LOW FREQUENCY MAGNETIC FIELDS INSIDE CARS.

Magnetic fields were compared inside passenger seats of electric, petrol and hybrid cars. While driving about 5 km in an urban environment, values were recorded and compared between car types. The magnetic flux densities of the cars were less than 2.6 µT. The magnitudes of the magnetic fields of petrol cars and hybrid cars were about the same and slightly lower for electric cars. Based on our measurements, values were less than 3% of the guidelines given for the general population or people using pacemakers.

Effects of tissue conductivity and electrode area on internal electric fields in a numerical human model for ELF contact current exposures.

Contact currents flow through the human body when a conducting object with different potential is touched. There are limited reports on numerical dosimetry for contact current exposure compared with electromagnetic field exposures. In this study, using an anatomical human adult male model, we performed numerical calculation of internal electric fields resulting from 60 Hz contact current flowing from the left hand to the left foot as a basis case. Next, we performed a variety of similar calculations with varying tissue conductivity and contact area, and compared the results with the basis case. We found that very low conductivity of skin and a small electrode size enhanced the internal fields in the muscle, subcutaneous fat and skin close to the contact region. The 99th percentile value of the fields in a particular tissue type did not reliably account for these fields near the electrode. In the arm and leg, the internal fields for the muscle anisotropy were identical to those in the isotropy case using a conductivity value longitudinal to the muscle fibre. Furthermore, the internal fields in the tissues abreast of the joints such as the wrist and the elbow, including low conductivity tissues, as well as the electrode contact region, exceeded the ICNIRP basic restriction for the general public with contact current as the reference level value.

Effect of power frequency harmonics on magnetic field measurements.

This paper presents a study of the effect of harmonic frequencies on magnetic field measurements. We introduced magnetic field meters in a known magnetic field of different frequencies: power frequency (50 Hz) as well as 3rd (150 Hz) and 5th (250 Hz) harmonic frequencies. Two magnetic field levels (0.25 A and 2.5 A) were used. A Helmholtz coil was applied to generate an exact magnetic field. The difference between the measurement results at harmonic frequencies and at power frequency was analyzed using the t-test for matched pairs. The test results show significant differences (P< or =0.01) for 13 out of 28 tests carried out, which is probably due to a curved frequency response near the power frequency. It is, therefore, essential to consider harmonic frequencies in magnetic field measurements in practice.

Influence of 50-Hz electric and magnetic fields on human blood pressure.

This investigation studied the effects of 50-Hz electric and magnetic fields on the pulse rate and blood pressure in humans. Electrocardiograms (ECG) and the blood pressure of 41 male volunteers were recorded using ambulatory methods. Twenty-six subjects were measured in and outside real fields and 15 subjects in and outside "sham' fields. The results of the ECG recordings have been presented earlier. This article deals with the analysis of the blood pressure measurements. Measurement took 3 hrs. First, the subjects spent 1 h outside the fields, then 1 h in real or "sham' fields, followed by 1 h outside the fields. The electric field strength varied from 3.5 to 4.3 kV/m and the magnetic flux density from 1.4 to 6.6 microT. When analysing the blood pressure, which was measured with a noninvasive cuff method, it could not be shown that the fields (< 4.3 kV/m and < 6.6 microT) affected diastolic or systolic blood pressure.

Evaluation of Epilepsy Expert--a decision support system.

Epilepsy Expert is a decision support system based on the International Classification of Epilepsies and Epileptic Syndromes (1989). The aim of this study was to evaluate the Epilepsy Expert. First the diagnostic performance was validated. This was done in 3 stages: collection of the patient cases, determination of the 'correct diagnoses' and testing the system. How the users perceived the functionality of the system was studied by using an inquiry. Three physicians, experts of epilepsy, from different hospitals were asked to choose 10 patients. In the patient description was a short history, a detailed description of the seizure, EEG findings and their own diagnosis. Next, each expert made a diagnosis of the cases supplied by other experts by using the International Classification of Epilepsies and Epileptic Syndromes. The 'correct diagnosis' (so-called majority agreement) was the diagnosis given by the majority of the experts. The diagnosis of each expert was compared with the 'correct diagnosis'. The diagnoses obtained by the Epilepsy Expert were then compared with the 'correct diagnoses'. In the evaluation the expert physicians agreed on 37% of cases and all 3 disagreed on 17%. A majority agreed on 25 cases, which were used in the evaluation. In these 25 cases the experts' (A,B,C) diagnoses were correct or partly correct in 100, 64, 80% of cases, respectively. The program's diagnoses were correct or partly correct in 80% (module I) and 76% (modules IV and V) of cases. In the evaluation Epilepsy Expert was found to be only partly successful. The main reason for this was the weakness of the international classification. However, the program seems to be very close to the level of the experts. According to this limited inquiry Epilepsy Expert is not suitable for clinical use, because it is, for example, too simple and does not contain enough information.

Evaluation of Sleep Expert--a computer-aided decision support system for sleep disorders.

Sleep Expert--a medical decision support system--is a prototype program, with knowledge based on the International Classification of Sleep Disorders (1990). The goal of this project was to evaluate Sleep Expert. In the evaluation project the knowledge of the program was first validated. Three physicians, experts in sleep disorders, were asked to choose 10 typical patient cases with sleep disorders, and to write a description. They also made a diagnosis for each case. Next, each expert made a diagnosis of the cases supplied by the other experts. They were not given the original diagnosis. The 'right diagnosis' (so-called majority agreement) was determined from the three diagnoses. Then the diagnosis of each expert was compared with the 'right diagnosis'. Two physicians, not experts in sleep disorders, were asked to make a diagnosis by using Sleep Expert. Compared to the 'right diagnosis' the diagnoses of each user (non-expert physician) were correct to 63 and 70% of cases, which is quite a good result, although it does not reach the level of the expert physicians (> or = 87%). The functionality of Sleep Expert was studied by using a limited inquiry. On the basis of the user inquiry Sleep Expert provided a useful clinical tool for non-experts.

The influence of 50 Hz electric and magnetic fields on the extrasystoles of human heart.

This investigation studied the effect of 50 Hz electric and magnetic fields on the extrasystoles of human heart. The electrocardiograms (ECG) of 27 transmission-line workers and 26 male volunteers were recorded with a Holter monitor both in and outside the fields. The electric field strength varied from 0.14 to 10.21 kV/m and the magnetic flux density from 1.02 to 15.43 microT. The measurement period was from half an hour to a few hours. Analysis of the ECG recordings showed that extrasystoles were as frequent outside the field as in the field. In some cases a small decrease in heart rate was observed after field exposure, but it is possible that the changes in the pulse rate were caused by small changes of work load.

Influence of 50 Hz electric and magnetic fields on the pulse rate of human heart.

This investigation studied the effects of 50 Hz electric and magnetic fields on the pulse rate of the human heart. The ECG (electrocardiograms) of 41 male volunteers were recorded with a Holter recorder. Twenty-six subjects were measured in and outside real fields, and 15 subjects were measured in and outside "sham" fields. The blood pressure and EEG (electroencephalogram) were also measured, but this article presents only the results of ECG recordings. The measurements took 3 h. The subjects were first sitting for 1 h outside the fields, then 1 h in the real or "sham" fields, and then, again, 1 h outside the fields. The electric field strength varied from 3.5 to 4.3 kV/m and the magnetic flux density from 1.4 to 6.6 microT. An analysis of the ECG recordings showed that the subjects' pulse rates were the same in and outside the fields. No response occurred when the subjects were exposed to real or "sham" fields.

Sleep Expert--an intelligent medical decision support system for sleep disorders.

A new type of associative knowledge-based decision support system (Sleep Expert) for the diagnosis and classification of sleep disorders is described. Sleep Expert is based on the International Classification of Sleep Disorders (1990). The programming system used was KnowledgePro (Windows), a high-level language that integrates object-oriented programming, hypertext and expert system technologies. Sleep Expert is an interactive program composed of 288 separate integrated submodules and 264 text files. The program includes eight reasoning questions about symptoms setting the limits for the diagnosis subset. The user obtains a list of possible diagnoses on the screen where he/she can examine their criteria. The program has been written in such a form that the user can freely associate and can move forwards and backwards. Detailed information is included in hypertext.

Computer-aided decision-making for epilepsy and sleep diagnostics.

The main objective of the study was first to develop two prototypes of decision support systems for epilepsy and sleep disorder diagnostics. The second goal was to examine medical decision-making with the help of these program examples and further to assess what requirements should be set to decision support systems for them to find their place in clinical work. Requirements were first defined for the systems to be developed. The requirements were, for the most part, successfully taken into consideration during the development process. Epilepsy Expert, a decision support system based on the International Classification of Epilepsies and Epileptic Syndromes (51) was then developed. An epilepsy expert was in a central role in the development work due to the nature of the classification. For sleep disorders Sleep Expert, a decision support system, was developed based on the International Classification of Sleep Disorders (52). In the developing of the system the role of experts in sleep disorders was minor as the international classification provided a good foundation for program knowledge. The knowledge of the programs was validated as follows. First, three experts were requested to provide 10 case descriptions, and then they made diagnoses of their colleagues' patients. On the basis of these diagnoses a majority agreement, 'the right diagnosis', was reached. From the same epilepsy cases the author made diagnoses with the aid of the decision tree of Epilepsy Expert. Two other physicians, who were not experts in sleep disorders, made diagnoses for sleep disorders using Sleep Expert. In the validation Epilepsy Expert proved partly incomplete, which was due in part to the weakness of the international classification. However, the section of the program whose diagnostics was based on clinical findings only was as good as the experts. In the validation of Sleep Expert the physicians who used the program did not achieve as good results as the experts. The functionality of the programs was evaluated with questionnaires. According to this limited inquiry Sleep Expert could be used in clinical work, whereas Epilepsy Expert was regarded as being weaker. As a whole Sleep Expert was better than Epilepsy Expert. The conclusions to be drawn from the study are: In the development phase factors related to users, knowledge, problem definition and the environmental adaptation of the system need to be taken into account. If international classifications are to be used as a basis for the systems' knowledge, classification should be sufficiently clear and precise in respect of individual diagnoses.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of 50 Hz electric and magnetic fields on the human heart.

This investigation studied the effect of 50 Hz electric and magnetic fields on the human heart. The electrocardiograms of 27 transmission-line workers and 26 male volunteers were recorded with a Holter recorder both in and outside the fields. The measurements took from half an hour to a few hours. The electric field strength varied from 0.14 to 10.21 kV/m and the magnetic flux density from 1.02 to 15.43 microT. Analysis of the ECG recordings showed that extrasystoles or arrhythmias were as frequent outside the field as in the field. In some cases a small decrease in heart rate was observed after field exposure.