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Biomedical subjects

N Singh

Publications and source records attributed to N Singh.

At least 433 records · Page 24Linked to original sources
PubMed1994

Further comments on the measurement of carotid stenosis from angiograms. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.

BACKGROUND AND PURPOSE: Three different methods for estimating the percentage of reduction in the diameter of the internal carotid artery (ie, stenosis) have been proposed in the literature. Further comparisons of the methods were carried out with the intent of recommending a current standard for determining the percentage of stenosis from angiograms. METHODS: Angiograms from 112 patients were obtained. For each angiogram, stenosis was estimated in the manner of the European Carotid Surgery Trial (ECST method), the North American Symptomatic Carotid Endarterectomy Trial (NASCET method), and by a method using the common carotid artery lumen diameter (CC method). RESULTS: Although there is much discrepancy among the estimates of stenosis arising from the three different methods for any particular patient, it is possible to predict (on average) the percentage of stenosis from one method to another. The relationship between the NASCET and CC methods is linear, with a mean ratio of distal internal carotid artery to common carotid diameter of 0.62 (SD of 0.11). The variability in the diameter of the common carotid artery lumen stabilizes only beyond 2.5 common carotid diameter units (approximately 20 to 30 mm by conventional angiography) proximal to the bifurcation. Unexpectedly, the relationships between both the ECST and NASCET methods and ECST and CC methods were parabolic (P < .001). The reasons underlying these departures from linearity are uncertain. CONCLUSIONS: The comparability of our results with those reported in the literature regarding the CC and NASCET methods provides further evidence of the reproducibility of methods measuring anatomic features that can be visualized on an angiogram. Disease of the internal carotid artery is one of the important causes of ischemic symptoms. Measuring the narrowest portion of the internal artery relative to the normal portion of the same artery, well beyond the bulb, is a logical method. Moreover, benefits of carotid endarterectomy for patients with 70% to 99% stenosis as determined by the NASCET method have been well established in a clinical trial. Converting from the NASCET method to the CC method, given that the CC method is neither superior nor easier to calculate, is not recommended.

Angiography↗
PubMed1994

Poly ADP ribosylation as a possible mechanism of microwave--biointeraction.

Electromagnetic fields (EMFs) affect the metabolism of the body including the nervous, endocrine, cardiovascular, hematological as well as the reproductive system. EMFs are environmental pollutants, thus posing a health hazard which can cause steric changes in the molecule located at the cell surface. Microwaves are known to cause chromosomal abberations and act as tumor promoters. The process involves a stream of signals from cell membrane to nucleus and other organelles. The present investigations aim to understand the mechanism of biological effects of microwaves (2.45 GHz). The effect was studied on poly ADP-ribosylation, which is a post translational modification of chromatin protein catalysed by the enzyme poly ADPR polymerase using NAD+ as the substrate. Poly ADP-ribosylation has been shown to be involved in several aspects of chromatin structure and function. Twenty-three days old rats weighing 42-48 gms were exposed at a microwave dose level of 1.0 mW/cm2. After exposure for sixty days the animals were sacrificed and an estimation of poly ADPR polymerase activity was undertaken in different organs of these animals. There was an increase of 20% in its activity in liver, 35% in testis, whereas brain showed a 53% decrease in diencephalon and 20% decrease in the cortex in the exposed animals as compared to their respective controls. There was no change in enzyme activity in spleen and kidney. This was accompanied by concomitant changes in NAD+ levels. The above results may be cited as important events in carcinogenesis and tumor promotion related to microwave exposure and the signal transduction mechanism involved. The goal is to shed light on complex ecogenetic interactions leading to cancer modulation of gene expression by epigenetic mechanism.

Animals↗
PubMed1994

Cell death by apoptosis.

Apoptosis has been the focus of considerable attention in recent years. Apoptosis/programmed cell death, is a morphologically distinct process of cell death in which cells die in a controlled manner, in response to specific stimuli, following an intrinsic programme. Apoptosis is a greek work which means "falling off", as of leaves from trees. So occurs in plants suggesting that apoptosis originated very early in biological evolution. This wide spread active process of self destruction is seen in a wide variety of tissues, and is an essential feature in both development and maintenance of multicellular animals. It is ascribed roles in the process of embryogenesis, differentiation, metamorphosis, neural development, epithelial turnover, aging, regulation of cell population of the immune system and tumor regression.

Apoptosis↗
PubMed1994

Transcutaneous bilirubinometry in the management of bilirubinemia in term neonates.

One hundred full term babies of both sexes were randomly selected for transcutaneous bilirubin index (TcBI) estimation at the forehead at 12-24 h intervals from the time of appearance of clinical jaundice till the serum bilirubin levels fell within safe limits. TcBI was correlated with serum bilirubin estimated by conventional diazo method. Forty babies required phototherapy, in 20 an area of 2.5 cm2 over the forehead was covered during phototherapy to make an unexposed 'window' for TcBI estimation. The other 20 newborns received phototherapy as such and TcBI was estimated on the forehead. There was a linear relationship between serum bilirubin level and TcBI estimated at the forehead (r = 0.9090; P < 0.001). Further a significant linear correlation between prephototherapy and post-phototherapy (covered and uncovered groups) TcBI and serum bilirubin levels also existed (r = 0.7979; P < 0.001). There was no significant difference between post-phototherapy TcBI estimated at the covered and uncovered areas of forehead. However, post-phototherapy values of TcBI were significantly lower than corresponding prephototherapy values at higher serum bilirubin levels (> 16 mg/dl).

Bilirubin↗
PubMed1994

Cutaneous cryptococcosis mimicking bacterial cellulitis in a liver transplant recipient: case report and review in solid organ transplant recipients.

Cutaneous cryptococcosis is an uncommon manifestation of disseminated cryptococcal disease. We report a liver transplant recipient presenting with onset over 3 days of progressive pain and swelling of the lower extremity and foot with erythema and heat. Cryptococcal cellulitis was documented, but in retrospect the clinical presentation was indistinguishable in presentation and appearance from acute bacterial cellulitis. The patient also proved to have concomitant cryptococcal septic arthritis; the presence of cryptococcal antigen in the synovial fluid allowed a rapid and definitive diagnosis. Subsequently, cultures of skin, synovial fluid, and blood were all positive for cryptococci. Cryptococcus should be considered in the differential diagnosis of bacterial cellulitis in a liver transplant recipient not responding to antibacterial therapy.

Ankle Joint↗
PubMed1994

An evaluation of the S-100 stain in the histological diagnosis of tuberculoid leprosy and other granulomatous dermatoses.

Forty biopsies of granulomatous dermatoses, 12 of which were tuberculoid leprosy (TL), were studied for patterns of nerve twig distribution using an immunoperoxidase technique for S-100 protein. Four distinct patterns of nerve twigs were identified: 1) within granulomas, 2) between granulomas, 3) within and between granulomas, and 4) undetectable nerve twigs in an adequate biopsy. Pattern 4 was seen exclusively in TL (p < 0.05). The other patterns occurred in nonleprosy dermatoses as well, suggesting that pattern 4 is the best indicator toward a diagnosis of TL. The granules of mycetoma and Mycobacterium leprae also stained positively with the S-100 stain.

Diagnosis, Differential↗
PubMed1994

Toxoplasma gondii infection & its association with iodine deficiency in a residential school in a tribal area of Maharashtra.

To determine the seroprevalence and incidence of toxoplasmosis, 194 random serum samples of school students aged 10 to 18 yr (n = 178), their teachers (n = 10) and food handlers (n = 6) from a residential tribal school situated in district Dhule, Maharashtra state of western India, were tested. The samples were tested for anti-toxoplasma IgG and IgM antibodies using enzyme linked immuno sorbent assay (ELISA). Active infection was confirmed by a stage-specific direct agglutination test (DAT) using acetone fixed tachyzoites of T. gondii. A serosurveillance for rubella immunity was also simultaneously carried out. The results showed that at the age of 10 yr, all the children were immune to rubella infection and toxoplasma seroprevalence was detected in 20 per cent of the children. Toxoplasma infection was prevalent in 42.8 per cent adolescents, at the age of 18 yr. The average seroprevalence rate of toxoplasma infection was not significantly different in male and female children. The incidence rate of toxoplasma infection was inversely related to increase in age. The school staff comprising teachers and food handlers (aged 27 to 45 yr) showed a toxoplasma seroprevalence rate of 75 per cent (P < 0.001). There was also a significant difference (P < 0.05) in the prevalence of toxoplasmosis in children with grade II goitre (46.1%) and grade I or no goitre (31.8 and 26.5% respectively). The possible association between iodine deficiency and toxoplasma infection is being reported for the first time in this preliminary study.

Adolescent↗
PubMed1993

The real-time resolution of proton-related transient-state steps in an enzymatic reaction. The early steps in the oxidative deamination reaction of bovine liver glutamate dehydrogenase.

We introduce a novel transient-state kinetic approach which can resolve proton and product time courses into a series of individual steps that comprise the reaction path. We have applied this approach to the oxidative deamination reaction catalyzed by bovine liver glutamate dehydrogenase, measuring both the product (NADPH) and proton time courses at various pH values. The global treatment (over all pH values) resolves the very early portion of this reaction quantitatively and provides a continuous time course for each of the six protonic species. We propose the following mechanism: L-glutamate binds to an open conformation of the enzyme-NADP complex, forming salt bridges between its alpha- and gamma-carboxyl groups and the protonated forms of enzyme lysine residues 114 and 90, respectively. In this position, the alpha-H atom of the substrate is too far from the nicotinamide ring for hydride transfer to occur. In the next step, three events occur in a concerted manner: lysine 126 loses a proton and acquires a single water molecule; the active site cleft closes; bulk water is expelled; the substrate and coenzyme are forced closer together and remain in a nonaqueous environment during the ensuing chemical events, returning to an open conformation only in time to allow the product release steps to occur. Thus, substrate binding accomplishes a number of important tasks which are themselves an integral part of the catalytic mechanism. Combining the novel transient state approach developed here with steady-state kinetic information can produce a detailed mechanistic resolution of otherwise hidden steps.

Amino Acid Sequence↗
PubMed1993

Beta-Lactam antibiotic-induced leukopenia in severe hepatic dysfunction: risk factors and implications for dosing in patients with liver disease.

PURPOSE: To determine if an association could be established for leukopenia and administration of beta-lactam antibiotic therapy in patients with hepatic dysfunction. If such an association could be found, to determine the incidence, timing, and risk factors for beta-lactam antibiotic-induced leukopenia. PATIENTS AND METHODS: Patients with hepatic dysfunction, i.e., liver transplant recipients as well as patients with end-stage liver disease awaiting liver transplantation, seen at our institution between October 1989 and October 1991, who received 7 or more days of antibiotics, were studied in a prospective observational fashion. Complete blood count was determined at baseline and followed until the completion of the antibiotic course or until the resolution of leukopenia in leukopenic patients. RESULTS: Leukopenia occurred after a mean of 6 days with 23% of the beta-lactam antibiotic courses as compared with 0% with the non-beta-lactam antibiotic courses (p = 0.046). Development of leukopenia correlated with the severity of liver disease. Patients developing leukopenia had worse synthetic hepatic function as evidenced by a lower serum albumin level (p < 0.01), a lower serum cholesterol level (p < 0.05), and a higher prothrombin time (p < 0.01) as compared with the patients without leukopenia. Leukopenic patients had a lower baseline white blood cell count (p < 0.051) and a lower baseline platelet count (p < 0.01) indicative of a greater degree of hypersplenism. Leukopenic patients received a higher mean daily dosage of cephalosporins as compared with nonleukopenic patients. CONCLUSION: beta-Lactam antibiotics when administered in usually recommended dosages can induce leukopenia in patients with hepatic dysfunction. The probable mechanism is impaired hepatic metabolism of the beta-lactam antibiotics resulting in bone marrow suppression of white cell precursors from excessive antibiotic concentrations. The more severe the hepatic dysfunction, the greater the risk. We propose a reduction in dosages of beta-lactam antibiotics when used in patients with hepatic dysfunction. Finally, we raise the possibility that this adverse drug effect is more common than currently recognized by physicians.

Adult↗