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Biomedical subjects

S Chandra

Publications and source records attributed to S Chandra.

At least 73 records · Page 4Linked to original sources
PubMed1999

Use of diffusion-weighted MRI and neurological deficit scores to demonstrate beneficial effects of isradipine in a rat model of focal ischemia.

The neuroprotective effects of isradipine, a 2,4-dihydropyridine calcium channel blocker, has been well studied in the rat model of focal ischemia (induced by middle cerebral artery occlusion, MCAO). The present study was designed to evaluate whether isradipine pretreatment caused early (0-3 h after stroke) ischemic changes in diffusion- weighted magnetic resonance imaging (DWI) and if such changes were predictive of previously documented protection in brain infarction. An initial dose-response study using neurological deficit scores and estimates of protection from brain infarction (by histology) showed that isradipine reduced cortical infarctions compared to vehicle-treated animals at most doses (between 1.25 and 5 mg/kg/day s.c. for 6 days) with the best results obtained at 5 mg/kg/day, where a 78.5% reduction was observed. This dose was utilized to perform the DWI study. Early quantitative estimates of infarct size, as measured by DWI at 1, 2 and 3 h after MCAO, were similar to those obtained with late histology at 24 h. These data indicate that in pretreatment protocols, DWI can be used to quantitatively predict areas at risk of permanent damage. This work also demonstrates that neurological deficits, developing from the damaged forebrain following focal stroke, may provide an index of isradipine's neuroprotective activity.

Animals↗
PubMed1999

Stereo augmented reality in the surgical microscope.

We present an augmented reality system that allows surgeons to view features from preoperative radiological images accurately overlaid in stereo in the optical path of a surgical microscope. The purpose of the system is to show the surgeon structures beneath the viewed surface in the correct 3-D position. The technical challenges are registration, tracking, calibration and visualisation. For patient registration, or alignment to preoperative images, we use bone-implanted markers and a dental splint is used for patient tracking. Both microscope and patient are tracked by an optical localiser. Calibration uses an accurately manufactured object with high contrast circular markers which are identified automatically. All ten camera parameters are modelled as a bivariate polynomial function of zoom and focus. The overall system has a theoretical overlay accuracy of better than 1 mm. Implementations of the system have been tested on seven patients. Recent measurements in the operating room conformed to our accuracy predictions. For visualisation the system has been implemented on a graphics workstation to enable high frame rates with a variety of rendering schemes. Several issues of 3-D depth perception remain unsolved, but early results suggest that perception of structures in the correct 3-D position beneath the viewed surface is possible.

Depth Perception↗
PubMed1999

Splenic tuberculosis: an unusual sonographic presentation.

Tuberculosis (TB) of the spleen is rare, especially in the immunocompetent. Recently there has been an increase in the incidence of splenic TB, primarily attributable to the raging HIV epidemic. Almost all cases of splenic TB present as multiple hypoechoic foci (< 2 cm) on ultrasonography. We present a case of a large solitary splenic tuberculoma in a middle-aged, non-immunosuppressed female, an employee at the local TB hospital. To the best of our knowledge, only two such cases have been described on ultrasound before. We suggest that, regardless of immune status, splenic TB should be considered as a diagnostic possibility when dealing with the solitary nodules of the spleen, especially when there is a history of exposure to or evidence of tuberculous foci elsewhere in the body.

Diagnosis, Differential↗
PubMed1999

Effect of endodontic smear layer and various solvents on the calcium ion diffusion through radicular dentin--an in vitro study.

External root resorption and ankylosis remains the major cause of failure of replanted teeth. This study was conducted to explore the different ways to increase the pH of periradicular area in order to overcome the problem of root resorption and ankylosis. 60 freshly extracted permanent anteriors were used after removing the crown at CEJ. After biomechanical preparation Ca (OH)2 was injected and assays were done using EDTA, Citric and tannic acid Assays were repeated. Calcium diffusion and pH in the root exterior was measured using spectrophotometer. Results showed that dentin is permeable to calcium & hydroxyl ions and placement of Ca (OH)2 in the canal resulted in its increased recovery and alkaline pH periradicularly. Smear layer removal did not result in significant increase in Ca++ recovery or alkaline pH however combination of EDTA & NaOCl was found best than the other two.

Calcium↗
PubMed1998

Hypo-osmotic shock of tobacco cells stimulates Ca2+ fluxes deriving first from external and then internal Ca2+ stores.

Hypo-osmotic shock of aequorin-transformed tobacco cells induces a biphasic cytosolic Ca2+ influx. Because both phases of Ca2+ entry are readily blocked by Ca2+ channel inhibitors, we conclude that the Ca2+ transients are mediated by Ca2+ channels. Evidence that the first but not second Ca2+ transient derives from external Ca2+ stores is that the first but not second influx is (i) eliminated by membrane-impermeable Ca2+ chelators, (ii) enlarged by supplementation of the medium with excess Ca2+, and (iii) reduced by the addition of competitive cations such as Mg2+ and Mn2+. Furthermore, entry of 45Ca during osmotic shock is prevented by inhibitors of the first but not second phase of Ca2+ entry. Evidence that the second wave of Ca2+ influx stems from release of intracellular Ca2+ is based on the above data plus observations that probable modulators of intracellular Ca2+ channels selectively block this phase of Ca2+ influx. Finally, a mechanism of communication between the two Ca2+ release pathways has become apparent, since perturbations that elevate or reduce the first Ca2+ transient lead to a compensating diminution/elevation of the second and vice versa. These data thus suggest that osmotic shock leads to the sequential opening of extracellular followed by intracellular Ca2+ stores and that these Ca2+ release pathways are internally compensated.

Aequorin↗
PubMed1998

Application of serial in vivo magnetic resonance imaging to evaluate the efficacy of endothelin receptor antagonist SB 217242 in the rat carotid artery model of neointima formation.

BACKGROUND: Alleviating vascular restenosis after percutaneous transluminal angioplasty remains a formidable challenge. Although multiple factors have been implicated in the pathophysiology of this vascular remodeling disorder, only limited therapeutic success has been achieved. Endothelin (ET)-1 has recently been implicated in the pathogenesis of neointimal growth. We report the in vivo efficacy of SB 217242, a nonpeptide dual ET(A)/ET(B) receptor antagonist with high oral bioavailability, in the rat carotid artery balloon angioplasty model. METHODS AND RESULTS: The lumen volumes of carotid arteries were estimated serially with magnetic resonance imaging (MRI) at baseline and at day 7 and day 14 after balloon catheter-induced denudation of the carotid arterial wall in the rat. Histomorphometric analysis was performed at day 14 after surgery to quantitate intimal hyperplasia. Statistical analysis was performed with ANOVA followed by post hoc Newman-Keuls multiple comparison test. In comparison to vehicle-treated animals, a 20% protection (P<0.05) from reduction was shown in the estimated lumen volume with long-term administration of SB 217242 (15 mg/kg BID p.o.). Histologic analyses indicated a 42% decrease (P<0.05) in neointimal growth. The MRI lumen volumes had a significant correlation with the corresponding histologic indices. CONCLUSIONS: Serial MRI provides the opportunity to assess the progression of vascular lumen volume in vivo after balloon angioplasty. MRI measurements can, in conjunction with in vitro histologic measurements, contribute to the understanding of the actions of pharmacologic agents in experimental models of neointima formation. With the use of serial MRI and histologic measurements, it is demonstrated that protection from both lumen volume reduction and neointima formation is obtained in this model by use of a potent, nonpeptide dual ET(A)/ET(B) receptor antagonist, SB 217242. Furthermore, this study provides additional support to the implication of ET-1 in the pathophysiology of neointima formation.

Angioplasty, Balloon↗
PubMed1998

Cardiac involvement in Dengue Haemorrhagic Fever.

We studied 17 consecutive patients of Dengue Haemorrhagic Fever/Dengue Shock Syndrome (DHF/DSS) to assess cardiac function by radionuclide ventriculography, echocardiography and electrocardiography (ECG) during the epidemic of Dengue virus type-2 (DEN-2) in Delhi, India (1996). Case definitions laid down by the WHO were followed. Fourteen patients were seropositive for Dengue infection. In radionuclide ventriculography study, the mean left-ventricular ejection fraction was 41.69 (5.04% (range 33-49%) and 7 patients had an ejection fraction less than 40%, global hypokinesia was detected in 12 (70.59%) patients. In echocardiography, the mean ejection fraction was 47.06 (3.8%). Eight patients had Dengue Shock Syndrome and the mean ejection fraction was 39.63% (4.97% in radionuclide ventriculography, out of which 5 patients had an ejection fraction below 40%. To find out the nature of myocardial involvement, 99m Tc-pyrophosphate imaging was done in 4 patients and it was discontinued further because no myocardial necrosis was detected in those patients. Five patients had ST and T changes in the electrocardiogram, radionuclide ventriculography and echocardiography revealed no abnormalities after 3 weeks of follow up and the ejection fraction was more than 50% in all cases. Global hypokinesia also improved and ECG changes reverted back to normal within 3 weeks. Acute reversible cardiac insult may be noticed in Dengue Haemorrhagic Fever/Dengue Shock Syndrome and could be responsible for hypotension/shock seen in some of these patients. Further studies are required to establish the pathogenic mechanisms of cardiac dysfunction in patients with Dengue Haemorrhagic Fever/Dengue Shock Syndrome.

Adolescent↗
PubMed1998

Combined mitral and aortic valvuloplasty by antegrade transseptal approach using Inoue balloon catheter.

OBJECTIVE: The purpose of this paper is firstly to highlight the ease with which the antegrade balloon aortic valvuloplasty can be performed with the Inoue balloon and secondly, the utility of the Inoue rubber nylon self-positioning balloon catheter used for twin valve dilatation. STUDY DESIGN: Percutaneous balloon valvuloplasty is being increasingly practised for treatment of multivalvular stenoses. We describe the case of a young (21 years), male who successfully underwent combined dilation of rheumatic mitral and aortic stenosis via the transseptal antegrade approach using Inoue balloon catheters for both valves. RESULT: Following the procedure, the mitral valve area increased from 0.6 cm2 to 1.7 cm2 and the peak systolic gradient across the aortic valve decreased from 100 mm Hg to 8 mm Hg without causing significant regurgitation at either. CONCLUSIONS: This report highlights the ease of performing balloon aortic valvuloplasty via the antegrade transvenous route and utilizing the advantages of Inoue balloon catheter.

Adult↗
PubMed1998

Balloon aortic valvuloplasty in young adults by antegrade, transseptal approach using Inoue balloon.

Transvenous, transseptal, antegrade balloon aortic valvuloplasty (BAV) was successfully performed in 16 consecutive young adults with noncalcific aortic stenosis using Inoue balloon catheter. There were 13 males and three females, with a mean age of 20.4 +/- 5.8 years (range 14-30 years). All the patients had normal left ventricular systolic function. All procedures were performed electively by the antegrade technique, except the initial index case in whom, the stenosed aortic valve could not be crossed retrogradely. Dilatation was performed using stepwise technique keeping the balloon:annulus ratio < or = 100% in all the cases. Transaortic peak systolic gradient decreased from 113.4 +/- 42.6 (range 70-210) mm Hg to 11.2 +/- 9.2 (range 4-32) mm Hg; P = 0.0005. Following BAV, three patients developed grade 2+ aortic regurgitation, who were managed medically. None of the patients developed tamponade, vascular complications, excessive bleeding, or thromboembolism. Significant left to right atrial shunt (Qp/Qs > or = 1.5:1) was observed in one case. The average procedure time was 20 +/- 8 min (range 18-35 min). On follow-up (n = 11 patients) at 4 +/- 1.5 months (range 2-7 months) all the patients were asymptomatic. Doppler transaortic peak systolic gradient was found to be 15 +/- 10.3 mm Hg (range 4-36 mm Hg). Antegrade BAV technique using Inoue balloon for noncalcific aortic stenosis in young adults is safe, effective and may be technically advantageous.

Adolescent↗
PubMed1998

Crosswire for recanalization of total occlusive coronary arteries.

Coronary angioplasty of total occlusions is technically difficult and is associated with limited success rates. The procedural outcome is mainly determined by the underlying pathological process. Recanalization of total occlusions is aimed at finding the passage with least resistance, without causing dissection or perforation. Several techniques have been advocated to improve the overall success rate. Recently, a new 0.014" Nitinol wire (Crosswire, Terumo) has been introduced as a tool, to achieve higher success rates for total occlusion angioplasty. The wire consists of an extremely flexible Nitinol-core, a platinum/iridium coil at the distal tip, and a hydrophilic polymer coating. Balloon angioplasty was attempted in 30 totally occluded coronary arteries with mean age of occlusion being 5 +/- 4 months (range 2-14 months). The initial five procedures were performed following failure of the conventional angioplasty guidewires. Subsequently, Cross-wire was used electively in all the cases. The lesion was crossed successfully in 90% (27/30) cases. Dissection of the coronary artery with subintimal entry was seen in two (7%) cases, and the rest (three cases) could not be crossed. Balloon angioplasty and stenting (n = 21) were performed with good immediate angiographic results. There were no myocardial infarctions or deaths. Fourteen of 16 patients, who had completed 6 months follow-up, were asymptomatic. Angiographic evidence of in-stent restenosis was demonstrable in one case. Successful recanalization of total coronary occlusions by using Cross-wire can be expected in 83% cases, with reasonable safety.

Adult↗
PubMed1998

Congenital maldevelopment of intervertebral disc simulating a neurofibroma.

Intervertebral disc herniation is a common cause of radiculopathy and myelopathy in adulthood. It is an uncommon tumor mimic. We report on an extradural disc associated with an osseous defect ostensibly caused by pressure erosion and appearing as a neural tumor. It showed homogeneous enhancement on a contrast-enhanced MR examination, leading to an erroneous diagnosis of nerve sheath tumor. An attempt has been made to explain the likely mechanism of formation accounting for the imaging appearances, along with a review of the literature.

Diagnosis, Differential↗
PubMed1998

Application of magnetic resonance imaging for evaluation of the efficacy of SB 217242 in neointimal formation.

Although several factors have been implicated in the pathophysiology of vascular neointimal formation and restenosis after balloon angioplasty, current therapies have failed to alleviate these conditions. Because endothelin-1 (ET-1) has been implicated in the pathogenesis of the neointimal growth, this study examined the in vivo efficacy of SB 217242, a potent nonpeptide mixed ETA/ETB receptor antagonist with high oral bioavailability, in the rat carotid balloon angioplasty model. A novel magnetic resonance imaging (MRI) approach was used for evaluation. MRI is a high-resolution, noninvasive spatial imaging modality that can serially monitor arterial luminal caliber in vivo, along with histologic evaluation. In vivo luminal volumes for the left carotid artery (LCA) were measured by MRI at baseline (before surgery) and again at 14 days after angioplasty. SB 217242 (30 mg/kg/day p.o.) was administered daily for 14 days after angioplasty. On day 14, SB 217242 provided 20% protection (p < 0.05) on neointimal-mediated decrease in luminal volume as measured by MRI. The non-ballooned right carotid arteries of both groups had significantly increased luminal volume on day 14 with respect to baseline values, indicating compensation for the decreased luminal size of the LCA. Histologic analysis of the mean intimal-to-medial ratio demonstrated that SB 217242 provided 42% (p < 0.05) protection. These results demonstrate that ET receptor antagonism can inhibit neointimal formation after balloon angioplasty and that MRI technology can provide valuable insight for noninvasive assessment of vascular lesion development.

Angioplasty, Balloon↗
PubMed1998

Systemin potentiates the oxidative burst in cultured tomato cells

Plants that have been wounded by insects or other herbivores may be more susceptible to infection by adventitious microbes. Wound-induced signal molecules, which serve to induce responses in the plant that retard further feeding, might also act to prepare a plant for possible pathogen attack. We have examined the effect of a wound-generated systemic messenger (systemin) on a pathogen-stimulated defense-response marker, the oxidative burst. We observed that neither systemin nor its inactive analog (A-17) was able to directly induce H2O2 biosynthesis in suspension-cultured tomato (Lycopersicon esculentum L.) cells, regardless of the duration of exposure of the cells to the two peptides. Similarly, neither systemin nor A-17 was capable of modifying an oligogalacturonide-elicited oxidative burst, as long as elicitor addition occurred within minutes of treatment with systemin or A-17. In contrast, preexposure of the cell cultures to systemin (but not to A-17) led to a time-dependent enhancement of the oligogalacturonide-elicited oxidative burst. By 12 h of exposure, the H2O2 biosynthetic capacity of systemin-treated cells exceeded that of the control cells by a factor of 16 +/- 2. A similar up-regulation by systemin of a mechanically stimulated oxidative burst was also observed. Because the systemin-induced augmentation in oxidant synthesis is quantitatively prevented by coincubation with 2 &mgr;M cycloheximide, and because the oxidative burst of oligogalacturonic acid-elicited control cells (no systemin exposure) is unaffected by preincubation with cycloheximide, we conclude that systemin enhancement of the tomato-cell oxidative burst requires protein synthesis.

Journal Article↗
PubMed1998

An analysis of synthetic processing of odor mixtures in the honeybee (Apis mellifera).

Both sensory transduction and central processing of odor mixtures can give rise to several different kinds of interaction, which can influence how well individual components are perceived and processed. In particular, odor mixtures are believed to give rise to 'configural' or 'synthetic' properties that are not characteristic of the components. However, the exact nature of these effects, particularly with regard to their expression in behavior, remains to be examined in detail. Here we use feature-negative and transwitching conditioning paradigms to show that honeybees can use configural cues in odor processing. However, the nature of these configural cues is not similar to that predicted by some models of conditioning. We propose that configural models may be capable of accounting for a substantial portion of odor mixture processing.

Animals↗
PubMed1998

Pulsed Doppler echocardiographic study of left ventricular diastolic function in patients with idiopathic dilated cardiomyopathy.

Dilated cardiomyopathy is basically regarded as a disease of left ventricular systolic dysfunction. There are only a few studies evaluating diastolic function in patients with dilated cardiomyopathy. To assess the LV diastolic function, 25 patients with idiopathic dilated cardiomyopathy and 20 age and sex matched normal subjects were studied with transmitral spectral tracings derived from pulsed Doppler echocardiography. All cardiomyopathy patients were in New York Heart Association class III to IV with dilated left ventricles and reduced systolic function (mean ejection fraction of 36.6 +/- 6.7 Vs 65 +/- 6 in normal subjects, p < 0.001). Patients with cardiomyopathy demonstrated an increased ratio of early to late diastolic velocity (E/A) (1.89 +/- 0.59 Vs 1.50 +/- 0.27 m/sec, p < 0.05), short deceleration time (E-E/2) (57.05 +/- 13.36 Vs 70.20 +/- 16.56 msec, p < 0.01) and short isovolumic relaxation time (IVRT) (53.5 +/- 22.7 Vs 72 +/- 12 msec, p < 0.05) as compared to normal subjects. The early filling fraction (EFF) was higher (0.71 +/- 0.11 Vs 0.66 +/- 0.06, p < 0.05) and atrial filling fraction (AFF) was lower (0.28 +/- 0.11 Vs 0.33 +/- 0.06, p < 0.05) in cardiomyopathy patients than in normal subjects. Our observations in a select group of dilated cardiomyopathy patients with advanced disease demonstrate a restrictive pattern on pulsed Doppler echocardiography.

Adult↗
PubMed1997

Reactivation of denatured proteins by domain V of bacterial 23S rRNA.

In vitro transcripts containing domain V of the 23S rRNA of Escherichia coli and Bacillus subtilis can reactivate denatured proteins almost as efficiently as the total 23S rRNA. Here we show that almost the full length of domain V is required for reactivation of denatured pig muscle lactate dehydrogenase and pig heart cytoplasmic malate dehydrogenase: the central loop of this domain alone is not enough for this purpose. The antibiotic chloramphenicol, which binds to domain V of 23S rRNA, can inhibit reactivation of these proteins completely. Activity is eliminated by EDTA at a concentration of <1 mM, even in the presence of 4 mM MgCl2, suggesting that the three-dimensional conformation of the RNA should be maintained for this activity.

Animals↗