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PubMed1988

Ecological structures recognized by means of entropy analysis: assessment of differences between entropy values.

A procedure is outlined for the assessment of differences between entropy values obtained from a data set. The problem posed is that of identifying the data matrix representing least uncertainty in the disposition of its elements from two or more given matrices. Monte Carlo simulations were used, through which the maximum and minimum entropy values that could be obtained from each data set were estimated. Such values could be obtained by randomly interchanging the elements of each matrix and may serve as references in estimating the degree of order or randomness that an original matrix possesses.

Ecology↗
PubMed2002

Entropy production and excess entropy in a nonequilibrium steady-state of single macromolecules.

Based on a recently developed formalism for mesoscopic stochastic dynamics of single macromolecules, such as motor proteins, in aqueous solution, we demonstrate mathematically the principle of the nonequilibrium thermodynamics originated by the Brussels group. The key concepts of excess entropy and excess entropy production, and their mathematical properties as well as physical interpretations, are discussed. The newly developed stochastic macromolecular mechanics is consistent with the general theory of nonequilibrium thermodynamics far from equilibrium, and more importantly, it bridges the abstract theory with the current experimental and modeling work on molecular motors and other biological systems in nonequilibrium steady state.

Journal Article↗
PubMed2005

Production rate of the coarse-grained Gibbs entropy and the Kolmogorov-Sinai entropy: a real connection?

We discuss the connection between the Kolmogorov-Sinai entropy hKS and the production rate of the coarse-grained Gibbs entropy rG. Detailed numerical computations show that the (often-accepted) identification of the two quantities does not hold in systems with intermittent behavior and/or very different characteristic times and in systems presenting pseudochaos. The basic reason for this is in the asymptotic (with respect to time) nature of hKS, while rG is a quantity related to short-time features of a system.

Journal Article↗
PubMed2006

Response Entropy is not more sensitive than State Entropy in distinguishing the use of esmolol instead of remifentanil in patients undergoing gynaecological laparoscopy.

BACKGROUND: Monitoring of analgesia remains a challenge during general anaesthesia. Activation of Response Entropy (RE) to painful stimuli has been suggested to be a sign of inadequate analgesia. We evaluated the ability of RE to be more sensitive than State Entropy (SE) in measuring nociception in patients undergoing gynaecological laparoscopy. Our hypothesis was that while keeping SE at a predetermined level, RE would be higher in patients receiving a beta-blocking agent (esmolol) instead of an opioid (remifentanil) during a propofol/nitrous oxide anaesthesia. METHODS: Fifty-one women aged between 22-53 years were randomly assigned to receive esmolol (n=25) or remifentanil (n=26). SE was kept at 50+/-5. RE and SE were recorded at an interval of 30 s to 2 min and the areas under the RE and SE value-time curves (AUCRE and AUCSE) were calculated during the time of intubation and start of surgery as well as during the entire anaesthesia. The difference between RE and SE recordings in both groups was determined by subtracting the AUCSE from the corresponding AUCRE. Movements of the patients were recorded. RESULTS: No significant differences were detected in any of the several AUC values between the groups. The difference between RE and SE recordings was similar in both groups. Every patient in the esmolol group moved some time during the procedure interfering with surgery while no one in the remifentanil group moved. CONCLUSION: In patients undergoing gynaecological laparoscopic day-case surgery, RE seems not to be more sensitive than SE in guiding the use of opioids during general anaesthesia.

Adrenergic beta-Antagonists↗
PubMed2005

Interpretation of approximate entropy: analysis of intracranial pressure approximate entropy during acute intracranial hypertension.

We studied changes in intracranial pressure (ICP) complexity, estimated by the approximate entropy (ApEn) of the ICP signal, as subjects progressed from a state of normal ICP (< 20-25 mmHg) to acutely elevated ICP (an ICP "spike" defined as ICP > 25 mmHg for < or = 5 min). We hypothesized that the measures of intracranial pressure (ICP) complexity and irregularity would decrease during acute elevations in ICP. To test this hypothesis we studied ICP spikes in pediatric subjects with severe traumatic brain injury (TBI). We conclude that decreased complexity of ICP coincides with episodes of intracranial hypertension (ICH) in TBI. This suggests that the complex regulatory mechanisms that govern intracranial pressure are disrupted during acute rises in ICP. Furthermore, we carried out a series of experiments where ApEn was used to analyze synthetic signals of different characteristics with the objective of gaining a better understanding of ApEn itself, especially its interpretation in biomedical signal analysis.

Adolescent↗
PubMed2001

Entropy-controlled asymmetric synthesis. How differential activation entropy is induced in chiral tethered reactions.

[figure: see text] Kinetic measurements to determine effective molarities of intramolecular reactions using 2,4-pentanediol and related tethers showed that methyl groups on the tether accelerate the major diastereomeric process but decelerate the minor process. The efficient promotion of stereocontrol is suggested to be due to chiral perturbation of the reaction rate through the entropy term. The conformation of the encounter complex of the reagent and reactant moieties was deduced by stereochemical analysis of the intramolecular adducts.

Journal Article↗
PubMed2006

Physicochemical attack against solid tumors based on the reversal of direction of entropy flow: an attempt to introduce thermodynamics in anticancer therapy.

BACKGROUND: There are many differences between healthy tissue and growing tumor tissue, including metabolic, structural and thermodynamic differences. Both structural and thermodynamic differences can be used to follow the entropy differences in cancerous and normal tissue. Entropy production is a bilinear form of the rates of irreversible processes and the corresponding "generalized forces". Entropy production due to various dissipation mechanisms based on temperature differences, chemical potential gradient, chemical affinity, viscous stress and exerted force is a promising tool for calculations relating to potential targets for tumor isolation and demarcation. METHODS: The relative importance of five forms of entropy production was assessed through mathematical estimation. Using our mathematical model we demonstrated that the rate of entropy production by a cancerous cell is always higher than that of a healthy cell apart from the case of the application of external energy. Different rates of entropy production by two kinds of cells influence the direction of entropy flow between the cells. Entropy flow from a cancerous cell to a healthy cell transfers information regarding the cancerous cell and propagates its invasive action to the healthy tissues. To change the direction of entropy flow, in addition to designing certain biochemical pathways to reduce the rate of entropy production by cancerous cells, we suggest supplying external energy to the tumor area, changing the relative rate of entropy production by the two kinds of cells and leading to a higher entropy accumulation in the surrounding normal cells than in the tumorous cells. CONCLUSION: Through the use of mathematical models it was quantitatively demonstrated that when no external force field is applied, the rate of entropy production of cancerous cells is always higher than that of healthy cells. However, when the external energy of square wave electric pulses is applied to tissues, the rate of entropy production of normal cells may exceed that of cancerous cells. Consequently, the application of external energy to the body can reverse the direction of the entropy current. The harmful effect brought about by the entropy flow from cancerous to healthy tissue can be blocked by the reversed direction of entropy current from the irradiated normal tissue around the tumor.

Journal Article↗