Response Entropy Research Articles

Unsteady Rotor Hub Passage Vortex Behavior in the Presence of Purge Flow in an Axial Low Pressure Turbine

The paper presents an experimental and computational study of the unsteady behavior of the rotor hub passage vortex in an axial low-pressure turbine. Different flow structures are identified as having an effect on the size, strength, shape, position, and the unsteady behavior of the rotor hub passage vortex. The aim of the presented study is to analyze and quantify the sensitivities of the different flow structures and to investigate their combined effects on the rotor hub passage vortex. Particular attention is paid to the effect of the rim seal purge flow and of the unsteady blade row interaction. The rotor under investigation has nonaxisymmetric end walls on both hub and shroud and is tested at three different rim seal purge flow injection rates. The rotor has separated pressure sides at the operating point under investigation. The nondimensional parameters of the tested turbine match real engine conditions. The 2-sensor fast response aerodynamic probe (FRAP) technique and the fast response entropy probe (FENT) systems developed by ETH Zurich are used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are taken and analyzed. Furthermore, the results of URANS simulations are compared to the measurements and the computations are also used to detail the flow field. The experimental results show a 30% increase of the maximum unsteadiness and a 4% increase of the loss in the hub passage vortex per percent of injected rim seal cooling flow. Compared to a free stream particle, the rim seal purge flow was found to do 60% less work on the rotor.

Drug interaction models are better predictors of tolerance/ response to noxious stimuli compared to individual measured parameters

Background and Goal of Study: This study continues the pursuit of the parameter with the best correlation to the probability of response to noxious stimuli of different intensity. We used data from a previous study by Heyse et al.1 on the interaction of sevoflurane and remifentanil to compare several parameters. Materials and Methods: After institutional review board approval, 40 adult patients were randomised to receive different combinations of sevoflurane (Sevo) and remifentanil (Remi) according to a criss-cross design. After reaching pseudo-steady state, the patients were assessed for tolerance of 'shake and shout' (SAS), tetanic stimulation (TET), insertion of laryngeal mask airway (LMA) and laryngoscopy (LAR). Bispectral index (BIS), state and response entropy (SE, RE), composite variability index (CVI) and surgical pleth index (SPI) were either recorded or computed from raw electroencephalographic and plethysmographic data retrospectively. Sevo and Remi concentrations were recorded. The combined potency of Sevo and Remi according to the fixed C50O hierarchical interaction model (U) and the noxious stimulation response index (NSRI) were the population-based predictors. We used the prediction probability (PK) to assess the performance of these parameters on the probability of response. Bootstrapping (n=1000) was used to produce 84%-confidence intervals of the PKs, with significance being achieved if the confidence intervals did not overlap (p <0.05). Results and Discussion: The parameter PKs per stimulus are summarised in Table 1.(Table Presented) The PK for U and NSRI were highest for all stimuli. Effect site concentrations of either Sevo or Remi alone were significantly worse predictors. BIS, SE, RE and CVI were significantly worse at predicting tolerance to the three painful stimuli, but similar to U and NSRI for SAS. SPI performed poorly overall. Conclusion: U and NSRI perform significantly better than EEG-derived parameters and single drug effect site concentrations in predicting tolerance to noxious stimuli. Therefore both U and NSRI could be useful parameters in anaesthetic practice.

Expectation and Entropy in Spoken Word Recognition: Effects of Age and Hearing Acuity

Background/Study Context: Older adults, especially those with reduced hearing acuity, can make good use of linguistic context in word recognition. Less is known about the effects of the weighted distribution of probable target and nontarget words that fit the sentence context (response entropy). The present study examined the effects of age, hearing acuity, linguistic context, and response entropy on spoken word recognition. Methods: Participants were 18 older adults with good hearing acuity (M age = 74.3 years), 18 older adults with mild-to-moderate hearing loss (M age = 76.1 years), and 18 young adults with age-normal hearing (M age = 19.6 years). Participants heard sentence-final words using a word-onset gating paradigm, in which words were heard with increasing amounts of onset information until they could be correctly identified. Degrees of context varied from a neutral context to a high context condition. Results: Older adults with poor hearing acuity required a greater amount of word onset information for recognition of words when heard in a neutral context compared with older adults with good hearing acuity and young adults. This difference progressively decreased with an increase in words’ contextual probability. Unlike the young adults, both older adult groups’ word recognition thresholds were sensitive to response entropy. Response entropy was not affected by hearing acuity. Conclusion: Increasing linguistic context mitigates the negative effect of age and hearing loss on word recognition. The effect of response entropy on older adults’ word recognition is discussed in terms of an age-related inhibition deficit.

Effects of caudal sufentanil supplemented with levobupivacaine on blocking spermatic cord traction response in pediatric orchidopexy

Caudal block is one of the most commonly used anesthetic techniques in subumbilical and genitourinary procedures. However, traditional administration of caudal levobupivacaine was inadequate on blocking peritoneal response during spermatic cord traction. The aim of this study was to evaluate whether the addition of caudal sufentanil to levobupivacaine provided better analgesia for children undergoing orchidopexy. Sixty-two patients, scheduled for right orchidopexy, received caudal block after induction. Group LS (n = 31) received levobupivacaine 0.25% 1 ml/kg plus sufentanil 0.5 μg/kg, and group L (n = 31) received levobupivacaine 0.25% 1 ml/kg only. HR or MAP fluctuation >20% or entropy increase >15% during spermatic cord traction was defined as inadequate anesthesia and was treated with increasing sevoflurane concentration. The number of children who needed sevoflurane rescue was counted, and postoperative side effects and quality of sleep were also recorded. There were no statistically significant differences between the two groups in age, weight, and duration of surgery. Two (6.45%) children in group LS required inspired sevoflurane rescue to block hemodynamic fluctuation during spermatic cord traction, as compared with 12 (38.71%) patients in group L (P < 0.001). At the time of exerting spermatic cord traction, the median HR was, respectively, 134 and 145 (P < 0.001); the corresponding response entropy (RE) and state entropy (SE) was 65 and 54, respectively, in group LS versus 76 and 65 in group L (P < 0.001). In pediatric orchidopexy, the addition of sufentanil to levobupivacaine for caudal blockade offers clinical benefit over levobupivacaine alone in blocking the spermatic cord traction response.

Permutation auto-mutual information of electroencephalogram in anesthesia

Objective. The dynamic change of brain activity in anesthesia is an interesting topic for clinical doctors and drug designers. To explore the dynamical features of brain activity in anesthesia, a permutation auto-mutual information (PAMI) method is proposed to measure the information coupling of electroencephalogram (EEG) time series obtained in anesthesia. Approach. The PAMI is developed and applied on EEG data collected from 19 patients under sevoflurane anesthesia. The results are compared with the traditional auto-mutual information (AMI), SynchFastSlow (SFS, derived from the BIS index), permutation entropy (PE), composite PE (CPE), response entropy (RE) and state entropy (SE). Performance of all indices is assessed by pharmacokinetic/pharmacodynamic (PK/PD) modeling and prediction probability. Main results. The PK/PD modeling and prediction probability analysis show that the PAMI index correlates closely with the anesthetic effect. The coefficient of determination R2 between PAMI values and the sevoflurane effect site concentrations, and the prediction probability Pk are higher in comparison with other indices. The information coupling in EEG series can be applied to indicate the effect of the anesthetic drug sevoflurane on the brain activity as well as other indices. The PAMI of the EEG signals is suggested as a new index to track drug concentration change. Significance. The PAMI is a useful index for analyzing the EEG dynamics during general anesthesia.

Preoperative pregabalin does not reduce propofol ED50: a randomized controlled trial

In many studies, gabapentinoids, such as pregabalin, have been shown to reduce preoperative anxiety. This anxiolysis is often accompanied by sedation, one of the most frequent side effects of pregabalin. We hypothesized that pregabalin taken preoperatively could reduce propofol requirements for induction of general anesthesia. A randomized double-blind placebo-controlled trial was conducted after approval by the local ethics committee. Fifty women aged 18-40 yr, American Anesthesiologists Society physical status I and II, and scheduled to undergo elective laparoscopic gynecologic procedures were enrolled after written consent. Treatment group patients were given pregabalin 150 mg po one hour before surgery while patients in the control group received a placebo. The primary outcome was the propofol dose required to achieve a targeted anesthetic depth in 50% of the population, i.e., effective dose (ED)50. The ED50 was estimated using Dixon's up-and-down methodology. The targeted anesthetic depth was defined based on predetermined entropy monitoring values (State Entropy [SE] < 50 and Response Entropy [RE]-SE < 10). As a secondary outcome, we tested if pregabalin reduced pre-induction anxiety levels which were measured on a 0-100 scale. The propofol ED50 was not statistically different between the pregabalin group (mean 1.33 mg·kg(-1); 95% confidence interval [CI] 1.23 to 1.43) vs the placebo group (mean 1.37 mg·kg(-1); 95% CI 1.28 to 1.46); P = 0.19. Also, pre-induction anxiety level was not different between groups (median 31; interquartile range [IQR] [10-52] vs median 42; IQR [4-71], respectively; P = 0.41). Preoperative pregabalin does not reduce propofol requirements in a population of healthy young women undergoing laparoscopic gynecologic procedures. This study failed to show a pre-induction anxiolytic effect of pregabalin in such a population. This trial was registered at www.clinicaltrials.gov (NCT01158859).

Entropy-guided end-tidal desflurane concentration during living donor liver transplantation

Background:The three phases of living donor liver transplantation (LDLT) represent different liver conditions. The aim is to study the required end-tidal desflurane concentration (ET-Des) guided with entropy monitoring for the depth of anesthesia.Methods:After the Ethics and Research Committee approval, 40 patients were included in this prospective study. Anesthesia was maintained with Desflurane-O2-air. State entropy (SE) and Response entropy (RE) were kept between 40 and 60.Results:Age and Model for End-stage Liver Disease (MELD) score were 45±10 years and 15.43±3.92, respectively. ET-Des were significantly lower in the anhepatic phase (2.8±0.4%) than in the pre-anhepatic and neohepatic phases (3.3±0.3%, 3.47±0.3%, respectively, P<0.001). The SE and RE for pre-anhepatic, anhepatic, and neohepatic phases were (45.6±3.7, 47.4±3.2), (44.7±2.1, 46.4±2.04), and (46.1±3.3, 47.9±3.3), respectively, with no significant changes between the phases, P > 0.05. Total operative time was 651±88 minutes, and for each phase it was 276±11, 195±55, and 191±24 minutes, respectively. Significant changes were found in hemoglobin g/dl and hematocrit % between the three phases (10.28±1.5, 30.48±4.3), (9.45±1.34, 28.36±4.1), and (8.88±1.1, 26.63±3.5), P<0.05. The heart rate and mean blood pressures were stable despite the cardiac index demonstrated a significant reduction during the anhepatic phase (2.99±0.22) when compared to the pre-anhepatic and neohepatic phases (3.60±0.29) and (4.72±0.32), respectively, (P<0.05). There was a significant correlation between CI and ET-Des% (r=0.604, P<0.05).Conclusion:Inhalational anesthetic requirements differed from one phase to another during LDLT, with requirements being the least during the anhepatic phase. Monitoring of the anesthesia depth was required, to avoid excess administration, which could compromise the hemodynamics before the critical time of reperfusion.

The effect of dexmedetomidine continuous infusion as an adjuvant to general anesthesia on sevoflurane requirements: A study based on entropy analysis

Background:Dexmedetomidine, a α2 agonist as an adjuvant in general anesthesia, has anesthetic and analgesic-sparing property.Aims:To evaluate the effect of continuous infusion of dexmedetomidine alone, without use of opioids, on requirement of sevoflurane during general anesthesia with continuous monitoring of depth of anesthesia by entropy analysis.Materials and Methods:Sixty patients were randomly divided into 2 groups of 30 each. In group A, fentanyl 2 mcg/kg was given while in group B, dexmedetomidine was given intravenously as loading dose of 1 mcg/kg over 10 min prior to induction. After induction with thiopentone in group B, dexmedetomidine was given as infusion at a dose of 0.2-0.8 mcg/kg. Sevoflurane was used as inhalation agent in both groups. Hemodynamic variables, sevoflurane inspired fraction (FIsevo), sevoflurane expired fraction (ETsevo), and entropy (Response entropy and state entropy) were continuously recorded. Statistical analysis was done by unpaired student's t-test and Chi-square test for continuous and categorical variables, respectively. A P-value < 0.05 was considered significant.Results:The use of dexmedetomidine with sevoflurane was associated with a statistical significant decrease in ETsevo at 5 minutes post-intubation (1.49 ± 0.11) and 60 minutes post-intubation (1.11 ±0.28) as compared to the group A [1.73 ±0.30 (5 minutes); 1.68 ±0.50 (60 minutes)]. There was an average 21.5% decrease in ETsevo in group B as compared to group A.Conclusions:Dexmedetomidine, as an adjuvant in general anesthesia, decreases requirement of sevoflurane for maintaining adequate depth of anesthesia.

Reduced sevoflurane consumption in cirrhotic compared to non-cirrhotic patients undergoing major hepatic surgery

BackgroundThere is evidence in literature that chronic hepatic patients need less anesthesia compared with healthy ones. Liver cirrhosis leads to a reduction in liver mass and hepatic blood flow with an effect on drug clearance and cardiovascular stability.AimTo evaluate sevoflurane consumption during entropy monitored general anesthesia in cirrhotic and non-cirrhotic patients during transition from consciousness to unconsciousness and throughout the procedure of major hepatic surgical procedures.Patients and methodsForty patients scheduled for major hepatic resection at the National Liver Institute, Menofiya University, Egypt, were studied prospectively and randomized into two equal groups. Group I (n. 20) cirrhotic patients (Child Pugh Grade A) with focal lesion, Group II (n. 20) healthy live liver donors undergoing major hepatectomies. Sevoflurane inhalational concentration was adjusted to achieve a state and response entropy of 40–60, and when RE increases 5–10 units above SE; more intravenous analgesics were given.ResultsMean (SD) Sevoflurane consumption in Group II showed higher consumption 23.5 (3.23) ml, compared to Group I 16 (2.19) ml. Mean (SD) sevoflurane consumption after 4 and 6 h from induction also showed a lower value in Group I 10.7(1.94), 9(1.22) ml, than in Group II 17.2(1.69), 14.1(2.19) ml, respectively. Mean (SD) end tidal sevoflurane concentration was lower in Group I 1.4(0.12) after 2 h from induction than in Group II 1.7(0.11). After 4 and 6 h from induction Group I demonstrated a lower value compared to Group II (P < 0.05.). Mean blood pressure, heart rate, urine output and CVP showed no significant changes during maintenance between the two groups.ConclusionThis study demonstrated that cirrhotic patients require less sevoflurane consumption and lower end-tidal concentration to maintain general anesthesia with entropy guidance. This could also have an important impact on the economic costs when applied on a larger scale.

VESTIBULAR ACTIVATION DIFFERENTIALLY MODULATES HUMAN EARLY VISUAL CORTEX AND V5/MT EXCITABILITY AND RESPONSE ENTROPY

Head movement imposes the additional burdens on vision of maintaining visual-acuity and determining the origin of retinal image motion (ie, self-motion vs object-motion). Although maintaining visual acuity during self-motion is...

Influência da anestesia venosa total, entropia e laparoscopia sobre o estresse oxidativo

BACKGROUND AND OBJECTIVES: Recent studies have correlated postoperative mortality with anesthetic mortality, especially with the depth of anesthesia and systolic blood pressure (SBP). The aim of this study is to evaluate the effects of the depth of total intravenous anesthesia (TIVA) using remifentanil and propofol, performed with monitoring of response entropy (RE) on blood concentrations of oxidative stress markers (TBARS and glutathione) during laparoscopic operations. METHOD: Twenty adult patients, ASA I, BMI 20-26 kg.m-2, aged 20 to 40 years, were randomly distributed into two groups: Group I underwent anesthetic-surgical procedure with RE maintained between 45 and 59, and Group II underwent anesthetic-surgical procedure with RE between 30 and 44. In both groups, the remifentanil and propofol infusion was controlled by the effector site (Es), adjusted to maintain RE desired values (Groups I and II) and always assessing the suppression rate (SR). Patients were evaluated in six periods: M1 (immediately before anesthesia), M2 (before tracheal intubation [TI]), M3 (5-minutes after TI), M4 (immediately before pneumoperitoneum [PPT]), M5 (1-minute after PPT), and M6 (1-hour after the operation). The following parameters were assessed at all times: SBP, DBP, HR, RE, SR, TBARS, and glutathione. RESULTS: We found increases in TBARS and glutathione in M5, both in Group I and Group II (p GI in M5, p < 0.05%) suggest interference of another factor (deep anesthesia) responsible for the increase in AM, probably as a result of increased autonomic nervous system depression and minor splanchnic self-regulation.

Influence of Total Intravenous Anesthesia, Entropy and Laparoscopy on Oxidative Stress

Recent studies have correlated postoperative mortality with anesthetic mortality, especially with the depth of anesthesia and systolic blood pressure (SBP). The aim of this study is to evaluate the effects of the depth of total intravenous anesthesia (TIVA) using remifentanil and propofol, performed with monitoring of response entropy (RE) on blood concentrations of oxidative stress markers (TBARS and glutathione) during laparoscopic operations. Twenty adult patients, ASA I, BMI 20-26 kg.m(-2), aged 20 to 40 years, were randomly distributed into two groups: Group I underwent anesthetic-surgical procedure with RE maintained between 45 and 59, and Group II underwent anesthetic-surgical procedure with RE between 30 and 44. In both groups, the remifentanil and propofol infusion was controlled by the effector site (Es), adjusted to maintain RE desired values (Groups I and II) and always assessing the suppression rate (SR). Patients were evaluated in six periods: M1 (immediately before anesthesia), M2 (before tracheal intubation [TI]), M3 (5-minutes after TI), M4 (immediately before pneumoperitoneum [PPT]), M5 (1-minute after PPT), and M6 (1-hour after the operation). The following parameters were assessed at all times: SBP, DBP, HR, RE, SR, TBARS, and glutathione. We found increases in TBARS and glutathione in M5, both in Group I and Group II (p<0.05), with higher values in Group II, and SR in three patients in Group II, immediately after PPT. Increased markers in Group I (M5) suggests an increase in anaerobic metabolism (AM) in the splanchnic circulation while the highest values seen in Group II (GII > GI in M5, p<0.05%) suggest interference of another factor (deep anesthesia) responsible for the increase in AM, probably as a result of increased autonomic nervous system depression and minor splanchnic self-regulation.

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localized hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded 1.5-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position, and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich two-sensor high temperature (260 °C) fast response aerodynamic probe (FRAP) technique and the fast response entropy. Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature, and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases traveling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

Spectral Entropy Monitoring Reduces Anesthetic Dosage for Patients Undergoing Off-Pump Coronary Artery Bypass Graft Surgery

The measurement of the depth of anesthesia is of clinical interest for patients undergoing off-pump coronary artery bypass graft (OPCAB) surgery in order to avoid intraoperative awareness and cardiac depression. Entropy recently was introduced as a monitor of anesthetic depth. This study was conducted to investigate the feasibility of entropy monitoring during the conduct of OPCAB surgery and to find out whether it reduced the anesthetic dosage for patients undergoing OPCAB surgery. A prospective, randomized, single-blind, controlled study. A teaching hospital. Seventy patients scheduled for OPCAB surgery were randomized to receive propofol-sufentanil anesthesia either with the entropy values visible (the entropy group, n = 35) or without the entropy values visible (the control group, n = 35). In the entropy group, propofol and sufentanil infusion rates were titrated to maintain a state entropy (SE) value of 45 to 55 and a response entropy (RE)-SE difference below 10 U. In the control group, patients were anesthetized to keep the heart rate and blood pressure within 25% of the baseline values. The course of surgery, the consumption of anesthetics, and intraoperative recall were recorded. Plasma levels of adrenocorticotropic hormone (ACTH) and cortisol were measured. The average SE during anesthesia was 50 ± 5 in the entropy group; the entropy values were lower in the control group (p < 0.05). Compared with the control group, propofol and sufentanil consumption were significantly less in the entropy group, which shortened the time to tracheal extubation (p < 0.05). Significantly, patients in the control group needed more phenylephrine to maintain arterial pressure than patients in the entropy group (p < 0.05). ACTH and cortisol release were prevented completely, and there was no intraoperative recall reported in the 2 groups. Entropy monitoring reduced propofol and sufentanil dosage for patients undergoing OPCAB surgery.

Response entropy changes after noxius stimulus

Small changes in the frequency of the electromyography could reflect an inadequate anesthetic or analgesic level, and it could be more specific than the hemodynamic monitors. The Datex-Ohmeda S/5 Entropy Module includes information about the electromyographic activity of the face muscles (response entropy--RE). The aim of our study is compare entropy and BIS ability to detect a nociceptive stimulus during a sevoflurane anesthesia. We designed an observational, prospective and descriptive study that included 20 patients. We performed sevoflurane anaesthesia induction, the end-tidal was kept at 3 and 4 %, during 15 min at each concentration, with no analgesic drug and no neuromuscular blocking agent, and we applied a nociceptive stimulus: tetanus 100 Hz, during 5 s. We set the standard monitorization, BIS, RE, and state entropy (SE) along the study. There was a significant difference between RE and SE post-noxious stimulus values at 3 and 4 % end-tidal sevoflurane (p < 0.05). Only RE changed significantly at the moment of the noxious stimulation at both sevoflurane concentrations studied (p < 0.05). In patients under general anesthesia only carried out with sevoflurane at concentrations that inhibit the movement to painful stimuli, the RE is a single parameter able to detect variations after the nociceptive stimulation.

Measuring the effects of sevoflurane on electroencephalogram using sample entropy

Monitoring the effect of anesthetic drugs on the neural system is a major ongoing challenge for anesthetists. During the past few years, several electroencephalogram (EEG)-based methods such as the response entropy (RE) as implemented in the Datex-Ohmeda M-Entropy Module have been proposed. In this paper, sample entropy is used to quantify the predictability of EEG series, which could provide an index to show the effect of sevoflurane anesthesia. The dose-response relation of sample entropy is compared with that of RE. EEG data from 21 subjects is collected during the induction of general anesthesia with sevoflurane. The sample entropy is applied to the EEG recording. Pharmacokinetic-pharmacodynamic modeling and prediction probability statistic are used to evaluate the efficiency of sample entropy in comparison with RE. Both methods track the gross changes in EEG, especially the occurrence of burst-suppression pattern at high doses of anesthetics. However, our method produces faster reaction to transients in EEG during the induction of anesthesia as indicated from the pharmacokinetic and pharmacodynamic modeled parameters and analysis around the point of loss of consciousness. Also, sample entropy correlated more closely with effect-site sevoflurane concentration than the RE. In addition, our proposed method exhibits greater resistance to noise in the EEG signals. The results demonstrate that sample entropy can estimate the sevoflurane drug effect on the EEG more effectively than the commercial RE index with a stronger noise resistance.

Processed Electroencephalogram and Depth of Anesthesia

Processed Electroencephalogram and Depth of Anesthesia

Feasibility of Closed-loop Titration of Propofol and Remifentanil Guided by the Spectral M-Entropy Monitor

This randomized controlled trial describes automated coadministration of propofol and remifentanil, guided by M-Entropy analysis of the electroencephalogram. The authors tested the hypothesis that a novel dual-loop controller with an M-Entropy monitor increases time spent within predetermined target entropy ranges. Patients scheduled for elective surgery were randomly assigned in this single-blind study using a computer-generated list, to either dual-loop control using a proportional-integral-derivative controller or skilled manual control of propofol and remifentanil using target-controlled-infusion systems. In each group, propofol and remifentanil administration was titrated to a state entropy target of 50 and was subsequently targeted to values between 40 and 60. The primary outcome was the global score, which included the percentage of state entropy or response entropy in the range 40-60, the median absolute performance error and wobble. Data are presented as medians [interquartile range]. Thirty patients assigned to the dual-loop group and 31 assigned to the manual group completed the study. The dual-loop controller was able to provide induction and maintenance for all patients. The Global Score of State Entropy was better maintained with dual-loop than manual control (25 [19-53] vs. 44 [25-110], P = 0.043), and state entropy was more frequently maintained in the range of 40-60 (80 [60-85] vs. 60 [35-82]%, P = 0.046). Propofol (4.1 [2.9-4.9] vs. 4.5 [3.4-6.3] mg · kg(-1) · h(-1)) and remifentanil (0.18 [0.13-0.24] vs. 0.19 [0.15-0.26] μg · kg(-1) · min(-1)) consumptions and the incidence of somatic side effects were similar. Intraoperative automated control of hypnosis and analgesia guided by M-Entropy is clinically feasible and more precise than skilled manual control.

Vestibular activation differentially modulates human early visual cortex and V5/MT excitability and response entropy.

Head movement imposes the additional burdens on the visual system of maintaining visual acuity and determining the origin of retinal image motion (i.e., self-motion vs. object-motion). Although maintaining visual acuity during self-motion is effected by minimizing retinal slip via the brainstem vestibular-ocular reflex, higher order visuovestibular mechanisms also contribute. Disambiguating self-motion versus object-motion also invokes higher order mechanisms, and a cortical visuovestibular reciprocal antagonism is propounded. Hence, one prediction is of a vestibular modulation of visual cortical excitability and indirect measures have variously suggested none, focal or global effects of activation or suppression in human visual cortex. Using transcranial magnetic stimulation-induced phosphenes to probe cortical excitability, we observed decreased V5/MT excitability versus increased early visual cortex (EVC) excitability, during vestibular activation. In order to exclude nonspecific effects (e.g., arousal) on cortical excitability, response specificity was assessed using information theory, specifically response entropy. Vestibular activation significantly modulated phosphene response entropy for V5/MT but not EVC, implying a specific vestibular effect on V5/MT responses. This is the first demonstration that vestibular activation modulates human visual cortex excitability. Furthermore, using information theory, not previously used in phosphene response analysis, we could distinguish between a specific vestibular modulation of V5/MT excitability from a nonspecific effect at EVC.

Effects of etomidate on bispectral index scale and spectral entropy during induction of anesthesia by means of the raw electroencephalographic and electromyographic characteristics.

BackgroundEtomidate frequently induces myoclonus, so it may affect electromyographics (EMG). And EMG commonly has an effect on the bispectral index scale (BIS) and spectral entropy. This study was performed to compare the effect of etomidate on BIS, response entropy (RE) and state entropy (SE) during induction of anesthesia.MethodsFifty patients (ASA I or II) scheduled for elective surgery were included in this study. Anesthesia was induced with etomidate (0.3 mg/kg) and rocuronium (0.6 mg/kg). Patients also inhaled 4 vol% sevoflurane and 100% oxygen and, then intubated. BIS, RE, SE and Modified Observer's Assessment of Alertness/Sedation Scale (MOAA/S) were measured 4 times (before injection of etomidate [T0], at loss of eyelash reflex [T1], 90 seconds after rocuronium injection [T2], and after intubation [T3]). We also checked whether myoclonus occurred.ResultsBaseline values (T0) were 93.1 ± 4.7 for BIS, 95.8 ± 3.7 for RE and, 87.3 ± 3.5 for SE. In comparison with T0, there were significantly differences in BIS (50.2 ± 16.3), RE (76.8 ± 18.5) and SE (66.3 ± 17.4) at T1 (all P < 0.05). There were no significant differences at T2 and T3. Thirty one patients had myoclonus. At the occurrence of myoclonus, RE and SE values significantly increased but not BIS (P < 0.05).ConclusionsIn patients with myoclonus, at the loss of consciousness, spectral entropy did not decrease where as BIS did, suggesting that BIS may evaluate hypnotic levels better than spectral entropy during induction of anesthesia with etomidate.