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Biomedical subjects

S Radhakrishnan

Publications and source records attributed to S Radhakrishnan.

At least 109 records · Page 6Linked to original sources
PubMed1973

A three-dimensional analytical (rheological) model of the human left ventricle in passive-active states. Nontraumatic determination of the in vivo values of the rheological parameters.

In this paper a three-dimensional continuum model of a mammalian left ventricle is formulated. The stresses in the model satisfy the conditions of zero stress on the outer (epicardial surface-representing) boundary. The strains of the model are obtained from the actual dynamic geometry measurements (obtained from cineangiocardiography). Since the left ventricular muscle is incompressible, the dilatational strain is zero and hence the (three-dimensional) deviatric stress components are related to the corresponding strain components by Maxwell and Voigt rheological model analogues of one-dimensional systems; the parameters of the model are series and parallel elastic (SE, PE) elements and the contractile element (CE) (representing the sarcomere). The incorporation of the rheological features of the cardiac muscle into the three-dimensional constitutive equations (for the three-dimensional continuum model of the left ventricle) is a feature of this paper. A procedure is presented to determine the parameters of the constitutive equations (i.e., the SE, PE, and the parameters of the force-velocity relation for the CE) for the left ventricle of a subject from data on the dimensions and chamber pressure of the left ventricle. The values of these parameters characterize the rheology of the left ventricular muscle of the subject. In order to demonstrate clinical application of the analyses, in vivo data of the subjects' left ventricular pressure and dimensions are obtained, and the analyses are applied to the data to determine (for each subject) the values and characteristics of the elastic elements and CEs.

Angiography↗
PubMedDate not supplied

Non surgical treatment in congenital heart disease.

Dilation of blood vessels transluminally was demonstrated by Dr Andreas Gruntzig in 1978. In 1982, Kan demonstrated that congenitally stenosed valve can be dilated with the use of cylindrical balloon and opened up new vistas in the non-surgical treatment of congenital heart lesions. Rapid progress has been now made in (1) Understanding of mechanism of success or failure of balloon dilation (2) Development of newer hardwares like low profile balloon, high pressure balloons, extra support wires which have contributed to increase in success rate of the procedures (3) Understanding the unnatural history of various congenital heart lesions from the vast data bank of Registries of balloon dilation. As a consequence balloon dilation has become the first procedure of choice in the treatment of valvar pulmonary stenosis and post surgical recurrent coarctation. Although an essentially palliative procedure for the treatment of valvar aortic stenosis and native coarctation beyond the neonatal period, non-randomised studies have shown results similar to that of surgical correction. Balloon dilation of pulmonary artery, pulmonary vein, venous baffles stenosis have shown poor overall results. Balloon dilation for sub-pulmonary stenosis like tetralogy of Fallot is controversial. The development of stents to keep dilated vessel open has also found a place in treatment of congenital heart lesions. Thus pulmonary artery stenosis, recurrent coarctation in adults, venous baffle obstruction, conduit stenosis which respond poorly to balloon dilation alone have shown promising early and mid term results with stents. The use of stents to keep the ductus open, recurrent coarctation in children, in right ventricular outflow tract obstruction is controversial. Development of devices to achieve closure of cardiac defects is relatively new. Patent arterial duct was the first defect to be closed with the help of devices and has shown good results on long term follow up. Recently stainless steel coils have been used to close dose small ducti (up to 3 mm) with very promising medium term results. Its use has also been extended to larger ducti (up to 7 mm). Devices used for closing atrial septal defects, ventricular septal defects are undergoing rapid development. In atrial septal defects its use is restricted to small defects in the fossa ovalis area and in ventricular defects, to only those which are in the muscular septum. Most of the devices in use today for atrial septal closure are relatively new and await long term results. The results achieved by non surgical treatment for many congenital heart lesions are essentially palliative and may require repeat interventions at some point in the unnatural history which increases the cost of treatment substantially. The reuse of balloons, guide wires in developing countries helps reduce the overall cost of the procedure.

Adult↗
PubMedDate not supplied

Multiple venous thromboses and membranous obstruction of inferior vena cava in association with hereditary protein C deficiency: a case report.

A forty year old male presented with multiple dilated venous channels over the whole body involving both inferior and superior vena caval territories, along with features of chronic liver disease and portal hypertension. On investigation, he was found to have membranous obstruction of the inferior vena cava (MOIVC) as well as obstruction of both brachiocephalic and right subclavian veins and 'hereditary protein C deficiency'. He was managed successfully by percutaneous transluminal balloon angioplasty for the inferior vena cava (IVC) obstruction and was doing well on follow-up.

Adult↗
PubMedDate not supplied

Simultaneous echocardiographic and catheterisation gradients and mitral valve area during balloon mitral valvuloplasty.

This study was aimed at estimating mean transmitral gradients by simultaneous Doppler echocardiography and cardiac catheterisation and determining mitral valve area by pressure half time, Gorlin's formula and two-dimensional echocardiography so as to assess the relative accuracy of these methods before and after balloon mitral valvuloplasty in patients with rheumatic mitral stenosis. Left atrium-left ventricular, pulmonary artery wedge-left ventricular and echo gradients were simultaneously recorded in 18 patients undergoing balloon mitral valvuloplasty. Mitral valve area was estimated by pressure half time, Gorlin's equation and two-dimensional echocardiography. The correlation between left atrium-left ventricular and echo mean gradient before balloon mitral valvuloplasty was 0.96 (p < 0.03). Between pulmonary artery wedge-left ventricular and echo mean gradient, it was 0.95 (p < 0.04). The correlations between left atrium-left ventricular and pulmonary artery wedge-left ventricular mean gradient were also good. After balloon mitral valvuloplasty, similar good correlations were seen. On subgrouping the patients into those with high and low pulmonary artery pressure, good correlation persisted both before and after balloon mitral valvuloplasty. Mitral valve area by all the methods were similar before balloon mitral valvuloplasty. After balloon mitral valvuloplasty, mitral valve area by pressure half time was the least and by two-dimensional echocardiography, the maximum. All the three methods are equally accurate in estimating transmitral gradients and mitral valve area in mitral stenosis before balloon mitral valvuloplasty. Two-dimensional echocardiography is the best to estimate mitral valve area after balloon mitral valvuloplasty. Echocardiography can replace haemodynamic measurement of gradients and mitral valve area before and after balloon mitral valvuloplasty. But pressure half time is not recommended for measuring mitral valve area immediately after balloon mitral valvuloplasty where two-dimensional echocardiography mitral valve area is to be employed.

Adolescent↗
PubMedDate not supplied

Infrequent occurrence of silent HBV infection among Indian patients with chronic liver disease.

OBJECTIVE: To investigate the occurrence of silent hepatitis B virus (HBV) infection among patients with chronic liver disease (CLD). METHODS: Plasma samples from 71 CLD patients including 9 HBsAg-positive individuals were tested for HBV DNA by nested polymerase chain reaction (nPCR), and for HBV serum markers, i.e., anti-HBc antibody, HBeAg and anti-HBe antibody. The individuals were also tested for hepatitis C virus (HCV) RNA and anti-HCV antibody. RESULTS: Among 62 HBsAg-negative patients, silent HBV infection was seen in only two (3.2%). Silent HBV infection was not found in any of the 26 patients who had evidence of HCV infection. One HBsAg-positive patient was positive for anti-HCV in the absence of HCV RNA. CONCLUSIONS: There is a low rate of silent HBV infection among patients with CLD in India, where HBV is moderately endemic. Silent HBV infection is not associated with HCV-related CLD, which is in contrast to reports from other HBV-endemic areas in Asia.

Chronic Disease↗
PubMedDate not supplied

Concurrent percutaneous atrial septal defect closure and pulmonary valvuloplasty.

Severe pulmonary valve stenosis in association with a large atrial septal defect is uncommon. Simultaneous percutaneous closure of the atrial septal defect and pulmonary valvuloplasty appears to be an attractive modality when compared to patients with these two lesions being subjected to surgery or being treated percutaneously at different sittings. We encountered two cases, both with significant pulmonary valvular stenosis associated with atrial septal defect (fossa ovalis type). Both lesions were successfully treated percutaneously in the same sitting. Pulmonary valvuloplasty was done initially and the atrial septal defect closed later to minimize catheter manipulation after device implantation.

Adolescent↗
PubMedDate not supplied

Predictive accuracy of commissural morphology and its role in determining the outcome following Inoue balloon mitral valvotomy.

BACKGROUND: Commissural morphology is an important predictor of outcome following balloon mitral valvotomy. The aim of this prospective study was to assess if the site of commissural splitting could be reliably predicted by echocardiography and whether the extent of commissural split affected the result of balloon mitral valvotomy. METHODS AND RESULTS: A total of 140 patients (mean age 29.1+/-8.6 years) were studied. Prediction of splitting was done based on the presence of echolucent dark zones as seen in the parasternal short-axis view on echocardiography. Of 102 patients in whom a split of both commissures was predicted, the prediction was accurate in 86% (88/102). Of 33 patients with a predicted unilateral split, the accuracy of prediction was 82% (27/33). In the 5 patients with bilateral commissural fibrosis (in whom none of the commissures were predicted to split), all had a unilateral split. Overall, 93 patients (66%) had a bilateral commissural split, 43 (31%) had a unilateral split, and 4 had no commissural split. All the latter 4 developed moderate-to-severe mitral regurgitation. Those with bilateral commissural split following balloon mitral valvotomy had lower transmitral gradients (5.53+/-1.46 v 7.4+/-1.2 3 mmHg, p = 0.03) and greater mitral valve area (1.83+/-0.15 v. 1.64+/-0.15 cm2, p<0.02), as compared to those with unicommissural split. The incidence of an increase in mitral regurgitation by > or = grade 1 was also lower in the former group (7.5% v. 28%). An optimal result with the first dilatation (using a balloon size <2 mm of the predicted size) was achieved more frequently in those with a bilateral split (18% vs 8%). Oversizing of the balloon by 2 mm (of the predicted size) was done more frequently (19% v. 7%) in those with unicommissural split. CONCLUSIONS: We conclude that the assessment of commissural morphology is possible with excellent predictive accuracy. In this study, those with bilateral commissural split had more favorable hemodynamic results with lower transmitral gradients. greater mitral valve area and lesser frequency of mitral regurgitation in contrast to those with unicommissural split.

Adolescent↗
PubMedDate not supplied

Asymptomatic coronary heart disease detected on epidemiological survey of urban population of Delhi.

A community based epidemiological study of coronary heart disease (CHD) was carried out in a random sample of 13723 adults in the age group of 25-64 years in the urban population of Delhi. The electrocardiogram (ECG) of all clinically detected CHD cases and of a sample of 5621 persons (selected on the basis of alternate household screened) without clinical manifestations of CHD, was obtained. Out of 5621 persons labelled as asymptomatic, CHD evidence of Q wave myocardial infarction (MI) was present in 80 ECGs (1.4%). Another 296 ECGs had ST & T changes vide Minnesota Code 4-1-1, 4-1-2, 5-1 and 5-2 acceptable as evidence of probable CHD. The overall prevalence rate of asymptomatic CHD was 6.7% (male 5.6%, female 7.6%). Silent MI was more common in the male patients (1.7% vs 1.1%, p < 0.001). However, ST-T changes were more common in female patients (6.5% vs 3.9%, p < 0.001). The ST-T changes showed a steady factor in asymptomatic CHD cases was hypertension in both sexes (male-45.2%, female-43.5%) p = NS. Obesity was present in 24% of male & 46.1% of female patients (p < 0.001). Family history was found in 20% cases of both sexes. Smoking was recorded in 34.9% male and 10.9% female patients with asymptomatic CHD (p < 0.001).

Adult↗
PubMedDate not supplied

Echocardiographic assessment of the size of aortic and pulmonary valve annulus before balloon valvoplasty.

Two dimensional echocardiographic measurements of the size of aortic and pulmonary valve annulus were made in 60 patients before balloon valvoplasty and compared to the angiographic measurements. Aortic valve annulus was measured in 34 patients (26 with valvar aortic stenosis and 8 with discrete subaortic stenosis) in the parasternal long axis or apical 5-chamber views. The pulmonary valve annulus was measured in 26 patients with valvar pulmonary stenosis (PS) in the parasternal short axis view of the right ventricular outflow view. The visualization of the annulus was good in all except 2 patients with valvar PS. Angiographic measurements of the aortic and pulmonary valve annulus were made in aortic root and right ventricular angiograms respectively, taken in both right and left anterior oblique views. There was an excellent correlation between the measurements of the annulus size by the two techniques (r value for pulmonary valve 0.91; for aortic valve 0.96; over all 0.94). Echocardiography can accurately measure valve annulus size and help in choosing balloon dilatation catheter of appropriate size before the valvoplasty procedure.

Adolescent↗