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Biomedical subjects

R Pratap

Publications and source records attributed to R Pratap.

16 recordsLinked to original sources
PubMed2005

Bilateral tension pneumothorax following rigid bronchoscopy: a report of an epignathus in a newborn delivered by the EXIT procedure with a fatal outcome.

We describe a case of a newborn baby with a prenatal diagnosis of an epignathus (oropharyngeal teratoma). With the potential for airway problems at birth, he was delivered by an elective EXIT (Extra Utero Intrapartum Treatment) procedure at 38 weeks of pregnancy. The airway was secured and rigid bronchoscopy performed. Initially he was stable, but developed cardiorespiratory difficulties 40 minutes after birth and died from a cardiac arrest 17 minutes later. Tension pneumothorax is a devastating complication that can occur with lower airway manipulation for anaesthesia and rigid bronchoscopy. The addition of positive pressure during mechanical ventilation converts the pneumothorax into a tension pneumothorax. The possibility of tension pneumothorax should be entertained in a mechanically ventilated patient whose ventilatory pressures are increasing, with diminishing cardiac output. A complicated case is presented, where the diagnosis was missed with a fatal outcome.

Bronchoscopy↗
PubMed2004

Face value?

Explore the source record for details and available documents.

Accidental Falls↗
PubMed2003

Multimodal map and complex basin of attraction of a simple hopper.

In this paper, we study the global dynamics of a simple passive mechanical model for hopping. The hopper is a two-mass, single-spring system constrained to move in the vertical direction (under gravity) above a rigid ground. The hopper model and its basic dynamics including the existence of incessant hopping motions have been reported elsewhere. Here, we extend the study to investigate the global dynamics of the hopper. The global map of the hopper is multimodal. We construct an approximate analytic map near the fixed points of the map and show that the fixed points exhibit one-way stability. We also show that the map is invariant under the inversion of the mass ratio of the hopper. Next, we construct the global basin of attraction of these fixed points and show that their structure is highly complex and retains form at finer scales. This structure of the basin of attraction contains regions where the fate of an arbitrary initial condition becomes unpredictable.

Journal Article↗
PubMed2001

Effect of time scales on the unfolding of neural attractors.

A study of the effect of time scales in brain dynamics on the unfolding of the attractors in the phase space, reconstructed by a time delay embedding of the EEG signal, was carried out. Applying the techniques of nonlinear time series analysis, the unfolding rate of the system attractor was determined by analyzing the variation of the correlation dimension parameter and subjecting it to a bi-parametric fit. The behavior of the parameter, which measures the rate of unfolding, was monitored for varying time scales in two cases: (a) normal eyes closed condition and (b) the pathological case of epilepsy. Significant results were obtained.

Brain↗
PubMed1999

Significance of time scales in nonlinear dynamical analysis of electroencephalogram signals.

We propose to show in this paper, that the time series obtained from biological systems such as human brain are invariably nonstationary because of different time scales involved in the dynamical process. This makes the invariant parameters time dependent. We made a global analysis of the EEG data obtained from the eight locations on the skull space and studied simultaneously the dynamical characteristics from various parts of the brain. We have proved that the dynamical parameters are sensitive to the time scales and hence in the study of brain one must identify all relevant time scales involved in the process to get an insight in the working of brain.

Adult↗
PubMed1998

Breast carcinoma in women under the age of 50: Relationship between p53 immunostaining, tumour grade, and axillary lymph node status.

There is evidence to suggest that breast carcinoma in young women behaves in a more aggressive manner than in older women. As positive immunostaining for p53 has also been associated with increased tumour aggressiveness, this study was aimed at finding out whether patients under the age of 50 years have a higher prevalence of p53 positivity in their tumours. The inter-relationships between age, p53, tumour grade, and axillary lymph node status were also investigated. Two hundred and twenty nine invasive carcinomas were studied. One hundred and eight patients were under the age of 50, and 121 were at or above that age. The specific p53 monoclonal antibody DO7 and the avidin-biotin complex immunoperoxidase technique were used. Fifty seven tumours (25 %) showed variable degrees of p53 positivity. The incidence of positivity was slightly higher in women under the age of 50 as compared with those at or above that age (29% (31/108) vs. 21% (26/121), respectively), but the difference was not statistically significant (p < 0.05). On the other hand, in invasive ductal carcinoma (191 cases), p53 positivity was significantly related to high tumour grade (7% in grade I [1/14], 19% in grade II [20/105], and 43% in grade III [31/72]; p < 0.0001 [I-II vs III]). p53 positivity was also significantly related to the presence of extensive (more than three) axillary lymph node metastases (p53 positivity being 22% in node negative tumours [40/178], 18% in tumours with three or less positive nodes [6/33], and 61% in tumours with more than 3 positive nodes [11/18]; p = 0.0033 [second vs third group]). Both features were also significantly more common in the younger age group. The results suggest that the slightly higher incidence of p53 positivity seen in tumours from younger patients, is probably related to the significantly higher incidence of grade III tumours in these patients.

Adult↗
PubMed1989

Antithrombotic effect of thiopurinol.

Antithrombotic activity of ten pyrazolo pyrimidine derivatives was tested in mouse pulmonary thromboembolism model. Out of these compounds, Thiopurinol (C5H4N4S) showed dose-dependent protection in mice from death/paralysis induced by collagen + adrenaline. It also caused dose-dependent inhibition of thrombus formation in the cat. Thiopurinol inhibited aggregation of platelets induced by ADP and arachidonic acid but did not inhibit superoxide generation. It had no antiinflammatory activity nor any effect on cardiovascular system. The results indicate that the antithrombotic activity of the compound is mediated via inhibition of platelet aggregation.

Allopurinol↗
PubMed1989

Collective modes in neural networks.

A theoretical model, based on response of a neural network to an external stimulus, was constructed to determine its collective modes. It is suggested that the waves observed in EEG records reflect the cooperative electrical activity of a large number of neurons. Further, an actual EEG time series was analyzed to deduce two dynamic parameters, dimension d of phase space of the neural system and the minimum number of variables nc necessary to describe the EEG pattern. We find d = 6.2 and nc = 11.

Artificial Intelligence↗
PubMed1988

Invariant characterization of neural systems.

It is shown that the invariant integral, viz., the Kolmogorov second entropy, is eminently suited to characterize EEG quantitatively. The estimation obtained for a "clinically normal" brain is compared with a previous result obtained from the EEG of a person under epileptic seizure.

Brain↗
PubMed1984

An evolutionary model of a neural network.

A very general model of an idealized neural network is proposed, in which the system is governed by an evolution equation. The equation determines the state of the network at time t greater than 0, if its state at time t = 0 and the kernel (in the equation) are known. It is shown that, by making specific assumptions about the kernal and the initial state, the evolution equation describes a distributed memory having the properties of recognition and association. In this case the model of the distributed memory is identical to that of Anderson and Cooper. Further, it is shown that by a different choice of the kernel, the evolution equation goes beyond the earlier model and is able to describe learning as a dynamic process.

Biological Evolution↗
PubMed1984

Mutagenic activity of methyl-substituted tri- and tetracyclic aromatic sulfur heterocycles.

A number of polycyclic aromatic sulfur heterocycles have been identified in coal-derived products and in shale oils. The mutagenic activity of some of these compounds, including dibenzothiophene, benzo[b]naphtho[1,2-d]thiophene, benzo[b]naphtho[2,1-d]thiophene and benzo[b]naphtho[2,3-d]thiophene have been determined using the Salmonella/microsome mutagenicity test. These compounds demonstrated either very weak or no mutagenic activity. The methyl derivatives of each of these four compounds were assayed for mutagenic activity. Salmonella typhimurium TA98 was used as the tester strain. All assays required a rat-liver homogenate metabolic activator. Five of the methylated derivatives, 1-methylbenzo[b]naphtho[1,2-d]thiophene, 3-methylbenzo[b]naphtho[1,2-d]thiophene, 1-methylbenzo[b]-naphtho[2,1-d]thiophene, 6-methylbenzo[b]naphtho[2,1-d]thiophene and 4-methylbenzo[b]naphtho[2,3-d]thiophene demonstrated mutagenic activity. However, activity was observed only at high concentrations of the metabolic activator.

Animals↗