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1.
P. Lövsund P. Å. Öberg S. E. G. Nilsson 《Medical & biological engineering & computing》1980,18(6):758-764
The purpose of this study was to compare the threshold values for magnetophosphenes and electrophosphenes under identical
experimental conditions. Such comparisons between the phosphene types would increase our knowledge of the mechanism of the
interaction between magnetic fields and electric current, respectively, and excitable tissue.
The phosphenes were generated in the frequency range 10–45 Hz at moderate magnetic flux densities [up to 40 mT (400 G)] and
electric currents up to 0.3 mA, respectively.
The first part of the study was devoted to the problem of how electrode location and consequent current directions influence
the threshold values of electrophosphenes. In the second part a comparison was made of the threshold values for electrophosphenes
and magnetophosphenes under identical experimental conditions apart from the stimulation method.
With electric-current stimulation in different directions no great differences were obtained with regard to the mean value
for the threshold values within the frequency range 10–30 Hz. However, from 30 Hz upwards a significant difference developed
between the threshold values for some of the curves.
When generating electrophosphenes and magnetophosphenes we found significant differences in the threshold values between approximately
25 and 45 Hz. Both types of phosphenes had a concurring sensitivity maximum at 20 Hz.
The deviations between the curves may be due, among other factors, to the generation of different current paths in electrical
and magnetic stimulation, respectively. 相似文献
2.
In international guidelines, basic restriction limits on the exposure of humans to low-frequency magnetic and electric fields are set with the objective of preventing the generation of phosphenes, visual sensations of flashing light not caused by light. Measured data on magnetophosphenes, i.e. phosphenes caused by a magnetically induced electric field on the retina, are available from volunteer studies. However, there is no simple way for determining the retinal threshold electric field or current density from the measured threshold magnetic flux density. In this study, the experimental field configuration of a previous study, in which phosphenes were generated in volunteers by exposing their heads to a magnetic field between the poles of an electromagnet, is computationally reproduced. The finite-element method is used for determining the induced electric field and current in five different MRI-based anatomical models of the head. The direction of the induced current density on the retina is dominantly radial to the eyeball, and the maximum induced current density is observed at the superior and inferior sides of the retina, which agrees with literature data on the location of magnetophosphenes at the periphery of the visual field. On the basis of computed data, the macroscopic retinal threshold current density for phosphenes at 20?Hz can be estimated as 10?mA m(-2) (-20%?to + 30%, depending on the anatomical model); this current density corresponds to an induced eddy current of 14 μA (-20%?to + 10%), and about 20% of this eddy current flows through each eye. The ICNIRP basic restriction limit for the induced electric field in the case of occupational exposure is not exceeded until the magnetic flux density is about two to three times the measured threshold for magnetophosphenes, so the basic restriction limit does not seem to be conservative. However, the reasons for the non-conservativeness are purely technical: removal of the highest 1% of electric field values by taking the 99th percentile as recommended by the ICNIRP leads to the underestimation of the induced electric field, and there are difficulties in applying the basic restriction limit for the retinal electric field. 相似文献
3.
P. Lövsund S. E. G. Nilsson P. Â. Öberg 《Medical & biological engineering & computing》1981,19(6):679-685
The effects of extremely low frequency (e.l.f.) electromagnetic fields on basal systems were studied.
Frog retinas were exposed to magnetic fields with frequencies and flux densities that have been shown to induce magnetophosphenes
in volunteers. The electrical activity in the retina induced by the field was recorded from the ganglion cell layer with a
microelectrode technique. A threshold value was obtained at approximately 20 mT, and a sensitivity maximum at 20 Hz. A significant
prolongation (4 ms) of the latency from light stimulus to response in the ganglion cell layer was obtained, if the preparation
was simultaneously and continuously exposed to a magnetic field. A study of the reaction of the ganglion cells to light and
to magnetic fields showed that those cells which were on-cells during light stimulation became off-cells during magnetic stimulation
andvice versa. The magnetic field response occurred within approximately 5 ms. while the light stimulus response occurred only after an
average of approximately 85 ms.
Addition of Na-aspartate or CoCl2 extinguished simultaneously the response both to light and to magnetic field stimuli. 相似文献
4.
Electrical and magnetic phosphenes, perceptions of light as a result of non-adequate stimulation of the eye by electrical
current or magnetic induction, respectively, are one of the cornerstones to justify limit values for extreme low-frequency
fields specified by statutory regulations. However, the mechanism and place of action, as well as the excitation threshold,
remain unknown until now. We suggest that the origin of phosphene excitation is the synaptic layer of the eye. The current
density threshold value for electrical phosphene excitation was numerically quantified for this area on the basis of a detailed
geometrical model in original submillimetre resolution and specifically measured conductivities in the LF range. The threshold
values found were 1.8 Am−2 at 60 Hz and 0.3 Am−2 at 25 Hz. These values are comparable with values of other excitable tissues. It has been shown that the current density
threshold for phosphene generation depends on small-scale structures not taken into account by previous models. 相似文献
5.
Closed-chest cardiac stimulation with a pulsed magnetic field 总被引:5,自引:0,他引:5
G. A. Mouchawar Dr J. D. Bourland J. A. Nyenhuis L. A. Geddes K. S. Foster J. T. Jones G. P. Graber 《Medical & biological engineering & computing》1992,30(2):162-168
Magnetic stimulators, used medically, generate intense rapidly changing magnetic fields, capable of stimulating nerves. Advanced
magnetic resonance imaging systems employ stronger and more rapidly changing gradient fields thant those used previously.
The risk of provoking cardiac arrhythmias by these new devices is of concern. In the paper, the threshold for cardiac stimulation
by an externally-applied magnetic field is determined for 11 anaesthetised dogs. Two coplanar coils provide the pulsed magnetic
field. An average energy of approximately 12kJ is required to achieve closed-chest magnetically induced ectopic beats in the
17–26kg dogs. The mean peak induced electric field for threshold stimulation is 213 Vm
−1
for a 571 μs damped sine wave pulse. Accounting for waveform efficacy and extrapolating to long-duration pulses, a threshold
induced electric field strength of approximately 30 Vm
−1
for the rectangular pulse is predicted. It is now possible to establish the margin of safety for devices that use pulsed
magnetic fields and to design therapeutic devices employing magnetic fields to stimulate the heart. 相似文献
6.
Motoyuki Fukuta MD Noboru Mizutani MD Katsuhisa Waseda MD 《Journal of artificial organs》2005,8(3):154-160
This study was designed to determine the susceptibility of implanted cardiac arrhythmia devices to electromagnetic interference
in and around a magnetically levitated linear motor car [High-Speed Surface Transport (HSST)]. During the study, cardiac devices
were connected to a phantom model that had similar characteristics to the human body. Three pacemakers from three manufacturers
and one implantable cardioverter–defibrillator (ICD) were evaluated in and around the magnetically levitated vehicle. The
system is based on a normal conductive system levitated by the attractive force of magnets and propelled by a linear induction
motor without wheels. The magnetic field strength at 40 cm from the vehicle in the nonlevitating state was 0.12 mT and that
during levitation was 0.20 mT. The magnetic and electric field strengths on a seat close to the variable voltage/variable
frequency inverter while the vehicle was moving and at rest were 0.13 mT, 2.95 V/m and 0.04 mT, 0.36 V/m, respectively. Data
recorded on a seat close to the reactor while the vehicle was moving and at rest were 0.09 mT, 2.45 V/m and 0.05 mT, 1.46 V/m,
respectively. Measured magnetic and electric field strengths both inside and outside the linear motor car were too low to
result in device inactivation. No sensing, pacing, or arrhythmic interactions were noted with any pacemaker or ICD programmed
in either bipolar and unipolar configurations. In conclusion, our data suggest that a permanent programming change or a device
failure is unlikely to occur and that the linear motor car system is probably safe for patients with one of the four implanted
cardiac arrhythmia devices used in this study under the conditions tested. 相似文献
7.
Jesus A. Tapia Agustin L. Herrera-May Pedro J. García-Ramírez Jaime Martinez-Castillo Eduard Figueras Amira Flores Elías Manjarrez 《Biomedical microdevices》2011,13(2):303-313
We describe a simple procedure to characterize a magnetic field sensor based on microelectromechanical systems (MEMS) technology,
which exploits the Lorentz force principle. This sensor is designed to detect, in future applications, the spiking activity
of neurons or muscle cells. This procedure is based on the well-known capability that a magnetic MEMS device can be used to
sense a small magnetic flux density. In this work, an electronic neuron (FitzHugh–Nagumo) is used to generate controlled spike-like
magnetic fields. We show that the magnetic flux density generated by the hardware of this neuron can be detected with a new
MEMS magnetic field sensor. This microdevice has a compact resonant structure (700 × 600 × 5 μm) integrated by an array of
silicon beams and p-type piezoresistive sensing elements, which need an easy fabrication process. The proposed microsensor
has a resolution of 80 nT, a sensitivity of 1.2 V⋅T−1, a resonant frequency of 13.87 kHz, low power consumption (2.05 mW), quality factor of 93 at atmospheric pressure, and requires
a simple signal processing circuit. The importance of our study is twofold. First, because the artificial neuron can generate
well-controlled magnetic flux density, we suggest it could be used to analyze the resolution and performance of different
magnetic field sensors intended for neurobiological applications. Second, the introduced MEMS magnetic field sensor may be
used as a prototype to develop new high-resolution biomedical microdevices to sense magnetic fields from cardiac tissue, nerves,
spinal cord, or the brain. 相似文献
8.
脉部磁场对细胞缝隙连接通讯功能影响的研究 总被引:10,自引:0,他引:10
本文用细胞内微注射法对不同强度的脉冲磁场对细胞缝隙连接通讯(GJIC)功能的效应进行了研究,并与正弦磁场的作用以及脉冲磁场所感生的不同电场的作用进行了比较和探索。研究发现0.41mT以上强度的脉冲磁场具有抑制GJIC的作用。这种作用与磁场强度有关,其抑制GJIC的效庆比正弦磁场为强。经相同磁场不同强度感应电场作用的比较。得出,GJIC的抑制主要由磁场引起,而与感应电场关系不大,本文首次从研究对GJIC的作用提供了脉冲磁场治疗的创伤愈合等有关理论依据。 相似文献
9.
Wang Y Xiang J Kotecha R Vannest J Liu Y Rose D Schapiro M Degrauw T 《Brain topography》2008,21(2):75-85
The present study investigated the spatial and frequency differences of neuromagnetic activities between the perception of
open- and closed-class words by using a 275-channel whole head magnetoencephalography (MEG) system. Two groups of words, 110
open-class and 110 closed-class, were presented visually and auditorily simultaneously. The data of 12 healthy subjects were
analyzed with synthetic aperture magnetometry (SAM) which can identify the frequency-dependent volumetric distribution of
evoked magnetic fields (EMFs). Both vocabulary classes elicited spectral power changes in the left inferior frontal gyrus
(Broca’s area) and left posterior-superior temporal gyrus (Wernicke’s area) within 70–120 Hz. However, the open-class words
elicited event-related desynchronization (ERD) while the closed-class words elicited event-related synchronization (ERS) in
the two areas within 70–120 Hz. In addition, the open-class words also elicited ERS in the right inferior frontal gyrus, right
middle frontal gyrus and right inferior parietal lobe within 1–8 Hz, but the closed-class words only elicited ERD in the right
inferior frontal gyrus within 1–8 Hz. Furthermore, there were ERD in the right posterior-superior temporal gyrus within 120–200 Hz
for the open-class words, but not for the closed-class words. These results indicate that open- and closed-class words are
processed differently in the brain, not only in the anatomical substrates, but also in the frequency range of neuromagnetic
activity. 相似文献
10.
The vibration problems relating to living bodies have so far been studied from the perspectives of engineering physiology
and psychology. This study shows the relationship between vibratory sensibility and temperature in the living body. Psychological
experiments were carried out by using the vibrometer of an acoustic calibration apparatus in sine, triangular and square waves.
The sensibility-threshold measurements were made using 30–700 Hz sine waves, 30–300 Hz triangular and sawtooth waves, or 30–250
Hz square waves. Each of ten subjects was kept seated. The average value of the vibratory levels, varied by ascending and
descending steps, was taken as that of the threshold. As the vibrometer in the apparatus used makes a noise at frequencies
greater than 250 Hz it was masked from the subject by presenting him with a different noise. The threshold curve for square
waves is lower by 12·3 dB than that for sine waves at about 30Hz. The threshold curve of the 26°C sine wave was lower by 10
dB than that of the 58°C sine wave vibration near 200 Hz. For example with a sine wave, at 58°C the amplitude threshold was
lowest at about 270 Hz, but at −11°C at about 200 Hz. At frequency stimulation higher than 120 Hz, as the temperature of the
contact point was lowered, the amplitude threshold increased and the frequency at which the threshold curve was at a minimum
shifted to a lower frequency. 相似文献
11.
Powerful actuation of magnetized microtools by focused magnetic field for particle sorting in a chip
Yoko Yamanishi Shinya Sakuma Kazuhisa Onda Fumihito Arai 《Biomedical microdevices》2010,12(4):745-752
This paper describes a novel powerful noncontact actuation of a magnetically driven microtool (MMT), achieved by magnetization
of the MMT and focusing of the magnetic field in a microfluidic chip for particle sorting. The following are the highlights
of this study: (1) an MMT was successfully fabricated from a mixture of neodymium powder and polydimethylsiloxane; the MMT
was magnetized such that it acted as an elastic micromagnet with a magnetic flux density that increased by about 100 times
after magnetization, and (2) a pair of sharp magnetic needles was fabricated adjacent to a microchannel in a chip by electroplating,
in order to focus the magnetic flux density generated by the electromagnetic coils below the biochip; these needles contribute
to miniaturization of an actuation module that would enable the integration of multiple functions in the limited area of a
chip. FEM analysis of the magnetic flux density around the MMT showed that the magnetic flux density in the setup with the
magnetic needles was around 8 times better than that in the setup without the needles. By magnetization, the drive frequency
of the MMT improved by about 10 times—from 18 Hz to 180 Hz. We successfully demonstrated the separation of copolymer beads
of a particular size in a chip by image sensing. 相似文献
12.
Summary To determine whether recognisable profiles of sway behaviour are characteristically found among normal subjects the energy
content of a contiguous series of bandwidths were computed from power density spectra of the sway behaviour of 29 young men
and 29 young women. No significant differences were observed over time either in the energy content or in the profile shape
of the power spectral density (PSD) records when these were subjected to a multivariate profile analysis of variance.
It was observed that the majority of energy in the power spectrum, viz. 90% (±4%) in the antero-posterior and 95% (±3%) in
the lateral direction, was below 2.0 Hz. Three dominant frequencies of sway were identifiable in 93% of subjects. The modal
frequencies in the antero-posterior direction were 0.30–0.45 Hz (primary), 0.60–0.75 Hz (secondary) and 1.05–1.20 Hz (tertiary),
and in the lateral direction 0.30–0.45 Hz (primary), 0.45–0.60 Hz (secondary) and 0.75–0.90 Hz (tertiary). These three dominant
frequencies were distributed over the full frequency range. An explanation of their origins was not sought but the suggestion
is made that they could be driven by common dynamic physiological events.
The patterns of energy distribution were simplified and quantified by the calculation of a difference-ratio index. The broad
dispersion of the values of this index precludes the suggestion that there could be any clustering of profiles.
It is concluded that the frequently postulated clustering of the sway patterns of young adults into recognisable and distinct
profiles is without firm foundation. Instead it is suggested that sway behaviour is probably normally and randomly distributed
about common respiratory, cardiac and perhaps also other dynamic physiological events.
This work has been carried out with the support of the Science Research Council 相似文献
13.
G. R. Wodicka P. D. DeFrain S. S. Kraman 《Medical & biological engineering & computing》1994,32(5):489-494
Sonic noise transmission from the mouth to six sites on the posterior chest wall is measured in 11 healthy adult male subjects
at resting lung volume. The measurement sites are over the upper, middle and lower lung fields and are symmetric about the
spine. The ratios of transmitted sound power to analogous sites over the right (R) and left (L) lung fields are estimated
over three frequency bands: 100–600 Hz (low), 600–1100 Hz (mid) and 1100–1600 Hz (high). A R-L dominance in transmission is
measured at low frequencies, with a statistically significant difference observed at the upper site. No significant asymmetry
is observed in any measurement site at mid or high frequencies. A theoretical model of sound transmission that includes the
asymmetrical anatomy of the mediastinal structures is in agreement with the observed asymmetry at low frequencies. These findings
suggest that the pathway of the majority of sound transmission from the trachea to the chest wall changes from a more radial
to airway-borne route over the measured frequency range. 相似文献
14.
介绍了我们研制的低频脉冲磁场发生仪。该磁场发生仪可输出频率0~100 Hz,磁感应强度150~800 m T 连续可调的脉冲磁场,频率和强度值均采用数码显示。使用表明,该仪器操作方便、性能可靠,可长时间稳定运行,已在本教研室电磁场生物效应的科研实验中得到广泛应用。 相似文献
15.
席晓莉 《生物医学工程学杂志》1999,(3):314-317
介绍了我们研制的低频脉冲磁场发生仪。该磁场发生仪可输出频率0~100Hz,磁感应强度150~800mT连续可调的脉冲磁场,频率和强度值均采用数码显示。使用表明,该仪器操作方便、性能可靠,可长时间稳定运行,已在本教研室电磁场生物效应的科研实验中得到了广泛应用。 相似文献
16.
This study investigated the neuromagnetic spatial and frequency differences between recognizing concrete and abstract words
using a 275 channel whole head magnetoencephalography (MEG) system. The stimuli consisted of 100 concrete words and 100 abstract
words which were presented visually and auditorily simultaneously. The data of 12 right-handed healthy subjects in six different
frequency bands were analyzed with synthetic aperture magnetometry (SAM) which can identify the frequency-dependent volumetric
distribution of the evoked magnetic field. Concrete and abstract words evoked a very similar neuromagnetic activation pattern
in the primary visual and auditory cortices. However, concrete words evoked stronger synchronization in the right hemisphere
and abstract words evoked stronger synchronization in the left hemisphere in 1–8 Hz. In addition, concrete words evoked more
desynchronization in the left posterior temporal and parietal cortex; while abstract words evoked a clear synchronization
in the left posterior temporal cortex and desynchronization in the left inferior frontal cortex in 70–120 Hz. Furthermore,
concrete words evoked clear desynchronization in the left inferior frontal cortex while abstract words evoked strong synchronization
in the left posterior temporal cortex in 200–300 Hz. These findings suggested that concrete words and abstract words are processed
differently in the brain not only in anatomical substrates, but also in the frequency band of neural activation. 相似文献
17.
Selmaoui B Lambrozo J Sackett-Lundeen L Haus E Touitou Y 《Journal of clinical immunology》2011,31(6):1105-1111
Some epidemiologic studies have suggested that extremely low frequency magnetic fields might affect human health and, in particular,
that the incidence of certain types of cancer might increase among individuals living or working in environments exposed to
such fields. This study is part of a broad study we conducted in humans. The study presented here was designed to look for
possible effects of acute exposure to 50-Hz magnetic fields (10 μT) on the interleukin 1 beta (IL-1β), interleukin 2 (IL-2),
interleukin 6 (IL-6), interleukin-1 receptor antagonist (IL-1RA), and the interleukin-2 receptor (IL-2R) production. Thirty-two
young men (20–30 years old) were divided into two groups (sham-exposed or control group and exposed group) of 16 subjects
each. All subjects participated in two 24-h experiments to evaluate the effects of both continuous and intermittent (1 h “off”
and 1 h “on” with the field switched “on” and “off” every 15 s) exposure to linearly polarized magnetic fields. The subjects
were exposed to the magnetic field from 2300 to 0800 while recumbent. Blood samples were collected during each session at
11:00, 17:00, 22:00, 01:00, 04:00, 06:00, and 08:00. Results showed that exposure to 50-Hz magnetic fields (10 μT) significantly
increases IL-6 when subjects were exposed to an intermittent magnetic field. However, no effect has been observed on interleukin
IL-1β, IL-2, IL-1RA, and IL-2R. 相似文献
18.
A dual dipole electric field probe has been used to measure surface electric fields in vivo on a human subject over a frequency range of 0.1-800 Hz. The low-frequency electric fields were induced by natural body movements such as walking and turning in the fringe magnetic fields of a 3 T magnetic resonance whole-body scanner. The rate-of-change of magnetic field (dB/dt) was also recorded simultaneously by using three orthogonal search coils positioned near to the location of the electric field probe. Rates-of-change of magnetic field for natural body rotations were found to exceed 1 T s(-1) near the end of the magnet bore. Typical electric fields measured on the upper abdomen, head and across the tongue for 1 T s(-1) rate of change of magnetic field were 0.15+/-0.02, 0.077+/-0.003 and 0.015+/-0.002 V m(-1) respectively. Electric fields on the abdomen and chest were measured during an echo-planar sequence with the subject positioned within the scanner. With the scanner rate-of-change of gradient set to 10 T m(-1) s(-1) the measured rate-of-change of magnetic field was 2.2+/-0.1 T s(-1) and the peak electric field was 0.30+/-0.01 V m(-1) on the chest. The values of induced electric field can be related to dB/dt by a 'geometry factor' for a given subject and sensor position. Typical values of this factor for the abdomen or chest (for measured surface electric fields) lie in the range of 0.10-0.18 m. The measured values of electric field are consistent with currently available numerical modelling results for movement in static magnetic fields and exposure to switched magnetic field gradients. 相似文献
19.
Sharon Barzelai Anat Dayan Micha S. Feinberg Radka Holbova Shlomo Laniado Mickey Scheinowitz 《Annals of biomedical engineering》2009,37(10):2093-2104
Previous studies have shown that pre-exposure of the heart to weak magnetic field reduces infarct size shortly after induction
of myocardial ischemia. To investigate the role of AC magnetic field with a frequency of 15.95–16 Hz and 80 mT on left ventricular
(LV) remodeling following chronic coronary occlusion and a short episode of ischemia followed by reperfusion (I/R). LV dimension
and function were measured using echocardiography. Femur bone marrow was isolated and cells were phenotyped for endothelial
linage and immuno stained for endothelial cells. The area at risk was measured using triphenyltetrazolium chloride staining.
A significant reduction of 27% in shortening fraction (SF) was measured following acute myocardial infarction (AMI) compared
with a 7% decrease in animals exposed to magnetic field (p < 0.04). A significantly higher number of colony forming units and endothelial progenitor cells were counted within the treated
groups subjected to magnetic field (p < 0.02). Exposing the heart to magnetic field prior to reperfusion did not show any preservation either on SF or on infarct
size. Magnetic field was protective in the AMI but not in the I/R model. The mechanisms underlying cardiac protection induced
by AC magnetic field following chronic injury deserves further investigation. 相似文献
20.
S. Ueno P. Lövsund Professor P. Åke Öberg 《Medical & biological engineering & computing》1986,24(5):521-526
The possible influence of time-varying magnetic fields on action potential in the lobster giant axon was studied. The axon membrane was excited by galvanic stimulation and the action potential was recorded intracellularly with microelectrodes. During the propagation of the action potential along the axon, alternating or pulsed magnetic fields were applied across the middle part of the axon to study whether or not magnetic fields have any effect on parameters such as conduction velocity and refractory period of the nerve fibre and amplitude, duration and shape of the action potentials. No effect on these parameters was observed under different flux densities and frequencies of the magnetic fields. When simulating the conductive properties of tissue surrounding the nerve with the aid of an external conducting loop with a load resistance, action potentials were generated which made it possible to study the threshold value of the induced eddy current for nerve excitation. Based on the results of the experiment, the influence of magnetic flux density, frequency, conductivity, induced EMF and induced eddy current density is discussed, and a method is proposed for estimating the threshold values of magnetic flux density for nerve excitation. 相似文献