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Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 199 records · Page 11Linked to original sources
PubMed1996

Spatial integration and cortical dynamics.

Cells in adult primary visual cortex are capable of integrating information over much larger portions of the visual field than was originally thought. Moreover, their receptive field properties can be altered by the context within which local features are presented and by changes in visual experience. The substrate for both spatial integration and cortical plasticity is likely to be found in a plexus of long-range horizontal connections, formed by cortical pyramidal cells, which link cells within each cortical area over distances of 6-8 mm. The relationship between horizontal connections and cortical functional architecture suggests a role in visual segmentation and spatial integration. The distribution of lateral interactions within striate cortex was visualized with optical recording, and their functional consequences were explored by using comparable stimuli in human psychophysical experiments and in recordings from alert monkeys. They may represent the substrate for perceptual phenomena such as illusory contours, surface fill-in, and contour saliency. The dynamic nature of receptive field properties and cortical architecture has been seen over time scales ranging from seconds to months. One can induce a remapping of the topography of visual cortex by making focal binocular retinal lesions. Shorter-term plasticity of cortical receptive fields was observed following brief periods of visual stimulation. The mechanisms involved entailed, for the short-term changes, altering the effectiveness of existing cortical connections, and for the long-term changes, sprouting of axon collaterals and synaptogenesis. The mutability of cortical function implies a continual process of calibration and normalization of the perception of visual attributes that is dependent on sensory experience throughout adulthood and might further represent the mechanism of perceptual learning.

Animals↗
PubMed1996

Bacteriophage lambda N protein alone can induce transcription antitermination in vitro.

Specific and processive antitermination by bacteriophage lambda N protein in vivo and in vitro requires the participation of a large number of Escherichia coli proteins (Nus factors), as well as an RNA hairpin (boxB) within the nut site of the nascent transcript. In this study we show that efficient, though nonprocessive, antitermination can be induced by large concentrations of N alone, even in the absence of a nut site. By adding back individual components of the system, we also show that N with nut+ nascent RNA is much more effective in antitermination than is N alone. This effect is abolished if N is competed away from the nut+ RNA by adding, in trans, an excess of boxB RNA. The addition of NusA makes antitermination by the N-nut+ complex yet more effective. This NusA-dependent increase in antitermination is lost when delta nut transcripts are used. These results suggest the formation of a specific boxB RNA-N-NusA complex within the transcription complex. By assuming an equilibrium model, we estimate a binding constant of 5 x 10(6) M-1 for the interaction of N alone with the transcription complex. This value can be used to estimate a characteristic dissociation time of N from the complex that is comparable to the dwell time of the complex at an average template position, thus explaining the nonprocessivity of the antitermination effect induced by N alone. On this basis, the effective dissociation rate of N should be approximately 1000-fold slower from the minimally processive (100-600 bp) N-NusA-nut+ transcription complex and approximately 10(5)-fold slower from the maximally processive (thousands of base pairs) complex containing all of the components of the in vivo N-dependent antitermination system.

Bacterial Proteins↗
PubMed1996

Role of Escherichia coli RNA polymerase alpha subunit in modulation of pausing, termination and anti-termination by the transcription elongation factor NusA.

The alpha subunit (alpha) of RNA polymerase (RNAP) is critical for assembly of polymerase and positive control of transcription initiation in Escherichia coli. Here, we report that alpha also plays a role in transcription elongation, and this involves a direct interaction between alpha and NusA factor. During in vitro transcription without NusA, alpha interacts with the nascent RNA, as revealed by photocrosslinking. When NusA is present, RNA crosslinks to NusA rather than to alpha. We show that this NusA-RNA interaction is diminished during transcription with an RNAP mutant that lacks the C-terminus of alpha beyond amino acid 235, including the so-called alpha CTD. The absence of alpha CTD also affects NusA's ability to enhance transcription pausing, termination at intrinsic terminators and anti-termination by the phage lambda Q anti-terminator, but not anti-termination by the lambda N anti-terminator. NusA functions are not recovered even when transcription with mutant RNAP is done with excess NusA, a condition which does restore NusA-RNA crosslinking. By affinity chromatography, we show that NusA interacts directly with alpha, and also with beta and beta', but not with mutant alpha. Hence, alpha-NusA interaction is vital for the control of transcript elongation and termination.

Bacterial Proteins↗
PubMed1996

Fine-needle aspiration biopsy of angio-immunoblastic lymphadenopathy.

In this article, we have described the fine-needle aspiration biopsy (FNAB) of five cases of angioimmunoblastic lymphadenopathy (AILD). FNAB of these cases showed large number of capillary fragments, along with polymorphous population of cells consisting of plenty of immunoblasts, plasma cells, eosinophils, and mast cells. Two cases showed clusters of clear cells. It is essential to have detailed clinical features for FNAB diagnosis of AILD. Histopathology is advisable in all the fresh cases. FNAB is helpful for screening and follow-up of AILD.

Adult↗
PubMed1996

The review process used by US health care plans to evaluate new medical technology for coverage.

OBJECTIVE: To examine the process and information used by medical directors (MDs) of private health plans to make medical coverage determinations for new medical technologies, and to assess the influence of plan characteristics on the process. DESIGN: Cross-sectional national survey. PARTICIPANTS: Two hundred thirty-one MDs at private health plans representing 66% and 72% of the US population covered by HMOs and indemnity plans, respectively. MEASUREMENTS: Actual and optimal review process, final decision authority, sources, and evidence used for technology coverage decisions. RESULTS: In 96% of plans, MDs take part in the medical policy review process for new technology. However, MDs have final authority over coverage decisions in only 27% of plans. Indemnity plans are more likely to assert that MDs should be responsible for final decisions, odds ration (OR) = 3.3 (95% confidence interval [95% CI] 1.4, 10). Optimal sources of information of new technology were journals, medical society statements or practice guidelines, and opinions of national experts. Actual sources of information used differed from optimal ones; local experts were used more often than is considered optimal (p < .001). For-profit plans were more likely than nonprofit plans to use national experts, OR 2.5 (95% CI 1.3, 5.0), and practice guidelines, OR 5.0 (95% CI 2.5, 10). Randomized trials (94% of MDs) meta-analyses (61%), and reviews (42%) were considered the best evidence for making coverage decisions. Barriers to making optimal decisions were lack of timely evidence on effectiveness and cost-effectiveness, not legal or regulatory issues; HMO, small, and nonprofit plans were two or three times more likely to list lack of cost-effectiveness data than their counterparts (p < .05). CONCLUSIONS: Although MDs are nearly always involved in the technology evaluation process, a minority of MDs retain final authority over coverage decisions. Evidence from strong scientific research designs is the most frequently cited basis for decisions, but there is need for more timely, rigorous scientific evidence on medical interventions. How a health plan evaluates a new medical technology for coverage varies with identifiable plan characteristics.

Cross-Sectional Studies↗
PubMed1996

The preterm prediction study: fetal fibronectin testing and spontaneous preterm birth. NICHD Maternal Fetal Medicine Units Network.

OBJECTIVE: To evaluate the presence of fetal fibronectin in the cervix and vagina as a screening test for spontaneous preterm birth. METHODS: Two thousand nine hundred twenty-nine women at ten centers were routinely screened every 2 weeks from 22-24 to 30 weeks for cervical and vaginal fetal fibronectin. A positive test was defined as a value equal to or greater than 50 ng/mL. The relation between a positive test at four gestational ages and spontaneous preterm birth at various intervals after the test was determined. RESULTS: In each testing period, 3-4% of the fetal fibronectin tests were positive. The correlation between cervical and vaginal fetal fibronectin at the same visit was always approximately 0.7 (P < .001), and that between cervical or vaginal fetal fibronectin in consecutive visits was between 0.17 and 0.25 (P < .001). The sensitivity of fetal fibronectin at 22-24 weeks to predict spontaneous preterm birth at less than 28 weeks was 0.63, and the relative risk for a positive versus negative test was 59. The specificity was always 96-98%, whereas the positive predictive value rose from 13% to 36% as the upper limit of the definition of preterm birth was increased from less than 28 to less than 37 weeks. The relative risk for spontaneous preterm birth after a positive fetal fibronectin test compared with a negative fetal fibronectin test varied substantially by testing period and by the definition of spontaneous preterm birth, but always remained greater than 4 and statistically significant. CONCLUSION: A positive cervical or vaginal fetal fibronectin test at 22-24 weeks predicted more than half of the spontaneous preterm births at less than 28 weeks (sensitivity 0.63). As the definition of spontaneous preterm birth was extended to include later gestational ages or when the fetal fibronectin test was performed later in pregnancy, the level of association between a positive fetal fibronectin test and spontaneous preterm birth, while remaining highly significant, tended to decrease. Although fetal fibronectin is an excellent test for predicting spontaneous preterm birth, we present no evidence that the use of this test will result in a reduction in spontaneous preterm birth.

Adult↗
PubMed1996

The preterm prediction study: maternal stress is associated with spontaneous preterm birth at less than thirty-five weeks' gestation. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network.

OBJECTIVE: Our purpose was to determine whether various measures of poor psychosocial status in pregnancy are associated with spontaneous preterm birth, fetal growth restriction, or low birth weight. STUDY DESIGN: Anxiety, stress, self-esteem, mastery, and depression were assessed at 25 to 29 weeks in 2593 gravid women by use of a 28-item Likert scale. Scores for each psychosocial subscale were determined, and an overall psychosocial score was calculated. Scores were divided into quartiles, and the lowest quartile scores were used to define poor psychosocial status. The percent spontaneous preterm birth, low birth weight, and fetal growth restriction in women with low and high psychosocial scores were compared. Logistic regression analyses provided the odds ratios and 95% confidence intervals. RESULTS: Analyses revealed that stress was significantly associated with spontaneous preterm birth and with low birth weight with odds ratios of 1.16, p = 0.003, and 1.08, p = 0.02, respectively, for each point on the scale. A low score on the combined scale or on any subscale other than stress did not predict spontaneous preterm birth, fetal growth restriction, or low birth weight. After multivariate adjustment was performed for psychosocial status, substance use, and demographic traits, black race was the only variable significantly associated with spontaneous preterm birth, fetal growth restriction, and low birth weight; stress and low education were associated with spontaneous preterm birth and low birth weight. CONCLUSION: Stress was associated with spontaneous preterm birth and low birth weight even after adjustment for maternal demographic and behavioral characteristics. Black race continues to be a significant predictor of spontaneous preterm birth, fetal growth restriction, and low birth weight even after adjustment for stress, substance use, and other demographic factors.

Adult↗
PubMed1996

The preterm prediction study: a clinical risk assessment system.

OBJECTIVE: Our aims were to develop a risk assessment system for the prediction of spontaneous preterm delivery using clinical information available at 23 to 24 weeks' gestation and to determine the predictive value of such a system. STUDY DESIGN: A total of 2929 women were evaluated between 23 and 24 weeks' gestation at 10 centers. Demographic factors, socioeconomic status, home and work environment, drug and alcohol use, and medical history were evaluated. Information regarding symptoms, cultures, and treatments in the current pregnancy were ascertained. Anthropomorphic and cervical examinations were performed. Univariate analysis and multivariate logistic regression were performed in a random selection, constituting 85% of the study population. The derived risk assessment system was applied to the remaining 15% of the population to evaluate its validity. RESULTS: A total of 10.4% of women were delivered of preterm infants. The multivariate models for spontaneous preterm delivery were highly associated with spontaneous preterm delivery (p < 0.0001). A low body mass index (<19.8) and increasing Bishop scores were significantly associated with spontaneous preterm delivery in nulliparous and multiparous women. Black race, poor social environment, and work during pregnancy were associated with increased risk for nulliparous women. Prior obstetric outcome overshadowed socioeconomic risk factors in multiparous women with a twofold increase in the odds of spontaneous preterm delivery for each prior spontaneous preterm delivery. Current pregnancy symptoms, including vaginal bleeding, symptomatic contractions within 2 weeks, and acute or chronic lung disease were variably associated with spontaneous preterm delivery in nulliparous and multiparous women. When the system was applied to the remainder of the population, women defined to be at high risk for spontaneous preterm delivery (> or = 20% risk) carried a 3.8-fold (nulliparous women) and 3.3-fold (multiparous women) higher risk of spontaneous preterm delivery than those predicted to be at low risk. However, the risk assessment system identified a minority of women who had spontaneous preterm deliveries. The sensitivities were 24.2% and 18.2% and positive predictive values were 28.6% and 33.3%, respectively, for nulliparous and multiparous women. CONCLUSIONS: Although it is possible to develop a graded risk assessment system that includes factors that are highly associated with spontaneous preterm delivery in nulliparous and multiparous women, such a system does not identify most women who subsequently have a spontaneous preterm delivery. This system has investigational value as the basis for evaluating new technologies designed to identify at-risk subpopulations.

Black People↗
PubMed1996

The preterm prediction study: risk factors in twin gestations. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network.

OBJECTIVE: Our purpose was to determine the association between the presence of bacterial vaginosis, fetal fibronectin, and a short cervix and the risk of spontaneous preterm birth of twins. STUDY DESIGN: We prospectively screened 147 women with twins at 24 and 28 weeks' gestation for more than 50 potential risk factors for spontaneous preterm birth. We also measured cervical length with ultrasound scans and tested for the presence of bacterial vaginosis. Fetal fibronectin level was evaluated every 2 weeks from 24 to 30 weeks' gestation. Outcomes included spontaneous preterm birth at < 32 weeks, < 35 weeks, and < 37 weeks. RESULTS: Among twin as compared with singleton pregnancies, a cervical length < or = 25 mm was more common at both 24 and 28 weeks, a statistically significant difference. There were no significant differences in most other risk factors. Of the factors evaluated by means of univariate analysis at 24 weeks, only a short cervix (< or = 25 mm) was consistently associated with spontaneous preterm birth. The odds ratio and 95% confidence interval for spontaneous preterm birth at < 32 weeks, < 35 weeks, and < 37 weeks were 6.9 (2.0 to 24.2), 3.2 (1.3 to 7.9), and 2.8 (1.1 to 7.7). At 28 weeks, a cervical length < or = 25 mm was not a strong predictor of spontaneous preterm birth. At both 28 weeks (odds ratio, 9.4; confidence interval, 1.0 to 67.7) and 30 weeks (odds ratio 46.1; confidence interval, 4.2 to 1381), a positive fetal fibronectin result was significantly associated with spontaneous preterm birth at < 32 weeks. Bacterial vaginosis at 24 or 28 weeks was not associated with spontaneous preterm birth of twins. Multivariate analysis confirmed the association between cervical length < or = 25 mm at the 24-week visit and spontaneous preterm birth and also confirmed that at 24 weeks the other risk factors were less consistently and often not statistically significantly associated with spontaneous preterm birth. Of the risk factors evaluated at 28 weeks, only a positive fetal fibronectin was associated with a significantly increased risk for spontaneous preterm birth. CONCLUSIONS: Most known risk factors for spontaneous preterm birth were not significantly associated with spontaneous preterm birth of twins. At 24 weeks, cervical length < or = 25 mm was the best predictor of spontaneous preterm birth at < 32 weeks, < 35 weeks, and < 37 weeks. Of the risk factors evaluated at 28 weeks, fetal fibronectin was the only statistically significant predictor of spontaneous preterm birth at < 32 weeks.

Adolescent↗
PubMed1996

A cost-effectiveness analysis of OKT3 induction therapy in cadaveric kidney transplantation.

We evaluated the cost-effectiveness of a standard immunosuppressive regimen versus an OKT3 induction regimen in cadaveric kidney transplant recipients. Cost estimates were based on results from a five-center randomized trial comparing the safety and efficacy of OKT3 induction with a conventional triple-drug regimen and financial data from the National Cooperative Transplantation Study, the Medicare Provider and Analysis Review database, and other sources. Patients received OKT3 (5 mg/day) by intravenous (IV) bolus injection for 10 to 14 consecutive days in conjunction with azathioprine, prednisone, and the delayed addition of cyclosporine (CsA) on day 11 (n = 105) or a conventional immunosuppressive regimen consisting of CsA, azathioprine, and prednisone (n = 102). The following measures were used to evaluate the two regimens: costs incurred between transplantation and graft failure; the effectiveness of the two regimens as defined by length of graft survival; and cost-effectiveness ratios through 5 years of observed follow-up and modeled through the expected duration of graft survival. Results showed that OKT3 induction uniformly adds $8,219 to the cost of the transplant hospitalization. However, most of this cost is offset by a reduction in the cost of treating rejection episodes in the OKT3 group (P = 0.002). A trend toward improved graft survival was detected in the OKT3 group (P = 0.158). Through 5 years of observed follow-up, costs per year of graft survival are $30,474 with OKT3 versus $32,687 with the conventional regimen. Modeled through the expected duration of graft survival, OKT3 induction costs $8,335 for each additional year of graft survival. Results are fairly insensitive to wide variations in baseline assumptions. We conclude that OKT3 induction improves the cost-effectiveness of kidney transplantation.

Anti-Infective Agents↗
PubMed1996

Awareness of providers' use of new medical technology among private health care plans in the United States.

In a national survey of medical directors at 231 U.S. private health care plans that cover over two thirds of the privately insured population, we studied whether medical directors are aware when a new technology, such as laser therapy, is being used in procedures for which claims are submitted, the factors alerting them to such use, and the factors prompting them to make a specific coverage decision for the technology. We also examined possible associations between health plans' characteristics (HMO versus indemnity, size, profit status, and time in operation) and their medical directors' awareness of the use of technologies, factors alerting medical directors to their use, and factors prompting specific coverage decisions. The majority of plans were generally not aware that laser technology was being used when it was billed under a general billing code, raising the possibility that less effective or less safe technologies could be introduced rapidly into the treatment of insured populations. Nonprofit and older plans were less likely to be aware that lasers were used in some procedures than for-profit and younger plans.

Analysis of Variance↗
PubMed1996

Intravesical capsaicin in neurologic impaired patients with detrusor hyperreflexia.

Capsaicin is known to be neurotoxic for C-fiber afferents. We investigated the intravesical application of capsaicin in the treatment of detrusor hyperreflexia (DH) in seven patients (ages 23-52) with neurologic impairment. The patients were evaluated with both ice-water cystometry and formal video-urodynamic studies. Four biweekly courses of intravesical capsaicin treatment were administered using increasing concentrations (100 microM, 500 microM, 1 mM, and 2 mM). Treatment effect was monitored using a bladder diary and urodynamic evaluation one month after capsaicin treatment. Prior to treatment, six of the seven patients demonstrated a positive ice-water test and DH. Two patients were not able to complete the study due to discomfort attributed to capsaicin. Five of the seven patients completed the four courses of increasingly concentrated capsaicin. Three patients noted symptomatic improvement while two did not. The mean urodynamic bladder capacity significantly increased from 124 +/- 39 ml pre-capsaicin to 231 +/- 62 ml one month post-capsaicin in the three patients with symptomatic improvement (p < 0.05). Urodynamic testing revealed that one of the six patients with a positive ice-water test lost that response after intravesical capsaicin. Intravesical capsaicin is a novel and promising treatment for detrusor hyperreflexia in neurologically impaired patients.

Administration, Intravesical↗