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Biomedical subjects

K P Unnikrishnan

Publications and source records attributed to K P Unnikrishnan.

16 recordsLinked to original sources
PubMed2005

Average annual risk of tuberculous infection in India.

Estimates of the prevalence of tuberculous infection among children 1-9 years of age were available for four defined zones of India from a recently concluded tuberculin survey. These were pooled together and the average annual risk of infection in the country was computed as 1.5%. It was higher in urban areas, at 2.2%, than in rural areas, at 1.3%. The results call for further intensification of tuberculosis control activities, especially in urban areas, greater involvement of private practitioners and information, education and communication (IEC) for high-risk groups, to reduce the diagnostic and treatment delay thereby reducing the transmission of infection in all settings.

Child↗
PubMed2005

Annual risk of tuberculous infection in four defined zones of India: a comparative picture.

SETTING: Twenty-six selected districts in India. OBJECTIVES: To estimate the average annual risk of tuberculous infection (ARTI) in four defined zones in the country. STUDY DESIGN: A tuberculin survey was conducted in selected clusters of 26 districts in four defined zones of India. Children 1-9 years of age were subjected to tuberculin testing with ITU PPD RT23 with Tween 80, and the maximum transverse diameter of induration was measured 72 h later. Prevalence of infection was estimated using the cut-off point method (Method I) and the mirror-image technique (Method II) among children without bacille Calmette-Guérin scar. Results from individual zones have been reported earlier, and the results from all four zones are presented here as a consolidated summary. RESULTS: The ARTI computed from estimated prevalence was found to be lowest in the southern zone (Method I: 1.1%, Method II: 1.0%). It was higher in the eastern zone (1.3% by both methods) and highest in the western (Method I: 1.8%, Method II: 1.6%) and northern zones (1.9% by both methods). The proportion of infected children was found to be significantly higher in urban than in rural areas in all zones. CONCLUSION: The intensified tuberculosis control efforts need to be sustained for many years.

Child↗
PubMed2004

Bradycardia and sinus arrest following saline irrigation of the brain during epilepsy surgery.

Adverse cardiac events during the intraoperative period are life-threatening. The authors report three episodes of severe bradycardia and sinus arrest that occurred in a patient undergoing anterior temporal lobectomy and amygdalo-hippocampectomy for the treatment of epilepsy. The first episode occurred during resection of the amygdala; the other two episodes were observed during subsequent irrigation of the exposed brain structures, most likely the brain stem structures, because of a rent that the surgeon had deliberately made into the basilar cistern for better anatomic appreciation of the structures to be excised. The patient responded well to treatment with no adverse outcomes. The probable mechanisms leading to this event are discussed; the authors excluded insular cortex stimulation, the effects of the anesthetic drugs used, and venous air embolism as a cause of bradycardia and sinus arrest. The amygdala resection was the most likely cause of the first episode of bradycardia; the second episode of bradycardia and sinus arrest occurred because of inadvertent stimulation of brain structures by the high temperature (42 degree C) of the saline used for irrigation. To counter its effects, saline irrigation at room temperature (20 degree C) was started, and this caused the third episode of bradycardia, most likely because of "temperature shock" of the exposed brain. Prompt communication with the surgical team and vigilance are crucial for the appropriate management of such an incident, which may pose a threat to life. Avoiding irrigation of the exposed brain with high-temperature saline may prevent such an incident.

Adolescent↗
PubMed2003

Annual risk of tuberculous infection in the northern zone of India.

OBJECTIVE: To estimate the annual risk of infection with tubercle bacilli in the northern zone of India. METHODS: A community-based cross-sectional tuberculin survey was conducted among children aged 1-9 years who lived in a sample of villages and urban blocks of six selected districts in a defined north zone of India. A two-stage cluster sampling method was used to select rural and urban clusters. A total of 48 624 children in 598 clusters were subjected to tuberculin testing with one tuberculin unit (1 TU) of PPD RT23 stabilized with Tween 80. The maximum transverse diameter of induration was measured about 72 hours after the test. FINDINGS: Among the 48 624 test-read children, 22 064 (45.4%) had a bacille Calmette-Gu rin (BCG) scar. On the basis of the frequency distribution of tuberculin reaction size among 25 816 children without a BCG scar, the prevalence of infection with tubercle bacilli was estimated as 10.3%. The annual risk of infection was computed as 1.9%. The proportion of infected children was significantly higher in urban than rural areas. CONCLUSION: The high rate of tuberculous infection in the north zone of India suggests the need for further intensification of tuberculosis control efforts on a sustained and long-term basis.

BCG Vaccine↗
PubMed2003

Thermal lens spectrum of organic dyes using optical parametric oscillator.

The wavelength dependence of thermal lens signal from organic dyes are studied using dual beam thermal lens technique. It is found that the profile of thermal lens spectrum widely differ from the conventional absorption spectrum in the case of rhodamine B unlike in the case of crystal violet. This is explained on the basis of varying contribution of nonradiative relaxations from the excited vibronic levels.

Coloring Agents↗
PubMed2003

Annual risk of tuberculous infection in the western zone of India.

SETTING: Rural and urban areas of six selected districts in the western zone of India. OBJECTIVES: To estimate the annual risk of tuberculous infection (ARI). DESIGN: A community-based, cross-sectional tuberculin survey was conducted among children aged 1-9 years residing in a sample of rural and urban areas of six districts in the western zone of India. Stratified two-stage cluster sampling was adopted for selection of rural and urban clusters. A total of 48473 children in 600 clusters underwent tuberculin testing with 1TU PPD RT23 with Tween 80; the induration was measured about 72 h after the test. RESULTS: The BCG scar was observed in 52% of the test-read children. Estimation of the prevalence of infection was based on the frequency distribution of tuberculin reaction size among 22259 children without BCG scar. Reactions > or = 15 mm were considered attributable to infection with tubercle bacilli. The prevalence of infection was estimated to be 9.3%, and the ARI computed from the estimated prevalence was 1.8%. The proportion of infected children was found to be significantly higher in urban than in rural areas. CONCLUSION: The high rate of ARI in the western zone of India calls for further intensification of tuberculosis control efforts.

Age Factors↗
PubMed1999

Role of feedback in mammalian vision: a new hypothesis and a computational model.

This paper presents a novel hypothesis on the function of massive feedback pathways in mammalian visual systems. We propose that the cortical feature detectors compete not for the right to represent the output at a point, but for exclusive rights to abstract and represent part of the underlying input. Feedback can do this very naturally. A computational model that implements the above idea for the problem of detection is presented and based on that we suggest a functional role for the thalamo-cortical loop during perception of lines. We show that the model successfully tackles the so called Cross problem. Based on some recent experimental results, we discuss the biological plausibility of our model. We also comment on the relevance of our hypothesis (on the role of feedback) to general sensory information processing and recognition.

Algorithms↗
PubMed1987

The inversion of sensory processing by feedback pathways: a model of visual cognitive functions.

The mammalian visual system has a hierarchic structure with extensive reciprocal connections. A model is proposed in which the feedback pathways serve to modify afferent sensory stimuli in ways that enhance and complete sensory input patterns, suppress irrelevant features, and generate quasi-sensory patterns when afferent stimulation is weak or absent. Such inversion of sensory coding and feature extraction can be achieved by optimization processes in which scalar responses derived from high-level neural analyzers are used as cost functions to modify the filter properties of more peripheral sensory relays. An optimization algorithm, Alopex, which is used in the model, is readily implemented with known neural circuitry. The functioning of the system is investigated by computer simulations.

Algorithms↗
PubMed1985

Periodic and nonperiodic burst responses of frog (Rana pipiens) retinal ganglion cells.

Neural activity of class 3 retinal ganglion cells was recorded in frog optic tectum, using extracellular microelectrodes. The stimuli were rectangular patches of contrast (light-on-dark or dark-on-light), applied within the previously determined receptive fields, for periods ranging from a few milliseconds to several seconds. ON and OFF responses were recorded for as long as 1 s following stimulation. Poststimulus time histograms revealed two types of responses, labeled periodic and nonperiodic bursters. The periodic bursters were characterized by periods of high activity separated by silent or near-silent intervals. The bursts occurred rhythmically with frequencies roughly between 15 and 50 Hz. Nonperiodic bursters generally showed both broad and sharp peaks in activity, but no regular periodicities. Activity profiles were flat initially, with silent periods appearing after the first few stimulus presentations, suggesting an inhibitory nature of the bursting process. The records were shown to combine the activities of several neurons. Analysis of the waveforms in real time made possible isolation of some units. In these cases, neurons exhibited a high degree of selective synchrony, i.e., the sharing of a portion of the activity profile, and notable differences at other times. These data have implications for the processing of visual information.

Action Potentials↗
PubMed1985

Brainstem control of sensory information: a mechanism for perception.

We have proposed a theory in which pathways ascending from the brainstem reticular formation control sensory centers in the dorsal thalamus and neocortex. We assumed that the sensory messages received at a given level are transformed by a stochastic process, called Alopex, in a way which maximizes responses in central feature analyzers. Perception is seen as a process involving a close cyclic interaction between brainstem and sensory relays. We discuss the specific case of visual information flow and the proposed modification of visual images at the level of the dorsal lateral geniculate nucleus (dLGN). Computer simulations of a simple model, representing the dLGN and reafferent control emanating from the reticular formation, show that sensory features are effectively enhanced and--in the absence of sensory input--quasi-sensory features may be generated by feedback of a simple scalar variable that is formed by the non-linear superposition of the responses of any number of feature analyzers. The model proposes a specific mechanism for such processes as visual imagery, hallucinations, and dreaming, and provides a framework for further studies into the nature of cognitive brain functions.

Afferent Pathways↗