Search PubMed⌕ Search

Biomedical subjects

D N Ghista

Publications and source records attributed to D N Ghista.

At least 37 records · Page 2Linked to original sources
PubMed1986

Biomechanical analysis and simulation of scoliosis surgical correction.

In scoliosis, presurgical determination of each patient's segmental spinal stiffness will permit model simulation of the surgical correction. It also permits calculation of the optimal combination of corrective forces applied to the spine by the internal fixation system. This information can help to optimize the surgical procedure, especially if calculated forces and corrections can be monitored during surgery. To this end, a finite-element model of the spine has been developed that determines segmental stiffness from data of spinal geometries, derived from the radiographs of the patient, taken with incremental distraction applied to the head. On this model, custom-tailored combinations of corrective forces are applied incrementally until optimal correction is obtained, for safe levels of distraction and lateral forces. With variations in the computer software, any desired surgical instrumentation system can be simulated. Instrumented distractor and compression forceps have been fabricated to monitor surgical forces and displacements, and to permit eventual implementation of the model recommendations. Comparison of surgically acquired correction with that predicted by the model is then carried out. Data on complete analysis of two cases of idiopathic scoliosis are presented. They show significant variations in segmental and interpatient stiffness values, and how spinal stiffness governs the amount of correction gained by the nature and magnitude of corrective forces.

Adult↗
PubMed1985

Thrombogenetic studies of bioprosthetic heart valve surfaces. I. In vitro platelet adhesion in a static system.

Contact angle measurements, histological examinations and platelet adhesion tests on native and glutaraldehyde-treated porcine aortic valve leaflets, are reported. Contact angles measured with water or saline on native and treated leaflets do not differ appreciably. Values of less than 10 degrees for both the dry and wet leaflets were observed. Histological examination of the native and fixed tissue surfaces was carried out with both optical and scanning electron microscopy. Native leaflet surfaces appeared to be smoother with longer and straighter fibres beneath the surface than treated leaflets. Platelet adhesion tests were performed with fresh, non-anticoagulated human whole blood as well as with platelet suspension. Static platelet adhesion tests were carried out by depositing droplets of blood on the test surface. The blood droplets were washed off after a contact time of 2 minutes for whole blood and up to 32 minutes for platelet suspension. The adhering platelets were microscopically observed and counted. The platelet density on the native leaflets was found to be significantly higher than on the treated tissues. However, the platelet density did not vary with glutaraldehyde concentration in the range from 0.2 to 1.0% (v/v).

Animals↗
PubMed1985

Electrodiagnostic model for motor unit action potential (MUAP) generation.

The paper presents the development of inverse analysis of EMG, in terms of a Linear Prediction Coding (LPC) model and its parametric simulation of recorded single motor-unit action potential, for electrodiagnosis of neuromuscular disorders due to motor neuron degeneration, regeneration after lesion, myopathy, etc.

Action Potentials↗
PubMed1984

A study of the first heart sound spectra in normal anesthetized cats: possible origins and chest wall influences.

Heart sound recordings were taken from cats. The heart sounds were recorded directly from the chest wall and through an esophageal tube. The phono transducer and the esophageal tube were both placed over the base of the heart. Ultrasound M-mode, or motion-mode, recordings were taken to study the mitral valve dynamics. After analogue to digital conversion, electrocardiogram gated first heart sounds of each phono record were analyzed by the fast Fourier transform to obtain a frequency spectrum. Relative energies in 15 Hz bandwidths up to 150 Hz were correlated with the mitral valve closing velocity of the anterior mitral leaflet, obtained from the M-mode echocardiograms. The closing velocity correlated best with the energy in the 30-45 Hz bandwidth and 60-75 Hz bandwidth for the externally and internally monitored phonocardiogram respectively. The chest wall acted as a low pass filter, that is, the wall favoured the transmission of low frequencies and the energy transmitted decreased as wall thickness increased.

Anesthesia↗
PubMed1981

Reexamination of the intraurethral pressure determination using CO2 perfusion: its monitoring mechanism, standardization, and employment for the determination of the urethral constitutive property.

Urethral closure pressure profile is intended to provide an index of urethral resistance to bladder output, enable an assessment of urinary continence, provide distinction between a distensible and fibrotic sphincter urethral segment, and contribute information to enable characterization of detrusor-sphincter dyssynergia. However, the intraurethral pressure is a function of the catheter size, the hole size through which fluid is perfused, the fluid perfusion rate and the distensibility of the urethral sphincter segment; for want of standardization, it is difficult to functionally interpret the value of the peak urethral pressure taken with a certain catheter at a given perfusion rate. We have catered to this lacunae by developing (i) the urethral closing pressure, as the peak intraurethral pressure for theoretical limiting cases of zero perfusion rate and urethral diameter, and (ii) the urethral stiffness as a relation between its wall tension and tensile strain. Their detailed analyses and clinical interpretations are provided.

Carbon Dioxide↗
PubMed1980

Biomedical Engineering at the Indian Institute of Technology, (Madras)-II.

The Biomedical Engineering Division of the Indian Institute of Technology in Madras engages in a program of research, development and teaching. A visitor to our institution would, at any time, find a considerable variety of projects and courses being followed as well as active consultation with industry and the medical profession.

Academies and Institutes↗
PubMed1979

Computer design synthesis of a below knee-Syme prosthesis.

A detailed design synthesis analysis of the BK Syme prosthesis is provided, to determine the socket's cutout orientation size and shape, cutout fillet shape, socket wall thickness distribution and the reinforced fiber distribution in the socket wall, for a minimally stressed structurally safe lightweight prosthesis. For analysis purpose, the most adverse socket loading is obtained at the push-off stage of gait; this loading is idealised as an axial in-plane loading on the bottom edge of the circular cylindrical socket shell whose top edge is considered fixed. Finite element stress analysis of the socket shell (with uniform and graded wall thickness) are performed for various orientations of the cutout and for various types of corner fillets. A lateral cutout with a streamline fillet is recommended. The wall material (i.e., thickness) distribution is determined so as to minimise the stresses, while ensuring that the wall material's stress limits are not exceeded. For such a maximally-stressed lightweight socket shell, the panels in the neighbourhood of the cutout are checked to ensure that they do not buckle under their acquired stresses. A fiber-reinforced laminated composite socket shell is also analysed, to recommend optimum variables in orientations and densities of reinforcing fibers.

Ankle↗