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Biomedical subjects

R Viswanathan

Publications and source records attributed to R Viswanathan.

At least 19 recordsLinked to original sources
PubMed1997

Physiological basis in the assessment of ecotoxicity of pesticides to soil organisms.

Earthworms are universally accepted as one of the most suitable and representative soil animals to be used for assessing chemical pollution in soils. Therefore, in this work earthworm species diverse in habitat and life-pattern are used and the effects of sublethal concentrations of terbuthylazine and carbofuran on the reproductive processes, respiration and excretion are investigated. The results show that even low and moderate concentrations of the pesticides can induce measurable physiological effects. Species-specific and substance-specific effects are noticeable in the worms.

Ammonia↗
PubMed1997

Lymphoma of the lumbar nerve root: case report.

BACKGROUND AND IMPORTANCE: Lymphoma deposits in the spine are typically extradural. However, we report the case of a 38-year-old man who had a peripheral T-cell lymphoma with both intra- and extradural involvement. CLINICAL PRESENTATION: The patient presented with a 3-month history of right hip and thigh pain. Computed tomography and magnetic resonance imaging revealed features indistinguishable from those of a benign neurofibroma, except for a small area of T2-weighted signal abnormality in the third lumbar vertebral body. INTERVENTION: A solitary lesion of the right third lumbar root with normal surrounding bone and soft tissue was excised at surgery. At immunohistopathological evaluation, a diagnosis was made of peripheral lymphoma. Postoperative evaluation did not reveal lymphoma in the cerebrospinal fluid, abdomen, chest, blood, or bone marrow. This case illustrates that lymphomas can grow in patterns indistinguishable from a tumor of a nerve root. Therefore, other treatment modalities would have been considered had the diagnosis of lymphoma been made preoperatively. CONCLUSION: Involvement of a solitary nerve root by lymphoma, although rare, should be suspected in all cases of nerve root neurofibroma, and magnetic resonance imaging should be performed. Even minor signal abnormalities in adjoining vertebrae signal the possibility of malignancy. Percutaneous biopsy of suspicious bony lesions and systemic evaluation can demonstrate other sites of involvement, enabling the confirmation of the diagnosis and appropriate treatment without recourse to surgery.

Adult↗
PubMed1996

Acute intraoperative brain herniation during elective neurosurgery: pathophysiology and management considerations.

OBJECTIVES: To describe operative procedures, pathophysiological events, management strategies, and clinical outcomes after acute intraoperative brain herniation during elective neurosurgery. METHODS: Review of clinical diagnoses, operative events, postoperative CT findings, intracranial pressure, and arterial blood pressure changes and outcomes in a series of patients in whom elective neurosurgery had to be abandoned because of severe brain herniation. RESULTS: Acute intraoperative brain herniation occurred in seven patients. In each patient subarachnoid or intraventricular haemorrhage preceded the brain herniation. The haemorrhage occurred after intraoperative aneurysm rupture either before arachnoidal dissection (three) or during clip placement (one); after resection of 70% of a recurrent hemispheric astroblastoma; after resection of a pineal tumour; and after a stereotactic biopsy of an AIDS lesion. In all patients the procedure was abandoned because of loss of access to the intracranial operating site, medical measures to control intracranial pressure undertaken (intravenous thiopentone), an intraventricular catheter or Camino intracranial pressure monitor inserted, and CT performed immediately after scalp closure. The patients were transferred to an intensive care unit for elective ventilation and multimodality physiological monitoring. Using this strategy all patients recovered from the acute ictus and no patient had intracranial pressure > 35 mm Hg. Although one patient with an aneurysm rebled and died three days later the other six patients did well considering the dramatic and apparently catastrophic nature of the open brain herniation. CONCLUSIONS: There are fundamental differences in the pathophysiological mechanisms, neuroradiological findings, and outcomes between open brain herniation occurring in post-traumatic and elective neurosurgical patients. The surprisingly good outcomes in this series may have occurred because the intraoperative brain herniation was secondary to extra-axial subarachnoid or intraventricular haemorrhage rather than intraparenchymal haemorrhage or acute brain oedema. Expeditious abandonment of the procedure and closure of the cranium may also have contributed to the often very satisfactory clinical outcome.

Adult↗
PubMed1996

Detection of sugarcane bacilliform virus in sugarcane germplasm.

Sugarcane bacilliform virus (SCBV), a badnavirus was found in sugarcane genotypes of Saccharum officinarum L., S. barberi Jesw., S. sinense Roxb., S. robustum Brand and Jesw., and Saccharum hybrids. In most of the suspected genotypes the virus was found associated with clear foliar symptoms. However, certain symptom-free clones carried the virus too. The virus was detected by immuno-electron microscopy (IEM) and enzyme-linked immunosorbent assay (ELISA) in suspected clones. The virions measured about 108-118 x 20-21 nm in size. The virus was serologically closely related to another badnavirus, banana streak virus (BSV). Virus titer was low in most of the genotypes. However, a close correlation between symptoms expression and virus titer existed in some genotypes.

Animals↗
PubMed1995

Liquid to hexatic to crystalline order in Langmuir-Blodgett films.

Atomic force microscope images of zinc arachidate (ZnA2) Langmuir-Blodgett films show that three- and five-layer films are "hexatic," with long-range bond-orientational order and short-range positional correlations of three to five lattice repeats. The monolayer in contact with the substrate is disordered. Films of seven or more layers of ZnA2 are crystalline. A population of dislocations, most likely originating at the substrate, disrupts the positional but not the orientational order of the lattice, leading to hexatic layers intermediate between crystal and liquid. The influence of the substrate propagates farther into ZnA2 films than into cadmium arachidate films because the molecular cohesion is much weaker in ZnA2 than in cadmium arachidate, as evidenced by a less dense molecular packing.

Chemical Phenomena↗
PubMed1995

CO2 production in three earthworm species exposed to terbuthylazine and carbofuran in food.

Studies were conducted in the laboratory to determine the influence of sublethal doses of pesticides on the respiration of earthworms. Three different lumbricids were exposed to different concentrations of terbuthylazine and carbofuran for up to 12 weeks by allowing them to feed on contaminated plant material. After different exposure periods the CO2 output of the worms was determined by gas chromatography. High terbuthylazine concentrations generally increased CO2 production, whereas the low concentration tended to decrease it, especially in two of the three species studied. Low carbofuran concentration increased the CO2 expired in all the species; the high dose negatively affected the respiration in Lumbricus terrestris and L. rubellus after 3 weeks and in Eisenia andrei after 4 weeks of exposure.

Animals↗
PubMed1995

The structure and stability of phospholipid bilayers by atomic force microscopy.

Atomic force microscopy (AFM) was used to investigate the structure, stability, and defects of the hydrophilic surfaces of Langmuir-Blodgett bilayer films of distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylethanolamine (DPPE) in the solid phase, and dilinoleoylphosphatidylethanolamine (DLPE) in the fluid phase. Their relative resilience to external mechanical stress by the scanning tip and by fluid exchange were also investigated. DPPE monolayers showed parallel ridges at the surface with a period of 0.49 nm, corresponding to the rows of aligned headgroups consistent with the known crystallographic structure. DSPC and DLPE monolayers did not show any periodic order. The solid DSPC and DPPE monolayers were stable to continued rastering by the AFM tip; however, the stability of DLPE monolayers depended on the pH of the aqueous environment. Structural defects in the form of monolayer gaps and holes were observed after fluid exchange, but the defects in DLPE monolayer at pH 11 were stable during consecutive scanning. At pH 9 and below, the defects induced by fluid exchange over DLPE monolayers were more extensive and were deformed easily by consecutive scanning of the AFM tip at a force of 10 nN. The pH dependence of resilience was explained by the increasing bending energy or frustration due to the high spontaneous curvature of DLPE monolayers at low pH. The tangential stress exerted by the AFM tip on the deformable monolayers eventually produced a ripple pattern, which could be described as a periodic buckling known as Shallamach waves.

Biophysical Phenomena↗
PubMed1994

Langmuir-Blodgett films.

The controlled transfer of organized monolayers of amphiphilic molecules from the airwater interface to a solid substrate was the first molecular-scale technology for the creation of new materials. However, the potential benefits of the technology envisioned by Langmuir and Blodgett in the 1930s have yet to be fully realized. Problems of reproducibility and defects and the lack of basic understanding of the packing of complex molecules in thin films have continued to thwart practical applications of Langmuir-Blodgett films and devices made from such films. However, modern high-resolution x-ray diffraction and scanning probe microscopy have proven to be ideal tools to resolve many of the basic questions involving thin organic films. Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett. Even these relatively simple systems present liquid, hexatic, and crystalline order; van der Waals and strained layer epitaxy on various substrates; wide variations in crystal symmetry and interfacial area with counterions; modulated superstructures; and coexisting lattice structures. The wide variety of possible structures presents both a challenge and an opportunity for future molecular design of organic thin-film devices.

Chemical Phenomena↗
PubMed1994

Nail gun injury to the brain: an unusual case of suicide.

An unusual case of fatal suicidal craniocerebral penetrating injury due to a nail gun is described. The victim, a 52 year old joiner experienced in the use of nail drivers, shot himself just above the forehead in the midline, driving the nail through his hypothalamus and midbrain. Death was delayed by nearly 24 hours.

Brain Injuries↗
PubMed1994

Stereotaxic brain biopsy in AIDS patients: does it contribute to patient management?

The authors analysed all cases of brain biopsy done in AIDS or HIV+patients at the Department of Clinical Neurosciences, Western General Hospital, Edinburgh, during the period 1989-92 to determine the clinical utility of the procedure. Thirteen lesions were biopsied revealing toxoplasmosis in five, lymphoma in four, progressive multifocal leucoencephalopathy in three, HIV encephalitis in two and encephalitis of unknown aetiology in one. One biopsy specimen contained abnormal tissue but was non-diagnostic. The median survival after biopsy was only 7 weeks, but preoperative immunological (median CD4 count 45) and clinical status of the patients were poor. Although the impact of tissue diagnosis on patient survival was minimal it did enable modification of drug therapy. The authors preliminary experience with biopsy in AIDS patients suggests that the diagnostic information obtained is of limited value in prolonging the lives of patients in poor immunological status, but may be useful in refining medical therapies for toxoplasmosis and progressive multifocal leucoencephalopathy. Whether biopsy should be performed earlier in the course of cerebral disease in an effort to prolong survival time remains unclear.

AIDS Dementia Complex↗
PubMed1993

Strained-layer van der Waals epitaxy in a Langmuir-Blodgett film.

Atomic force microscope images of Langmuir-Blodgett films of lead and manganese fatty acid salts show that these monolayers have long-range order and are oriented with respect to the mica substrate, although the lattice symmetries of the monolayers and substrate are dramatically different. The surface lattice of sequentially thicker films evolves toward the bulk structure while retaining the substrate alignment. This behavior is in distinct contrast to films of cadmium fatty acid salts on mica, or all films on amorphous silicon oxide, in which the monolayer structure is disordered and a three-layer-thick film displays the bulk structure.

Adsorption↗