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G A Bekey

Publications and source records attributed to G A Bekey.

8 recordsLinked to original sources
PubMed2001

Winds of change.

Explore the source record for details and available documents.

Artificial Intelligence↗
PubMed1982

Optimal inputs for parameter determination of inert gas washout from the lung.

The nitrogen washout test will yield more information about the distribution of pulmonary ventilation if a pattern of inspired gas concentrations is utilized other than the standard series of 100% oxygen breaths. The input breathing pattern which yields optimal results will vary with the specific features of the lung being studied but typically includes breaths of air, particularly in the last third of the washout. Using computerized, mathematical techniques, optimal inputs were selected for washout tests of duration 10, 20, 30 and 40 breaths for each of six lung models, ranging from a unicompartmental to a highly non-uniform 'diseased' lung. Knowing these optimal inputs we were able to devise a nominal input which was similar to the optimal inputs for all models. For a 10 breath test this nominal input pattern utilized a breath of air at breath 7. For a 20 breath test, air is utilized at breaths 12, 14, 15, 19; for 30, air at 19, 21, 22, 23, 29 and for a 40-breath test, air at breaths 19, 24, 28, 30, 31, 32 and 39. The 30-breath nominal sequence was compared with the conventional oxygen-only washout and a 31-breath pseudo-random binary (PRB) input. Comparisons were made using computer simulated washouts as well as actual tests on human subjects. The 30-breath nominal input was always superior to the standard washout and was superior to the PRB input for all models except the lung ventilated with vital capacity breaths. We conclude that a significant advantage is gained by substituting the recommended sequences of breaths in studies of the dynamics of gas exchange in the lung.

Humans↗
PubMed1981

EMG-force relationships in skeletal muscle.

This article reviews the history of attempts to define in quantitative terms the relationship between a processed electromyographic signal and the corresponding force produced by skeletal muscle. Numerous reports have indicated a linear relationship between isometric force and rectified, integrated EMG. These reports, the nature of their experiments, and the disagreements among them are reviewed. Particular attention is given to the effects of the signal processing in the final results, including type and location of electrodes, amplification, signal isolation, etc. The effect of joint position and level of muscular effort in the isometric case are discussed. Various proposed mathematical models of the force-EMG relationship are presented and analyzed. The concluding section of the paper summarizes the current areas of agreement and disagreement and comments on the feasibility of obtaining force-EMG relation in the presence of movement.

Animals↗
PubMed1980

Analysis of errors in parameter estimation with application to physiological systems.

The accuracy of parameter estimation applied to physiological systems is analyzed. The method of analysis is applicable to procedures utilizing minimization of squared output error and a nonlinear dynamic system model. Three major sources of estimation error are described: 1) measurement error, 2) modeling error, and 3) optimization error. Measurement errors affect values used for the system output, the model input, and nonestimated parameters of the model. Modeling errors are due to failure to adequately describe the structure of the system and to numerical errors that occur in the digital computer solution of the model equations. Linearization by use of Taylor series expansions in the region of the nominal solution is used to obtain an expression for the covariance matrix of the parameter estimates in terms of the covariance matrix of each error source. The analysis is applied to the example of cardiac output estimation from respiratory measurements. The results demonstrate that an analysis of system identifiability is not sufficient to ensure usable estimates and that systematic error analysis is essential for assessing the usefulness of parameter estimation techniques.

Cardiac Output↗