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Biomedical subjects

R Sreenivasan

Publications and source records attributed to R Sreenivasan.

8 recordsLinked to original sources
PubMed2005

Complexity analysis of dense array EEG signal reveals sex difference.

This article deals with the complexity aspects of the recorded electroencephalogram (EEG) signal from male and female subjects. The analysis follows direct application of time series measures of global linear complexity and characterization of the embedded complexity in the signals using the nonlinear statistic of approximate entropy. The study reveals significant differences in complexity between the two sex groups during passive, no-task conditions, whereas no apparent variation exists during a mental task state. The detection of subtle changes as well as the ease in presenting a global picture of the complexity variation on the human cortical surface makes the nonlinear statistic a better marker of system complexity.

Adult↗
PubMed2004

Complexity quantification of dense array EEG using sample entropy analysis.

In this paper, a time series complexity analysis of dense array electroencephalogram signals is carried out using the recently introduced Sample Entropy (SampEn) measure. This statistic quantifies the regularity in signals recorded from systems that can vary from the purely deterministic to purely stochastic realm. The present analysis is conducted with an objective of gaining insight into complexity variations related to changing brain dynamics for EEG recorded from the three cases of passive, eyes closed condition, a mental arithmetic task and the same mental task carried out after a physical exertion task. It is observed that the statistic is a robust quantifier of complexity suited for short physiological signals such as the EEG and it points to the specific brain regions that exhibit lowered complexity during the mental task state as compared to a passive, relaxed state. In the case of mental tasks carried out before and after the performance of a physical exercise, the statistic can detect the variations brought in by the intermediate fatigue inducing exercise period. This enhances its utility in detecting subtle changes in the brain state that can find wider scope for applications in EEG based brain studies.

Adult↗
PubMed2003

Mapping of regions within the vaccinia virus complement control protein involved in dose-dependent binding to key complement components and heparin using surface plasmon resonance.

The vaccinia virus complement control protein (VCP) is involved in modulating the host inflammatory response by blocking both pathways of complement activity through its ability to bind C3b and C4b. Other activities arise from VCP's ability to strongly bind heparin. To map regions within VCP involved in binding complement and heparin experimentally, surface plasmon resonance (SPR) and recombinantly expressed VCP (rVCP) constructs were employed. Using C3b or heparin as the immobilized ligand, various rVCP constructs were tested for their ability to bind. Results suggest that VCP is the smallest functional unit able to bind C3b, thereby blocking complement activity, and only a single site, the large basic region near the C-terminus, is involved in heparin binding. Kinetic analysis was also performed to determine the relative binding affinities between rVCP and complement (C3-MA and C4b), as well as rVCP and heparin. rVCP was found to possess a significantly greater affinity for C3-MA than C4b, as indicated by the 1.50e3-fold greater association rate constant (k(a)). This study provides insights for the design of new therapeutic proteins capable of blocking complement activation.

Binding Sites↗
PubMed2003

Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis.

Rectification of the electromyographic (EMG) signal is a commonly used pre-processing procedure that allows detection of significant coherence between EMG and measured cortical signals. However, despite its accepted and wide-spread use, no detailed analysis has been presented to offer insight into the precise function of rectification. We begin this paper with arguments based on single motor unit action potential (AP) trains to demonstrate that rectification effectively enhances the firing rate information of the signal. Enhancement is achieved by shifting the peak of the AP spectrum toward the lower firing rate frequencies, whilst maintaining the firing rate spectra. A similar result is obtained using the analytic envelope of the signal extracted using the Hilbert transform. This argument is extended to simulated EMG signals generated using a published EMG model. Detection of firing rate frequencies is obtained using phase randomised surrogate data, where the original EMG power spectrum exceeds the averaged rectified surrogate spectra at integer multiples of firing rate frequencies. Model simulations demonstrate that this technique accurately determines grouped firing rate frequencies. Extraction of grouped firing rate frequencies prior to coherency analyses may further aid interpretation of significant cortico-muscular coherence findings.

Action Potentials↗
PubMed1997

Binding of monomeric and oligomeric porphyrins to human glioblastoma (U-87MG) cells and their photosensitivity.

The binding of monomeric (Hp) and oligomeric (PHE) forms of porphyrin to glioblastoma (U-87MG) cells and the photosensitization of these cells have been studied. Upon binding to U-87MG cells, Hp and PHE exhibited fluorescence bands at 615 and 636 nm, respectively. The fluorescence and absorption spectra of Hp, HpD and PHE, measured in different solvents, suggest that the 615 nm band may arise due to the binding of monomeric as well as aggregated forms of porphyrin to the hydrophilic sites in the cells whereas the 636 nm band may be due to the binding of an aggregated form of porphyrin to the hydrophobic sites. The photosensitivity of cells and photo-induced lipid peroxidation were measured as a function of light dose. Cells were found most photosensitive to PHE followed by HpD and Hp. The photosensitivity of cells correlates well with the fluorescence intensity of cell bound dye at 636 nm. These results suggest that the binding of the oligomeric component of HpD to hydrophobic sites in the cells is responsible for the enhancement in the photosensitivity.

Brain Neoplasms↗
PubMed1994

Hematoporphyrin derivative binding and photosensitization in human glioblastoma cells: comparison of exponential and plateau phase cells.

Plateau phase glioblastoma (U 87MG) cells were found more photosensitive than the exponentially growing cells. In both phases of growth, the photosensitivity showed further enhancement on incubating the cells with HpD for longer duration. Plateau phase cells accumulated more HpD than exponential phase cells for shorter duration of incubation with HpD, however, for longer duration of incubation, the amount of drug uptake was almost the same in both phases of growth. Fluorescence spectra of cell bound HpD showed a difference in spectral intensity distribution in exponential and plateau phase cells. In exponential phase cells, the fluorescence maximum of cell bound HpD was at 615 nm whereas in plateau phase cells the same was at 636 nm.

Brain Neoplasms↗
PubMedDate not supplied

Lymphoma associated antigen (LAA)--a unique biomarker for lymphomas.

A lymphoma associated antigen (LAA) isolated from pooled lymph nodes of confirmed Hodgkin's and non-Hodgkin's lymphomas has been purified and characterized. Using a xenogenic rabbit anti-serum, enzyme-linked immunosorbent assay (ELISA) and RIA were developed for LAA. LAA was detected in the sera of all confirmed lymphomas, the test being negative for normals, for patients with benign lymphadenitis and various other types of cancers. Except for a very few false positive results, no false negative was observed. LAA was identified in urine, CSF, saliva and gastric juice of a few lymphoma patients, and the test proved to be of diagnostic potential, as for a few patients it had a lead time of a few months over the histological diagnosis. In order to render the LAA test more precise and specific, monoclonal antibodies were generated by both in vitro and in vivo immunization procedures. Seven monoclonals were generated, viz. 7D6, 7D2, 7G2, 7C5, 6G2, 23B7 and 23G11, which exhibited cytoplasmic staining of frozen sections of malignant lymphoid tissues of B cell derived non-Hodgkin's lymphomas. Two of these monoclonal antibodies, 7D6 and 23B7, revealed strong cytoplasmic staining of frozen sections, impression smears and cytospin specimens of B cell non-Hodgkin's lymphomas. The reactivity was very weak or negative for T cell lymphomas. The test was negative for Hodgkin's disease and controls. These results were confirmed by dot blotting, immunoprecipitation and immunofluorescence study. By ELISA with a sensitivity of 15 ng/ml, serum LAA levels for lymphomas were in the range 72-1250 ng/ml. LAA could not be detected in the sera of normals and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗