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Biomedical subjects

G Ramachandran

Publications and source records attributed to G Ramachandran.

At least 37 records · Page 2Linked to original sources
PubMed1996

A preliminary study of apolipoprotein E genotype and psychiatric manifestations of Alzheimer's disease.

We evaluated the frequency of depression and psychosis in 46 patients with AD and 135 control subjects with the apolipoprotein (APO) E3/3 or E3/4 genotype. Patients with AD and the APOE3/4 genotype had a more than threefold increase in the signs of depression and psychosis when compared with either patients with the APOE3/3 genotype or to control subjects. Our preliminary study suggests that the phenotype of AD associated with the epsilon 4 allele is more likely to include psychiatric manifestations.

Aged↗
PubMed1995

Evaluation of an infrared open-path spectrometer using an exposure chamber and a calibration cell.

This study evaluated the use of a controlled exposure chamber and calibration cell to investigate the performance of open-path remote sensing instruments for workplace monitoring of pollutants. An open-path infrared spectrometer was deployed in a chamber, and a range of homogeneous air concentrations were generated using the tracer gas sulfur hexafluoride (SF6). Open-path measurements were compared with point-sample measurements taken along the beam and analyzed using an infrared (IR) and electron capture detector (ECD). A five-compartment calibration cell placed in the optical path was used to simulate heterogeneous concentrations of pollutants. Fifteen concentration patterns were created by injecting different volumes of SF6 into each compartment. Open-path spectrometer measurements were compared with compartment concentrations measured using an ECD. Results indicated that stable homogeneous and heterogeneous concentrations of SF6 were generated in the controlled exposure chamber and five-compartment calibration cell, respectively. Overall, individual open-path measurements were within 20% of point samples measured with the IR and ECDs. The open-path spectrometer measurements had a consistent positive bias of about 12%. Exposure chamber experiments uncovered remote sensing instrument design aspects that could adversely impact its use for indoor monitoring. The weight and size of the instrument make it useable only in a fixed position, thus limiting spatial coverage of the beam in a room. The instrument components were not air-tight, resulting in overestimation of some open-path concentrations. A controlled test chamber and a long calibration cell placed in the optical path are useful tools for evaluating a variety of open-path spectrometer instrument performance issues relevant to industrial hygiene monitoring.

Air Pollutants, Occupational↗
PubMed1994

Multidisciplinary treatment of biliary tract cancers.

Ninety-six patients referred for radiation therapy to Washington University affiliated institutions with tumors of the extrahepatic biliary tree form the basis of this report. Patients were examined with regard to demographic factors, tumor primary site, presenting symptoms, methods of diagnosis, and methods of management. The median survival of all 96 patients in this series was 11 months. There was no significant difference between patients with gallbladder cancer and patients with cancer of the biliary ductal system. There was a statistically significant improvement in survival in those patients undergoing resection as management or as a component of the management of their tumors (P = 0.02). Patients receiving > 4,000 cGy of radiation therapy had an improved survival compared to those patients receiving < or = 4,000 cGy of radiation therapy (P = 0.003). While surgical resection improved survival for those patients undergoing removal of all gross tumor, this effect was noted especially in patients with gallbladder cancer.

Adult↗
PubMed1994

Evaluation of optical source-detector configurations for tomographic reconstruction of chemical concentrations in indoor air.

This article reports on numerical studies to evaluate and compare optical remote sensing configurations for tomographically reconstructing pollutant concentrations in indoor air. With a remote sensing/computed tomography system, two-dimensional maps of pollutant concentrations with good spatial resolution can be created for an entire room. The successful use of such a system for exposure assessment, ventilation assessment, or source monitoring depends on the remote sensing configuration. A systematic method was developed to evaluate the performance of 10 configurations. One hundred and twenty test maps were reconstructed with an algebraic reconstruction method using all 10 configurations; reconstruction quality was evaluated using 4 criteria. Reconstruction quality was related to the number and location of detectors in the room and the complexity of the test maps. Configurations using the same number of detectors placed in different locations resulted in reconstructions that differed in quality. The effect of reducing the number density of rays on reconstruction quality was studied. Based on these simulations, two configurations that used four detectors to scan the room were selected, and their performance was evaluated in the presence of various levels of measurement noise. Two configurations that used four detectors were most suited for exposure assessment. It was found that when designing a configuration, the number and independence of rays should be maximized. Results underscored the need to thoroughly test configurations through numerical studies prior to field implementation; a wide variety of concentration maps, relevant to the application, should be tested under both ideal and nonideal sampling conditions.

Air Pollutants↗
PubMed1994

Evaluation of algorithms for tomographic reconstruction of chemical concentrations in indoor air.

Numerical studies were performed to evaluate and compare four different algorithms for tomographically reconstructing pollutant concentrations in indoor air measured with an optical remote sensing system. With a remote sensing/computed tomography system, two-dimensional maps of air concentrations can be created for an entire room with good spatial and temporal resolution. The success of such a system for characterizing the flow of contaminants in air, exposure assessment, and leak detection depends on the choice of tomographic reconstruction algorithm. A systematic method was developed to evaluate the performance of four algorithms: ART, ART3, SIRT, and SART. One hundred and twenty test maps were reconstructed by each algorithm under ideal and nonideal sampling conditions, and image quality was evaluated using four criteria. The nonideal sampling conditions included simulation of measurement noise and reduction in the number density of rays. Performance of the algorithms was found to be intimately related to the number of peaks in the test maps. The importance of using multiple measures of image quality was underscored by the fact that for some sampling conditions simulated, performance of the algorithms was judged differently depending on the evaluation criteria. Results indicated that using numerical studies is successful for evaluating such algorithms.

Air Pollutants, Occupational↗
PubMed1993

Alteration of structure and mobility of erythrocyte aggregates under normal- to microgravity conditions.

An experimental analysis of the aggregates structure and their mobility under normal- and micro-g conditions is carried out. Fresh well mixed erythrocyte suspensions in plasma at 8.0% hematocrit are placed in a glass chamber and on-line video microscopic recording of the aggregation process under microgravity condition is carried out. The analysis of aggregate structure and mobility are carried out by an IBM-PC/AT based image processing system. The results show that (a) under normal gravity conditions the velocity of the formed aggregates depend on their sizes which tend to grow further by interacting with single cells and small aggregates, (b) under microgravity conditions the mobility of the aggregates reduces to zero and an alteration in their structural parameters is observed.

Erythrocyte Aggregation↗
PubMed1992

A simple scheme to improve compliance in patients taking tuberculosis medication.

Compliance with prescribed treatment remains a major problem in the control of tuberculosis worldwide. We describe a simple method of improving patient compliance with hospital-based treatment. Eighty-two patients paid a deposit at the start of their treatment which entitled them to cheaper drugs and was refundable on completion of the prescribed course. Sixty-two per cent of patients completed the course compared with 23% of retrospective controls. A direct relationship was found between the amount of deposit paid and the rate of completion. Reasons why poor patients (who paid a lower deposit) may default are discussed, as are the merits of short-course drug regimens. It is recommended that similar schemes be assessed elsewhere.

Humans↗
PubMed1992

Salivary cortisol in the assessment of adrenocortical function in patients with pulmonary tuberculosis.

Adrenocortical function was assessed on the basis of changes in salivary cortisol in patients with pulmonary tuberculosis and the findings compared with those in healthy subjects. A method of direct radioimmunoassay of salivary cortisol was standardized and the sensitivity was 0.8 nmol/l. Cortisol levels in saliva were significantly higher in the patients than in the healthy subjects (P less than 0.001). The diurnal rhythm of cortisol secretion was disturbed in the patients with a significant increase in salivary cortisol beyond 1800 h. While dexamethasone caused an appreciable suppression (87%), stimulation with ACTH (tetracosactrin) resulted in a marked increase in salivary cortisol, the increase being significantly higher in the healthy subjects than in the patients (P less than 0.001). Attempts to classify subjects as positive or negative responders to tetracosactrin based on increases in salivary cortisol in relation to plasma cortisol changes were however not successful, as the agreement between the two methods ranged from 73 to 80 per cent with various criteria used.

Adrenal Cortex↗
PubMed1991

Reconstruction of out-of-plane cardiac displacement patterns as observed on the chest wall during various phases of ECG by capacitance transducer.

The out-of-plane displacements due to cardiac action have been measured on the chest wall by an electronic distance measurement technique which is based on the variation of the capacitance between the probe and moving surface. The displacements were measured at 36 locations over the entire cardiac region along with ECG and were directly fed to an IBM PC/AT computer after A/D conversion. From these data, the displacement patterns for the whole region during the complete cardiac cycle could be reconstructed in a perspective view. The sequential analyses of the displacements shows the details of the cardiac events and the results obtained are in agreement with other techniques. The averaged displacements over various regions of the heart for normal subjects have also been presented.

Analog-Digital Conversion↗
PubMed1991

Reconstruction of sequential cardiac in-plane displacement patterns on the chest wall by laser speckle interferometry.

Time-average speckle interferometry has been applied to obtain displacement patterns on the chest wall produced by cardiac action, in the absence of breathing, during various phases of the cardiac cycle. This has been achieved by an electronic shutter, controlled by the electrocardiogram of the subject. The recorded holographic plates processed under identical conditions are scanned by the pointwise method to obtain the absolute displacements at various locations corresponding to the activities of the various cardiac chambers and values. These data are transformed to a 40 x 30 matrix by an interpolation method and, from this, three-dimensional displacement plots are reconstructed by an IBM PC/AT computer. These patterns shown the displacements over the entire cardiac area corresponding to the activities of various regions during the cardiac cycle. The apex and aortic valve areas show the maximum displacements during the systolic phase. During the diastolic phase the activities over the low pressure atrial regions are also observed. The results obtained outline the functional details of the normal heart and the activities over various areas are in agreement with that of other noncontact techniques.

Algorithms↗
PubMed1990

Adrenocortical function in patients with pulmonary tuberculosis.

Adrenocortical function was studied in patients with pulmonary tuberculosis and the findings compared with those in healthy subjects. Plasma cortisol levels in newly diagnosed patients were appreciably higher than in the healthy subjects (P less than 0.001). A normal (positive) response to ACTH (tetracosactrin) stimulation was observed in 35 (97%) of 36 healthy subjects, 15 (56%) of 27 newly diagnosed patients with tuberculosis and 5 (42%) of 12 chronic cases (i.e. those who had had the disease for more than 3 years); the difference between the healthy subjects and the two groups of tuberculosis patients was highly significant (P less than 0.001). Dexamethasone caused an appreciable decrease in the plasma cortisol levels of tuberculosis patients. Considering the diurnal variation of cortisol secretion, there was a steady decline in the cortisol levels between 08:00 and 20:00 in the healthy subjects (P = 0.02); in the tuberculosis patients, however, there was a decrease up to 16:00 followed by a significant increase (P = 0.05), and the mean value at 20:00 was similar to that at 08:00.

Adrenal Cortex↗
PubMed1990

Fracture resistance of dowel channel preparations with various dentin thickness.

This in vitro study consisted of 40 cast dowel core made of technique metal alloy. They were divided into 4 groups of dowel channels with 1 mm facial dentin thickness, 2 mm facial dentin thickness, 1 mm facial dentin thickness with 60 degrees bevel for the metal collar and 2 mm facial dentin thickness with 60 degrees bevel in the metal collar, respectively. The fracture resistance under horizontal force were compared by using Instron machine. From the study, it was found that more than 1 mm thickness of labial dentin wall of post channel is required to prevent root fracture under horizontally directed force and an addition of 2 mm collar in the core around the root enhanced the resistance to root fracture. It was also found that adequate post diameter should be present when technique metal was used to prevent dowel failure due to bending under force.

Analysis of Variance↗
PubMed1989

Three-dimensional reconstruction of cardiac displacement patterns on the chest wall during the P, QRS and T-segments of the ECG by laser speckle interferometry.

A noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall. These displacements are then reconstructed in the form of three-dimensional plots, during the P, QRS and T-waves of the ECG. A comparison of these patterns shows that the mechanical activity of each region varies significantly during these phases of cardiac cycle. As these displacements depend on the clinical status of the heart, its use with a cardiac patient shows the functional changes of the affected regions in the form of alteration of these patterns.

Electrocardiography↗