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Biomedical subjects

R Mohan

Publications and source records attributed to R Mohan.

53 records · Page 3Linked to original sources
PubMed1986

Retinal revascularisation in diabetic retinopathy.

The case history of a 33-year-old diabetic patient who has had diabetes for 24 years is presented. When first seen in 1975 he had bilateral proliferative retinopathy with new vessels in the retinal periphery. He had large areas of capillary non-perfusion lateral to the macula in the right eye associated with the new vessels. Nine years later, after extensive repeated photocoagulation, revascularisation of large areas previously not perfused were seen. The vessels are in the plane of the retina and do not have the appearance of new vessels.

Adult↗
PubMed1986

Apocytochrome c induces pH-dependent vesicle fusion.

The ability of apocytochrome c and the heme containing respiratory chain component, cytochrome c, to induce fusion of phosphatidylcholine (PC) small unilamellar vesicles containing 0-50 mol % negatively charged lipids was examined. Both molecules mediated fusion of phosphatidylserine (PS):PC 1:1 vesicles as measured by energy transfer changes between fluorescent lipid probes in a concentration- and pH-dependent manner, although cytochrome c was less potent and interacted over a more limited pH range than the apocytochrome c. Maximal fusion occurred at pH 3, far below the pKa of the 19 lysine groups contained in the protein (pI = 10.5). A similar pH dependence was observed for vesicles containing 50 mol % cardiolipin (CL), phosphatidylglycerol (PG), and phosphatidylinositol (PI) in PC but the apparent pKa values varied somewhat. In the absence of vesicles, the secondary structure of apocytochrome c was unchanged over this pH range, but in the presence of negatively charged vesicles, the polypeptide underwent a marked conformational change from random coil to alpha-helix. By comparing the pH dependencies of fusion induced by poly-L-lysine and apocytochrome c, we concluded that the pH dependence derived from changes in the net charge on both the vesicles and apocytochrome c. Aggregation could occur under conditions where fusion was imperceptible. Fusion increased with increasing mole ratio of PS. Apocytochrome c did induce some fusion of vesicles composed only of PC with a maximum effect at pH 4. Biosynthesis of cytochrome c involves translocation of apocytochrome c from the cytosol across the outer mitochondrial membrane to the outer mitochondrial space where the heme group is attached. The ability of apocytochrome c to induce fusion of both PS-containing and PC-only vesicles may reflect characteristics of protein/membrane interaction that pertain to its biological translocation.

Animals↗
PubMed1979

A method of correction for curvature and inhomogeneities in computer aided calculation of external beam radiation dose distributions.

This paper deals with the problem of finding the effective pathlength along a ray passing through a patient's outline and internal structure. The pathlength contributes to the correction applied for curvature and inhomogeneities in the computer-aided calculation of external beam radiation dose distributions. The pathlength is found by first determining the intersections of the ray with the contours defining the patient's body and the interior inhomogeneities. From these intersections the geometric length within each contour is obtained. This information is then employed in a treatment planning program for high energy gamma and X-rays and electrons, in which the radiation dose distribution is computed taking into account the actual inhomogeneous tissue structures. Other applications of the techniques described to problems in the field of radiation therapy are briefly discussed.

Computers↗
PubMed1977

Oak poisoning of cattle in Ohio.

Fourteen cases of oak poisoning were diagnosed at the Ohio Veterinary Diagnostic Laboratory, Reynoldsburg, Oh, in the fall of 1976. The poisoning was attributed to ingestion of oak shrubs, oak leaves, and acorns. Clinical signs included anorexia, rumen atony, hemorrhagic diarrhea, subcutaneous edema, and abnormal renal function. Perirenal edema and hemorrhage, ascites, hydrothorax, and hemorrhagic enteritis were frequently encountered pathologic changes. Histologic examination of the kidney revealed multifocal necrosis of the proximal convoluted tubules, which is a characteristic feature of this type of poisoning.

Animals↗
PubMedDate not supplied

Pancreatic B-cell function in relation to diabetic retinopathy in Asian Indian NIDDM patients.

Pancreatic B-cell function in relation to diabetic retinopathy was studied in 195 NIDDM patients with long-standing diabetes. Background diabetic retinopathy (BDR) was present in 95 (48.7%) and proliferative retinopathy (PDR) in 17 (8.7%) of the subjects. There was no significant difference between the BDR, PDR, and non-retinopathy groups with respect to age, age at diagnosis of diabetes and HbA1 values. Mean duration of diabetes was higher in the PDR group (p less than 0.05). Serum C-peptide values showed no correlation with the presence of retinopathy or with the duration of diabetes. The C-peptide values were widely scattered in patients with BDR and PDR showing no association between pancreatic B-cell reserve and occurrence or severity of retinopathy in NIDDM patients. Thus, decreased pancreatic B-cell reserve does not appear to be a risk factor for diabetic retinopathy in NIDDM patients.

Blood Glucose↗
PubMedDate not supplied

Computer-compatible patient contour plotter.

The use of a compact, mobile, relatively inexpensive electromechanical patient-contouring mechanism is described. The system utilizes a Numonics Model 224 graphics digitizer suspended over the patient. The digital X and Y coordinates of the patient contour in either of multiple, parallel transverse, or sagittal planes are inherently accurate to within +/-0.25 mm over a total reading are of 60X90 cm. Display features include the interface to an analog 11-in.X17-in. X-Y plotter with a variable scale-down factor for those contours which would otherwise be larger than the plotting surface. The system is easy to use and may also be readily interfaced for on-line entry of patient contours to calculator- or minicomputer-based treatment-planning systems.

Computers↗
PubMedDate not supplied

Compensators for three-dimensional treatment planning.

Presented here is a method of designing compensators for a single beam or one or more pairs of beams, not necessarily parallel opposed. The objective is to produce a flat distribution in a plane that may be perpendicular to the central ray or may be an arbitrarily oriented plane, for example, a plane that bisects the hinge angle between two beams. The method takes into account not only surface irregularities but also tissue inhomogeneities, hinge angles between beams, distance from the source, and even "horns" in the beam. The design process employs convolution of Monte Carlo generated pencil beams with photon fluence distributions, appropriately modified for the presence of beam modifiers (blocks and compensators), to compute dose in a flat homogeneous phantom. Corrections for inhomogeneities and surface curvature are applied by using computerized tomography information to determine the effective path length through tissue. Multiple interactions are used to arrive at a compensator that properly incorporates changes in radiation transport, and therefore dose distribution, resulting from the presence of beam-shaping devices. In each iteration it is assumed that the required reduction in dose at a point can be achieved by reducing the fluence along the ray joining the source to computation point proportionately. The compensator design is represented as a finely spaced matrix of thickness values which is entered into a prorammable milling maching for fabrication. Dose measurements in phantom exposed to 6-MV x rays with and without compensation are presented.

Equipment Design↗
PubMedDate not supplied

Clinically relevant optimization of 3-D conformal treatments.

In this paper a method of computer-aided optimization of 3-D conformal treatment plans is presented which incorporates models to predict the clinical consequences of resulting dose distributions. Even though these models are simplistic, it is submitted that their intelligent use leads to treatment plans which indicate lower normal tissue complications and higher tumor control. Dose distribution data, biological models, and observed normal tissue and tumor response data are used to compute tumor control and normal tissue complication probabilities for each of the critical normal structures encountered in a treatment plan. These quantities are combined into a single score using an objective function which incorporates the importance of each end point as assessed by the physician. Using the "simulated annealing" method of optimization, the beam weights are adjusted to maximize the score. Additional constraints are applied to ensure consistency of the results of optimization with the judgment of the physician. These optimization methods have been applied to conformal treatment plans consisting of multiple fixed fields with conformal field shaping. The results indicate that the methods presented have considerable potential.

Aged↗
PubMedDate not supplied

A model for computer-controlled delivery of 3-D conformal treatments.

Three-dimensional conformal radiation treatments are highly complex and may comprise a large number of coplanar and noncoplanar beams, virtually all of which are shaped and may also employ arbitrary intensity modulation. The delivery of such treatments with conventional means is highly labor intensive and limited to a relatively small number of fields. A generalized model for a system that can deliver 3-D conformal treatments rapidly and safely using a computer-controlled treatment machine equipped with a multileaf collimator is presented. The model emphasizes the separation of tasks between an external computer programmed by the user institution and a control computer proprietary to the treatment machine manufacturer. The treatment scheme that is employed consists of a sequence of fixed fields, called segments, which are delivered in succession without human intervention. Settings for all segments, derived from a 3-D conformal treatment planning system, are downloaded by the external computer into the control computer of the treatment machine. During patient setup, the control computer enables the operator to step through computer-controlled setup of the segments without radiation to ensure the absence of collisions, and to allow the adjustment of setup parameters if necessary. The external computer verifies the treatment setup and permits the control computer to carry out the treatment segment by segment. Safety aspects of the model and anomalous situations which may arise are discussed.

Computer Simulation↗
PubMedDate not supplied

Acanthamoeba keratitis--a report of two cases.

Two cases of unilateral corneal ulcers caused by Acanthamoeba are reported. Neither of the patients had contact lenses at any time. The diagnosis was confirmed by Giemsa stain and cultures of the corneal scrapings.

Acanthamoeba↗
PubMedDate not supplied

Comparative efficacy of atenolol and labetalol in essential hypertension--a double blind cross over trial.

In a double blind cross-over drug trial, antihypertensive effects (resting and after dynamic exercise) of atenolol and of labetalol were studied in 20 patients of mild to moderate essential hypertension. Both drugs exhibited almost equal antihypertensive response, and were well tolerated. Haemodynamic variables (HR, SBP, DBP and RPP), both at rest and after maximal tread mill exercise, were significantly altered (P less than 0.001) by both drugs. Exercise capacity was observed to be marginally improved by atenolol. Although the antihypertensive effect, when compared between the two drugs, was not statistically significant, individual suitability or comparison revealed a preference for atenolol in 17 patients and for labetalol in 3 patients.

Adult↗
PubMedDate not supplied

Steroid induced glaucoma and cataract.

Long term use of topical & systemic steroids produce secondary open angle glaucoma similar to chronic simple glaucoma. The increased IOP caused by prolonged steroid therapy is reversible but the damage produced by it is irreversible. In this study, we analysed 25 patients (44 eyes) with steroid induced glaucoma, who reported to us with dimness of vision, haloes and elevated I.O.P. and were using steroids for long duration due to various causes. The behaviour of the I.O.P. due to different steroid preparations, the type of lenticular change, and the management of those cases are discussed in this paper. From our study we conclude that dexamethasone and betamethasone both topical as well as systemic are more potent in producing glaucoma and cataract than medrysone and prednisolone. The condition is reversible without permanent damage when the duration of steroid therapy is short and vice versa.

Adolescent↗