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Biomedical subjects

E Ott

Publications and source records attributed to E Ott.

At least 19 recordsLinked to original sources
PubMed2000

Testing whether two chaotic one dimensional processes are dynamically identical

Consider the situation where two individuals observe the same chaotic physical process but through time series of different measured variables (e.g., one individual measures a temperature and the other measures a voltage). If the two individuals now use their data to reconstruct (e.g., via delay coordinates) a map, the maps they obtain may appear quite different. In the case where the resulting maps appear one dimensional, we introduce a method to test consistency with the hypothesis that they represent the same physical process. We illustrate this method using experimental data from an electric circuit.

Journal Article↗
PubMed2000

Measurement of wave chaotic eigenfunctions in the time-reversal symmetry-breaking crossover regime

We present experimental results on eigenfunctions of a wave chaotic system in the continuous crossover regime between time-reversal symmetric and time-reversal symmetry-broken states. The statistical properties of the eigenfunctions of a two-dimensional microwave resonator are analyzed as a function of an experimentally determined time-reversal symmetry-breaking parameter. We test four theories of one-point eigenfunction statistics and introduce a new theory relating the one-point and two-point statistical properties in the crossover regime. We also find a universal correlation between the one-point and two-point statistical parameters for the crossover eigenfunctions.

Journal Article↗
PubMed2000

Lagrangian chaos and the effect of drag on the enstrophy cascade in two-dimensional turbulence

We investigate the effect of drag force on the enstrophy cascade of two-dimensional Navier-Stokes turbulence. We find a power law decrease of the energy wave number (k) spectrum that is faster than the classical (no-drag) prediction of k(-3). It is shown that the enstrophy cascade with drag can be analyzed by making use of a previous theory for finite lifetime passive scalars advected by a Lagrangian chaotic fluid flow. Using this we relate the power law exponent of the energy wave number spectrum to the distribution of finite time Lyapunov exponents and the drag coefficient.

Journal Article↗
PubMed2000

The Bradykinesia Akinesia Incoordination Test (BRAIN TEST), an objective and user-friendly means to evaluate patients with parkinsonism.

The BRAIN TEST, a computerized alternating finger tapping test, was performed on 154 patients with parkinsonism to assess whether the test could be used as an objective tool to evaluate reliably the severity of Parkinson's disease (PD). Patients were instructed to tap two marked computer keyboard keys as fast and as accurately as possible for 60 seconds. The test generates the following variables: (1) kinesia score (KS)--number of keystrokes/min, (2) akinesia time (AT)--cumulative time that keys are depressed, (3) dysmetria score (DS)--a weighted score generated from incorrectly hit keys and corrected for speed, and (4) arrhythmia score (AS)--variance of the time interval between individual keystrokes. Among parkinsonian patients, we found a significant correlation between the four test parameters and PD rating scores of the Hoehn & Yahr, Schwab & England, and Unified PD Rating Scales (KS, AS, and AT p <0.001 and DS p <0.05). When compared with 73 parkinsonian patients 73 age- and sex-matched control subjects showed significantly higher KS and lower AT (p <0.001) as well as lower DS and AS (p = 0.05). The BRAIN TEST is a reliable and practical tool for evaluating the severity of parkinsonism and for distinguishing subjects with parkinsonism from normal control subjects. A version of the BRAIN TEST is available by FTP on the worldwide web (http://www.anaesthetist.com/software/brain.htm).

Adult↗
PubMed2000

Spiral wave dynamics in oscillatory inhomogeneous media.

The effect of a long length scale static inhomogeneity on spiral wave dynamics is studied in the two-dimensional complex Ginzburg-Landau equation. We find that the inhomogeneity leads to the formation of a dominant spiral domain that suppresses other spiral domains, and that the spiral vortices slowly drift in the presence of an inhomogeneity with a velocity that is proportional to the local parameter gradients. We derive an expression for the spiral vortex drift velocity and present examples of both fixed point and limit cycle attractors of the spiral vortices.

Kinetics↗
PubMed2000

Optimal periodic orbits of continuous time chaotic systems

In previous work [B. R. Hunt and E. Ott, Phys. Rev. Lett. 76, 2254 (1996); Phys. Rev. E 54, 328, (1996)], based on numerical experiments and analysis, it was conjectured that the optimal orbit selected from all possible orbits on a chaotic attractor is "typically" a periodic orbit of low period. By an optimal orbit we mean the orbit that yields the largest value of a time average of a given smooth "performance" function of the system state. Thus optimality is defined with respect to the given performance function. (The study of optimal orbits is of interest in at least three contexts: controlling chaos, embedding of low-dimensional attractors of high-dimensional dynamical systems in low-dimensional measurement spaces, and bubbling bifurcations of synchronized chaotic systems.) Here we extend this previous work. In particular, the previous work was for discrete time dynamical systems, and here we shall consider continuous time systems (flows). An essential difference for flows is that chaotic attractors can have embedded within them, not only unstable periodic orbits, but also unstable steady states, and we find that optimality can often occur on steady states. We also shed further light on the sense in which optimality is "typically" achieved at low period. In particular, we find that, as a system parameter is tuned to be closer to a crisis of the chaotic attractor, optimality may occur at higher period.

Journal Article↗
PubMed2000

Target waves in the complex ginzburg-landau equation

We introduce a spatially localized inhomogeneity into the two-dimensional complex Ginzburg-Landau equation. We observe that this can produce two types of target wave patterns: stationary and breathing. In both cases, far from the target center, the field variables correspond to an outward propagating periodic traveling wave. In the breathing case, however, the region in the vicinity of the target center experiences a periodic temporal modulation at a frequency, in addition to that of the wave frequency of the faraway outward waves. Thus at a fixed point near the target, the breathing case yields a quasiperiodic time variation of the field. We investigate the transition between stationary and breathing targets, and note the existence of hysteresis. We also discuss the competition between the two types of target waves and spiral waves.

Journal Article↗
PubMed1998

Induction of anesthesia by titration of eltanolone compared with thiopental and etomidate for coronary artery bypass grafting.

STUDY OBJECTIVE: To evaluate whether induction of anesthesia with eltanolone in coronary artery bypass graft (CABG) patients is associated with greater hemodynamic stability than either thiopental sodium or etomidate. DESIGN: Randomized, controlled study. SETTING: University hospital. PATIENTS: 75 ASA physical status III and IV patients scheduled for elective CABG over 18 years of age, with left ventricular ejection fraction over 30%. INTERVENTIONS: The participants were prospectively randomized into three groups, each group consisting of 25 patients. Anesthesia was induced by titration of either eltanolone, thiopental sodium, or etomidate. The end point was "loss of verbal contact." MEASUREMENTS AND MAIN RESULTS: Hemodynamic variables were recorded in the awake state, 2 minutes after induction, after administration of fentanyl 0.01 mg/kg, and 2 and 5 minutes after intubation. After induction of anesthesia, cardiac index (CI) decreased from 2.6 +/- 0.5 to 2.2 +/- 0.5 Lxmin-1xm-2 in the eltanolone group and remained at this value throughout the study period in contrast to the control groups. After fentanyl was given, mean arterial pressure was significantly lower in the case of eltanolone (69 +/- 15 mmHg) compared with thiopental (81 +/- 19 mmHg) and etomidate (84 +/- 18 mmHg). Mean arterial pressure remained significantly lower at the points of measurement after intubation. Two minutes after intubation, CI was likewise significantly lower in the eltanolone group (2.2 +/- 0.4 Lxmin-1xm-2) compared with the thiopental group (2.7 +/- 0.7 Lxmin-1xm-2). CONCLUSIONS: Eltanolone produces more hemodynamic depression compared with etomidate and thiopental when administered in combination with fentanyl 10 micrograms/kg.

Aged↗
PubMed1997

[Evaluation of vascular risk factors in patients with Parkinson syndrome].

A vascular etiology of Parkinson's disease (PD) has been long debated. In order to search for an ischemic basis of PD we assessed the clinical symptomatology of a consecutive group of 60 PD patients and compared their frequency of cerebrovascular risk factors, carotid atherosclerosis and ischemic brain lesions with age-matched groups of stroke patients and normals. There were 16 (27%) subjects with PD who also had symptoms of cerebrovascular disease. The frequencies of carotid stenoses, ischemic brain lesions and most of cerebrovascular risk factors seen in the latter group was comparable with those of stroke patients and significantly higher than in the investigational subsets of patients with "pure" PD and normals. Only one (1.6%) individual with PD presented signs suggestive of an ischemic etiology of parkinsonism. These findings suggest that cerebrovascular disease occurs in approximately one fourth of patients with PD, but seldomly is causally related.

Aged↗
PubMed1997

Bolus administration of eltanolone, thiopental, or etomidate does not affect systemic vascular resistance during cardiopulmonary bypass.

OBJECTIVE: To discover possible effects on systemic vascular resistance of the anesthetic induction agent eltanolone in comparison with thiopental and etomidate. The measurements were performed during cardiopulmonary bypass to maintain a constant cardiac output (approximately pump flow). DESIGN: The patients were prospectively randomized in three groups to receive either eltanolone, thiopental, or etomidate. SETTING: University hospital as a single center. PARTICIPANTS: Seventy-five patients scheduled for elective coronary artery bypass grafting. INTERVENTIONS: The anesthetic induction agents were repeated at the same dosage when cardiopulmonary bypass was instituted. The respective mean dosages were eltanolone, 0.41 +/- 0.1 mg/kg; thiopental, 2.88 +/- 0.62 mg/kg; etomidate, 0.26 +/- 0.06 mg/kg. MEASUREMENTS AND MAIN RESULTS: Systemic vascular resistance was calculated from the mean of a triple measurement (normal pump flow and +/- 20%). Points of measurement were before, and 2 and 5 minutes after injection of the hypnotic agent. None of the injected drugs made a significant change in the systemic vascular resistance. A small (not significant) decrease from 1,295 +/- 296 dyne/s/cm-5 to 1,196 +/- 323 dyne/s/cm-5 (mean +/- SD) was seen in the eltanolone group, whereas the other patients did not show any change during the study period. CONCLUSIONS: The reason for the significant reduction of the arterial pressure attributed to anesthetic induction by eltanolone may be more a cardiodepressive effect than a direct vasodilation.

Anesthetics, Intravenous↗
PubMed1997

Radiosurgical lesioning of the caudate nucleus as a treatment for parkinsonism: a preliminary report.

In ten patients with parkinsonism a radiosurgical operation with the Gamma Knife was performed in which a small lesion was created in the head of the caudate nucleus bilaterally. Preoperatively, in all cases bradykinesia was the main complaint and in all patients conventional drug treatment no longer resulted in a satisfactory response. After a follow-up period of one month six patients showed clear benefit. There was no complication or side effect that could be related to this form of treatment. Pre- and post-operative testing was performed with the Unified Parkinson Rating Scale and with objective motor tasks. The main improvement seen concerned bradykinesia and rigidity: tremor was ameliorated to a lesser extent. Possible mechanisms underlying the improved motor function are discussed as well as the role of lesioning of the striatum in light of transplantation neurosurgery.

Aged↗
PubMed1996

[Awakening from anesthesia and recovery of cognitive function after desflurane or isoflurane].

UNLABELLED: Desflurane is a new volatile anaesthetic with an extremely low blood/gas partition coefficient of 0.42. This should provide a rapid recovery from anaesthesia. METHODS: We studied 100 adult patients, ASA class I or II, undergoing elective orthopaedic surgery randomly assigned to anaesthesia with desflurane (n = 50) or isoflurane (n = 50) supplemented by nitrous oxide in oxygen. Clorazepat was given for premedication, fentanyl and thiopental for induction of anaesthesia, followed by maintenance with desflurane or isoflurane as clinically appropriate. Emergence from anaesthesia was measured as well as return of cognitive functions (extended Aldrete score, digit symbol substitution test, and visual analogue scales [VAS]). RESULTS: While the demographic characteristics and administrated doses of fentanyl and thiopental were comparable, the recovery profiles in both groups were different. After discontinuation of the volatile anaesthetics, times to extubation and ability to follow simple commands were significantly shorter after desflurane than after isoflurane. Extended Aldrete scores, estimation of the patients' physical condition, results of the digit symbol substitution test, measuring cognitive functions, and rates of drowsiness and weakness on VAS showed better recovery with less impairment of cognitive function in the desflurane group than in isoflurane patients even 120 min after anaesthesia. VAS pain scores and doses of analgesic drugs given within the first 2 postoperative hours, however, showed no significant differences. Desflurane patients were also judged fit for discharge from the recovery room significantly faster. CONCLUSIONS: Our results demonstrate that desflurane anaesthesia, even when supplemented by premedication, intraoperative opioids, and nitrous oxide may offer clinical advantages over isoflurane as far as the post-anaesthetic recovery profile is concerned.

Adult↗