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N C Singh

Publications and source records attributed to N C Singh.

14 recordsLinked to original sources
PubMed2001

Estimating spatio-temporal receptive fields of auditory and visual neurons from their responses to natural stimuli.

We present a generalized reverse correlation technique that can be used to estimate the spatio-temporal receptive fields (STRFs) of sensory neurons from their responses to arbitrary stimuli such as auditory vocalizations or natural visual scenes. The general solution for STRF estimation requires normalization of the stimulus-response cross-correlation by the stimulus autocorrelation matrix. When the second-order stimulus statistics are stationary, normalization involves only the diagonal elements of the Fourier-transformed auto-correlation matrix (the power spectrum). In the non-stationary case normalization requires the entire auto-correlation matrix. We present modelling studies that demonstrate the feasibility and accuracy of this method as well as neurophysiological data comparing STRFs estimated using natural versus synthetic stimulus ensembles. For both auditory and visual neurons, STRFs obtained with these different stimuli are similar, but exhibit systematic differences that may be functionally significant. This method should be useful for determining what aspects of natural signals are represented by sensory neurons and may reveal novel response properties of these neurons.

Acoustic Stimulation↗
PubMed1996

Acute hemodynamic and neurohoromonal effects of furosemide in critically ill pediatrics patients.

OBJECTIVES: To study the acute hemodynamic effects of furosemide in critically ill pediatrics patients, the temporal relationship between hemodynamic changes and changes in neuroendocrine axis, and the temporal relationship between hemodynamic changes and urine output. DESIGN: Prospective study. SETTING: Pediatric intensive care unit in a tertiary care university center. PATIENTS: Fourteen critically ill pediatric patients who clinically required diuretic therapy. INTERVENTIONS: Before and after furosemide administration, hemodynamic and neurohormonal measurements were taken. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and neurohormonal responses to acute diuretic therapy were measured in 14 pediatric patients treated with furosemide (1 mg/kg/dose). Cardiac index deteriorated by 10 mins after drug administration (-9.4+/-3.9%, p<.05) and was associated with an increase in systemic vascular resistance (17.1+/-4.8%, p<.05). There was a subsequent increase in cardiac index (20+/-4.9%, p<.05) at 30 mins, with a decrease in systemic vascular resistance (-11.5+/-5.2%, p<.05). These hemodynamic changes were associated with marked increases in renin and norepinephrine concentrations and an increase in urinary prostaglandin release. The hemodynamic and neurohormonal effects had their onset before maximum diuresis. CONCLUSION: Intravenous furosemide administration in acutely ill pediatric patients results in an acute but transient deterioration in cardiac function that appears to parallel the neuroendocrine changes rather than the acute diuresis.

Adolescent↗
PubMed1996

A portable nitric oxide scavenging system designed for use on neonatal transport.

OBJECTIVE: To evaluate a portable scavenging system for nitric oxide and its oxides, designed for use on neonatal transport. DESIGN: A prospective evaluation of the nitric oxide scavenging system, using a neonatal transport incubator ventilator and a test lung. SETTING: Laboratory of a tertiary care children's hospital. INTERVENTIONS: The scavenging system was tested, using a neonatal transport incubator with attached ventilator, ventilator circuit, and a neonatal test lung. Nitric oxide was administered on the inspiratory limb, and nitric oxide and its oxides were measured in the expiratory gas after passing through the scavenger. MEASUREMENTS AND MAIN RESULTS: A modified scrubber assembly was filled with 50% activated charcoal and 50% aluminas potassium permanganate pellets (3). Three wire meshes were placed before, in between, and after the two chemicals to facilitate gas flow. Using the maximum FIO2, with a nitric oxide concentration of 120 parts per million (ppm), the test lung continuous flow ventilation (FIO2 of 0.86, peak inspiratory pressure of 30 cm H2O, positive end-expiratory pressure of 6 cm H2O) and respiratory rate of 60 breaths/min) was performed for 4 hrs with each of four freshly prepared scavenging systems. A fifth scavenging system was tested for a 12-hr period. The mean composition of the exhaled gases for 4 hrs were: nitric oxide 0.01 +/- 0.03 (SD) ppm, nitric dioxide 0.06 +/- 0.06 ppm, and other oxides 0.05 +/- 0.09 ppm. After 12 hrs of 120 ppm of inhaled nitric oxide, the fifth scavenger system had undetectable nitric oxide, nitric dioxide, and other oxides in the exhaled gas. Normal room air contained between 0.0 and 0.03 ppm of nitric oxide, 0.0 and 0.02 ppm of nitric dioxide, and 0.0 and 0.02 ppm of other oxides. CONCLUSION: Nitric oxide, nitric dioxide, and other dioxides can be safely scavenged by this portable scavenging system, allowing safe administration of nitric oxide free from environmental contamination with nitric oxide and its oxides.

Critical Care↗
PubMed1995

Declaring pediatric brain death: current practice in a Canadian pediatric critical care unit.

OBJECTIVE: To document the criteria used to declare brain death in a pediatric critical care unit (PCCU). DESIGN: Retrospective chart review. SETTING: Regional PCCU in southwestern Ontario. PATIENTS: Sixty patients 16 years of age or less declared brain dead from January 1987 through December 1992. OUTCOME MEASURES: Presence or absence of documentation of irreversible deep coma, nonresponsive cranial nerves, absent brain-stem reflexes, persistent apnea after removal from ventilator, presence or absence of blood flow detected by radioisotope scanning, presence or absence of electroencephalographic evidence of electrocerebral activity. RESULTS: The 60 patients accounted for 1.5% of all PCCU admissions; 17 were under 1 year of age. In 39 cases brain death was diagnosed using clinical criteria ("certified brain death"), which could not be fully applied in the remaining 21 cases ("uncertifiable but suspected brain death"). Electroencephalography and cerebral blood-flow studies with technetium-99m hexamethyl-propyleneamine oxime were used as ancillary tests in 16 patients with certified brain death and in 17 with uncertifiable but suspected brain death who survived long enough to be tested. Electrocerebral silence was demonstrated in all nine patients who underwent electroencephalography. Cerebral blood flow was undetectable in 26 of the 30 patients tested, and an abnormal pattern of blood flow was seen in the remaining 4, all of whom received a diagnosis of certified brain death. CONCLUSIONS: Pediatricians in this large tertiary care referral centre are using clinical criteria based on the 1987 guidelines of the CMA to diagnose brain death in pediatric patients, including neonates. When clinical criteria cannot be fully applied, ancillary methods of investigation are consistently used. Although the soundness of this pattern of practice is established for adults and older children, its applicability to neonates and infants still needs to be validated.

Adolescent↗
PubMed1994

Prolonged survival in neonatal nemaline rod myopathy.

Two children are reported who are notable exceptions to the rule of early mortality reported for neonates with severe nemaline rod myopathy. Their conditions improved progressively from birth with full pediatric critical care unit support. They achieved respiratory independence at 22 months and 15 months and now at ages 29 months and 17 months, respectively, they are cognitively normal and demonstrating progressive improvement in muscle strength.

Child Development↗
PubMed1994

Usefulness of (Tc 99m) HM-PAO scan in supporting clinical brain death in children: uncoupling flow and function.

OBJECTIVE: To determine the usefulness of (Tc 99m) HM-PAO scan in supporting the clinical diagnosis of brain death. DESIGN: Retrospective review. SETTING: Paediatric Intensive Care Unit. SUBJECTS: A total of 39 paediatric patients had HM-PAO scans conducted to confirm the presence of brain death or to assess the degree of brain injury. INTERVENTIONS: All patients had (Tc 99m) HM-PAO injected before the scan was conducted. MEASUREMENTS AND MAIN RESULTS: Fifty-four scans were done in 39 patients. The majority of cerebral injury was as a result of closed head injury or asphyxia/anoxia. There were 20 scans which demonstrated no cerebral blood flow (CBF); however, in 26 situations patients were clinically brain dead. All of the patients who continued to have CBF in the presence of clinical brain death sustained asphyxial/anoxic injuries. CONCLUSIONS: The HM-PAO scan is a useful non-invasive portable tool for supporting the diagnosis of brain death when there is absent CBF. However, continued flow may be present in asphyxial/anoxic injuries in the presence of clinical brain death.

Adolescent↗
PubMed1994

Lower anion gap increases sensitivity in predicting elevated lactate.

OBJECTIVE: The normal reference range for the anion gap (AG) has recently been questioned by several authors. Lowering the upper limit of normal of the AG has been found to be more sensitive in predicting elevated lactate in critically ill adults. The objectives of this study are i) to define a new upper limit of normal of the AG in a study population of healthy adult volunteers, ii) to determine the sensitivity, specificity, the positive predictive value and the negative predictive value of the new upper limit for AG in detecting elevated lactate in critically ill children and to compare these results to the old upper limit of normal of AG (16 mmol/l), iii) to construct a receiver-operating-characteristic (ROC) curve for anion gap as a predictor of elevated lactate, iv) to determine the relationship between anion gap and serum lactate levels in critically ill patients. DESIGN: A prospective, cohort study. SETTING: Paediatric Intensive Care Unit of a University Hospital. SUBJECTS: Part I: Convenience sample of healthy adult volunteers to provide a reference range for anion gap calculation. Part II: Consecutive children admitted to the Paediatric Intensive Care Unit who had lactate levels measured for clinical reasons. MEASUREMENTS: Part I: Electrolytes and blood gases were measured from blood samples drawn from 25 adult volunteers. The reference range for AG was calculated using the equation, AG = Na - (Cl + HCO3). The upper limit of normal was calculated as mean + 2 SD. Part II: Eligible ICU patients were included in this study if they had lactate, electrolytes and blood gases obtained simultaneously. The AG was calculated as above. The new upper limit of normal AG was compared to an AG of 16 for diagnosing an elevated plasma lactate. RESULTS: The mean anion gap in the normal population was 9.4 +/- 1 mmol/l with 11 mmol/l being used as the new upper limit of normal. Thirty-six ICU patients had 189 arterial blood samples from which lactate, electrolytes and blood gas were measured simultaneously. The sensitivity, specificity, positive predictive value and negative predictive value of using an AG of 11 mmol/l as the upper limit of normal were 86%, 40%, 65% and 69% respectively, compared to 49%, 84%, 80% and 55% respectively using the upper limit of normal of AG of 16 mmol/l. The ROC curve supported lowering the upper limit of normal for the anion gap to predict an elevated lactate. There was a linear relationship between anion gap and serum lactate levels. CONCLUSIONS: An AG of 11 mmol/l as the upper limit of normal has a higher sensitivity and higher negative predictive value but lower specificity and lower positive predictive value for detecting elevated lactate in critically ill children.

Acid-Base Equilibrium↗
PubMed1993

Attitudes and practices of pesticide users in Saint Lucia, West Indies.

This article reports the results of a Saint Lucia survey, part of a larger program, that was the first to document the prevalence of suboptimal safety practices among vector control and farm workers using pesticides in the English-speaking Caribbean. Among other things, the survey found that many of 130 pesticide users surveyed were unaware that the skin and eyes were important potential routes of absorption. Over a quarter said they had felt ill at some point as a result of pesticide use. About half the respondents said they had received more than "introductory" training in safe pesticide use, and most said they always found labels or directions affixed to pesticide containers. However, about half said they never or only sometimes understood the labels, and many of those who said they understood did not always follow the instructions. About a quarter of the smokers said they smoked while using pesticides; about a sixth of the survey subjects said they ate food while using pesticides; and over 60% said they never wore protective clothing.

Adolescent↗
PubMed1992

Uncoupled cerebral blood flow and metabolism after severe global ischemia in rats.

In a rat model of complete global brain ischemia (neck tourniquet) lasting either 3 min or 20 min, we monitored global CBF (sagittal sinus H2 clearance) and CMRO2 for 6 h to test the hypothesis that delayed postischemic hyperemia and uncoupling of CBF and CMRO2 occur depending on the severity of the insult. Early postischemic hyperemia occurred in both the 3-min and 20-min groups (p less than 0.05 vs. baseline values) and resolved by 15 min. Hypoperfusion occurred in the 3-min group between 15 and 60 min postischemia (approximately 23% reduction), and in the 20-min group from 15 to 120 min postischemia (approximately 50% reduction) (p less than 0.05), and then resolved. CMRO2 was not significantly different from baseline at any time after ischemia in the 3-min group. After 20 min of ischemia, however, CMRO2 was decreased (approximately 60%) throughout the postischemic period (p less than 0.05). At 5 min after ischemia, CBF/CMRO2 was increased in both groups but returned to baseline from 60 to 120 min postischemia. In the 3-min group, CBF/CMRO2 remained at baseline throughout the rest of the experiment. However, in the 20-min group, CBF/CMRO2 once again increased (approximately 100%), reaching a significant level at 180 min and remaining so for the rest of the 6-h period (p less than 0.05). These data demonstrate biphasic uncoupling of CBF and CMRO2 after severe (20 min) global ischemia in rats. This relatively early reemergence of CBF/CMRO2 uncoupling after 180 min of reperfusion is similar to that observed after prolonged cardiac arrest and resuscitation in humans.

Animals↗
PubMed1992

Comparison of continuous versus intermittent furosemide administration in postoperative pediatric cardiac patients.

OBJECTIVE: To compare the effects of furosemide administered by intermittent iv infusion vs. continuous iv infusion on urine output, hemodynamic variables, and serum electrolyte concentrations. DESIGN: Prospective, randomized trial. SETTING: Pediatric ICU. PATIENTS: Postoperative pediatric cardiac patients. INTERVENTIONS: Patients were assigned to either the continuous iv infusion or the intermittent infusion groups. The intermittent group received 1 mg/kg iv of furosemide every 4 hrs to be increased by 0.25 mg/kg iv every 4 hrs to a maximum of 1.5 mg/kg iv if the urine output was less than 1 mL/kg.hr. The continuous infusion group received an initial furosemide dose of 0.1 mg/kg iv (minimum 1 mg) followed by an iv infusion rate of 0.1 mg/kg.hr of furosemide to be doubled every 2 hrs to a maximum of 0.4 mg/kg.hr if the urine output was less than 1 mL/kg.hr. MEASUREMENTS AND MAIN RESULTS: Demographic variables, fluids, electrolyte and inotropic requirements were the same in both groups. A significantly (p = .045) lower daily dose of furosemide (4.90 +/- 1.78 vs. 6.23 +/- 0.62 mg/kg.day) in the continuous iv infusion group produced the same 24-hr urine volume as that of the intermittent group. There was more variability in urine output in the intermittent group as well as more urinary losses of sodium (0.29 +/- 0.15 vs. 0.20 +/- 0.06 mmol/kg.day, p = .0007) and chloride (0.40 +/- 0.20 vs. 0.30 +/- 0.12 mmol/kg.day, p = .045). CONCLUSION: Furosemide administered by continuous iv infusion is advantageous in the post-operative pediatric patient because of a more controlled and predictable urine output with less drug requirement and less urinary loss in sodium and chloride.

Cardiac Surgical Procedures↗
PubMed1991

Physiological responses to endotracheal and oral suctioning in paediatric patients: the influence of endotracheal tube sizes and suction pressures.

OBJECTIVE: To study the influence of varying outer suction catheter (SC) diameter (OD) to inner endotracheal tube (ETT) diameter (ID) and suction pressures (SP) on heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP), arterial oxygen saturation (SaO 2) and intracranial pressure (ICP) during ETT and oral suctioning. An additional aim was to define an optimal suction catheter size that would prove easy to introduce and be rapidly effective in clearing secretions with the least physiological alteration. DESIGN: Prospective study. SETTING: Paediatric intensive care unit. PATIENTS: Ventilated paediatric patients. INTERVENTION: Patients had ETT suctioning performed in a random fashion using suction catheters with SC outer diameter to inner ETT diameter of approximately 0.4, 0.7 and 0.9 using varying pressures (80, 100, 120 mmHg). Using the medium size suction catheter (OD/ID = 0.7) at 100 mmHg of suction pressure, oral suctioning was compared to ETT suctioning. MEASUREMENTS AND MAIN RESULTS: Seventeen patients were studied (age 6.5 + 5 months). All suction catheters at varying pressures resulted in similar transient alterations in HR, RR, MAP, SaO 2 and ICP following ETT suctioning. Significant changes were seen in SaO 2, HR and ICP, irrespective of the catheter diameter or suction pressure. Oral suctioning resulted in similar trends and magnitude of changes as for ETT suctioning in MAP, RR, HR, and ICP, but less change occurred in the SaO 2 (p less than 0.05). The catheters with OD/ID of 0.7 were easiest to introduce and most effective in clearing secretions. CONCLUSION: Our study suggests that: 1. Tracheal toilet using variations in OD/ID ratios and SP within limits tested resulted in similar significant adverse changes in HR, ICP and SaO 2 and similar trends in RR and MAP. 2. Based on the ease of introduction and the effectiveness of clearing secretions, a medium SC (OD/ID = 0.7) is most appropriate for infants and children. 3. Oral suctioning also results in adverse physiological changes, therefore similar precautions to those taken during tracheal suctioning should be followed for oral suctioning.

Blood Pressure↗
PubMedDate not supplied

Report of an outbreak of diarrhoeal disease caused by cholera followed by rotavirus in Manipur.

An outbreak of acute diarrhoeal disease between August and October 1985 in 3 districts of Manipur state was investigated amongst 9,29,077 population at risk. The overall attack rate and case fatality rate were 0.2% and 0.9% respectively. Hospital records revealed that 58.8% of cases occurred amongst older children above 5 years of age. V.cholera was isolated from 25.3% of cases sampled. Interestingly, increased frequency in weekly admission of cases amongst children during first two years of life increased in the beginning of October when the original peak of diarrhoeal outbreak was about to decline. The October peak was caused by rotavirus which could be detected from 50.0% of diarrhoeal children in this age group. This possibly reflected beginning of the usual rotavirus diarrhoea season in the locality.

Adolescent↗