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Biomedical subjects

G F Inbar

Publications and source records attributed to G F Inbar.

At least 19 recordsLinked to original sources
PubMed1992

Simulation method for cardiac stroke volume estimation by intracardiac electrical impedance measurement.

Using the electrical impedance measurement technique to investigate stroke volume estimation, three models of the ventricle were simulated. A four-electrode impedance catheter was used; two electrodes to set up an electric field in the model and the other two to measure the potential difference. A new approach, itself an application of the quasi-static case of a method used to solve electromagnetic field problems, was used to solve the electric field in the model. The behaviour of the estimation is examined with respect to the electrode configuration on the catheter and to catheter location with respect to the ventricle walls. Cardiac stroke volume estimation was found to be robust to catheter location generating a 10 per cent error for an offset of 40 per cent of the catheter from the chamber axis and rotation of 20 degrees with respect to the axis. The electrode configuration has a dominant effect on the sensitivity and accuracy of the estimation. Certain configurations gave high accuracy, whereas in others high sensitivity was found with lower accuracy. This led to the conclusion that the electrode configuration should be carefully chosen according to the desired criteria.

Electric Impedance↗
PubMed1991

Walking cycle recording and analysis for FNS-assisted paraplegic walking.

In closed-loop functional neuromuscular stimulation (FNS)-assisted paraplegic walking, there is a need for reference leg motion trajectories that describe the desired walking cycle. These reference trajectories were defined as the angular changes between the leg segments, as measured by an electrogoniometer system. For each leg, the hip, knee and ankle trajectories of normal individuals during slow walking were measured and sampled over a number of cycles. Additionally, foot contact with the ground was measured to synchronise the various walking trajectories. Each joint's angular trajectory was averaged over a number of walking cycles, using an interpolation method based on a discrete Fourier transform (DFT) and inverse DFT technique, to expand all the signals to the same length. In this way an average walking cycle was obtained for each trial, representing the six averaged leg motion trajectories for one walking cycle. Angular trajectories and walking parameters for slow and normal walking were compared so as to investigate principles of walking cycle adaptation necessary to stabilise the body during slow walking. In general, angular trajectories were similar for different subjects, but different for different walking speeds, due to the greater demands on maintaining stability during slow walking. It can be concluded that normal speed walking consists of separate, unstable phases, whereas slow speed walking, relevant for paraplegic walking, requires stabilising each separate phase of the walking cycle.

Ankle Joint↗
PubMed1989

The role of short-term visuo-spatial memory in control of rapid multi-joint prehensive movements.

How memorized visuo-spatial information influences motor control and whether this information is able to replace the feedback processing in cases of visual deprivation was studied using an unrestrained finger- and hand-movement paradigm. Nineteen right-handed subjects were asked to grasp and lift a small block with the index finger and thumb of the right hand, as quickly as possible. The efficiency of motor performance was analysed by measuring the grasping time derived from tangential velocity profiles of the fingertips. The data revealed significantly shorter grasping times under continuous visual guidance than during blind grasping. Grasping times increased under conditions with stepwise prolongation of visual deprivation time prior to the movement onset. The results support the general concept that within the first seconds of visual deprivation, stored visuo-spatial information can partly compensate for the lack of continuous visual feedback.

Adult↗
PubMed1985

Relation between electromyogram and force in fatigue.

The relationship between the surface electromyogram (SEMG) and force was examined during maximal voluntary contraction (MVC). Isometric MVC of elbow flexors were studied in 18 subjects who performed 27 trials, each consisting of six MVCs lasting 45 s at intervals of 30 s. There was a decrease in the median frequency (Fm) of the SEMG and of the compound action potentials (CAP) during MVC. The CAPs demonstrated that the fall in Fm was associated with a proportional increase in signal power, whereas CAP amplitude did not decrease, indicating intact neuromuscular transmission. The SEMG root-mean-square amplitude remained fairly constant, progressively deviating from force with time of contraction (r = 0.40). When SEMG amplitude was corrected for the Fm change, it tracked force more closely (r = 0.68), indicating a fall in motoneuron drive during MVC. The corrected SEMG was used to calculate the change in the generalized firing rate of motoneurons. The firing rate decreased 60% in the first and sixth contractions, tracked force closely, and corresponded to the firing rate fall seen in late adaptation of motoneurons (r = 0.90, P less than 0.001).

Action Potentials↗
PubMed1978

Physiological model analysis of involuntary human-voice tremor.

Frequency variations in the human voice result from voluntary and involuntary changes in the parameters of the vocal system. The present work deals with involuntary frequency perturbations from two theoretical aspects: 1) the influence of pitch period variations on frequency changes in the band-limited signal which results from the resonant characteristics of the vocal tract; 2) the physiological parameters of the vocal system which are potentially able to govern involuntary frequency changes. It is shown that the modulation function of the vocal-cord wave can theoretically be derived from its harmonics using FM demodulation techniques, and that higher distortion may appear at higher harmonics. It is also shown that involuntary geometirical changes of the vocal tract and its terminal impedance as well as tension and initial-area changes of the vocal cord--changes well within the physiological range--can influence frequency changes in the human voice. The present results are correlated with our reported experimental findings on involuntary voice tremor, used in psychological stress evaluation. The role of the central nervous system, and possible mechanisms for these phenomena, are discussed.

Humans↗