PubMed Health⌕ Search

Biomedical subjects

B Subramanian

Publications and source records attributed to B Subramanian.

9 recordsLinked to original sources
PubMed2003

Influence of Adyar river in the coastal waters of Chennai (Madras), Bay of Bengal.

The impact of the river Adyar which is influenced by industrial wastes and domestic sewage from the city of Chennai (Madras), on the hydrobiology of coastal water in the Bay of Bengal was evaluated. Reduction in pH, dissolved oxygen (DO), nitrite, nitrate, primary productivity and increase of ammonia, phosphate, silicate, heavy metals, biological oxygen demand (BOD), chlorophyll pigments, particulate organic carbon (POC), respiration, suspended solids, ATP, and bacteria in the mixing site during low tide indicated that the Adyar water was heavily polluted and ultimately affect the quality of coastal water near the vicinity of mixing zone. The effects are diluted or nullified as the distance increased from the mixing site due to heavy mixing and littoral current. During high tide, the flow was completely stopped and little or no effect was recorded. The light, water current and wave action are the important factors which minimize the pollution impacts in the receiving coastal water.

Ammonia↗
PubMed2001

Progression of heterogeneous breast tumors.

Two possible pathways of breast tumor progression were investigated by searching for values of transition rates that could reproduce the clinically observed co-occurrence frequencies of grades of ductal carcinoma in situ and grades of invasive ductal carcinoma in heterogeneous tumors. Two different pathways were analysed, a linear pathway with seven parameters, and a nonlinear pathway with three parameters. In each pathway ductal carcinoma in situ (DCIS) is a progenitor of invasive carcinoma (IDC). In the linear pathway breast tumor progression is along increasing grades: DCIS 1-DCIS 2-DCIS 3-IDC 1-IDC 2-IDC 3. In the nonlinear pathway progression of DCIS and progression of IDC can proceed in parallel steps, and in addition, with transitions from each grade of DCIS to a corresponding grade of IDC. The biological pathways were interpreted mathematically as compartment models with transition rates between stages in an explicit series of coupled differential equations. Two methods were used to search for transition rates that could reproduce the observed co-occurrence frequencies, a limited empirical search and an extensive genetic algorithmic search. Neither search method, with either pathway, could find a combination of transition rates that would reproduce the set of observed co-occurrence frequencies. We conclude that neither the linear pathway, nor the nonlinear pathway considered here, is an adequate description of progression in heterogeneous breast tumors. This quantitative investigation lends support to previous evidence from histopathology and molecular biology that the grades of DCIS and IDC seen together in heterogeneous breast tumors may not be obligate steps in tumor progression.

Breast Neoplasms↗
PubMed1998

Safe touch temperatures for hot plates.

A finite difference heat transfer model has been developed to predict the Safe Touch Temperatures (STT) for plates made of different materials. SST can be defined as the highest temperature at which no pain is felt when the surface is touched for a long enough period to allow safe handling of the equipment. The criterion used to quantify damage is the "damage function" that was originally proposed by Henriques and Moritz. There are several uncertainties present in the physiological and thermal properties of the skin that give rise to a solution range rather than a single solution. Certain simplifying assumptions are made that tend to yield solutions for STT that are toward the lower or "safe" end of the solution range. The model developed is a two-dimensional axisymmetric model in cylindrical coordinates. A finite difference scheme that uses the Alternating Direction Implicit method is used to solve the problem. It is a second-order scheme in both space and time domains. A parametric analysis of the model is performed to isolate those factors that affect the STT to the greatest extent. Data are presented for a variety of cases, which cover commonly observed ranges in material and geometric properties. It is found that the material properties, namely thermal conductivity and volumetric heat capacity, and the plate thickness ratio are the three most important parameters. These three parameters account for a range of STT from 56 degrees C-100 degrees C with thick metals at the low end and thin metals and plastics in the high range. This method represents a significant improvement over existing standard practices.

Body Temperature Regulation↗
PubMed1997

Primary sequence of baboon CR1 demonstrates concerted evolution within the CR1 gene.

Complement receptor type one (CR1) in primates has several remarkable structural features including a size polymorphism (Mr 190000, 220000, 250000 and 280000) in man, multiple size variants (Mr 55000-220000) among non-human primates, and a partial amino-terminal duplication (CR1-like gene) that appears to encode the short (55000-70000) forms expressed on primate erythrocytes. In general, these short CR1 forms, some of which are GPI anchored, are expressed on erythrocytes and the 220000 molecular weight CR1 form is expressed on PBMC, except in man, where only the 220000 molecular weight form has been detected. In addition, the Mr 220000 human CR1 sequence carries several long internal repeats of up to 99% homology. It has been suggested that the highest homology is maintained by gene conversion and/or unequal crossover. To address further the evolutionary and biologic implications of these multiple forms, a 6 kb cDNA encoding baboon CR1(220) was identified by RTPCR using human CR1 primers. Its sequence contains the expected 30 complement control protein repeats (CCP) and demonstrates an overall homology to human CR1 of 95.4% at the nucleotide level and 93.2% at the amino acid level. As in human CR1, the first 28 CCP maintain the characteristic "seven CCP-long homologous repeats (LHR)" organization. Analysis of baboon CR1(220) indicates that horizontal or concerted evolution has maintained a high degree (> 98%) of identity between corresponding CCP within the LHRs from CCP 4 to CCP 19, while this homology region extends from CCP 3 to CCP 18 in man. In contrast, substitutions occurring in other CCP are not propagated to the corresponding sites of other LHR. Sequence differences in CCP 1, 2 and 3 are likely to be related to the acquisition of enhanced C3b binding capability by this amino-terminal region of the protein. Thus, the sequence data strongly support the hypotheses that gene conversion and or unequal crossover events have driven the evolution of the protein in regions of high homology while selective forces, probably ligand binding requirements, have maintained the regions of divergence.

Amino Acid Sequence↗
PubMed1982

Combined therapy with verapamil and propranolol in chronic stable angina.

The comparative efficacy of verapamil (360 mg daily) and propranolol (240 mg daily) was evaluated with computerized treadmill exercise in 22 patients with chronic stable angina in a placebo-controlled double-blind crossover study with 4 weeks on each active phase. Fourteen of these patients still had angina despite active drug therapy and they were further treated with a combination of verapamil (360 mg) and propranolol (120 mg) for 4 weeks. The mean exercise time for these patients taking placebo was 4.8 +/- 0.22 minutes (mean +/- standard error of the mean) and this increased to 6.8 +/- 0.64 minutes with propranolol and 8.0 +/- 0.5 minutes with verapamil. A further increase to 10.1 +/- 0.88 minutes was observed with the combination of both drugs and seven patients became symptom-free. S-T segment criteria improved with both drugs, and combination therapy produced a further reduction in peak S-T depression. Electrocardiographic ambulatory monitoring showed no evidence of conduction defects and mean hourly heart rates were similar to those seen with propranolol alone. Left ventricular function indexes were not significantly different from those obtained with propranolol. Combination therapy with verapamil and propranolol appears to be efficacious in the treatment of selected patients with severe chronic stable angina. The patients need to be carefully monitored for adverse effects.

Adult↗
PubMed1981

Long-term antianginal action of verapamil assessed with quantitated serial treadmill stress testing.

The long-term efficacy of verapamil in a dose of 360 mg daily in patients with chronic stable angina pectoris was assessed by quantitated serial treadmill exercise tests. Twenty-eight patients were investigated with a placebo-controlled, double-blind, crossover protocol of 2 weeks each and afterward all patients were put on long-term therapy. Exercise tests were performed at the end of the placebo period and after 2, 4, 8, 16, 24 and 52 weeks of verapamil therapy. All 28 experienced angina during treadmill tests on placebo and the mean (+/- standard error of the mean) exercise time was 6.6 +/- 0.5 minutes. This increased to 9.2 +/- 0.8 minutes at 2 weeks and 50 11.2 +/- 0.8 minutes at 4 weeks. Fifteen and 20 of the 28 patients became angina-free during treadmill exercise at 2 and 4 weeks, respectively. The consumption of nitroglycerin showed a similar improvement. The improvement was maintained at 1 year of follow-up. The on-line computer-analyzed S-T segment changes showed a statistically significant improvement at all follow-up periods. Withdrawal of verapamil produced a return to pretreatment levels. The adverse effects noted were constipation in seven patients and reversible P-R interval prolongation in two. No heart failure occurred in any patient. These findings suggest that verapamil possesses a powerful and sustained antianginal action and, in a dose of 360 mg daily, merits a place as a primary therapeutic agent in the management of chronic stable angina.

Adult↗
PubMed1980

Exercise-induced S-T segment elevation in variant angina.

Five patients with known ischemic heart disease had an unusual pattern of S-T segment depression during treadmill exercise testing followed by S-T segment elevation and chest pain in the postexercise period. Thallium-201 scintigraphy revealed reversible exercise-induced myocardial ischemia, in areas supplied by severely narrowed coronary arteries as documented by coronary arteriography. Ambulatory electrocardiographic recording for S-T segment shift using a frequency-modulated system showed S-T segment depressions and elevations at rest in the same leads that showed similar shifts during exercise tests. Three of the five patients had a myocardial infarction within 8 weeks of diagnosis, and two died. This syndrome may be associated with severe coronary artery disease and may have a very poor prognosis.

Ambulatory Care↗