bluuebunny/crossref_metadata_2025 huggingface dataset:
Causal Democracy and Causal Contributions in Developmental Systems Theory
Authors: Oyama Susan
Published: February 2004

In reworking a variety of biological concepts, Developmental Systems Theory (DST) has made frequent use of parity of reasoning. We have done this to show, for instance, that factors that have similar sorts of impact on a developing organism tend nevertheless to be invested with quite different causal importance. We have made similar arguments about evolutionary processes. Together, these analyses have allowed DST not only to cut through some age-old muddles about the nature of development, but also to effect a long-delayed reintegration of development into evolutionary theory.

Our penchant for causal symmetry, however (or ‘causal democracy’, as it has recently been termed), has sometimes been misunderstood. This paper shows that causal symmetry is neither a platitude about multiple influences nor a denial of useful distinctions, but a powerful way of exposing hidden assumptions and opening up traditional formulations to fruitful change.
Neuroethology and the Philosophy of Cognitive Science
Authors: Keeley Brian L.
Published: February 2004

Neuroethology is a branch of biology that studies the neural basis of naturally occurring animal behavior. This science, particularly a recent program calledcomputational neuroethology, has a similar structure to the interdisciplinary endeavor of cognitive science. I argue that it would be fruitful to conceive of cognitive science as the computational neuroethology of humans. However, there are important differences between the two sciences, including the fact that neuroethology is much more comparative in its perspective. Neuroethology is a biological science and as such, evolution is a central notion. Its target organisms are studied in the context of their evolutionary history. The central goal of this paper is to argue that cognitive science can and ought to be more comparative in its approach to cognitive phenomena in humans. I show how the domain of cognitive phenomena can be divided up into four different classes, individuated by the relative phylogenetic uniqueness of the behavior. I then describe how comparative evidence can enrich our understanding in each of these different arenas.
Self-Deception and Confabulation
Authors: Hirstein William
Published: February 2004

Cases in which people are self-deceived seem to require that the person hold two contradictory beliefs, something which appears to be impossible or implausible. A phenomenon seen in some brain-damaged patients known as confabulation (roughly, an ongoing tendency to make false utterances without intent to deceive) can shed light on the problem of self-deception. The conflict is not actually between two beliefs, but between two representations, a ‘conceptual’ one and an ‘analog’ one. In addition, confabulation yields valuable clues about the structure of normal human knowledge-gathering processes.
Bohmian Insights into Quantum Chaos
Authors: Cushing James T.
Published: February 2004

The ubiquity of chaos in classical mechanics (CM), as opposed to the situation in standard quantum mechanics (QM), might be taken as speaking against QM being the fundamental theory of physical phenomena. Bohmian mechanics (BM), as a formulation of quantum theory, may clarify both the existence of chaos in the quantum domain and the nature of the classical limit. Two interesting possibilities are (i) that CM and classical chaos are included in and underwritten by quantum mechanics (BM) or (ii) that BM and CM simply possess a common region of (noninclusive) overlap. In the latter case, neither CM nor QM alone would be sufficient, even in principle, to account for all of the physical phenomena we encounter. In this talk I shall summarize and discuss the implications of some recent work on chaos and on the classical limit within the framework of BM.
There's No Time Like the Present (in Minkowski Spacetime)
Authors: Savitt Steven F.
Published: February 2004

Mark Hinchliff concludes a recent paper, “The Puzzle of Change,” with a section entitled “Is the Presentist Refuted by the Special Theory of Relativity?” His answer is “no.”

I respond by arguing that presentists face great difficulties in merely stating their position in Minkowski spacetime. I round up some likely candidates for the job and exhibit their deficiencies.
Inductive Risk and Values in Science
Authors: Douglas Heather
Published: February 2004

Although epistemic values have become widely accepted as part of scientific reasoning, non-epistemic values have been largely relegated to the “external” parts of science (the selection of hypotheses, restrictions on methodologies, and the use of scientific technologies). I argue that because of inductive risk, or the risk of error, non-epistemic values are required in science wherever non-epistemic consequences of error should be considered. I use examples from dioxin studies to illustrate how non-epistemic consequences of error can and should be considered in the internal stages of science: choice of methodology, characterization of data, and interpretation of results.
Chance and Macroevolution
Authors: Millstein Roberta L.
Published: February 2004

When philosophers of physics explore the nature of chance, they usually look to quantum mechanics. When philosophers of biology explore the nature of chance, they usually look to microevolutionary phenomena such as mutation or random drift. What has been largely overlooked is the role of chance in macroevolution. The stochastic models of paleobiology employ conceptions of chance that are similar to those at the microevolutionary level, yet different from the conceptions of chance often associated with quantum mechanics and Laplacean determinism.
Some Problems for “Alternative Individualism”
Authors: Wilson R. A.
Published: February 2004

This paper points to some problems for the position that D.M. Walsh calls “alternative individualism,” and argues that in defending this view Walsh has omitted an important part of what separates individualists and externalists in psychology. Walsh's example of Hox gene complexes is discussed in detail to show why some sort of externalism about scientific taxonomy more generally is a more plausible view than any extant version of individualism.
The Persistence of Memory: Surreal Trajectories in Bohm's Theory
Authors: Barrett Jeffrey A.
Published: February 2004

In this paper I describe the history of the surreal trajectories problem and argue that in fact it is not a problem for Bohm's theory. More specifically, I argue that one can take the particle trajectories predicted by Bohm's theory to be the actual trajectories that particles follow and that there is no reason to suppose that good particle detectors are somehow fooled in the context of the surreal trajectories experiments. Rather than showing that Bohm's theory predicts the wrong particle trajectories or that it somehow prevents one from making reliable measurements, such experiments ultimately reveal the special role played by position and the fundamental incompatibility between Bohm's theory and relativity. They also provide a striking example of the theory-ladenness of observation.
Law and Explanation in Biology: Invariance is the Kind of Stability That Matters
Authors: Woodward Jim
Published: February 2004

This paper develops an account of explanation in biology which does not involve appeal to laws of nature, at least as traditionally conceived. Explanatory generalizations in biology must satisfy a requirement that I callinvariance, but need not satisfy most of the other standard criteria for lawfulness. Once this point is recognized, there is little motivation for regarding such generalizations as laws of nature. Some of the differences between invariance and the related notions of stability and resiliency, due respectively to Sandra Mitchell and Brian Skyrms, are explored.
Bayesian Confirmation of Theories That Incorporate Idealizations
Authors: Shaffer Michael J.
Published: February 2004

Following Nancy Cartwright and others, I suggest that most (if not all) theories incorporate, or depend on, one or more idealizing assumptions. I then argue that such theories ought to be regimented as counterfactuals, the antecedents of which are simplifying assumptions. If this account of the logical form of theories is granted, then a serious problem arises for Bayesians concerning the prior probabilities of theories that have counterfactual form. If no such probabilities can be assigned, then posterior probabilities will be undefined, as the latter are defined in terms of the former. I argue here that the most plausible attempts to address the problem of probabilities of conditionals fail to help Bayesians, and, hence, that Bayesians are faced with a new problem. In so far as these proposed solutions fail, I argue that Bayesians must give up Bayesianism or accept the counterintuitive view that no theories that incorporate any idealizations have ever really been confirmed to any extent whatsoever. Moreover, as it appears that the latter horn of this dilemma is highly implausible, we are left with the conclusion that Bayesianism should be rejected, at least as it stands.
Reductionism in a Historical Science
Authors: Rosenberg Alex
Published: February 2004

Reductionism is a metaphysical thesis, a claim about explanations, and a research program. The metaphysical thesis reductionists advance (and antireductionists accept) is that all facts, including all biological facts, are fixed by the physical and chemical facts; there are no non-physical events, states, or processes, and so biological events, states and processes are “nothing but” physical ones. The research program can be framed as a methodological prescription which follows from the claim about explanations. Antireductionism does not dispute reductionism's metaphysical claim, but rejects the explanatory claim and so the methodological moral. To a first approximation what reductionists and anti-reductionists disagree about is whether explanations in functional biology can be or need to be explained or completed or perhaps replaced by explanations in terms of molecular biology. And this disagreement over the adequacy of explanations in functional biology drives a significant methodological disagreement with consequence for the research program of biology.
Cognitive Scientific Realism
Authors: Rohrlich Fritz
Published: February 2004

Our cognitive capabilities force us into a description of the world by levels. But theories on different levels result in descriptions that differ qualitatively. Therefore, the resulting incommensurability requires ontological bridges between such theories. These are obtained uniquely when the equations of the reduced theory are compared with a suitable limit of the equations of the reducing theory. Four case studies from theoretical physics and astronomy support this claim, two for theories of composites and two for non-composites (field theories). There results a coherent view of a single real world despite its ontological pluralism. The cumulativity of scientific knowledge is thus ensured and realism is supported.
The Thesis of Theory-Laden Observation in the Light of Cognitive Psychology
Authors: Estany Anna
Published: February 2004

The aim of this paper is to analyze a philosophical question (neutrality vs. theoryladenness of observation) taking into consideration the empirical results of Cognitive Psychology (theories of perception). This is an important debate because the objectivity of science is at stake. In the Philosophy of Science there are two main positions with regard to observation, those of C. Hempel and N. R. Hanson. In the Philosophy of Mind there are also two important contrasting positions, those of J. Fodor and Paul M. Churchland. I will analyze the consequences of recent theories of perception and vision developed within Cognitive Science for classical epistemological theses about observation.
The Impact of Newton'sPrincipiaon the Philosophy of Science
Authors: McMullin Ernan
Published: February 2004

As the seventeenth century progressed, there was a growing realization among those who reflected on the kind of knowledge the new sciences could afford (among them Kepler, Bacon, Descartes, Boyle, Huygens) that hypothesis would have to be conceded a much more significant place in natural philosophy than the earlier ideal of demonstration allowed. Then came the mechanics of Newton'sPrincipia, which seemed to manage quite well without appealing to hypothesis (though much would depend on how exactly terms like “force” and “attraction” were construed). If the science of motion could dispense with causal hypothesis and the attendant uncertainty, why should this not serve as the goal of natural philosophy generally? The apparent absence of causal hypothesis from the highly successful new science of motion went far towards shaping, in different ways, the account of scientific knowledge given by many of the philosophers of the century following, notable among them Berkeley, Hume, Reid, and Kant. This “Newtonian” interlude in the history of the philosophy of science would today be accounted on the whole a byway. ThePrincipia, despite its enormous achievement in shaping subsequent work in mechanics, was from the beginning too idiosyncratic from an epistemic standpoint to serve as model for the natural sciences generally.
Predictive Similarity and the Success of Science: A Reply to Stanford
Authors: Psillos Stathis
Published: February 2004

P. Kyle Stanford (2000) attempts to offer a truth-linked explanation of the success of science which, he thinks, can be welcome to antirealists. He proposes an explanation of the success of a theory T1 in terms of its predictive similarity to the true theory T of the relevant domain. After raising some qualms about the supposed antirealist credentials of Stanford's account, I examine his explanatory story in some detail and show that it fails to offer a satisfactory explanation of the success of science.
The Recently Claimed Observation of Atomic Orbitals and Some Related Philosophical Issues
Authors: Scerri Eric R.
Published: February 2004

The main thrust of the paper involves a theoretical and philosophical analysis of the claim made in September 1999 that atomic orbitals have been directly imaged for the first time. After a brief account of the recent claims the paper reviews the development of the orbit and later orbital concepts and analyzes the theoretical status of atomic orbitals. The conclusion is that contrary to these claims, atomic orbitals have not in fact been observed. The non-referring nature of modern atomic orbitals is discussed in the context of Laudan's writings on realism, the success of theories, and whether or not scientific terms refer. I conclude that the failure to observe orbitals is a good prima facie case for divorcing the success of theories from the question of whether their central terms refer. The added relevance of this case is that it concerns a current and highly successful theory. Finally, the relevance of this ‘floating model’ to contemporary discussions on scientific models is briefly considered.
Causal Loops and the Independence of Causal Facts
Authors: Dowe Phil
Published: February 2004

According to Hugh Mellor in Real Time II (1998, Ch. 12), assuming the logical independence of causal facts and the ‘law of large numbers’, causal loops are impossible because if they were possible they would produce inconsistent sets of frequencies. I clarify the argument, and argue that it would be preferable to abandon the relevant independence assumption in the case of causal loops.
The Theory-Ladenness of Observation and the Theory-Ladenness of the Rest of the Scientific Process
Authors: Brewer William F. , Lambert Bruce L.
Published: February 2004

We use evidence from cognitive psychology and the history of science to examine the issue of the theory-ladenness of perceptual observation. This evidence shows that perception is theory-laden, but that it is only strongly theory-laden when the perceptual evidence is ambiguous or degraded, or when it requires a difficult perceptual judgment. We argue that debates about the theory-ladenness issue have focused too narrowly on the issue of perceptual experience, and that a full account of the scientific process requires an examination of theory-ladenness in attention, perception, data interpretation, data production, memory, and scientific communication. We conclude that the evidence for theory-ladenness does not lead to a relativist account of scientific knowledge.
Perceptual Symbols and Taxonomy Comparison
Authors: Chen Xiang
Published: February 2004

Many recent cognitive studies reveal that human cognition is inherently perceptual, sharing systems with perception at both the conceptual and the neural levels. This paper introduces Barsalou's theory of perceptual symbols and explores its implications for philosophy of science. If perceptual symbols lie in the heart of conceptual processing, the process of attribute selection during concept representation, which is critical for defining similarity and thus for comparing taxonomies, can no longer be determined solely by background beliefs. The analogous nature of perceptual symbols and the spatial nature of intraconceptual relations impose new constraints on attribute selection. These constraints help people with different background beliefs select compatible attributes, which constitute a common “platform” for taxonomy comparison.
Determinism, Realism, and Probability in Evolutionary Theory
Authors: Weber Marcel
Published: February 2004

Recent discussion of the statistical character of evolutionary theory has centered around two positions: (1) Determinism combined with the claim that the statistical character is eliminable, a subjective interpretation of probability, and instrumentalism; (2) Indeterminism combined with the claim that the statistical character is ineliminable, a propensity interpretation of probability, and realism. I point out some internal problems in these positions and show that the relationship between determinism, eliminability, realism, and the interpretation of probability is more complex than previously assumed in this debate. Furthermore, I take some initial steps towards a more adequate account of the statistical character of evolutionary theory.
Modeling Evolution in Theory and Practice
Authors: Plutynski Anya
Published: February 2004

This paper uses a number of examples of diverse types and functions of models in evolutionary biology to argue that the demarcation between theory and practice, or “theory model” and “data model,” is often difficult to make. It is shown how both mathematical and laboratory models function as plausibility arguments, existence proofs, and refutations in the investigation of questions about the pattern and process of evolutionary history. I consider the consequences of this for the semantic approach to theories and theory confirmation. The paper attempts to reconcile the insights of both critics and advocates of the semantic approach to theories.
Pluralism and Sex: More Than a Pragmatic Issue
Authors: Fehr Carla
Published: February 2004

The evolution of sexual reproduction is a case of explanatory pluralism, meaning that there is more than one explanation for this phenomenon. I use the concept of a domain to more clearly explicate the various explananda that can be found in this case. I argue that although pluralism with respect to some types of domains can be decreased using van Fraassen's pragmatics of explanation, there remains an important class of domain, an orthogonal domain, for which this is not the case.
Explaining Information Transfer in Quantum Teleportation
Authors: Duwell Armond
Published: February 2004

In this paper I introduce a new species of teleportation which I use to evaluate three explanations of information transfer in quantum teleportation. I will argue that two explanations fail to explain the “physical effect” of teleportation. I will also argue that that information transfer, understood as something more than simple qubit transfer, is not necessary for teleportation to occur.
Can the Bundle Theory Save Substantivalism from the Hole Argument?
Authors: Parsons Glenn , McGivern Patrick
Published: February 2004

One of the most serious theoretical obstacles to contemporary spacetime substantivalism is Earman and Norton's hole argument. We argue that applying the bundle theory of substance to spacetime points allows spacetime substantivalists to escape the conclusion of this argument. Some philosophers have claimed that the bundle theory cannot be applied to substantival spacetime in this way due to problems in individuating spacetime points in symmetrical spacetimes. We demonstrate that it is possible to overcome these difficulties if spatiotemporal properties are viewed as tropes rather than universals.
Black Hole Remnants and Classical vs. Quantum Gravity
Authors: Bokulich Peter
Published: February 2004

Belot, Earman, and Ruetsche (1999) dismiss the black hole remnant proposal as an inadequate response to the Hawking information loss paradox. I argue that their criticisms are misplaced and that, properly understood, remnants do offer a substantial reply to the argument against the possibility of unitary evolution in spacetimes that contain evaporating black holes. The key to understanding these proposals lies in recognizing that the question of where and how our current theories break down is at the heart of these debates in quantum gravity. I also argue that the controversial nature of assessing the limits of general relativity and quantum field theory illustrates the significance of attempts to establish the proper borders of our effective theories.
Simulations, Models, and Theories: Complex Physical Systems and Their Representations
Authors: Winsberg Eric
Published: February 2004

Using an example of a computer simulation of the convective structure of a red giant star, this paper argues that simulation is a rich inferential process, and not simply a “number crunching” technique. The scientific practice of simulation, moreover, poses some interesting and challenging epistemological and methodological issues for the philosophy of science. I will also argue that these challenges would be best addressed by a philosophy of science that places less emphasis on the representational capacity of theories (and ascribes that capacity instead to models) and more emphasis on the role of theory in guiding (rather than determining) the construction of models.
Racism and Human Genome Diversity Research: The Ethical Limits of “Population Thinking”
Authors: Gannett Lisa
Published: February 2004

This paper questions the prevailing historical understanding that scientific racism “retreated” in the 1950s when anthropology adopted the concepts and methods of population genetics and race was recognized to be a social construct and replaced by the concept of population. More accurately, a “populational” concept of race was substituted for a “typological one”—this is demonstrated by looking at the work of Theodosius Dobzhansky circa 1950. The potential for contemporary research in human population genetics to contribute to racism needs to be considered with respect to the ability of the typological-population distinction to arbitrate boundaries between racist society and nonracist, even anti-racist, science. I point out some ethical limits of “population thinking” in doing so.
Science and Values: Are Value Judgments Always Irrelevant to the Justification of Scientific Claims?
Authors: Intemann Kristen
Published: February 2004

Several feminist theorists have claimed that feminist values ought to influence theory choice. Susan Haack has argued that this is implausible because normative claims about what ought to be the case can never provide justification for descriptive claims. I argue against one of the premises of Haack's argument. Furthermore, I attempt to show that the most promising defense of this premise would cast doubt on a second premise of Haack's argument. My aim is to open up the possibility that value judgments can play a legitimate role in theory choice.
Counterfactual Histories: The Beginning of Quantum Physics
Authors: Pessoa Osvaldo
Published: February 2004

This paper presents a method for investigating counterfactual histories of science. A central notion to our theory of science are “advances” (ideas, data, etc.), which are units passed among scientists and which would be conserved in passing from one possible history to another. Advances are connected to each other by nets of causal influence, and we distinguish strong and weak influences. Around sixty types of advances are grouped into ten classes. As our case study, we examine the beginning of the Old Quantum Theory, using a computer to store and process historical information. We describe four plausible possible histories, along with six other implausible ones.
On the Reality of Gauge Potentials
Authors: Healey Richard
Published: February 2004

Classically, a gauge potential was merely a convenient device for generating a corresponding gauge field. Quantum-mechanically, a gauge potential lays claim to independent status as a further feature of the physical situation. But whether this is a local or a global feature is not made any clearer by the variety of mathematical structures used to represent it. I argue that in the theory of electromagnetism (or a non-Abelian generalization) that describes quantum particles subject to a classical interaction, the gauge potential is best understood as a feature of the physical situation whose global character is most naturally represented by the holonomies of closed curves in space-time.
Models and the Unity of Classical Physics: Nancy Cartwright's Dappled World
Authors: Smith Sheldon R.
Published: February 2004

In this paper, I examine the claim that any physical theory will have an extremely limited domain of application because 1) we have to use distinct theories to model different situations in the world and 2) no theory has enough textbook models to handle anything beyond a highly simplified situation. Against the first claim, I show that many examples used to bolster it are actually instances of application of the very same classical theory rather than disjoint theories. Thus, there is a hidden unity to the world of classical physics that is usually overlooked (by, for example, Nancy Cartwright who argues for the claims above). Against the second claim, I show that the practice of classical physics involves an enormous (infinite) number of models the use of which cannot be written off as merely ad hoc. Thus, although classical physics cannot, of course, model every situation in nature, it has a much larger domain than some would have us believe.
What is ‘Normal‘? An Evolution-Theoretic Foundation for Normic Laws and Their Relation to Statistical Normality
Authors: Schurz Gerhard
Published: February 2004

Normic lawshave the form “if A, then normally B.” They are omnipresent in everyday life and non-physical ‘life’ sciences such as biology, psychology, social sciences, and humanities. They differ significantly from ceteris-paribus laws in physics. While several authors have doubted that normic laws are genuine laws at all, others have argued that normic laws express a certain kind of prototypical normality which is independent of statistical majority. This paper presents a foundation for normic laws which is based ongeneralized evolution theoryand explains their omnipresence, lawlikeness, and reliability. It is argued that the fact that normic laws are a product of evolution must establish a systematic connection between prototypical and statistical normality.
Selection, Indeterminism, and Evolutionary Theory
Authors: Glymour Bruce
Published: February 2004

I argue that results from foraging theory give us good reason to think some evolutionary phenomena are indeterministic and hence that evolutionary theory must be probabilistic. Foraging theory implies that random search is sometimes selectively advantageous, and experimental work suggests that it is employed by a variety of organisms. There are reasons to think such search will sometimes be genuinely indeterministic. If it is, then individual reproductive success will also be indeterministic, and so too will frequency change in populations of organisms employing such search.
Laryngoscopic Intubation
Authors: Mulcaster Julian T. , Mills Joanna , Hung Orlando R. , MacQuarrie Kirk , Law J. Adam , Pytka Saul , Imrie David , Field Chris
Published: February 2004

Background

Many healthcare professionals are trained in direct laryngoscopic tracheal intubation (LEI), which is a potentially lifesaving procedure. This study attempts to determine the number of successful LEI exposures required during training to assure competent performance, with special emphasis on defining competence itself.

Methods

Analyses were based on a longitudinal study of novices under training conditions in the operating room. The progress of 438 LEIs performed by the 20 nonanesthesia trainees was monitored by observation and videotape analysis. Eighteen additional LEIs were performed by experienced anesthesiologists to define the standard. A generalized linear, mixed-modelling approach was used to identify key aspects of effective training and performance. The number of tracheal intubations that the trainees were required to perform before acquiring expertise in LEI was estimated.

Results

Subjects performed between 18 and 35 laryngoscopic intubations. However, statistical modeling indicates that a 90% probability of a "good intubation" required 47 attempts. Proper insertion and lifting of the laryngoscope were crucial to "good" or "competent" performance of LEI. Traditional features, such as proper head and neck positions, were found to be less important under the study conditions.

Conclusions

This study determined that traditional LEI teaching for nonanesthesia personnel using manikin alone is inadequate. A reevaluation of current standards in LEI teaching for nonanesthesia is required.
Optimal Oxygen Concentration during Induction of General Anesthesia
Authors: Edmark Lennart , Kostova-Aherdan Kamelia , Enlund Mats , Hedenstierna Göran
Published: February 2004

Background

The use of 100% oxygen during induction of anesthesia may produce atelectasis. The authors investigated how different oxygen concentrations affect the formation of atelectasis and the fall in arterial oxygen saturation during apnea.

Methods

Thirty-six healthy, nonsmoking women were randomized to breathe 100, 80, or 60% oxygen for 5 min during the induction of general anesthesia. Ventilation was then withheld until the oxygen saturation, assessed by pulse oximetry, decreased to 90%. Atelectasis formation was studied with computed tomography.

Results

Atelectasis in a transverse scan near the diaphragm after induction of anesthesia and apnea was 9.8 +/- 5.2 cm2 (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm2 (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm2 (0.2 +/- 0.2%) in the groups breathing 100, 80, and 60% oxygen, respectively (P < 0.01). The corresponding times to reach 90% oxygen saturation were 411 +/- 84, 303 +/- 59, and 213 +/- 69 s, respectively (P < 0.01).

Conclusion

During routine induction of general anesthesia, 80% oxygen for oxygenation caused minimal atelectasis, but the time margin before unacceptable desaturation occurred was significantly shortened compared with 100% oxygen.
Differential Effects of Propofol and Sevoflurane on Heart Rate Variability
Authors: Kanaya Noriaki , Hirata Naoyuki , Kurosawa Saori , Nakayama Masayasu , Namiki Akiyoshi
Published: February 2004

Background

Propofol is reported to reduce both sympathetic and parasympathetic tone; however, it is not clear whether the changes in heart rate variability are associated with depth of anesthesia. The purposes of the present study were (1) to evaluate the changes in heart rate variability at different depths of hypnosis and (2) to compare the effects of propofol on heart rate variability with that of sevoflurane.

Methods

Thirty patients were randomly allocated into the propofol or sevoflurane for induction of anesthesia. The depth of hypnosis was monitored by the Bispectral Index (BIS). Spectral analysis of heart rate variability using a maximum-entropy method resulted in a characteristic power spectrum with two main regions, a high frequency (HF) and a low frequency (LF). Hemodynamics, entropy, LF, HF, and LF/HF were monitored when the patients were awake and after induction of anesthesia.

Results

Both propofol and sevoflurane decreased blood pressure in a BIS-dependent manner, whereas heart rate showed no significant changes during the study period. In the propofol group, entropy and HF decreased with a reduction in the BIS value. Although LF decreased after induction of anesthesia, propofol caused no further decrease in LF in spite of a reduction in the BIS value. In the sevoflurane group, LF decreased with a reduction in the BIS value. Entropy and HF decreased after induction of anesthesia (BIS at 80); however, no further decreases were observed in spite of a reduction in the BIS value.

Conclusions

Induction of anesthesia with propofol decreased blood pressure, entropy, and HF in a BIS-dependent manner, indicating that propofol reduces cardiac parasympathetic tone depending on the depth of hypnosis. Conversely, sevoflurane did not show the BIS-dependent decreases in heart rate, blood pressure, HF, and entropy, indicating that sevoflurane has little or no effect on cardiac parasympathetic tone.
Hypothermia and the Approximate Entropy of the Electroencephalogram
Authors: Levy Warren J. , Pantin Enrique , Mehta Sachin , McGarvey Michael
Published: February 2004

Background

The electroencephalogram is commonly used to monitor the brain during hypothermic cardiopulmonary bypass and circulatory arrest. No quantitative relationship between the electroencephalogram and temperature has been elucidated, even though the qualitative changes are well known. This study was undertaken to define a dose-response relationship for hypothermia and the approximate entropy of the electroencephalogram.

Methods

The electroencephalogram was recorded during cooling and rewarming in 14 patients undergoing hypothermic cardiopulmonary bypass and circulatory arrest. Data were digitized at 128 Hz, and approximate entropy was calculated from 8-s intervals. The dose-response relationship was derived using sigmoidal curve-fitting techniques, and statistical analysis was performed using analysis of variance techniques.

Results

The approximate entropy of the electroencephalogram changed in a sigmoidal fashion during cooling and rewarming. The midpoint of the curve averaged 24.7 degrees C during cooling and 28 degrees C (not significant) during rewarming. The temperature corresponding to 5% entropy (T 0.05 ) was 18.7 degrees C. The temperature corresponding to 95% entropy (T 0.95 ) was 31.3 degrees C during cooling and 38.2 degrees C during rewarming ( P < 0.02).

Conclusions

Approximate entropy is a suitable analysis technique to quantify the electroencephalographic changes that occur with cooling and rewarming. It demonstrates a delay in recovery that is of the same magnitude as that seen with conventional interpretation of the analog electroencephalogram and extends these observations over a greater range of temperatures.
Isoflurane Pretreatment Inhibits Lipopolysaccharide-induced Inflammation in Rats
Authors: Plachinta Roman V. , Hayes John K. , Cerilli Lisa A. , Rich George F.
Published: February 2004

Background

Previous studies have indicated that volatile anesthetic pretreatment protects cells from inflammation; therefore, the authors hypothesized that pretreatment with isoflurane may attenuate the hemodynamic and pathologic changes to the vasculature that are associated with inflammation.

Methods

Rats received intravenous lipopolysaccharide or saline placebo with and without pretreatment with isoflurane (1.4% for 30 min immediately before lipopolysaccharide). Mean arterial pressure (MAP) and response to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) vasodilators were assessed hourly for 6 h. Tumor necrosis factor-alpha concentrations, arterial blood gases, and vascular histology were also determined.

Results

Lipopolysaccharide decreased MAP and vasodilation to acetylcholine and sodium nitroprusside. Lipopolysaccharide also caused acidosis, endothelial swelling, and endothelial detachment from the smooth muscle. Isoflurane pretreatment prevented the decrease in MAP for 5 h and attenuated the decrease at 6 h. Pretreatment increased the vasodilation to acetylcholine in lipopolysaccharide rats to control concentrations but had no effect on sodium nitroprusside. In control rats, isoflurane pretreatment increased the response to acetylcholine and sodium nitroprusside but had no effect on MAP. Isoflurane pretreatment prevented the acidosis and endothelial damage to mesenteric and aortic vessels, and attenuated the increase in tumor necrosis factor-alpha associated with lipopolysaccharide-induced inflammation.

Conclusion

Pretreatment with 30 min of isoflurane attenuated the decrease in MAP and endothelium-dependent vasodilation, the acidosis, the increase in tumor necrosis factor-alpha, and the damage to the vascular endothelium associated with lipopolysaccharide-induced inflammation in rats. This study suggests that isoflurane pretreatment may protect the vasculature during inflammation.
Ketamine Differentially Blocks Sensory Afferent Synaptic Transmission in Medial Nucleus Tractus Solitarius (mNTS)
Authors: Jin Young-Ho , Bailey Timothy W. , Doyle Mark W. , Li Bai-yan , Chang Kyoung S. K. , Schild John H. , Mendelowitz David , Andresen Michael C.
Published: February 2004

Background

Ketamine increases blood pressure and heart rate by unknown mechanisms, but studies suggest that an intact central nervous system and arterial baroreceptors are required. In the brain stem, medial nucleus tractus solitarius receives afferents from nodose neurons that initiate cardiovascular autonomic reflexes. Here, the authors assessed ketamine actions on afferent medial nucleus tractus solitarius synaptic transmission.

Methods

Ketamine was applied to horizontally sliced brain stems. Solitary tract (ST) stimulation evoked excitatory postsynaptic currents (eEPSCs) in medial nucleus tractus solitarius neurons. Capsaicin (200 nm) block of ST eEPSCs sorted neurons into sensitive (n = 19) and resistant (n = 23). In nodose ganglion slices, shocks to the peripheral vagal trunk activated afferent action potentials in sensory neurons classified by conduction velocities and capsaicin.

Results

Ketamine potently (10-100 mciro m) blocked small, ST-evoked -methyl-d-aspartate synaptic currents found only in a subset of capsaicin-resistant neurons (6 of 12). Surprisingly, ketamine reversibly inhibited ST eEPSC amplitudes and induced synaptic failure at lower concentrations in capsaicin-sensitive than in capsaicin-resistant neurons (P < 0.005; n = 11 and 11). Spontaneous EPSCs using non- -methyl-d-aspartate receptors were insensitive even to 1-3 mm ketamine, suggesting that ST responses were blocked presynaptically. Similarly, ketamine blocked C-type action potential conduction at lower concentrations than A-type nodose sensory neurons.

Conclusion

The authors conclude that ketamine inhibits postsynaptic -methyl-d-aspartate receptors and presynaptic afferent processes in medial nucleus tractus solitarius. Unexpectedly, capsaicin-sensitive (C-type), unmyelinated afferents are significantly more susceptible to block than capsaicin-resistant (A-type), myelinated afferents. This differentiation may be related to tetrodotoxin-resistant sodium currents. Since C-type afferents mediate powerful arterial baroreflexes effects, these differential actions may contribute to ketamine-induced cardiovascular dysfunction.
Pharmacokinetic–Pharmacodynamic Modeling of Rocuronium in Case of a Decreased Number of Acetylcholine Receptors
Authors: De Haes Ann , Proost Johannes H. , De Baets Mark H. , Stassen Maurice H. W. , Houwertjes Martin C. , Wierda J. Mark K. H.
Published: February 2004

Background

In myasthenic patients, the sensitivity for nondepolarizing relaxants is increased and the time course of effect is prolonged due to a reduced number of functional acetylcholine receptors at the neuromuscular junction. The authors investigated both the performance of the link model proposed by Sheiner and a pharmacodynamic-pharmacokinetic model taking into account the number of unbound acetylcholine receptors in myasthenic pigs.

Methods

After obtaining the approval of the Animal Experiments Committee of their institution, the authors studied eight myasthenic pigs and eight control pigs. Myasthenia gravis was induced by injecting Torpedo acetylcholine receptors in weeks 1 and 4. On the day of the experiments, the pigs were anesthetized and intubated, and the appropriate muscles and nerves were prepared for the measurements. Rocuronium was administered by infusion to reach 90% twitch height block. Arterial blood was sampled during onset and offset of effect, and the plasma concentration of rocuronium was measured with high-performance liquid chromatography. Plasma concentration-time effect data were analyzed using two different pharmacokinetic-pharmacodynamic models, the link model according to Sheiner and a pharmacokinetic-pharmacodynamic model taking into account the unbound receptor concentration. Muscles were removed after the experiment for laboratory analysis of the acetylcholine receptor concentration.

Results

All eight pigs of the myasthenic group developed clinical signs of myasthenia gravis (muscle weakness) and showed increased sensitivity toward rocuronium. Pharmacokinetic modeling revealed no significant differences between myasthenic and control pigs. In pharmacokinetic-pharmacodynamic analysis, visual inspection as well as the Akaike Information Criterion (3,605 3,769) and the residual SD (3.2 3.6%) revealed a better fit for the unbound receptor model in myasthenic animals compared to the Sheiner model. Pharmacokinetic-pharmacodynamic analysis with the unbound receptor model demonstrated a decreased EC50 of 0.27 micro m (ranging from 0.17 to 0.59 micro m) compared to 2.71 micro m (ranging from 2.42 to 4.43 micro m) in control animals. The results of the Sheiner pharmacokinetic-pharmacodynamic analysis were in the same range. Both the laboratory analysis and pharmacokinetic-pharmacodynamic modeling showed a decrease in receptor concentration of more than 75%.

Conclusion

Both the Sheiner model and the unbound receptor model may be used to fit plasma concentration-effect data of rocuronium in pigs. The unbound receptor concentration model, however, can explain the observed differences in the time course of effect, based on receptor concentration.
Effects of Preemptive Analgesia on Pain and Cytokine Production in the Postoperative Period
Authors: Beilin Benzion , Bessler Hanna , Mayburd Eduard , Smirnov Genady , Dekel Arie , Yardeni Israel , Shavit Yehuda
Published: February 2004

Background

The postoperative period is associated with increased production of proinflammatory cytokines, which are known to augment pain sensitivity, among other effects. In a previous study, the authors found that patients treated with patient-controlled epidural analgesia (PCEA) exhibited attenuated proinflammatory cytokine response in the postoperative period. In the present study, the authors examined whether preemptive analgesia continued with PCEA may further attenuate the proinflammatory cytokine response and reduce pain sensitivity in the postoperative period. They compared cytokine production in two groups of patients, one receiving PCEA, the other receiving preemptive epidural analgesia continued by PCEA.

Methods

Female patients hospitalized for transabdominal hysterectomy were randomly assigned to one of two pain management techniques: PCEA or preemptive epidural analgesia followed by PCEA (PA + PCEA). Postoperative pain was assessed using the visual analog scale. Blood samples were collected before, 24, 48, and 72 h following surgery. Production of the following cytokines was assessed in stimulated peripheral blood mononuclear cells: interleukin (IL)-1beta, tumor necrosis factor alpha, IL-6, IL-1ra, IL-10, and IL-2.

Results

Patients of the PA + PCEA group exhibited lower pain scores throughout the 72 h postoperatively, compared with patients of the PCEA group. In patients of the PA + PCEA group in the postoperative period, production of IL-1beta, IL-6, IL-1ra, and IL-10 was significantly less elevated, while IL-2 production was significantly less suppressed.

Conclusions

Proinflammatory cytokines are key mediators of illness symptoms, including hyperalgesia. The present results suggest that preemptive epidural analgesia is associated with reduced postoperative pain and attenuated production of proinflammatory cytokines.
Preoperative Cardiac Events in Elderly Patients with Hip Fracture Randomized to Epidural or Conventional Analgesia
Authors: Matot Idit , Oppenheim-Eden Arieh , Ratrot Ruand , Baranova Julia , Davidson Elyad , Eylon Sharon , Peyser Amos , Liebergall Meir
Published: February 2004

Background

Perioperative myocardial ischemia occurs in 35% of unselected elderly patients undergoing hip fracture surgery. Perioperative epidural analgesia may reduce the incidence of adverse cardiac events.

Methods

The effect of early administration of epidural analgesia during the stressful period, on cardiac events was evaluated in a prospective randomized study in 68 patients with hip fractures who either had known coronary artery disease or were at high risk for coronary artery disease. On admission to the emergency room, patients were assigned to receive a usual care analgesic regimen (intramuscular meperidine, control group, n = 34) or continuous epidural infusion of local anesthetic and opioid (epidural group, n = 34). Monitoring in the preoperative period included a preoperative history and physical examination, daily assessment of cardiac adverse events, serial electrocardiograms, cardiac enzymes, and pain scores.

Results

Preoperative adverse cardiac events were significantly more prevalent in the control group compared with the epidural group (7 of 34 0 of 34; = 0.01). Adverse cardiac events included fatal myocardial infarction in three, fatal congestive heart failure in one, nonfatal congestive heart failure in one, and new onset atrial fibrillation in two. The incidence of intraoperative and postoperative adverse cardiac events was similar for the two groups. The significant difference between groups in the incidence of preoperative cardiac events prompted interruption of the study after the planned interim analysis.

Conclusions

The authors' data indicate that compared with conventional analgesia, early administration of continuous epidural analgesia is associated with a lower incidence of preoperative adverse cardiac events in elderly patients with hip fracture who have or are at risk for coronary artery disease. Preoperative epidural analgesia may be advantageous for this surgical population.