993

A lingering elevation of Cai accompanies inhibition of inositol 1,4,5 trisphosphate-induced Ca release in Limulus ventral photoreceptors.

Injection of inositol 1,4,5 trisphosphate (InsP3) into Limulus ventral photoreceptors causes an elevation of intracellular free Ca concentration (Cai) and depolarizes the photoreceptors. When measured with the photoprotein aequorin, the InsP3-induced Cai increase follows the time course of depolarization and declines within 1-2 s. However, sensitivity to further injections of InsP3 remains suppressed for several tens of seconds. The possibility that the suppression of Ca release (feedback inhibition) is due to a small lingering elevation of Cai, below the existing detection limit of aequorin, was investigated by measuring Cai with Ca-sensitive electrodes. Double-barreled, Ca-selective microelectrodes were used to pressure inject InsP3 and measure Cai at the same point. Light or InsP3 injections into the light-sensitive compartment depolarized the photoreceptors and induced an elevation of Cai that persisted for tens of seconds. Injections of InsP3 during the decay of Cai showed that sensitivity to InsP3 recovered as resting Cai approached the prestimulus level. The relationship between elevated Cai and feedback inhibition was very steep. An elevation of Cai of 1 microM or more was associated with inhibitions of 79 +/- 12.4% (SEM; n = 7) for the InsP3-induced Cai increase and of 76 +/- 8% for depolarizations. With a residual Cai elevation of 0.01 microM or less, the mean inhibition was 10 +/- 7.4% for InsP3-induced Cai increase and 6.6 +/- 4% for InsP3-induced depolarization. Injections of InsP3 into a light-insensitive compartment within the cell induced elevations of Cai with no associated depolarizations or feedback inhibition. To verify that a sustained elevation of Cai is necessary for inhibition of InsP3-induced Cai increase and depolarization, we injected ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) between two injections of InsP3. Injection of 1 mM EGTA or the related Ca chelator BAPTA, delivered 750 ms after the first injection of InsP3, restored the peak depolarization caused by the second injection of InsP3 to > 80 +/- 3% of control, compared with 13 +/- 8% without an intervening injection of EGTA. Measurement of Cai with aequorin showed that an intervening injection of EGTA partially restored the InsP3-induced Cai increase. The results suggest that feedback inhibition of InsP3-induced Cai increase and depolarization is mediated by a lingering elevation of Cai and not by depletion of intracellular Ca stores.

Aequorin↗
PubMed1993

Nifedipine inhibits the effects of almitrine in patients suffering from pulmonary artery hypertension secondary to chronic obstructive pulmonary disease.

It has been suggested that almitrine improves the local ventilation/perfusion ratio by enhancing hypoxic pulmonary vasoconstriction (HVC), leading to an increase in pulmonary vascular resistance (PVR) and PaO2. The goal of the present study was to determine if pulmonary vasodilation induced by nifedipine inhibits the enhancement of HVC (and consequently of PaO2), in patients suffering from chronic obstructive pulmonary disease (COPD). Two groups of 10 patients were compared in a controlled, double-blind study. Hemodynamics and blood gases were measured during continuous infusion of placebo or almitrine (8 micrograms/kg/min). Two hours after the onset of the infusion, a single dose of nifedipine (10 mg) was given sublingually. Almitrine infusion was followed by an increase in PaO2 (20%) and PVR (48%). In the almitrine group, after nifedipine, the PVR decreased 33% and PaO2 dropped to baseline while in the placebo group the PVR decreased 22% and PaO2 fell to 11% below baseline. In COPD patients, nifedipine inhibits almitrine-induced pulmonary vasoconstriction.

Almitrine↗
PubMed1993

Inhibition of nerve stimulation-induced vasodilatation in corpora cavernosa of the pithed rat by blockade of nitric oxide synthase.

1. The effect of inhibition of nitric oxide synthase by NG-nitro-L-arginine methyl ester (L-NAME) on nerve stimulation-induced vasodilation in corpora cavernosa was studied in the pithed rat. Corporal vasodilation was estimated by the increase in ratio (corpora cavernosal pressure/systemic blood pressure; CP/BP) following electrical stimulation of the sacral part of the spinal cord. 2. L-NAME (2, 5, 10 and 25 mg kg-1) caused an increase in BP and a dose-dependent inhibition of the rise in the CP/BP ratio following stimulation. 3. The inhibitory effect of L-NAME (25 mg kg-1) on the corporal response to spinal cord stimulation, as well as the pressor response, was partially prevented by prior administration of L- but not D-arginine (400 mg kg-1, i.v.). 4. L-NAME (20 mg kg-1, i.v.) did not inhibit the rise in corporal pressure resulting from direct intracavernosal administration of papaverine (400 micrograms over 2 min). However, this response was inhibited by 5-hydroxytryptamine (20 micrograms kg-1, i.v.). 5. The results are indicative of a role of nitric oxide (NO) in the corporal vasodilator response to erectile stimulation.

Amino Acid Oxidoreductases↗
PubMed1992

The CD19/CD21 signal transducing complex of human B lymphocytes includes the target of antiproliferative antibody-1 and Leu-13 molecules.

CD19 is a member of the Ig superfamily expressed on the surface of B lymphocytes that may be involved in the regulation of B cell function. Immunoprecipitation studies with B cell lines solubilized by digitonin have shown CD19 to be part of a multimolecular complex that includes CD21 (CR2) and other unidentified proteins. In this study, two of the CD19-associated proteins were identified as TAPA-1, which is expressed on most cell types, and Leu-13, which is expressed on subsets of lymphoid cells. TAPA-1 and Leu-13 are physically associated in many cell lineages. CD19 and CD21 mAb each specifically coprecipitated proteins of the same size as those precipitated by TAPA-1 and Leu-13 mAb from B cell lines and cDNA-transfected K562 cell lines. Western blot analysis with a TAPA-1 mAb verified the identity of TAPA-1 in CD19 and CD21 immunoprecipitated materials. In addition, when TAPA-1 or Leu-13 were crosslinked and patched on the cell surface, all of the CD19 comigrated with TAPA-1 and some of the CD19 comigrated with Leu-13. Furthermore, mAb binding to CD19, CD21, TAPA-1, and Leu-13 on B cell lines induced similar biologic responses, including the induction of homotypic adhesion, inhibition of proliferation, and an augmentation of the increase in intracellular [Ca2+] induced by suboptimal cross-linking of surface Ig on B cell lines. Together, these data suggest that TAPA-1 and Leu-13 are broadly expressed members of a signal transduction complex in which lineage-specific proteins, such as CD19 and CD21, provide cell-specific functions.

Antigens, CD↗