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Biomedical subjects

L A Newberg

Publications and source records attributed to L A Newberg.

At least 19 recordsLinked to original sources
PubMed1995

An algorithm for analysing probed partial digestion experiments.

A partial digestion of DNA (e.g. cosmid. Lambda, YAC, chromosome) is performed and the lengths of thoses fragments which hybridize to a labeled probe are measured using gel electrophoresis. We give an efficient algorithm that takes as input this experimental data and proposes one or more candidate solutions. Each solution designates the location of each restriction site and specifies the endpoints of each fragment. (Further experiments can then be designed to select the correct solution from this small set of candidates.) The algorithm works well even when the experiment gives inexact values for the lengths.

Algorithms↗
PubMed1994

Finding a most likely clone ordering from oligonucleotide hybridization data.

Using an extension of a statistical model given by E. Lander and M. Waterman, we define the a posteriori probability of a clone ordering based upon oligonucleotide hybridization data. We give algorithms for computing the likelihood of a clone ordering and for finding a clone ordering of maximum likelihood. The dynamic programming algorithm for computing likelihoods runs in time O(mnc), where m is the number of oligonucleotide probes, n is the number of clones, and c is the coverage of the clone library. We use the Expectation-Maximization technique to maximize likelihoods.

Algorithms↗
PubMed1987

MAPMAKER: an interactive computer package for constructing primary genetic linkage maps of experimental and natural populations.

With the advent of RFLPs, genetic linkage maps are now being assembled for a number of organisms including both inbred experimental populations such as maize and outbred natural populations such as humans. Accurate construction of such genetic maps requires multipoint linkage analysis of particular types of pedigrees. We describe here a computer package, called MAPMAKER, designed specifically for this purpose. The program uses an efficient algorithm that allows simultaneous multipoint analysis of any number of loci. MAPMAKER also includes an interactive command language that makes it easy for a geneticist to explore linkage data. MAPMAKER has been applied to the construction of linkage maps in a number of organisms, including the human and several plants, and we outline the mapping strategies that have been used.

Chromosome Mapping↗
PubMed1985

Nimodipine improves outcome when given after complete cerebral ischemia in primates.

Twenty-seven pigtailed monkeys (Macaca nemestrina) were subjected to 17 min of complete cerebral ischemia followed by 96 h of intensive care treatment. Fourteen of the monkeys were assigned randomly to the treatment group and received nimodipine 10 micrograms . kg-1 5 min postischemia followed by 1 microgram . kg-1 . min-1 for 10 h. Six monkeys (three treated) failed to meet preestablished protocol criteria and were excluded. The remaining treated and untreated monkeys were well matched for age, sex, and other physiologic variables. Neurologic outcome at 96 h postischemia was significantly better in the nimodipine-treated monkeys than in the controls. Eight of the 11 treated animals had an apparent normal level of consciousness; four of these had no detectable neurologic deficits and a fifth had only a slight motor apraxia. Only two of the 10 untreated animals had an apparent normal level of consciousness, and all had major neurologic deficits. Histopathologic examination showed variable ischemic neuronal change and infarction to involve gray matter in distal arterial perfusion zones. Significant white matter changes were not observed. A histopathologic scoring system yielded a significantly better mean score for the treated group than for the untreated group, and there was significant correlation between neurologic function and histopathologic findings. The authors conclude that nimodipine improves the neurologic outcome when given after an episode of complete cerebral ischemia in primates, and they recommend controlled clinical trials in patients resuscitated after cardiac arrest.

Animals↗
PubMed1985

Cerebral and systemic effects of hypotension induced by adenosine or ATP in dogs.

The authors evaluated the systemic and cerebral hemodynamic and metabolic effects of 1 h of hypotension to a mean arterial pressure of either 50 mmHg or 40 mmHg induced by intravenous adenosine or ATP in dogs maintained on 70% nitrous oxide and 0.1% halothane. Following the hypotensive period, brain biopsy specimens were taken for the determination of cerebral metabolites and calculation of the energy charge. Hypotension induced by either adenosine or ATP produced a marked 40-62% decrease in systemic vascular resistance with little change in cardiac index or oxygen consumption but resulted in a mild metabolic acidosis. Because of a profound decrease in cerebral perfusion pressure with hypotension (to 31-33 mmHg at an MAP of 50 mmHg and 22-24 mmHg at an MAP of 40 mmHg) CBF decreased 54-65% and was inadequate to meet the unchanged cerebral oxygen demands, resulting in some anaerobic metabolism with an accumulation of lactate. While the ease with which one can induce and maintain hypotension with these agents may be advantageous in clinical practice, the effects of adenosine and ATP on cerebral hemodynamics and metabolism may offer no advantage over other hypotensive agents.

Acidosis↗
PubMed1984

Cerebral resuscitation: advances and controversies.

Brain protection is the prevention or amelioration of neuronal damage occurring after a hypoxic or ischemic event. Controversies in this field focus on whether incomplete global ischemia may produce a worse insult than does complete global ischemia; whether barbiturates provide protection following complete global ischemia; and whether the calcium entry blockers have a role in brain protection. Current knowledge dictates that incomplete ischemia coupled with hyperglycemia will cause a severe cerebral lactic acidosis and produce a worse insult than does complete ischemia. In the absence of hyperglycemia complete cerebral ischemia produces more neuronal damage. The barbiturates have been shown to provide protection in focal ischemia and incomplete global ischemia in which neuronal function is still present, but have not been shown to provide protection following complete global ischemia. Those calcium entry blockers with cerebral vascular selectivity may well provide some brain protection following complete cerebral ischemia by ameliorating the postischemic hypoperfusion state.

Acidosis↗
PubMed1984

Cerebral blood flow and neurologic outcome when nimodipine is given after complete cerebral ischemia in the dog.

Ten minutes of complete cerebral ischemia was produced in 26 dogs by temporary ligation of the aorta and the venae cavae. Twenty dogs received nimodipine, a calcium entry blocker, 10 micrograms kg-1 i.v. 2 min after the ischemic period, followed by 1 microgram kg-1 min-1 for 2-3 h. Six dogs received only the solvent used for nimodipine. Fourteen dogs received nimodipine for 3 h and were subsequently evaluated neurologically up to 48 h postischemia. In the 12 other dogs, CBF and metabolism were followed for 2 h postischemia while either nimodipine or the solvent only was infused. The results were compared to previously published results for untreated dogs and dogs given nimodipine before the ischemic event. Nimodipine had the same effect on postischemic CBF whether started before or after the ischemic event, nearly doubling the flow when compared with untreated controls, whereas the solvent alone caused only a slight increase in CBF over control. By contrast, nimodipine initiated in the preischemic period significantly improved the neurologic outcome, but when initiated in the postischemic period the results were equivocal, such that the outcome was not significantly different from either the untreated group or the group in which nimodipine was initiated preischemia. Metabolic measurements did not give any indication of a specific effect of nimodipine, nor could the metabolic results be used as an indicator of neurologic outcome. The results are consistent with a beneficial effect of nimodipine following complete cerebral ischemia; however, evaluation of neurologic functional effects will require a more sensitive model.

Animals↗
PubMed1984

Systemic and cerebral effects of isoflurane-induced hypotension in dogs.

The systemic and cerebral effects of hypotension induced with isoflurane were examined in 12 dogs. Hypotension to a mean arterial pressure of either 50 mmHg or 40 mmHg for 1 h was produced by 2.5 +/- 0.1-2.9 +/- 0.3% end-expired isoflurane anesthesia. Before and during the period of hypotension the following were measured or derived: arterial and pulmonary artery pressures; arterial, mixed venous, and sagittal sinus blood gases; cardiac output and cerebral blood flow; whole body and cerebral oxygen consumption; systemic and cerebral vascular resistance; intracranial pressure, serum lactate, and pyruvate concentrations; and blood glucose. At the end of the period of hypotension, brain biopsy specimens were taken for the determination of ATP, ADP, AMP, phosphocreatine, lactate, and pyruvate concentrations. Isoflurane-induced hypotension produced a significant decrease in systemic vascular resistance (27-43%) associated with a significant decrease in cardiac output (39-42%) and a smaller decrease in whole-body oxygen consumption (14-21%). Isoflurane also produced a significant decrease in cerebral oxygen consumption (40-44%) accompanied by a decrease in cerebral blood flow (60-62%). Following both the 40 and 50 mmHg periods of hypotension, the cerebral energy state was normal, indicating the preservation of normal aerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1983

Nimodipine improves cerebral blood flow and neurologic recovery after complete cerebral ischemia in the dog.

Ten minutes of complete ischemia was produced in 11 dogs by temporary ligation of the aorta. Immediately before the ischemic episode, the dogs received nimodipine, a new calcium entry blocker, 10 micrograms kg-1, i.v., followed by an infusion of 1 microgram kg-1 min-1 for 2 h. Post-ischemic cerebral blood flow and metabolism were measured for 120 min in six dogs. Neurologic recovery was evaluated 48 h post-ischemia in five dogs. The results were compared to previously determined controls. Nimodipine nearly doubled cerebral blood flow in the delayed post-ischemic hypoperfusion period, compared to untreated dogs (approximately 45% versus 25% of pre-ischemic control values), but had no significant effect on metabolism. Nimodipine also improved neurologic recovery. Four of five treated dogs were normal and one was moderately damaged, whereas six of seven controls were either severely damaged or dead. This suggests that the delayed hypoperfusion state occurring after complete cerebral ischemia probably does contribute to the ultimate neurologic damage, and that nimodipine offers a potential protective effect.

Animals↗
PubMed1983

Failure to induce malignant hyperthermia in myotonic goats.

Six goats with myotonia congenita were exposed for 1 h to 1% halothane and a single injection of suxamethonium i.v. in an attempt to induce malignant hyperthermia. No evidence of malignant hyperthermia occurred. Suxamethonium did produce a myotonic response in each goat, lasting 10-20s, which was accompanied by a transient increase in aerobic metabolism as indicated by a decrease in PvO2 from 6.6 to 5.7 kPa, an increase in PaCO2 from 5.1 to 6.1 kPa and an increase in PVCO2 from 5.5 to 6.3 kPa. There was no evidence of any metabolic acidosis since the transient changes in pH and buffer base were consistent with the increase in carbon dioxide tension. It is concluded that in goats myotonia congenita does not predispose to susceptibility to malignant hyperthermia.

Animals↗
PubMed1983

The cerebral metabolic effects of isoflurane at and above concentrations that suppress cortical electrical activity.

The effects of 1.4-6.0% end-expired isoflurane on cerebral metabolism and hemodynamics were examined in dogs. A dose-related decrease in cerebral oxygen consumption (CMRO2) occurred until there was suppression of cortical electrical activity as reflected by the onset of an isoelectric electroencephalogram. This occurred at an end-expired concentration of 3% isoflurane when the mean CMRO2 was 2.02 ml X 100 g-1 X min-1. Thereafter, increasing concentrations of isoflurane to 6% had no further effect on the CMRO2. Brain biopsies taken at the end of the study revealed normal concentrations of ATP and phosphocreatine and a normal energy charge. Despite a normal cerebral energy state, there was a mild, dose-related, cerebral lactic acidosis (up to 2.84 mumol/g) that accompanied a mild systemic acidosis. It is concluded that the cerebral metabolic changes produced by isoflurane are secondary to an effect on cortical electrical activity, that abolition of this activity can be produced in dogs by a clinically relevant concentration of isoflurane (3%) without marked systemic hemodynamic effects, and that concentrations of isoflurane necessary to abolish cortical activity have no direct toxic effect on cerebral metabolic pathways.

Animals↗
PubMed1983

Cerebral protection by isoflurane during hypoxemia or ischemia.

The cerebral metabolic effects of isoflurane suggest that it may provide a degree of cerebral protection similar to that demonstrated for barbiturates. Accordingly, the possible cerebral protection afforded by isoflurane against hypoxemia and ischemia was studied in mice and dogs, respectively. In mice breathing 5% oxygen survival time was increased significantly over control in groups exposed to 1.0% and 1.4% isoflurane. At higher concentrations (2.0% and 3.0%) it is presumed that cardiorespiratory depression contributed to shorter survival times. In six dogs the effects of 3% isoflurane on the rates of cerebral ATP and phosphocreatine depletion and lactate accumulation during incomplete global ischemia were compared with six control dogs exposed to N2O. Incomplete global ischemia was produced by acute hemorrhagic hypotension to 30 mmHg for 9 minutes, a situation that does not abolish cortical electrical activity (active EEG). In the dogs exposed to isoflurane, the cerebral energy stores of ATP and PCr and the cerebral energy charge were sustained at significantly higher levels than in dogs exposed to N2O, and the cerebral lactate accumulation was significantly less in the initial 7 minutes of hypotension. It is concluded that in the circumstances of oxygen deprivation insufficient to abolish cortical electrical activity, isoflurane, like the barbiturates, can provide some cerebral protection presumably by depressing cortical electrical activity and cerebral metabolism.

Animals↗
PubMed1975

Nitrogen and bolus closing volumes: differences after histamine-induced bronchoconstriction.

Studies in normal subjects have shown that there is little difference in the size of the closing volume when measured by either the nitrogen methods or a bolus method. In this study we have examined the changes in closing volume following histamine-induced bronchoconstriction. In five normal subjects histamine resulted in a reduction in the vital capacity, an increase in the residual volume, and an increase in the airway resistance. The size of the closing volume measured by a bolus method increased after induced bronchoconstriction (0.52 +/- 0.15 1 to 0.74 +/- 0.17 1). With the nitrogen method the closing volume became smaller (0.51 +/- 0.19 1 to 0.17 +/- 0.17 1). Similar differences between the two methods are demonstrated in patients with asthma. The suggested explanation for these differences lies in the different methods used to establish a concentration gradient of gas in the lung. If there is "air trapping" the nitrogen method may fail to establish a concentration gradient.

Adult↗