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Biomedical subjects

A Patwardhan

Publications and source records attributed to A Patwardhan.

49 records · Page 3Linked to original sources
PubMed1989

Axial loading studies of unstable intertrochanteric fractures of the femur.

An experimental four-part unstable intertrochanteric (IT) femoral fracture was created with either a large or small posteromedial fragment (PMF). Sixty-eight adult embalmed femoral anatomic specimens were fractured and subjected to axial loading after fixation. The maximum load prior to failure for femora from the same anatomic specimen was compared to differentiate between different methods of fixation. In the presence of the large PMF variation, anatomic reduction and fixation allowed the femur to resist an average maximum load 57% greater than identical fractures with the fragment excluded. Fixation of the small PMF increased construct strength by an average of 17% over no fixation. The PMF is the keystone to mechanical stability for IT fractures of the femur. When anatomic reduction is possible, its fixation becomes progressively more critical as its size increases.

Aged↗
PubMed1986

A method for the identification of in-vivo segmental stiffness properties of the spine.

A numerical algorithm is used to estimate in-vivo segmental stiffness properties of individual spine segments based upon existing load-displacement data. A static nonlinear finite element model stimulates a pathological spine and corrective instrumentation system. A systematic procedure for establishing the model's stiffness parameters is described, in the form of a nonlinear constrained optimal design problem. The numerical method is demonstrated using as an example a case of adolescent idiopathic scoliosis requiring corrective surgery.

Adolescent↗
PubMed1983

Load-bearing characteristics of lumbar facets in normal and surgically altered spinal segments.

An in-vitro experimental study was carried out to measure the induced loading on human lumbar facets due to varying amounts of compressive axial load. Testing was done on L2-L3 and L4-L5 spinal motion segments obtained from cadavers at autopsy. The compressive loading was applied to the spinal specimens in first a neutral position and then in an extended position. The motion segments were tested in a normal state and after facetectomy of the left facet. Contact pressures were quantified using pressure-sensitive film. This film was inserted between the articulating surfaces of the two facet joints prior to placing axial loads on the motion segments. In addition to recording pressure, the film was also used to quantify contact area. This provided sufficient information to compute the total facet loadings for all cases studied. Results of this study show how facet loads, peak pressures and contact areas change with respect to the various loads, positions and states studied. In particular this study shows that the absolute facet loads remain relatively constant with increasing segmental compressive loads such that the facet load expressed as a percent of load applied to the segment decreases with increasing axial loads. It also shows that the contact area moves cranially at L2-L3 and caudally at L4-L5 with increasing loads in extension. Furthermore, this study indicates that the load on the remaining facet is reduced substantially after a facetectomy although peak pressure increases. Finally, this study demonstrates the substantial difference in facet loadings between L2-L3 segments and L4-L5 segments.

Biomechanical Phenomena↗
PubMedDate not supplied

Heart rate variability during sympatho-excitatory challenges: comparison between spontaneous and metronomic breathing.

Respiration influences heart rate variability, leading to the suggestion that respiration should be controlled to assess autonomic function by using heart rate variability. Clearly, control of respiration is advantageous or even essential in several experimental circumstances. However, control of respiration, by itself, produces a small, but significant, increase in mean heart rate and a decrease in respiratory synchronous variation in heart rate. We tested whether, in some experimental situations, it may be possible to arrive at similar interpretation about autonomic function with and without using control of respiratory rate. Heart rate spectral powers from nine subjects were compared between spontaneous and metronomic breathing during two sympatho-excitatory stresses, lower body negative pressure (LBNP) and head up tilt (HUT). The normalized spectral powers in supine and HUT during spontaneous breathing were: 0.43 and 0.75 in very low (VLF) and 0.28 and 0.09 in high frequency (HF) regions. The powers during metronomic breathing were: 0.36 and 0.82 (VLF) and 0.36 and 0.09 (HF). The powers in supine and LBNP during spontaneous breathing were: 0.43 and 0.81 (VLF) and 0.28 and 0.06 (HF). The powers during metronomic breathing were: 0.36 and 0.80 (VLF) and 0.36 and 0.07 (HF). All p values were <0.05. Therefore, changes in heart rate spectral powers during HUT and LBNP were similar during metronomic breathing and spontaneous breathing. These results suggest that in experimental designs such as in our study, using metronomic breathing may not provide any additional insight into autonomic function than that can be obtained during spontaneous breathing.

Adult↗
PubMedDate not supplied

First metatarsophalangeal joint arthrodesis: quantitative mechanical testing of six-hole dorsal plate versus crossed screw fixation in cadaveric specimens.

Quantitative strength analysis of first metatarsophalangeal joint arthrodesis was performed using two fixation techniques: a small 6-hole plate with an interfragmentary screw or two crossed lag screws. Twelve matched-pair fresh-frozen cadaveric specimens (24 trials) were used for direct comparison of each of the two fixation techniques. All joint surfaces were prepared with power conical reamers utilizing a standard technique. The fixation construct was stressed to failure on each specimen using a computer-integrated materials tester. Fixation stiffness defined as force (load) over displacement and point of ultimate failure was evaluated. The six-hole plate and interfragmentary screw fixation method was a statistically stiffer form of fixation (p > .01) and displayed a greater point of ultimate failure (p > .002) under the laboratory conditions.

Aged↗
PubMedDate not supplied

Triple arthrodesis stabilization: a quantitative analysis of screw versus staple fixation in fresh cadaveric matched-pair specimens.

Qualitative analyses of midfoot stabilization in triple arthrodeses utilizing bone staple versus 4.5-mm cannulated cancellous screw fixation, with and without washers, were performed in fresh cadaveric specimens. Twenty-two trials (11 matched-pair feet) were used for direct comparison. Stiffness, defined as force/displacement, was determined at each talonavicular and calcaneocuboid joint. Ultimate load failure points of each specimen were also calculated. Trial results showed no statistically significant difference in stiffness or ultimate failure between these two forms of midfoot fixation for triple arthrodeses.

Arthrodesis↗
PubMedDate not supplied

Boronated monoclonal antibody 225.28S for potential use in neutron capture therapy of malignant melanoma.

The concept of conjugating boron cluster compounds to monoclonal antibodies has been examined by several groups of research workers in boron neutron capture therapy (BNCT). The procedures reported to date for boronation of monoclonal antibodies resulted in either an inadequate level of boron incorporation, the precipitation of the conjugates, or a loss of immunological activity. The present report describes the conjugation of dicesium-mercapto-undecahydrododecaborate (Cs2B12H11SH) to 225.28S monoclonal antibody directed against high molecular weight melanoma-associated antigens (HMW-MAA), using poly-L-ornithine as a "bridge" to increase the carrying capacity of the antibody and to minimize change in the conformational structure of antibody. The method produces a boron content of 1,300 to 1,700 B atoms per molecule 225.28S while retaining the immunoreactivity. Characterization in terms of the homogeneity of the conjugation of the boron-monoclonal antibody conjugates has been studied by gel electrophoresis and ion-exchange HPLC.

Antibodies, Monoclonal↗
PubMedDate not supplied

Bispectral energies within electrocardiograms during ventricular fibrillation are correlated with defibrillation shock outcome.

We investigated whether the degree of phase coupling among orthogonal electrocardiograms during ventricular fibrillation (VF) was correlated with defibrillation shock outcome. We used cross bispectrum to estimate the degree of phase coupling. In dogs, VF was electrically induced and terminated with a defibrillation shock with a 50% probability of success. The defibrillation shock was delivered between the right ventricular apex and a subcutaneous patch electrode. Bispectra were integrated within 8.7-11.7, 8.7-11.7 Hz bandwidths and compared between those trials for which the defibrillation shocks were successful (206 trials, 49%) and unsuccessful (221 trials, 51%) in terminating VF. Results showed that between 200 and 1000 ms before defibrillation shock, unsuccessful trials had greater bispectral energy than successful trials (p<0.05). Although correlations between degree of phase coupling and shock outcome do not indicate causal relationship or predictability, they provide further evidence of the organization during fibrillation. We discuss the nonstationary wavelet hypothesis, previously proposed in the literature by other investigators, as one of the possible mechanisms to explain the correlation between bispectral energy and shock outcome.

Animals↗
PubMedDate not supplied

The inverted Z bunionectomy: quantitative analysis of the scarf and inverted scarf bunionectomy osteotomies in fresh cadaveric matched pair specimens.

Quantitative analyses of the Scarf/Z and inverted Scarf/Z bunionectomy osteotomy procedures utilizing two-screw fixation were performed in fresh cadaveric specimens. Eighteen trials (nine matched pair feet) were used for direct comparison. Ultimate strength and failure areas were examined. Trial results revealed a strong statistically significant positive effect. The inverted Z approach was found, on average, 1.6 times stronger in resisting simulated weightbearing forces on the capital fragment to failure than that of the traditional Z bunionectomy osteotomy.

Aged↗