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showing 10 items of 7541 documents
Precision of a commercial hartmann-shack aberrometer: limits of total wavefront laser vision correction.
2012
Purpose To assess the intrasession and intersession precision of higher-order aberrations (HOAs) measured using a commercial Hartmann-Shack wavefront sensor (Zywave; Bausch & Lomb) in refractive surgery candidates. Design Prospective, experimental study of a device. Methods To analyze intrasession repeatability, 1 experienced examiner measured 30 healthy eyes 5 times successively. To study intersession reproducibility, the same clinician obtained measurements from another 30 eyes in 2 consecutive sessions at the same time of day 1 week apart. Results For intrasession repeatability, excellent intraclass correlation coefficients (ICCs) were obtained for total ocular aberrations, total HOAs, a…
Neural net classification of REM sleep based on spectral measures as compared to nonlinear measures
2001
In various studies the implementation of nonlinear and nonconventional measures has significantly improved EEG (electroencephalogram) analyses as compared to using conventional parameters alone. A neural network algorithm well approved in our laboratory for the automatic recognition of rapid eye movement (REM) sleep was investigated in this regard. Originally based on a broad range of spectral power inputs, we additionally supplied the nonlinear measures of the largest Lyapunov exponent and correlation dimension as well as the nonconventional stochastic measures of spectral entropy and entropy of amplitudes. No improvement in the detection of REM sleep could be achieved by the inclusion of …
Nonlinear analysis of continuous ECG during sleep II. Dynamical measures
2000
The hypothesis that cardiac rhythms are associated with chaotic dynamics implicating a healthy flexibility has motivated the investigation of continuous ECG with methods of nonlinear system theory. Sleep is known to be associated with modulations of the sympathetic and parasympathetic control of cardiac dynamics. Thus, the differentiation of ECG signals recorded during different sleep stages can serve to determine the usefulness of nonlinear measures in discriminating ECG states in general. For this purpose the following six nonlinear measures were implemented: correlation dimension D2, Lyapunov exponent L1. Kolmogorov entropy K2, as well as three measures derived from the analysis of unsta…
Surrogate data analysis of sleep electroencephalograms reveals evidence for nonlinearity
1996
We tested the hypothesis of whether sleep electroencephalographic (EEG) signals of different time windows (164 s, 82 s, 41 s and 20.5 s) are in accordance with linear stochastic models. For this purpose we analyzed the all-night sleep electroencephalogram of a healthy subject and corresponding Gaussian-rescaled phase randomized surrogates with a battery of five non-linear measures. The following nonlinear measures were implemented: largest Lyapunov exponent L1, correlation dimension D2, and the Green-Savit measures delta 2, delta 4 and delta 6. The hypothesis of linear stochastic data was rejected with high statistical significance. L1 and D2 yielded the most pronounced effects, while the G…
Alterations of Continuous MEG Measures during Mental Activities
2000
In a pilot study, we investigated the topography of 11 continuous MEG measures for the eyes-opened and eyes-closed condition together with three simple mental tasks (mental arithmetic, visual imagery, word generation). One-minute recordings for each condition from 16 right-handed subjects were analyzed. The electrophysiological measures consisted of 6 spectral band measures together with spectral edge frequency and spectral entropy, plus the time-domain-based entropy of amplitudes (ENA) and the nonlinear measures correlation dimension D2 and Lyapunov exponent L1. In summary, our results indicate a pronounced task-dependent difference between the anterior and the posterior region, but no lat…
Optical factors influencing the amplitude of accommodation
2017
AbstractThe purpose of this work was to find plausible predictors among optical parameters that may explain the inter-individual differences in subjective amplitude of accommodation not explained by age. An exploratory multivariable regression analysis was carried out retrospectively on a dataset with 180 eyes from 97 subjects (ages ranged from 20 to 58years). Subjective amplitudes of accommodation were recorded with the use of a custom-made Badal system. A commercial aberrometer was used to obtain each eye’s wavefront during the full range of accommodation. The plausible predictors under study were pupil diameter in the unaccommodated eye, its reduction with accommodation; fourth- and six-…
Deterministic chaos and the first positive Lyapunov exponent: a nonlinear analysis of the human electroencephalogram during sleep
1993
Under selected conditions, nonlinear dynamical systems, which can be described by deterministic models, are able to generate so-called deterministic chaos. In this case the dynamics show a sensitive dependence on initial conditions, which means that different states of a system, being arbitrarily close initially, will become macroscopically separated for sufficiently long times. In this sense, the unpredictability of the EEG might be a basic phenomenon of its chaotic character. Recent investigations of the dimensionality of EEG attractors in phase space have led to the assumption that the EEG can be regarded as a deterministic process which should not be mistaken for simple noise. The calcu…
No association between periodontal disease and GHQ-12 in a Brazilian Police population
2010
Objectives: We attempt to investigate a possible association between periodontal disease (PD) and mental disorders (MD) in a population of Brazilian Police. Study Method: From a total study population consisting of 803 policemen, 345 police officers were obtained by a sample calculation using the finite population correction who were randomly selected in Montes Claros, Minas Gerais, Brazil. Patients who had been prescribed steroids or those diagnosed with diabetes and cardiovascular diseases were excluded from this study. The General Health Questionnaire (GHQ-12) was used to assess mental disorders. Odds ratios (ORs) for periodontal diseases severity and their respective 95% confidence inte…
Reliability and validity of the form 90 interview.
2004
<i>Objective:</i> Alcohol consumption is a central variable in substance abuse research and treatment. The study reports the psychometric characteristics of the German version of the Form 90 interview for the assessment of recent alcohol consumption. <i>Method:</i> Reliability was evaluated in a test-retest study (7 days) with 30 consecutively admitted psychiatric inpatients with alcohol dependence. Validity of Form 90 was assessed with a second sample of 60 alcohol-dependent inpatients. <i>Results:</i> Form 90 demonstrated good to excellent retest reliability for the central variables of alcohol consumption. Retest reliability Pearson correlation coeffic…
Inverse Effects of Midlife Occupational and Leisure Time Physical Activity on Mobility Limitation in Old Age-A 28-Year Prospective Follow-Up Study
2014
Objectives: To evaluate in a sample of initially middle-aged municipal employees whether leisure time (LPA) or occupational physical activity (OPA) was associated with mobility limitation (ML) in old age. Design: Prospective population-based follow-up. Setting: Municipalities in Finland. Participants: Public sector employees from the Finnish Longitudinal Study on Municipal Employees (FLAME) initially aged 44 to 58 (N = 5,200). Measurements: Baseline data were collected in 1981, including LPA (average exercise within previous year: inactive (no exercise), moderate (some form of exercise ?1 time per week), vigorous (brisk exercise ?1 time per week)) and OPA (usual activities at work within pr…