PubMed Health⌕ Search

Biomedical subjects

P N Tandon

Publications and source records attributed to P N Tandon.

At least 19 recordsLinked to original sources
PubMed1995

A new model for blood flow through an artery with axisymmetric stenosis.

Presented herein are the studies on the flow behavior of a blood type suspension through a circular tube with an axisymmetric stenosis. The suspension of the cells in plasma is represented by a layered fluid model, with a marginal cell-free layer of the suspending medium near the wall, a central core region and an annular layer of a biviscous fluid layer. It is understood that the proposed model may contribute to the inbuilt mechanism for drag reduction and prevention of the further development of the stenosis. The concept of lubricating pipe lining for transporting various industrial fluids is well represented through three-layered core-annular flows. The governing equations are solved numerically by using finite element method. The velocity fields, including separation and reattachment points, and the distribution of pressure and wall shear stresses have been brought out and discussed. The results of the analysis show that the presence of the marginal cell-free layer reduces the wall shear stresses and the length of the flow reversal zone. The non-Newtonian character of the suspension is helpful in reducing the abnormal effects of the stenosis. The model thus establishes the inbuilt character of blood for decreasing the stresses and this, in turn, reduces the load on the heart in propelling the blood.

Animals↗
PubMed1994

Anterior encephaloceles: a report of 30 cases.

Thirty cases of anterior encephalocele treated in our centre over an 18-year period (from 1973 to 1990) are presented. At the time of surgery over 60% of the patients were under the age of 2 years, and 40% were aged under 1 year. Only one child was over 10 years of age. Twenty-six patients had the fronto-ethmoidal type of defect, while two each had frontonasal- and naso-orbital-type lesions. Twenty-five children had varying degrees of hypertelorism. Four had an enlarged head and four microcephaly. In 26 patients one-stage repair of the encephalocele and reconstruction of the orbits was undertaken. A ventriculoperitoneal shunt was performed prior to definitive surgery in three patients with gross hydrocephalus. There was no postoperative mortality. Six patients had postoperative CSF rhinorrhoea, three of them requiring a lumboperitoneal shunt. This study highlights the role of one-stage repair of this defect.

Age Factors↗
PubMed1994

A new model for synovial joint lubrication.

A new approach to synovial joint lubrication is presented using Bingham fluid as lubricant between the approaching porous cartilagenous surfaces. It is presumed that the thickness of the core formed, due to thickly concentrated hyaluronic acid molecules, increases as the surfaces come closer. This is due to the withdrawal of the base fluid through the boosted lubrication mechanism, leading to the formation of lubricating gel. This gel ultimately acts as boundary lubricant which prevents cartilage-to-cartilage contacts very briefly during a gait cycle. For most of the gait cycle, fluid film lubrication persists, and this fluid supports greater loads which are due to the development of increased pressures as compared with viscous lubricants. Thus, normal joints possess an in-built mechanism to support greater loads, at the load-bearing joints, with less friction and wear.

Cartilage, Articular↗
PubMed1994

A model for the nutritional transport in capillary-tissue exchange system.

By introducing the lubrication theory to the squeezing flow of the plasma between the cell and the vessel wall, an analysis of the flow and the nutritional transport within the tissue has been presented in this paper. Cells are assumed to flow in a single file, with axi-symmetric shapes. The concentration profiles of the dissolved nutrients within the tissue have been drawn under the assumption of the uniform distribution in the capillary due to continuous mixing in bolus flows between the 2 adjacent cells in the capillary. The analysis concludes that, in diseased state, the penetration depth for the substance in the tissue decreases and the cells in the deeper region do not get sufficient nutrition for their survival and they die out.

Algorithms↗
PubMed1994

Developing blood flow in the entrance region of an artery.

Presented herein are the studies of the flow behaviour of blood in the entrance region of a segment of an artery. The artery has an axisymmetric mild stenosis developed right from the entry cross section. The blood has been represented by a Bhingham fluid model which also takes the core region, formed due to axial migration of the red blood cells, into account. The flow in the artery has been divided into two regions developing boundary layer and a central core region. A fourth degree velocity profile satisfying the boundary conditions at the wall and the matching conditions at the core and the boundary layer interface is introduced in the governing momentum integral equation. The indicated integration provides a relation for the boundary layer thickness for each axial position. The results for the pressure distribution, entrance length and the wall shear stresses are discussed for the various values of the parameters involved in the analysis. The analysis predicts that the entrance length increases as the stenosis grows and therefore the heart has to put in more energy into transporting blood. It seems that there is some inbuilt mechanism which keeps the entry region of every segment to a minimum in normal arteries at each junction. This length increases in pathological states leading to various types of hypertensive diseases due to the formation and growth of the stenosis.

Algorithms↗
PubMed1994

A mathematical model for blood flow through an arterial bifurcation.

By introducing the finite element technique, a study of blood flow through an arterial bifurcation is presented in this paper. The blood is represented by a modified model of thixotropic power-law fluids, for which the parametric values for blood, both in normal and pathological states, have already been established. The results for the velocity profiles, pressure and wall shear stress distributions are elucidated and discussed for normal old and diseased states. The separation and reattachment points are also located for different values of the Reynolds number and the flow behaviour index (n) of the model representing the blood. The analysis identifies low shear stress zones behind the stenosis along the outer wall and high shear stresses downstream of the apex. The increasing percentage of the stenosis and the increasing values of the Reynolds number facilitate the high shear stress zones, whereas the thixotropy of the blood depicts an inbuilt mechanism of reducing high shear stresses as well as flow reversal regions.

Algorithms↗
PubMed1993

A model for blood flow through a stenotic tube.

This article deals with the introduction of the modified Casson's fluid model as the true representation for the blood for the steady laminar flow through a small diameter artery with axi-symmetric identical double stenoses in series. The governing equations are solved by using the finite element method. The results for the velocity profiles, the pressure and the wall shear stress distributions in addition to the location and length of the flow reversal zones have been brought out and discussed in reference to the severity of the disease. It has been observed that the non-Newtonian nature of the blood helps in reducing the magnitude of the peak wall shear stress at the throat and the length of the reversed flow regions in the post stenotic dilatation.

Arterial Occlusive Diseases↗
PubMed1992

A study of nutritional transport in capillary-tissue exchange system.

A two region flow model has been developed for a capillary-tissue exchange unit. Nutrient dissolved in plasma enters into the tissue from capillary through diffusion, filtration and osmosis. The governing non-linear coupled partial differential equations in the two regions (capillary and tissue) have been solved separately with suitable boundary and matching conditions. The results for the variation of Taylor's-Diffusivity Coefficient and concentration of a nutrient in the tissue region have been brought out for various values of the parameters involved in the analysis and discussed. It has been particularly noted that the penetration depth in the tissue for the nutritional transport can be considered as an important diagnostic parameter for many cardiovascular diseases.

Biological Transport↗
PubMed1992

Ultrastructural study of mixed growth hormone & prolactin secreting pituitary adenomas.

An ultrastructural study was done on 15 mixed growth hormone (GH) and prolactin (PRL)-secreting pituitary adenomas surgically removed from acromegalic patients with hyper-prolactinaemia, in order to see whether the 2 hormones were present in the same cell or in different cells. Double labelling immunogold technique was used for simultaneous ultrastructural localization of GH and PRL. It was found that each neoplastic cell in these 15 tumours (30 to 50 cells were studied in each case) contained 4 populations of granules viz., (i) granules positive for only GH; (ii) granules positive for only PRL; (iii) granules positive for both GH and PRL; and (iv) granules negative for both GH and PRL (unlabelled). Though the relative percentage of these 4 types of granules varied from cell to cell even within the same tumour, the major population (49.9 to 96%) was constituted by the mixed granules showing labelling for both GH and PRL. Almost all the cells examined from each tumour appeared to be mammosomatotrophs. Thus, the study indicated that mammosomatotroph adenomas are perhaps more common among mixed GH and PRL--secreting pituitary adenomas than previously believed. It could be important to recognize these tumours from the therapeutic point of view.

Acromegaly↗
PubMed1991

Biphasic model of the trabecular meshwork in the eye.

A biphasic continuum model for the flow of intraocular fluid, the aqueous humour, in the trabecular meshwork is proposed in the paper. The model considers the meshwork as a circular ring with uniform thickness of homogeneous, isotropic, viscoelastic material swollen with continuously percolating aqueous humour. The model further assumes the permeability of the meshwork as a function of dilation in its solid phase. The study considers steady and quasisteady states. Approximate solutions to the problem are obtained by Picard's type iterative procedure and computational results for the dimensionless solid displacement, permeability and pressure profiles are presented. It is concluded that intraocular pressure has a permeability-decreasing effect, whereas the elasticity of the meshwork shows a permeability-increasing effect. Thus, rising intraocular pressure develops a further rise in itself, whereas the elasticity tends to diminish the intraocular pressure through facilitating aqueous outflow.

Aqueous Humor↗
PubMed1991

Comparative study of bone growth by pulsed electromagnetic fields.

Pulsed electromagnetic fields have been widely used for treatment of non-united fractures and congenital pseudarthrosis. Several electrical stimulation systems such as air-cored and iron-cored coils and solenoids have been used the world over and claimed to be effective. Electrical parameters such as pulse shape, magnitude and frequency differ widely, and the exact bone-healing mechanism is still not clearly understood. The study attempts to analytically investigate the effectiveness of various parameters and suggests an optimal stimulation waveform. Mathematical analysis of electric fields inside the bone together with Fourier analysis of induced voltage waveforms produced by commonly used electrical stimulation wave-forms has been performed. A hypothesis based on assigning different weightings to different frequencies for osteogenic response has been proposed. Using this hypothesis astonishingly similar effective values of electric fields have been found in different systems. It is shown that effective electric field rather than peak electric field is the main parameter responsible for osteogenesis. The results are in agreement with experimental findings made on human beings by different investigators.

Electric Stimulation Therapy↗
PubMed1991

Fetal nigral grafts in the anterior eye chamber of adult rats: a long-term morphological study.

Substantia nigral grafts of 16 and 17 gestation days showed phenotypic characteristics in the anterior eye chamber of adult rats until the third month after transplantation. Thereafter by the sixth month a number of neurons showed somal and dendritic thickening, reduced population of endoplasmic reticulum, increase in lysosomes, and clear areas devoid of organelles, indicating age changes. These changes were progressive and affected more neurons by the end of 1 year, the longest period studied. The observations suggest that the maturation of nigral neurons is independent of specific afferent input, whereas target influence is necessary for the continued maintenance of the mature neurons. All the synapses observed in the transplant were of the asymmetric variety, reminiscent of the few intrinsic synapses of the intact nigra. This suggested establishment of mutual connectivity among the transplanted neurons in the absence of a target and the type of synapse formed may have been influenced by the local environment. Large glial processes, very prominant during the 4- to 6-month period became less significant afterward but continued to be present until the end of the period studied. Though there was no morphological evidence of lymphocytic infiltration, this might suggest an immunologic reaction.

Aging↗
PubMed1991

A porous implant model for a knee joint.

A study of the lubrication mechanism occurring in knee joint replacement is presented. The idealized model has been shown to produce results consistent with those in normal situations. In the present problem viscoelastic fluid has been considered to represent the synovial fluid in the fluid-film region and purely viscous Newtonian fluid in the porous layer due to filtration. Because of exact solution not being possible for the governing non-linear partial differential equations, the perturbation method has been used to obtain approximate solutions. The effect of an increase in the viscoelastic parameter of the lubricant is similar to that of an increase in concentration of hyaluronic acid molecules in synovial fluid. Important deductions are made for load carrying capacity and coefficient of friction and it has been shown that the slip velocity plays an important role in maintaining the self-adjusting nature of human joints.

Biomechanical Phenomena↗
PubMed1991

Ageing changes in the transplants of fetal substantia nigra grafted to striatum of adult rat.

Fetal nigral neurons from 16 and 17 gestational days were transplanted into the intact striatum of adult rat. On different post-transplantation days (30-360 days), the structural and immunohistochemical details of the transplants were studied. The grafted neurons matured and showed phenotypical characteristics comparable to that of normal nigral neurons in adult rats until 180 days. Tyrosine hydroxylase-positive neurons were seen not only in the transplant but also in the adjacent host striatum. Tyrosine hydroxylase-positive fibres were also seen extending for a short distance into the host striatum. A large number of synapses in the transplants were of asymmetric type, containing clear round vesicles. These synapses resembled the few intrinsic type present in the normal substantia nigra. On the other hand, the predominant type 2 synapses with pleomorphic vesicles in the normal nigra were infrequently encountered in the transplants. On the 300th day, the cytoplasm of a few of the neurons showed ageing changes in the form of clear spaces, paucity of organelles especially rough endoplasmic reticulum, membrane-bound vacuoles and increase in the lipofuscin population. In addition, localized thickening of the soma and the dendrites were seen in relation to randomly distributed neurons. By 360 days, more than one quarter (26%) of the total neurons showed these changes indicating ageing. The number per unit volume of normal neurons decreased significantly when compared to the transplants on 60 and 90 days. In the substantia nigra of age-matched control, except for an increase in the lysosomal population, other ageing changes were not detectable. The neurons of intact substantia nigra of the host rat, chronologically 4-8 months older than the transplanted neurons, also appeared normal but for lipofuscin granules. The present study provides morphological evidence for rapid ageing of neurons in the long term nigral transplants. These observations raise fresh doubts regarding permanent survival of grafted neurons in the host brain. Studies so far conducted are after prior nigral lesions. Trophic factors following lesions of the host tissue may have influenced the long term survival of the transplanted neurons. On the other hand, such changes may have been missed since no detailed morphological investigations of the long term transplants have been done so far.

Aging↗
PubMed1991

Collet-Sicard syndrome resulting from closed head injury: case report.

A 67-year-old man developed paralysis of the right ninth, tenth, eleventh, and twelfth cranial nerves (Collet-Sicard syndrome) after sustaining a closed head injury. Plain x-ray films of the skull revealed two linear fractures of the occipital bone (one of them probably traversing through the right occipital condyle) and a prominent soft-tissue shadow in the region of the nasopharynx, suggestive of a skull base fracture. The patient was managed conservatively. This is the only case of unilateral multiple caudal cranial nerve palsies (IX through XII), seen by us over a 20-year period, from among more than 5,000 moderate to significant head injuries.

Accessory Nerve↗