Stable Interval Research Articles

ECG Response: February 25, 2014

HomeCirculationVol. 129, No. 8ECG Response: February 25, 2014 Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBECG Response: February 25, 2014 Originally published25 Feb 2014https://doi.org/10.1161/CIRCULATIONAHA.114.008852Circulation. 2014;129:922IntroductionA 20-year-old female college student presents to the college health service with complaints of an irregular heart rate. She does not have any known cardiac disease but has noted palpitation in the past. However, the palpitations have lasted for only 1 to 2 hours and have been infrequent. She has never seen a physician for these palpitations. However, she has never noted her heartbeat to be irregular.The rhythm in ECG A is irregular, and there is no pattern to the irregularity. Therefore, the rhythm is irregularly irregular. There are only 3 supraventricular rhythms that are irregularly irregular: sinus arrhythmia (1 P-wave morphology and stable PR interval); wandering atrial pacemaker (or multifocal atrial rhythm), which has a rate <100 bpm, or multifocal atrial tachycardia, which has a rate >100 bpm (≥3 different P-wave morphologies without any 1 dominant P wave); or atrial fibrillation (no organized atrial activity). There are no organized P waves noted before any of the QRS complex; hence, this is atrial fibrillation. Two different QRS complex morphologies are noted. The narrow complexes (complexes 6, 12, and 14; +) have a normal duration and morphology. The wide QRS complexes (duration, 0.16 second; *) have a tall R wave in lead V1, but the morphology is not typical for a right bundle-branch block nor do they resemble a left bundle branch block. Therefore, they do not have a morphology typical for aberration due to a bundle branch block. In addition, there is positive concordance across the precordium (ie, tall R wave in V1-V6). These features are seen with direct myocardial activation (ie, QRS complex that is ventricular, paced or due to Wolff-Parkinson-White). The QRS complexes are very irregular and are therefore not likely ventricular in origin. There are no pacing stimuli seen. More important, there is no relationship between QRS complex width (duration) and rate (or RR interval). It can be seen that there are narrow complexes associated with fast rates (short RR intervals) (└┘) and wide QRS complexes at slow rates (long RR intervals; ↔). This is not seen with typical rate-related aberration but is associated with an accessory pathway or pre-excitation, specifically Wolff-Parkinson-White syndrome.Download figureDownload PowerPointECG B is her baseline ECG, which was obtained after sinus rhythm was restored. The rhythm is regular at a rate of 60 bpm. There is a P wave before each QRS complex (+), and there is a stable but short PR interval (0.12 second). The P wave is positive in leads I, II, aVF, and V4 through V6. Hence, this is a normal sinus rhythm with a short PR interval. The QRS complex morphology is identical to what was seen in ECG A. The widened QRS complex is due to a “slurred” upstroke (↑), known as a delta wave. The delta wave is due to initial activation that is directly through the ventricular myocardium and thus slow; there is then fusion with later activation through the normal conduction system. The short PR interval and the delta wave are characteristic of a Wolff-Parkinson-White pattern. The presence of a Q wave in leads I and aVL (▴), and the positive delta wave in lead V1 are seen with a left lateral bypass tract. The QT/QTc intervals are slightly prolonged (480/480 milliseconds) but are normal when the prolonged QRS complex duration is considered (420/420 milliseconds). Because the QT interval includes the QRS complex, ST segment, and T wave, prolongation of the QRS complex duration needs to be considered when establishing the QTc interval. The amount of widening of the QRS complex that is above the normal width needs to be subtracted from the QT interval measurement before the QT is corrected for heart rate.Download figureDownload PowerPointPlease go to the journal’s Facebook page for more ECG Challenges: http://goo.gl/cm4K7. Challenges are posted on Tuesdays and Responses on Wednesdays.FootnotesCorrespondence to Philip J. Podrid, MD, West Roxbury VA Hospital, Section of Cardiology, 1400 VFW Pkwy, West Roxbury, MA 02132. E-mail [email protected] Previous Back to top Next FiguresReferencesRelatedDetails February 25, 2014Vol 129, Issue 8 Advertisement Article InformationMetrics © 2014 American Heart Association, Inc.https://doi.org/10.1161/CIRCULATIONAHA.114.008852PMID: 24566067 Originally publishedFebruary 25, 2014 PDF download Advertisement

Identification of Contamination Control Strategy for Fluid Power System Using an Inexact Chance-Constrained Integer Program

An inexact chance-constrained integer programming (ICIP) method is developed for planning contamination control of fluid power system (FPS). The ICIP is derived by incorporating chance-constrained programming (CCP) within an interval mixed integer linear programming (IMILP) framework, such that uncertainties presented in terms of probability distributions and discrete intervals can be handled. It can also help examine the reliability of satisfying (or risk of violating) system constraints under uncertainty. The developed method is applied to a case of contamination control planning for one typical FPS. Interval solutions associated with risk levels of constraint violation are obtained. They can be used for generating decision alternatives and thus help designers identify desired strategies under various environmental, economic, and system reliability constraints. Generally, willingness to take a higher risk of constraint violation will guarantee a lower system cost; a strong desire to acquire a lower risk will run into a higher system cost. Thus, the method provides not only decision variable solutions presented as stable intervals but also the associated risk levels in violating the system constraints. It can therefore support an in-depth analysis of the tradeoff between system cost and system-failure risk.

Hopf Bifurcation Analysis in a Modified Price Differential Equation Model with Two Delays

The paper investigates the behavior of price differential equation model based on economic theory with two delays. The primary aim of this thesis is to provide a research method to explore the undeveloped areas of the price model with two delays. Firstly, we modify the traditional price model by considering demand function as a downward opening quadratic function, and supply and demand functions both depending on the price of the past and the present. Then the price model with two delays is established. Secondly, by considering the price model with one delay, we get the stable interval. Regarding another delay as a parameter, we studied the linear stability and local Hopf bifurcation. In addition, we pay attention to the direction and stability of the bifurcating periodic solutions which are derived by using the normal form theory and center manifold method. Afterwards, the study turns to simulate the results through numerical analysis, which shows that the provided method is valid.

Synchronization of Chaotic Delayed Neural Networks via Impulsive Control

This paper is concerned with the impulsive synchronization problem of chaotic delayed neural networks. By employing Lyapunov stability theorem, impulsive control theory and linear matrix inequality (LMI) technique, several new sufficient conditions ensuring the asymptotically synchronization for coupled chaotic delayed neural networks are derived. Based on these new sufficient conditions, an impulsive controller is designed. Moreover, the stable impulsive interval of synchronized neural networks is objectively estimated by combining the MATLAB LMI toolbox and one of the two given equations. Two examples with numerical simulations are given to illustrate the effectiveness of the proposed method.

ECG Response: December 24/31, 2013

HomeCirculationVol. 128, No. 25ECG Response: December 24/31, 2013 Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBECG Response: December 24/31, 2013 Originally published24 Dec 2013https://doi.org/10.1161/CIRCULATIONAHA.113.007191Circulation. 2013;128:2810A 64-year-old man presents to the emergency room with a history of 2 hours of substernal chest discomfort that radiates to his lower jaw and left arm. The discomfort is associated with severe diaphoresis. Physical examination demonstrates a blood pressure of 150/90 mm Hg, bibasilar rales, and an S4. Initial cardiac biomarkers are normal. However, based on the clinical presentation and the initial ECG (ECG A) the patient undergoes an urgent cardiac catheterization and an intervention is performed. On the following day a second ECG is obtained (ECG B).Download figureDownload PowerPointECG A: There is a regular rhythm at a rate of 120 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 sec). The P waves are positive in leads I, II, aVF, and V4–V6. Hence this is a sinus tachycardia. The QRS complex duration is normal (0.08 sec). There are beat to beat changes in the axis (ie, a normal axis between 0° and +90°, ^; positive QRS complex in leads I and aVF) alternating with an extreme leftward axis between −30° and −90° (▴; positive QRS complex in leads I and negative QRS complex in leads II and aVF). There are 2 causes for an extreme left axis (ie, an inferior wall myocardial infarction in which there is a deep initial Q wave in leads II and aVF or a left anterior fascicular block in which the QRS complex in leads II and aVF has an rS morphology). This extreme leftward axis is a left anterior fascicular block. There is J point and ST segment elevation in leads V2–V6 (↓), consistent with an extensive ST segment elevation myocardial infarction of the anterior wall. The QT/QTc intervals are normal (280/400 ms). Also noted are beat to beat changes in the amplitude of the QRS complexes in leads V5–V6 (→), which is QRS or electric alternans. QRS or electric alternans is seen in several conditions including an acute ST elevation myocardial infarction, any rapid supraventricular tachycardia, decompensated heart failure, and a severe cardiomyopathy. In these situations the cause is beat to beat changes in calcium fluxes. QRS alternans is also seen in a large pericardial effusion or tamponade and the cause is shifting of the heart in a fluid filled pericardial sac. The beat to beat change in axis is possibly a manifestation of the QRS alternans, although it may also reflect an intermittent left anterior fascicular block resulting from the acute myocardial infarction.ECG B: The ECG obtained a day after the cardiac catheterization shows a regular rhythm at a rate of 64 bpm. There is a P wave before each QRS complex (+) with a stable PR interval (0.20 sec). The P wave is positive in leads I, II, aVF, and V4–V6, hence this is a normal sinus rhythm. The QRS complex duration is normal (0.08 sec), and there is an extreme left axis between −30° and −90° (positive QRS complex in lead I and negative QRS complex in leads II and aVF). This is a left anterior fascicular block which is now persistent. There is a QS complex in leads V1–V2 (↓), consistent with an anteroseptal myocardial infarction and T wave inversions in leads I, II, aVR (positive T wave in aVR is actually inverted), aVL, aVF, and V2–V6 (^). The T waves are symmetrically inverted, consistent with the recent ischemic event.Please go to the journal’s Facebook page for more ECG Challenges: http://goo.gl/cm4K7. Challenges are posted on Tuesdays and Responses on Wednesdays.FootnotesCorrespondence to Philip J. Podrid, MD, West Roxbury VA Hospital, Section of Cardiology, 1400 VFW Parkway, West Roxbury, MA 02132. E-mail [email protected] Previous Back to top Next FiguresReferencesRelatedDetails December 1, 2013Vol 128, Issue 25 Advertisement Article InformationMetrics © 2013 American Heart Association, Inc.https://doi.org/10.1161/CIRCULATIONAHA.113.007191PMID: 24366590 Originally publishedDecember 24, 2013 PDF download Advertisement SubjectsElectrocardiology (ECG)

Can we predict long-term remission after somatostatin analog withdrawal in patients with acromegaly? Results from a multicenter prospective trial

Somatostatin analogs (SSAs) represent the mainstay of therapy in acromegaly. One of the potential disadvantages is the expected need to maintain therapy indefinitely in previously non-irradiated patients. The aim of this multicenter prospective open trial was to evaluate the likelihood of successful discontinuation of SSA therapy in well-controlled acromegalic patients who fulfilled very strict criteria: two or more years of treatment with the long-acting SSA octreotide LAR (OCT-LAR), a stable dose and injections interval every 4 weeks or longer for the previous year, GH levels <2.5 ng/ml and normal IGF-1 levels for age, a tumor remnant <10 mm, no history of radiotherapy, and no use of cabergoline or pegvisomant over the previous 6 months. Disease recurrence was defined as an increase of IGF-1 to levels above 1.2-fold the upper limit of normal (ULN). Out of 220 patients, 20 patients (12 women and 8 men; mean age, 48.1 ± 10.3 years; age range, 27-64) treated for 2.74 ± 0.64 years (range, 2.0-4.4) were included in this prospective study and OCT-LAR therapy was stopped. Four patients (20 %) remained without clinical and biochemical/neuroradiological evidence of disease recurrence after 12-18 months of follow-up. Sixteen patients (80 %) relapsed biochemically within 9 months after drug withdrawal and restarted OCT-LAR at the same previous dose. Compared to recurring subjects, non-recurring patients had significantly lower mean IGF-1 (× ULN) levels but there were some overlapping values in both groups. No other characteristic could be identified as a predictor of successful OCT-LAR discontinuation. Our findings demonstrated that OCT-LAR withdrawal, though rare, is possible in well-selected acromegalic patients treated for at least 2 years and considered optimally controlled in hormonal and neuroradiological terms.

ECG Response: October 1, 2013

HomeCirculationVol. 128, No. 14ECG Response: October 1, 2013 Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBECG Response: October 1, 2013 Originally published1 Oct 2013https://doi.org/10.1161/CIRCULATIONAHA.113.005949Circulation. 2013;128:1586–1587ECG Challenge: A 66-year-old woman with a history of diabetes mellitus, hyperlipidemia, and rheumatoid arthritis presents to her primary care physician with complaints of intermittent lightheadedness. She has not experienced syncope. With the lightheadedness, she has noted her heart rate to be slow, often at ≈40 bpm. She denies any other cardiac symptoms. While in the office, she has a sudden onset of lightheadedness, and an ECG is obtained.Download figureDownload PowerPointThere is a regular rhythm at a rate of 32 bpm. The QRS complex has a normal duration (0.08 second) and a normal morphology. The axis is extremely leftward between −30° and −90° (positive QRS complex in lead I and negative QRS complex in leads II and aVF with an rS morphology). Causes of an extreme left axis include an inferior wall myocardial infarction in which there is a deep Q wave in leads II and aVF or a left anterior fascicular block in which there is an rS morphology in leads II and aVF. This is a left anterior fascicular block. The QT/QTc intervals are normal (460/340 milliseconds). P waves are seen before each QRS complex (+), with a stable PR interval of 0.40 second. The P wave is positive in leads I, II, aVF, and V4 through V6. This represents a sinus rhythm with a first-degree atrioventricular (AV) block or prolonged AV conduction. A second sinus P wave is seen after each QRS complex (*); it is not followed by a QRS complex and hence is nonconducted. The presence of an occasional on time but not conducted P wave defines a second-degree AV block, and because every other P wave is nonconducted, this represents a 2:1 AV block or AV conduction. The second-degree AV block may be either Mobitz type I or Wenckebach, which is attributable to a conduction abnormality in the AV node, or Mobitz type II, which is attributable to a conduction abnormality within the His-Purkinje system. When there is a continuous pattern of 2:1 AV block, the block may be Mobitz type I or II. The etiology can only be established if there is a change in the pattern of conduction, ie two sequentially conducted P waves (if PR interval stable it is Mobitz II, if PR interval lengthens it is Mobitz I) or the development of complete heart block (escape junctional rhythm it is Mobitz I, escape ventricular rhythm it is Mobtiz II). It can be seen that the PP interval is not constant, but there is a repeating pattern such that the PP interval surrounding the QRS complex is slightly shorter (↔, 0.80 sec) than the PP interval without a QRS complex (└┘, 0.96 sec). This is called ventriculophasic arrhythmia. Proposed mechanisms include enhanced sinus node artery pulsatile blood flow with ventricular contraction that increased the automaticity of the sinus node, stretch of the right atrium and sinus node with ventricular contraction that augments sinus node automaticity, and changes in baroreceptor output resulting from the stroke volume caused by ventricular contraction.FootnotesCorrespondence to Philip J. Podrid, MD, West Roxbury VA Hospital, Section of Cardiology, 1400 VFW Pkwy, West Roxbury, MA 02132. E-mail [email protected] Previous Back to top Next FiguresReferencesRelatedDetails October 1, 2013Vol 128, Issue 14 Advertisement Article InformationMetrics © 2013 American Heart Association, Inc.https://doi.org/10.1161/CIRCULATIONAHA.113.005949PMID: 24081954 Originally publishedOctober 1, 2013 PDF download Advertisement

Experimental protection and revival of quantum correlation in open solid systems

Quantum correlation quantified by quantum discord has been demonstrated experimentally as important physical resources in quantum computation and communication for some cases even without the presence of entanglement. However, since the interaction between the quantum system and the noisy environment is inevitable, it is essential to protect quantum correlation from lost in the environment and to characterize its dynamical behavior in the real open systems. Here we showed experimentally in the solid-state P:Si system the existence of a stable interval for the quantum correlation in the beginning until a critical time $t_c \approx 166$ ns of the transition from classical to quantum decoherence. To protect the quantum correlation, we achieved the extension of the critical time by 50 times to $8 \mu$s by applying a two-flip dynamical decoupling (DD) pulse sequence. Moreover, we observed the phenomenon of the revival of quantum correlation, as well as classical correlation. The experimental observation of a non-decay interval for quantum correlation and the great extension of it in an important solid-state system with genuine noise makes the use quantum discord as physical resources in quantum information processing more practicable.

ECG Response: August 20, 2013

HomeCirculationVol. 128, No. 8ECG Response: August 20, 2013 Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBECG Response: August 20, 2013 Originally published20 Aug 2013https://doi.org/10.1161/CIRCULATIONAHA.113.005120Circulation. 2013;128:869ECG Challenge: A 67-year-old man recently underwent radical neck surgery for pharyngeal cancer. Three days later, he developed severe muscle twitching and spasms and sharp chest pain. An ECG was obtained.The rhythm is regular at a rate of 78 bpm. There is a P wave (+) before each QRS complex with a stable PR interval (0.16 second). The P waves are positive in leads I, II, aVF, and V4 through V6. Hence, this is a normal sinus rhythm. The QRS complex duration is normal (0.08 second) and has a normal axis (between 0° and 90°, positive QRS complex in leads I and aVF). The QRS complex has a normal morphology, although there is poor R-wave progression in leads V1 and V2. This is likely a normal variant, although an old anteroseptal myocardial infarction should be considered. The QT/QTc intervals are prolonged (480/540 milliseconds). There are 2 different patterns for QT prolongation. The first is delayed repolarization in which the long-QT interval is the result of a long ST segment (^) and the T wave is normal in duration. This pattern is seen with either hypocalcemia or hypomagnesemia, which results in a prolongation in phase 2 of the action potential and hence a delay in the onset of repolarization. This type of QT prolongation is not associated with any cardiac abnormalities; specifically, it is not associated with torsade des pointes. The second pattern is called prolonged repolarization in which there is a widening of the T wave (prolongation in the T-wave duration). This is often the result of a slow efflux of potassium during phase 3 of the action potential, which prolongs repolarization or the refractoriness of the membrane. This is a long-QT pattern that is associated with the development of torsade des pointes, or a long-QT syndrome. The long-QT interval in this situation may be acquired, a result of therapy with a drug that interferes with the efflux of potassium during repolarization (eg, the class III antiarrhythmic drugs), or congenital, a result of a channelopathy that causes a prolongation in membrane refractoriness. In this ECG, the pattern is one of delayed repolarization as there is a long ST segment (^) and a normal T wave. The patient likely developed hypocalcemia as a result of hypoparathyroidism due to the recent neck surgery.Download figureDownload PowerPoint Previous Back to top Next FiguresReferencesRelatedDetails August 20, 2013Vol 128, Issue 8 Advertisement Article InformationMetrics © 2013 American Heart Association, Inc.https://doi.org/10.1161/CIRCULATIONAHA.113.005120PMID: 23960258 Originally publishedAugust 20, 2013 PDF download Advertisement SubjectsElectrocardiology (ECG)

Interval observers for discrete-time systems

Interval observers are constructed for discrete-time systems. First, time-invariant interval observers are proposed for a family of nonlinear systems. Second, it is shown that, for any time-invariant exponentially stable discrete-time linear system with additive disturbances, time-varying exponentially stable discrete-time interval observers can be constructed. The latter result relies on the design of time-varying changes of coordinates, which transform a linear system into a nonnegative one. Copyright © 2013 John Wiley & Sons, Ltd.

Fault detection based on robust adaptive thresholds: A dynamic interval approach

A dynamic interval approach for the fast computation of robust adaptive thresholds for a class of uncertain linear systems is the subject of this paper. An extension of recent results about the design of stable interval observers for linear systems with additive time-varying zonotopic input bounds is proposed. It allows the explicit computation of adaptive thresholds ensuring a guaranteed robustness with respect to structured and bounded disturbances which can be not only additive but also multiplicative. Moreover, the constant term (center) of the uncertain time-varying state matrix need not be diagonalizable thanks to results based on a Jordan decomposition. A sufficient condition not only ensuring the stability of the initial uncertain model but also the nondivergence of the computed adaptive thresholds is given. A numerical example dealing with fault detection in an electrical drive illustrates the proposed scheme.

Nonlinear predictive control for maximization of CO2 bio-fixation by microalgae in a photobioreactor

In the framework of environment preservation, microalgae biotechnology appears as a promising alternative for CO₂ mitigation. Advanced control strategies can be further developed to maximize biomass productivity, by maintaining these microorganisms in bioreactors at optimal operating conditions. This article proposes the implementation of Nonlinear Predictive Control combined with an on-line estimation of the biomass concentration, using dissolved carbon dioxide concentration measurements. First, optimal culture conditions are determined so that biomass productivity is maximized. To cope with the lack of on-line biomass concentration measurements, an interval observer for biomass concentration estimation is built and described. This estimator provides a stable accurate interval for the state trajectory and is further included in a nonlinear model predictive control framework that regulates the biomass concentration at its optimal value. The proposed methodology is applied to cultures of the microalgae Chlorella vulgaris in a laboratory-scale continuous photobioreactor. Performance and robustness of the proposed control strategy are assessed through experimental results.

Inexact two-stage stochastic credibility constrained programming for water quality management

In this study, an inexact two-stage stochastic credibility constrained programming (ITSCCP) method is developed and applied to the water quality management system. It incorporates the credibility constrained programming, two-stage stochastic programming and interval programming within an optimization framework, so that uncertainties expressed as intervals, probabilistic and possibilistic distributions can be effectively communicated. The study area is the Xiangxi River Basin of the Three Gorges Reservoir (TGR), the largest reservoir in China. The significant advantage of the ITSCCP water quality management model is that it can reflect the tradeoffs between the predefined economic targets and the associated environmental penalties, as well as the fuzziness of the pollution load capacities. Stable interval solutions can be obtained by using the two-step interactive solution algorithm. A spectrum of potential pollution abatement options with varied levels of system-failure risk can be generated. The resulting solutions show that the proposed method can provide scientific bases for water quality management and other environmental systems problems.

Analysis and Evaluation on Compaction Property of Energy-Saving and Environment-Protecting Road Material

The paper uses a new energy-saving and environment-protecting road material. On the basis of comparative analysis with the road all performance of hot mix asphalt SBS modified asphalt mixture, focuses on the compaction property at the new material lower construction temperature. The results show that the energy-saving and environment-protecting road material can effectively guarantee the performance of asphalt mixture and asphalt pavement after construction temperature is lower 30°C, forming a stable compaction interval and extend the construction time. Also can reduce the emissions of harmful gases on asphalt mixing and construction process, to save energy and protect environment.

A Cholinergic Mechanism for Reward Timing within Primary Visual Cortex

Neurons in rodent primary visual cortex (V1) relate operantly conditioned stimulus-reward intervals with modulated patterns of spiking output, but little is known about the locus or mechanism of this plasticity. Here we show that cholinergic basal forebrain projections to V1 are necessary for the neural acquisition, but not the expression, of reward timing in the visual cortex of awake, behaving animals. We then mimic reward timing invitro by pairing white matter stimulation with muscarinic receptor activation at a fixed interval and show that this protocol results in the prolongation of electrically evoked spike train durations out to the conditioned interval. Together, these data suggest that V1 possesses the circuitry and plasticity to support reward time prediction learning and the cholinergic system serves as an important reinforcement signal which, invivo, conveys to the cortex the outcome of behavior.

Stable Interval Observers in ${\BBC}$ for Linear Systems With Time-Varying Input Bounds

This technical note deals with the design of stable interval observers and estimators for continuous-time linear dynamic systems under uncertain initial states and uncertain inputs enclosed within time-varying zonotopic bounds. No monotony assumption such as cooperativity is required in the vector field: the interval observer stability directly derives from the stability of the observer state matrix, where any poles (real or complex, single or multiple) are handled in the same way.

Ideal ballooning modes, shear flow and the stable continuum

There is a well-established theory of ballooning modes in a toroidal plasma. The cornerstone of this is a local eigenvalue λ on each magnetic surface—which also depends on the ballooning phase angle k. In stationary plasmas, λ(k) is required only near its maximum, but in rotating plasmas its average over k is required. Unfortunately in many cases λ(k) does not exist for some range of k, because the spectrum there contains only a stable continuum. This limits the application of the theory, and raises the important question of whether this ‘stable interval’ gives rise to significant damping. This question is re-examined using a new, simplified, model—which leads to the conclusion that there is no appreciable damping at small shear flow. In particular, therefore, a small shear flow should not affect ballooning mode stability boundaries.

Reference Intervals for and Validation of Recalibrated Immunoassays for Trypsinogen-1 and Trypsinogen-2

To the Editor: Serum trypsinogen assays are used as diagnostic and prognostic tools for cystic fibrosis and acute pancreatitis (AP) (1, 2). Calibrator stability is a challenge in these assays, because trypsinogen readily autoactivates and subsequently autodegrades. Furthermore, the reference intervals described thus far have been based on samples from a limited number of individuals (1, 3). We recalibrated a new immunoassay for trypsinogen-2 and a previously described assay for trypsinogen-1 (1) with stable calibrators (2, 4) and report reference intervals for these 2 analytes in serum. We have produced new monoclonal antibodies and developed a time-resolved immunofluorometric assay for trypsinogen-2, as previously described (1). Monoclonal antibodies F87–9E6 and F88–8F7 were used as capture antibody and tracer antibody, respectively. To prevent activation, we produced stable mutated (Lys23Gln) trypsinogen-1 and trypsinogen-2 by recombinant technology (2, 4) and used them to recalibrate both the previously described trypsinogen-1 assay (1) and the new trypsinogen-2 assay. In this assay, the calibrators covered the concentration interval of 1.0 to 1000 μg/L, the limit of detection was 0.24 μg/L, and …

A template for reliable assessment of resident operative performance: Assessment intervals, numbers of cases and raters

Operative performance rating (OPR) instruments have been developed to assess operative performance (OP). To guide program implementation, this study determined: 1) Appropriate intervals for OP progress decisions, 2) Number of OPRs and raters required per interval to achieve reproducible results. 21 surgeons rated 897 OPs (3 procedures) by 36 residents. Six-month PGY intervals were compared to determine length of stable operative performance intervals. Variance component analyses established rating factor importance. Generalizability analyses and decision studies determined number of OPRs required for reproducible OP decisions (reliabilities = 0.80). Resident OPRs are stable across single PGY years. 2.3 OPRs/resident/month provided a dependable basis for annual or semi-annual resident OP decisions. Results were similar for all procedures and training years. Rater idiosyncrasies accounted for most score variation (63% when interaction effects involving rater idiosyncrasies were included). Resident ability was the next most important source of variation (12%). Procedure was a less important source (5%). Annual resident OP decisions are supported. 2.3 OPRs per month provide a dependable basis for judging resident OP. These numbers are sufficient regardless of training year or procedure mix though efforts should be made to balance procedure mix. Multiple raters should rate each resident to control for rater idiosyncrasies.

Duration of off-loading and recurrence rate in Charcot osteo-arthropathy treated with less restrictive regimen with removable walker

ObjectiveRecent literature on acute diabetic Charcot osteoarthropathy (CA) reports unusually long periods of off-loading. Data suggest that this might increase the re-currence rate. Subsequently we evaluated the influence of duration of off-loading on the risk of required re-casting. Research Design and MethodsIn this retrospective consecutive series from 2000 to 2005, 56 people with diabetes and an acute Charcot foot were included. The inclusion criteria were an initial persistent temperature difference more than 2°C between the two feet, oedema, and typical hot spots on a bone scintigram, radiology, and a typical clinical course. Treatment was off-loading in a removable cast and 2 crutches. In-door walking was allowed. Gradually augmented weight bearing was prescribed when the skin temperature difference had decreased to a level less than 2°C and edema had subsided. Re-casting was required for immediate exacerbation during re-load as well as for recurrence — defined as new swelling and skin temperature difference of more than 2°C in the same foot occurring after a stable interval of at least one month after full weight bearing. ResultsThe duration of off-loading for all patients was 141±21days (mean±SD). Three patients (5%) were re-casted immediately for exacerbation after re-load and 7 patients (12 %) after recurrence of the CA. Duration of re-casting was 79±44days. The primary period of off-loading was not statistically significantly different for those not requiring versus those requiring re-casting: 142±24days compared to 134±41days. Neither were the differences in demographic data, metabolic regulation, BMI or localization of CA. ConclusionsPatients with risk of exacerbation or recurrence of CA could not be identified in the present study and there was no relation to the duration of off-loading. Nevertheless off-loading periods with immobilisation should be kept as short as possible, due to other side effects. This can be obtained by early gradual augmented re-loading.