In vivo gas trapping induced by nitrous oxide

Repeated vital capacity (VC) breaths in 17 anesthetized and curarized dogs induced a small but significant increase in residual volume (RV). This trapping was greatly enhanced when a mixture of 80% N2O and 20% O2 (N2O-O2) was used instead of air. VC breaths with N2O-O2 also increased closing volume, closing capacity and closing pressure determined with 133Xe. Successive quasi-static pressure volume (PV) curves of the lung showed a shift to the right at high lung volume and to the left at low lung volume. Again these changes were more impressive with N2O-O2). The PV curve of the chest wall was unchanged. Insufflations from RV were necessary to produce the gas trapping. Increase in RV was positively related to the size of the inspired volume, to N2O concentration, and inversely related to the inspiratory flow rate. Vagotomy, intravenous isoproterenol, and intravenous propanolol did not alter the phenomena. We propose that these observations can be explained by the presence of foam in the airways and that N2O leads to an increase of foam by osmotic liquid shift into the bronchioli, and/or to an increase in bubble's size by gas diffusion.     

Variability of performance in a vigilance task.

An experiment was conducted to determine the effect of signal pattern and frequency on the variability of S's performance in a vigilance task. Ss were 12 male college students who watched 3 dials during 3 consecutive 27-min. periods. Real signals occurred alone in 1 period while 2 different patterns of dummy signals were added in the other 2 periods. It was found that dummy signals which occurred at semiregular intervals were more effective in reducing S's variability than those which occurred at nonregular intervals. It was also found that variability increased with time. It is concluded that use of a semiregular pattern of dummy signals would be one way of improving performance on a vigilance task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Redistribution of spatial representation in the hippocampus of aged rats performing a spatial memory task.

Young and old rats performed on a maze according to a forced-choice and then a spatial memory procedure either in the same or a different environment. Aged rats were slower to learn the spatial memory task when tested in the same, but not in a different, room. One interpretation of this pattern of results is that although old rats learn new rules as quickly as young rats, they show less flexibility with old rules and familiar spatial information. Impaired choice accuracy during asymptote performance suggests poor processing of trial-unique information by old rats. Spatial correlates of hippocampal CA1 and hilar cells varied with task demand: CA1 cells of aged rats showed more spatially selective place fields, whereas hilar cells showed more diffuse location coding during spatial memory, and not forced-choice, tests. Such representational reorganization may reflect a compensatory response to age-related neurobiological changes in the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex cues in estimating and performing a simple motor task

The present study examined direct behavioral effects of sex cues in a modified level of aspiration experiment for 60 male and 60 female undergraduates. Each S was provided a constant referent score (25), identified as the average score, average score for men, or average score for women. E's sex was controlled and its effects examined. Male Ss estimated and performed significantly higher than female Ss. All Ss provided the average score for the men estimated and performed lower than Ss provided the average score for women. Effect of E's sex was nonsignificant. Results were discussed in terms of behavioral effects of sex-role stereotypes and the implications of such effects for future research.     

The role of error density and set in a vigilance task.

To study ability to detect certain signals while persistently looking for them, 216 students were involved in proofreading tasks. Results were sought pertaining to error detection as a function of error density, false detections at various error levels, influence of previous density on present detection, and false detections after shifts in error density. All vigilance tasks may be subject to decreasing efficiency at extremely high error levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feedback and response mode in performing a Bayesian decision task.

In a complex decision-making situation 64 male undergraduates received data generated by 1 of 3 hypotheses according to specified conditional probabilities. Ss inferred which hypothesis had generated the data or estimated the probability of each hypothesis given the data. Feedback was given after each trial either as the hypothesis which generated the data or the probability that each hypothesis generated the data calculated by Bayes' theorem. The percentage of trials when Ss chose the most probable hypothesis was significantly higher for the groups responding with a single hypothesis than for the probability response groups, and higher for the Bayesian probability feedback groups than for the groups receiving no feedback. The Bayesian probability feedback group also gave probability responses which were much closer to the optimal probabilities than did the no-feedback group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prefrontal neuronal activity in rhesus monkeys performing a delayed anti-saccade task

Patients with damage to the dorsolateral prefrontal cortex are impaired on cognitive tasks such as the Wisconsin Card Sort Test, the Stroop Test and an anti-saccade paradigm, in which sensory-guided habitual responses must be suppressed in favour of conceptually or memory-guided responses. We report here recordings from prefrontal neurons in rhesus monkeys trained to perform a delayed anti-saccade task based on tests that have been used with humans. Activity in the same prefrontal neurons was recorded across conditions when saccades were made toward a remembered target, and also when this prepotent response was suppressed and a saccade in the opposite direction required. Our findings show that most prefrontal neurons code the location of the visual stimulus in working memory, and that this memory can be engaged to suppress as well as prescribe a response. These results establish, in a subset of prefrontal neurons, the iconic nature of the memory code, and suggest a role for visual memory in response suppression.     

Maintainance of vigilance in an auditory monitoring task.

4 levels of critical signal frequency and 3 levels of task complexity were compared for their effect on vigilance in an auditory monitoring task. Proportionate omission errors increased as the frequency of signals decreased, as expected. However, complexity (defined as the number of categories of critical signals) had an unexpected effect in that relatively poor performance occurred with increased complexity. The results were interpreted as suggesting caution in the use of artificial signals as a means to overcome loss of vigilance in monitoring tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potential of succinylcholine-induced neuromuscular blockade by nitrous oxide

To evaluate the potentiating effect of nitrous oxide on the succinylcholine (SCh)-induced neuromuscular blockade, 0.16, 0.20, 0.25 or 0.31 mg.kg-1 of Sch was given during thiamylal-fentanyl anesthesia with or without nitrous oxide, and the evoked electromyograph of hypothenar muscles was measured. ED50 and ED95 in the group receiving nitrous oxide were 0.187 and 0.301 mg.kg-1, and 0.218 and 0.389 mg.kg-1 in the group not receiving nitrous oxide respectively. In the presence of nitrous oxide, the dose-response curve (DRC) was shifted to the left significantly (P < 0.01). By the multiple regression analysis, the degree of the neuromuscular blockade was shown to be affected by dose and nitrous oxide. It was demonstrated that nitrous oxide decreased electromyographically measured SCh requirements by 16.1%. In addition, the dose-effect relationship for SCh-induced neuromuscular blockade varied widely, and gender did not affect the degree of block.     

Maximum acceptable frequencies for females performing a drilling task in different wrist postures

This paper presents a study on the effect of wrist posture; flexion, extension, ulnar deviation, and radial deviation on maximum acceptable frequencies (MAF) for a drilling task using a psychophysical approach. Twelve females were selected from a college population to serve as subjects and an adjustable workstation was used to simulate a drilling task. The results revealed that flexion, extension, and radial deviation all had a significant effect on MAF but, ulnar deviation did not. The postures have been ranked in order of possible risk of contributing to CTD injury, with neutral having the lowest rank (lowest risk) and flexion having the highest rank (greatest risk).     

Doubling the rate of signal presentation in a vigilance task during sleep deprivation.

An experiment was conducted to test the effect of doubling the amount of work required of Ss after loss of sleep. Ss were required to detect defined sequences of 3 digits ("signals") within an apparently random series. Digits were presented continuously for 30 min. either at 1 per sec. (slow) or 2 per sec. (fast). The slow condition contained 20 signals; the fast condition 40. Slow and fast groups were tested on 3 successive days of a 60-hr. vigil and 2 similar groups under control conditions. The results showed that loss of sleep affects performance under fast less than under slow. These and other results suggested that stimulation reduces the effect of sleepiness on performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of nitric oxide synthesis in hepatic perturbations induced in rats by a necrogenic dose of thioacetamide

1. The biological actions of nitric oxide (NO), a highly diffusible and short-lived radical, range from signal transduction to cytotoxicity. The present study investigated whether NO is released in the course of liver necrosis and regeneration induced by a single necrogenic dose of thioacetamide (6.6 mmol kg-1 body wt) to rats. Samples of liver were obtained at 0, 3, 12, 24, 48, 72 and 96 h after thioacetamide administration. 2. Inducible nitric oxide synthase (iNOS) activity was determined in purified liver homogenates and a sharp 6 fold increase (P < 0.001) in iNOS activity was recorded at 48 h of intoxication, followed by a slight but progressive increase at 72 and 96 h. Changes in the expression of iNOS, as detected by its mRNA levels, were parallel to the NOS enzyme activity. Hepatocyte NO synthesis showed a progressive increase at 24, 48 and 72 h, to 8 (P < 0.001), 13 (P < 0.001) and 13 (P < 0.001) times the initial values, respectively. 3. In isolated Kupffer cells, where initial NO release was ten fold higher than in hepatocytes, a progressive increase was detected from 48 h which reached two fold of initial at 72 h of intoxication (192%; P < 0.001). Hepatic cyclic GMP concentration did not change significantly. However, mitochondrial aconitase activity decreased markedly at 12 and 24 h of intoxication showing a sharp increase towards normal values at 48 h which was maintained at 72 and 96 h. 4. As protein kinase C (PKC) is one of the likely candidates to mediate iNOS expression, translocation (activation) of PKC was assayed in hepatocytes, and a significant two fold increase (P < 0.001) between 48 and 96 h after thioacetamide intoxication was observed. When peritoneal macrophages from control rats were incubated with serum from thioacetamide-treated rats, a sharp increase in NO release was detected with serum obtained at 48 h, reaching at 96 h a value four fold (P < 0.001) that of the control. 5. These results suggest that iNOS activity and NO release play a role in the pathophysiological mechanisms that trigger post-necrotic hepatocellular regeneration following thioacetamide administration.     

Cold water immersion modulates the reinforcing effects of nitrous oxide in healthy volunteers.

The purpose of this study was to determine if a contextual variable manipulation, water temperature of a bath in which a forearm was immersed, would modulate the reinforcing effects of nitrous oxide (N?O) in healthy volunteers (N?=?12). Each of 2 separate choice experiments consisted of a lukewarm water session and a cold water session. Each session consisted of 3 trials: The 1st 2 were sampling trials in which participants inhaled either 100% oxygen or 40% N?0 for 25 min, and the last trial was a 25-min choice trial, in which participants chose between the 2 agents. In each of the 3 trials, participants immersed their forearm in either ice-cold or lukewarm water for 3 min. A variant of the McNemar test revealed that participants were more likely to choose N?O on cold water sessions than on warm water sessions. The authors conclude that N?O was more reinforcing when participants forearms were immersed in ice-cold water than when immersed in lukewarm water. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aerobic fitness and response variability in preadolescent children performing a cognitive control task.

Objective: To investigate the relationship between aerobic fitness and cognitive variability in preadolescent children. Method: Forty-eight preadolescent children (25 males, 23 females, mean age = 10.1 years) were grouped into higher- and lower-fit groups according to their performance on a test of aerobic capacity (VO2max). Cognitive function was measured via behavioral responses to a modified flanker task. The distribution in reaction time was calculated within each participant to assess intraindividual variability of performance. Specifically, the standard deviation and coefficient variation of reaction time were used to represent cognitive variability. Results: Preadolescent children, regardless of fitness, exhibited longer reaction time, increased response variability, and decreased response accuracy to incongruent compared to congruent trials. Further, higher-fit children were less variable in their response time and more accurate in their responses across conditions of the flanker task, while no group differences were observed for response speed. Conclusion: These findings suggest that fitness is associated with better cognitive performance during a task that varies cognitive control demands, and extends this area of research to suggest that intraindividual variability may be a useful measure to examine the relationship between fitness and cognition during preadolescence. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The reduction of nitrous oxide to dinitrogen by Escherichia coli

Escherichia coli K12 reduces nitrous oxide stoichiometrically to molecular nitrogen with rates of 1.9 mumol/h x mg protein. The activity is induced by anaerobiosis and nitrate. N2-formation from N2O is inhibited by C2H2 (Ki approximately 0.03 mM in the medium) and nitrite (Ki = 0.3 mM) but not by azide. A mutant defective in FNR synthesis is unable to reduce N2O to N2. The reaction in the wild type could routinely be followed by gas chromatography and alternatively by mass spectrometry measuring the formation of 15N2 from 15N2O. The enzyme catalyzing N2O-reduction in E. coli could not be identified; it is probably neither nitrate reductase nor nitrogenase. E. coli does not grow with N2O as sole respiratory electron acceptor. N2O-reduction might not have a physiological role in E. coli, and the enzyme involved might catalyze something else in nature, as it has a low affinity for the substrate N2O (apparent Km approximately 3.0 mM). The capability for N2O-reduction to N2 is not restricted to E. coli but is also demonstrable in Yersinia kristensenii and Buttiauxella agrestis of the Enterobacteriaceae. E. coli is able to produce NO and N2O from nitrite by nitrate reductase, depending on the assay conditions. In such experiments NO2- is not reduced to N2 because of the high demand for N2O of N2O-reduction and the inhibitory effect of NO2- on this reaction.     

Correction for cardiac output calculations by the nitrous oxide technique

Calculations of cardiac output using the N2O technique as described by Becklake et. al. (J. Appl. Physiol. 17: 579, 1962) result in spurious values when barometric pressure or body temperature deviates from 760 Torr or 37.0 degrees C, respectively. Nitrous oxide (N2O) uptake (VN2O) must be corrected to standard pressure, dry at 37.0 degrees C.     

Effects of anticipatory alerting signals and a compatible secondary task on vigilance performance.

This visual vigilance study simulated an industrial inspection task in which Ss were alerted to possible targets by a semiautomatic detection device. 1 experimental group was forewarned of possible targets by a buzzer with 1-sec foreperiod and rested between alerting signals. A 2nd experimental group worked on a problem-solving secondary task instead of resting between buzzes. A control group observed the display continuously. Other variables of interest were sex of O, target type, and size of display window. It was found that: (1) performance by alerted groups was far superior to that of controls and continued to improve throughout the task, (2) a vigilance decrement was not in evidence in any condition, (3) the problem-solving task did not interfere with detection performance, (4) male and female Ss performed equally well, and (5) Ss engaged in the problem-solving task greatly underestimated the duration of the detection task and reported it "interesting" while the other groups estimated duration accurately and indicated boredom. (16 ref.) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The haemodynamic effects of adrenergic receptor blockade or stimulation druing nitrous oxide anaesthesia in dogs

The effects of ventilation with nitrous oxide in oxygen on myocardial blood flow any oxygen metabolism were investigated in 31 mongrel dogs. The results of this study showed that, compared with controls, hyperoxic nitrous oxide mixtures did not cause any great changes in myocardial haemodynamics, despite a decrease in cardiac output and an increase in systemic vascular resistance. Normoxic nitrous oxide mixtures produced an increase of the coronary blood flow due to decreased coronary vascular resistance. To what extent this coronary vasodilatation resulted from a increased myocardial metabolism or from a direct effect of nitrous oxide on the coronary vascular bed cannot be quantified from the present results.     

Conditioned responses of monkey locus coeruleus neurons anticipate acquisition of discriminative behavior in a vigilance task

Impulse activity was recorded extracellularly from noradrenergic neurons in the nucleus locus coeruleus of three cynomolgus monkeys performing a visual discrimination (vigilance) task. For juice reward, the subjects were required to release a lever rapidly in response to an improbable target stimulus (20% of trials) that was randomly intermixed with non-target stimuli presented on a video display. All locus coeruleus neurons examined were phasically and selectively activated by target stimuli in this task. Other task events elicited no consistent response from these neurons (juice reward, lever release, fix spot stimuli, non-target stimuli). With reversal of the task contingency, locus coeruleus neurons ceased responding to the former target stimuli, and began responding instead to the new target (old non-target) stimuli. In addition, the latency of locus coeruleus response to target stimuli increased after reversal (by about 140 ms) in parallel with a similar increase in the latency of the behavioral response. These results indicate that the conditioned locus coeruleus responses reflect stimulus meaning and cognitive processing, and are not driven by physical sensors attributes. Notably, the reversal in locus coeruleus response to stimuli after task reversal occurred rapidly, hundreds of trials before reversal was expressed in behavioral responses. These findings indicate that conditioned responses of locus coeruleus neurons are plastic and easily altered by changes in stimulus meaning, and that the locus coeruleus may play an active role in learning the significance of behaviorally important stimuli.