Biomedical subjects

S Gergely

Publications and source records attributed to S Gergely.

6 recordsLinked to original sources

PubMed1989

Determination of myocardial depolarization and repolarization times using the unipolar ventricular evoked potential: contrasting effects of stimulus interval and isoprenaline in the isolated perfused rabbit heart.

The effects of changes in stimulus interval and the infusion of isoprenaline upon myocardial depolarization and repolarization times have been determined using the unipolar ventricular evoked potential. An isolated perfused rabbit heart was the experimental vehicle and the stimulus-to-R wave (St-R) and R wave-to-end (R-E) of complex time intervals were used as measures of depolarization and repolarization times, respectively. Variation in the stimulus interval was shown to have highly statistically significant effects upon both of the parameters of the unipolar paced evoked potential that were investigated. Myocardial repolarization time is increased at longer intervals, while activation time is reduced. Isoprenaline was found to reduce the duration of the R-E interval of the unipolar ventricular evoked potential when infused at a constant rate at a fixed stimulus interval. At the maximum concentration of the drug, when stimulus interval was just shorter than the intrinsic RR interval, it was estimated that one third of the total change in the R-E interval was due purely to the effects of decreased stimulus interval. It proved impossible to identify any effect of isoprenaline infusion upon the St-R interval. The absence of any effect of isoprenaline on the St-R interval of the evoked potential suggests that it may serve as a monitor of purely stimulus interval dependent variations of the signal.

Animals↗

PubMed1988

The ventricular intracardiac unipolar paced-evoked potential in an isolated animal heart.

The endocardial unipolar paced evoked response has excited a great deal of interest due to its possible use in the measurement of the metabolic state of the body and other pacer-related areas. Although rate-responsive pacing utilizing this signal has been clinically evaluated, little is known regarding the behavior of the components of this waveform under normal physiological conditions. We have developed an electronic circuit which allows the recording of the evoked response within a few milliseconds of a pacing stimulus of 5 V and 0.5 ms duration being applied using a single unipolar, smooth platinum electrode of 14 mm2 surface area. The paced evoked response was measured using a total of 20 isolated rabbit heart preparations. Five were run for 8 hours and the remaining fifteen were run for 5 hours. Our results indicate that the waveform components of the evoked response remain stable while the preparation is viable, but that two of the time-related measurements change with loss of viability. A significant lengthening of the stimulus-R interval was seen together with a dramatic shortening of the R-T period. The net result of these changes was an overall reduction of 17% in the complex duration. In addition, we found the R-T shortening to be a sensitive measure of myocardial integrity. We conclude that the combination of our interface charge elimination circuit and the isolated heart preparation has proved a useful system for the investigation of the paced evoked potential. Furthermore, the loss of myocardial viability has a complex action on this response.

Animals↗

PubMed1987

Platinum pacemaker electrodes: origins and effects of the electrode-tissue interface impedance.

Investigation of the unipolar properties of the paced-evoked response requires special measures to eliminate the post-stimulus potential, and this in turn requires a knowledge of the properties of the electrode-tissue interface which is not supplied by any single source in the literature. We have therefore drawn together published information and some of our own experimental results. The behavior of a particular type of pacemaker electrode was investigated in vitro under a range of conditions. The application of DC potentials revealed an extremely nonlinear voltage-current characteristic with conduction thresholds at about +1 V and -1 V. Small signal AC response to applied voltages well within these values (20 mV pk-pk) was found to be linear when a nonpolarizable counterelectrode was used. Nonlinearities were introduced by the use of a stainless steel counterelectrode. The response of an in vitro model of a paced patient to voltage pulses (amplitude 5 V, duration 0.5 ms) was also investigated. We have made extensive use of previously published work to demonstrate the mechanisms underlying these results and also their relationship to each other. We have concluded with some theoretical comments upon the design requirements for a device to eliminate the post-stimulus afterpotential in order to detect the paced-evoked response.

Electric Conductivity↗

PubMed1979

A BSc level option in biomedical electronics.

1. The application of electronic instruments in medical diagnosis and therapy is well established. 2. There is a demand for electronic engineers both in industry and in the Health Service at all ranges of educational attainment. 3. It is possible to identify a set of objectives for a first degree course in Biomedical Electronics. An important element of this course should be the provision of practical experience in industry and in hospitals. 4. Such courses are available both in Europe and in the United States. Although the postgraduate course provision was satisfactory in the UK in the early seventies, only one full time undergraduate course was in operation. 5. A sandwich course can be designed in Biomedical Electronics as a major option of an existing BSc course in Electrical and Electronic Engineering. Provision can be made for entering and leaving the option. The option can be arranged to follow the guidelines laid down by the IEE for exemption from its educational requirements. 6. The option described started at the Lanchester Polytechnic in Coventry in September 1977.

Electronics, Medical↗

PubMed1977

A microprocessor controlled multi-channel evoked potential data acquisition system.

A stored program control system is described for the acquisition of evoked potential (EP) data. It is a small, portable and flexible system with a variety of input and output possibilities. The system presents a low cost solution to the problem of acquisition of evoked potential data. A novel method of converting and reducing sixteen channels of EEG analogue data to their digital equivalent is shown. It is adaptable for the inter active control of experiments and is sophisticated enough to deal with the complexities of experimental control as well as data manipulation. One of the major advantages of the system is that both the sequencing of the functions and their detailed make-up can be readily altered by programming to meet the individual requirements of any given situation.

Analog-Digital Conversion↗

PubMed1975

Delayed signal EEG trigger.

Long EEG recordings are often necessary to capture the signals in the short period just before an epileptic attack. This procedure has many disadvantages. The equipment described below enables only the signals of interest to be recorded. It is designed to operate in conjunction with a commercial electroencephalograph and consists of a signal store with a programmable series of logic gates for sensing the onset of an epileptic discharge and activating the chart recorder. The particular system described has a signal bandwidth of d.c. to 25 Hz in all 16 channels, and, because of their particular clinical diagnostic importance, all signals for the 20 seconds immediately preceding the discharge are recorded. The recording can take place for up to one hour after the attack and, if a second attack should occur, it can also be recorded similarly to the first one.

Computers↗