The interference threshold of cardiac pacemakers in electric 50 Hz fields

The aim of the study was to determine a 'worst-case' and a 'real-case' interference threshold for implanted cardiac pacemakers (CPM) in electric 50 Hz fields as they appear in highvoltage plants, e.g. beneath high voltage overhead lines. For this purpose the resulting electrical potential distribution within the thorax area of volunteers from an external homogeneous electrical 50 Hz field was measured. Different factors such as different body geometries as well as inspiration and expiration of the lung were considered. Measurements showed that 1 per 1 kV m^-1     

The interference threshold of cardiac pacemakers in electric 50 Hz fields

The aim of the study was to determine a 'worst-case' and a 'real-case' interference threshold for implanted cardiac pace-makers (CPM) in electric 50 Hz fields as they appear in high-voltage plants, e.g. beneath high voltage overhead lines. For this purpose the resulting electrical potential distribution within the thorax area of volunteers from an external homogeneous electrical 50 Hz field was measured. Different factors such as different body geometries as well as inspiration and expiration of the lung were considered. Measurements showed that 1 per 1 kV m(-1) unimpaired electrical field strength (RMS) an interference voltage of about 180 microVpp as real-case value an 400 microVpp as worst-case value would occur at the input of a unipolar ventricularly controlled, left pectorally implanted cardiac pacemaker. Therefore, it is possible under worst-case conditions but unlikely under practice-relevant conditions that an implanted cardiac pacemaker is disturbed by present electric 50 Hz fields beneath high voltage overhead lines.     

Electric fields induced in humans and rodents by 60 Hz magnetic fields

Numerical computations are used to evaluate electric field dosimetry for high-resolution anatomically based inhomogeneous models of a human male child, and male and female rats and mice, under exposure to 60 Hz uniform magnetic field sources of three perpendicular orientations. The goal is to compare the child data to previously computed adult dosimetry and to evaluate the accuracy of linear scaling of organ dosimetry between species. It is expected that this work will aid in the design and interpretation of experiments involving rodents. It is found that child-to-adult and mouse-to-rat organ dosimetry shows the expected linear dependence on the geometric scale factor between models. The comparison between mice and the human child shows that postural and individual organ differences do have significant effects, and that care is required in scaling-based extrapolation of rodent experiment results to humans. However, for unrestrained animals, linear scaling appears to be a reasonable and conservative approach. Most of the rodent organ fields, for at least one field orientation, are greater than those expected from linear scaling.     

Modelling fields induced in humans by 50/60 Hz magnetic fields: reliability of the results and effects of model variations

This paper presents a comparison of anatomically realistic human models and numerical codes in the dosimetry of power frequency magnetic fields. The groups at the University of Victoria and the National Radiological Protection Board have calculated the induced electric fields in both their 'UVic and 'NORMAN' models using independently developed codes. A detailed evaluation has been performed for a uniform magnetic field at 60 Hz. Comparisons of all dosimetric metrics computed in each particular model agree within 2% or less. Since in situ measurements cannot be performed in humans, and achievable accuracy of measurements in models and animals is not likely to be better than 10-15%, the comparisons presented should provide confidence limits on computational dosimetry. An evaluation of the effect of model size, shape and resolution has also been performed and further illuminated the reasons for differences in induced electric fields for various human body models.     

Influence of skin temperature on heat pain threshold in humans

We compared the effect of skin temperature on the critical threshold temperature eliciting heat pain with the effect of skin temperature on the response latency to the first heat pain sensation in healthy human subjects. Also, we determined the effect of the duration of a heat stimulus ramp on pain threshold. Furthermore, we determined the effect of skin temperature on mechanically induced pain. We found that the latency to the first pain sensation induced by a radiant heat stimulus was significantly decreased with an increase in the skin temperature (25–35 °C). However, independent of the rate of the stimulus rise (3–10 °C/s) and independent of the stimulus location (hairy vs glabrous skin), the threshold temperature for eliciting the heat pain sensation, determined with a contact thermostimulator, was not changed by a change in the skin temperature in the same subjects. With a fast rate of stimulus rise, a higher pain threshold was obtained than with a slow rise of stimulus temperature. However, this difference was found only with subject-controlled ascending stimuli (method of limits) but not with experimenter-controlled, predetermined stimulus ramps (method of levels). The heat pain threshold was higher in the glabrous skin of the hand than in the hairy skin of the forearm. With increasing stimulus duration (2.5–10s), the threshold temperature eliciting the heat pain sensation was significantly decreased. The mechanically induced pain threshold was not influenced by the skin temperature. The results indicate that the critical temperature for eliciting heat pain is independent of the skin temperature in humans. However, a change in skin temperature is an important source of an artefactual change in heat pain sensitivity when the radiant heat method (latency or energy) is used as an index of pain sensitivity. With a method dependent on reaction time (the method of limits), the heat pain threshold was artefactually increased, with fast rates of stimulus rise due to the long delay of slowly conducting heat pain signals in reaching the brain. With an increase in the duration of the heat stimulus, the critical temperature for eliciting pain sensation was significantly decreased, which may be explained by central neuronal mechanisms (temporal summation).     

Influence of inspiratory threshold load on cardiovascular responses to controlled breathing at 0.1 Hz

Slow, deep breathing is being used as a self‐management intervention for various health conditions including pain and hypertension. Stimulation of the arterial baroreceptors and increased vagal modulation are among the proposed mechanisms for the therapeutic effects of slow, deep breathing. We investigated whether adding inspiratory threshold load can enhance the cardiovascular responses to controlled breathing at the frequency of 0.1 Hz, a common form of slow, deep breathing. Healthy volunteers (N = 29) performed controlled breathing at 0.1 Hz (6 breaths/minute) without load and with inspiratory threshold loads of 5 cmH₂O and 10 cmH₂O. Respiratory airflow, heart rate, and blood pressure were continuously recorded. The amplitude of the systolic blood pressure variation during respiratory cycles increased with increasing loads. Respiratory sinus arrhythmia was higher during controlled breathing at 0.1 Hz with the load of 10 cmH₂O compared to without load. Baroreflex sensitivity was not affected by loads. The effect of loads on respiratory sinus arrhythmia was mediated by increasing the amplitude of systolic blood pressure variation during respiratory cycles. These results suggest that applying small inspiratory threshold loads during controlled breathing at 0.1 Hz increases cardiac vagal modulation by this breathing exercise. This effect seems to be mediated by stronger stimulation of the arterial baroreceptors because of larger systolic blood pressure swings along the respiratory cycle. The potential benefit of long‐term practice of controlled breathing at 0.1 Hz with inspiratory threshold loads on baroreflex function and cardiac vagal control needs to be investigated, particularly in pain and hypertension patients.     

Intra- and inter-hemispheric coupling of electroencephalographic 8-13 Hz rhythm in humans and force of static finger extension

Information on equipment and subcellular distribution of nitric oxide synthase (NOS) isoforms in myenteric neurons and pacemaker cells (ICC) might help to identify nitric oxide (NO) pathway(s) acting on gastrointestinal motility. In sections of mouse colon labelled with neuronal (n)NOS, endothelial (e)NOS and inducible (i)NOS antibodies, all myenteric neurons co-expressed eNOS and iNOS and a subpopulation of them co-expressed nNOS. ICC co-expressed nNOS and eNOS. In the neurons, nNOS-labeling was intracytoplasmatic, in the ICC at cell periphery. In both cell types, eNOS-labeling was on intracytoplasmatic granules, likely mitochondria. In conclusion, myenteric neurons and ICC co-express several NOS isoforms with specific subcellular distribution. Different nNOS splice variants are presumably present: intracytoplasmatic nNOSbeta and nNOSalpha producing neurogenic NO, plasma membrane-bound nNOSalpha producing ICCgenic NO. eNOS might be implicated in mitochondrial respiration and, in ICC, also in pacemaker activity. Neurons express iNOS also in basal condition.     

Effects of sleep deprivation on event-related fields and alpha activity during rhythmic force production

The influence of sleep deprivation (SD) on event-related fields and the distribution of power over the scalp of MEG imaged brain activity was studied during acoustically paced rhythmic force production. At the behavioral level, SD resulted in a reduction of the lag (negative asynchrony) between produced forces and acoustic stimuli at higher movement tempos. Principal component analysis of the accompanying MEG activity showed that auditory- and motor-evoked fields were attenuated after SD and revealed an anterior shift of power towards more frontal channels. These results were interpreted in terms of a change of central processing of afferent sensory input due to SD.     

Effects of experimental pain on jaw muscle activity during goal-directed jaw movements in humans

To study the effects of masseter muscle pain on jaw muscle electromyographic (EMG) activity during goal-directed tasks. Mandibular movement was tracked and EMG activity was recorded from bilateral masseter, and right posterior temporalis, anterior digastric, and inferior head of lateral pterygoid muscles in 22 asymptomatic subjects at postural jaw position, and during three tasks: (a) protrusion, (b) contralateral (left), (c) open jaw movement. Tasks were performed during three conditions: control (no infusion), test 1 [continuous infusion into right masseter of 4.5% hypertonic saline to achieve 30–60 mm pain intensity on 100-mm visual analog scale (VAS)], and test 2 (isotonic saline infusion; in 16 subjects only); the sequence of hypertonic and isotonic saline was randomized. The average EMG root-mean-square values at 0.5 mm increments of mid-incisor-point displacement were analysed using linear mixed effects model statistics (significance: P < 0.05). Right masseter hypertonic saline infusion resulted in significantly (P < 0.0005) more pain (mean ± SD VAS 47.3 ± 14.3 mm) than isotonic infusion (12.2 ± 17.3 mm). Although there was evidence of inter-subject variation, the principal EMG findings were that the significant effects of hypertonic saline-induced pain on EMG activity varied with the task in which the muscle participated irrespective of whether the muscle was an agonist or an antagonist in the tasks. The direction of the hypertonic saline-induced pain effect on EMG activity (i.e., whether the hypertonic saline-induced EMG activity was less than or greater than control EMG activity) could change with the magnitude of jaw displacement. Hypertonic saline infusion had no significant effect on postural EMG activity in any of the recorded jaw muscles. The data suggest that under constrained goal-directed tasks, the pattern of pain-induced changes in jaw muscle EMG activity is not clear cut, but can vary with the task performed, jaw displacement magnitude, and the subject being studied.     

电磁场对动物免疫系统的影响及其机理

电磁场产生的生物效应已引起极大的关注。本文从其对动物免疫系统的影响及其产生的机理两方面揭示不同条件下,电磁场影响生物机体免疫功能,促进或抑制细胞凋亡,间接地抑制或刺激细胞生长分化、分裂增值的宏观及微观效应,将成为将来提高生物体免疫系统功能的重要手段。     

50Hz磁场长期暴露对大龄大鼠学习记忆及脂质过氧化反应的影响

目的探讨长期0.1mT 50Hz磁场暴露对大龄大鼠学习记忆及海马组织的超氧化物歧化酶(SOD)、Na+-K+-ATP酶、Ca2+-Mg2+-ATP酶活性与丙二醛(MDA)水平的影响.方法应用Morris水迷宫方法测定动物的空间学习记忆能力;应用试剂盒分别测定SOD、Na+-K+-ATP酶、Ca2+-Mg2+-ATP酶活性及MDA水平.结果 10d 0.1mT 50Hz磁场暴露对大龄大鼠的学习记忆功能无明显影响.长期(4个月或8个月)0.1 mT 50Hz磁场暴露能使大鼠的逃避潜伏期明显延长,穿环系数显著减少,表明人鼠的空间学习记忆能力受损.长期磁场暴露也使大龄人鼠海马组织及其线粒体的SOD活件降低,MDA水平升高,Na+-K+-ATP酶和Ca2+-Mg2+-ATP酶活性降低.结论长期0.1 mT 50Hz磁场暴露可损伤大龄大鼠的学习记忆能力,此作用可能与其增强海马组织的脂质过氧化反应有关.     

Effects of pulsed electromagnetic fields on human articular chondrocyte proliferation

Low-energy, low-frequency pulsed electromagnetic fields (PEMFs) can induce cell proliferation in several cell culture models. In this work we analysed the proliferative response of human articular chondrocytes, cultured in medium containing 10% FBS, following prolonged exposure to PEMFs (75 Hz, 2.3 mT), currently used in the treatment of some orthopaedic pathologies. In particular, we investigated the dependence of the proliferative effects on the cell density, the availability of growth factors and the exposure lengths. We observed that PEMFs can induce cell proliferation of low density chondrocyte cultures for a long time (6 days), when fresh serum is added again in the culture medium. In the same conditions, in high density cultures, the PEMF-induced increase in cell proliferation was observed only in the first three days of exposure. The data presented in this study show that the availability of growth factors and the environmental constrictions strongly condition the cellular proliferative response to PEMFs.     

Effects of naloxone on dental pain threshold following muscle exercise and low frequency transcutaneous nerve stimulation: a comparative study in man

Previous studies have shown that muscle exercise and low frequency transcutaneous nerve stimulation (TNS) give rise to an analgesic effect in humans and animals. Endorphin has been proposed to mediate this analgesia. In this investigation, the effect of muscle exercise and low frequency TNS, on dental pain thresholds was studied and the possible involvement of endorphinergic mechanisms was investigated using naloxone as an antagonist. Dental pain thresholds were measured in 11 volunteers following leg or arm exercise and after low frequency TNS of the hands or face. After exercise (20 min) or stimulation (30 min) either 0.8 mg naloxone (2 ml) or saline (2 ml) was injected i.v. in a double-blind fashion. Pain thresholds were measured repetitively before and after exercise or stimulation. Both leg and arm exercise increased pain threshold. Stimulation of the hands also increased pain threshold, but less than arm exercise. A marked increase in pain threshold was seen after face stimulation. These changes in pain threshold were unaffected following injections of either naloxone or saline, except for an early and short-lasting reduction when naloxone was injected following arm exercise. The increases in pain threshold following muscle exercise and after low frequency TNS, showed similarities suggesting that a common mechanism might be involved. The pain threshold increase after arm exercise could only be partially mediated by endorphinergic mechanisms.     

脉冲电磁场对小鼠成骨细胞归巢基因的作用

目的 研究脉冲电磁场（PEMF）对小鼠成骨细胞上与造血干细胞（HSC）归巢、增殖有关基因的作用.方法 9周龄C57BL/6J小鼠,采用频率70 Hz、电磁场强度2 mT的PEMF作用4～5周,每周作用6d,对照组小鼠不接受PEMF作用.作用结束后,取双侧股骨和胫骨,胶原酶消化、分离细胞,再经磁珠和流式分选、收集ALCAM＋Sca-1-成骨细胞,最后通过表达谱芯片和定量PCR检测ALCAM＋Sca-1-成骨细胞上与HSC归巢、增殖有关的基因.结果 PEMF作用下,成骨细胞上Jagl（其对应HSC上的受体为Notch）和Ang-1（其对应HSC上的受体为Tie-2）的表达增强.结论 PEMF可能通过对ALCAM＋Sca-1-成骨细胞上与HSC归巢和自我更新有关基因的作用,调控HSC.     

Influence of electromagnetic fields on the electrical activity of rabbit cerebral cortex

Summary The effect of electromagnetic fields on the bioelectric activity of cerebral cortex was investigated on 98 rabbits. As established, the electromagnetic field provokes signal changes in the electroencephalogram: Increased intensity of the magnetic field raises the reaction of the cerebral cortex. Exclusion of various receptor fields (of hearing, vision, smell, vestibular apparatus) had no effect on the reaction of the brain to the action of the electromagnetic field. This led to a suggestion on the possibility of direct action of electromagnetic fields on the brain.Reported at the Conference on Problems of the Electrophysiology of the Central Nervous System, Moscow, 1958.(Presented by Active Member AMN SSSR V. V. Parin) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny Vol. 49, No. 5, pp. 63–67, May, 1960     

脉冲电磁场对破骨细胞和成骨细胞前体细胞作用的研究

目的 研究脉冲电磁场（PEMFs）对破骨细胞和成骨细胞前体细胞的作用。方法单独离体PEMFs作用：取8周龄雌性SD大鼠股骨骨髓细胞,根据PEMFs作用方式分为4个剂量组和对照组．分别进行成纤维细胞集落形成单位（CFU—F）和粒／巨噬细胞集落形成单位（CFU—GM）培养观察。活体结合离体PEMFs作用：取8周龄雌性SD大鼠随机分为3组：2—70组、OVX组和SHAM组,其中2．70组．OVX组进行双侧卵巢切除手术,SHAM组不切除卵巢。术后12周对2—70组大鼠进行PEMFs作用,OVX组和SHAM组不进行PEMFs作用。作用结束后,取大鼠股骨骨髓。根据体外培养过程中是否继续接受PEMFs作用,分为2—70PEMFs作用组／未作用组、OVXPEMFs作用组侏作用组、SHAMPEMFs作用组／未作用组,分别进行CFU．F和CFU．GM培养观察。结果单独离体PEMFs作用时,与对照组相比,4个剂量组的CFU-GM减少,CFU．F增加;活体结合离体PEMFs作用时,剂量组的CFU—F均增加,而CFU—GM各组间均无显著差异。结论单独离体PEMFs作用时,PEMFs对体外培养的破骨细胞前体细胞有抑制作用,对成骨细胞前体细胞增殖有促进作用;活体结合离体PEMFs作用时,PEMFs对成骨细胞前体细胞增殖有促进作用,但未见对破骨细胞前体细胞的抑制作用。     

Effects of extremely low-frequency electromagnetic fields on morphine-induced conditioned place preferences in rats

In the present study, we examined the effects of extremely low-frequency (ELF) electromagnetic fields on morphine-induced conditioned place preferences in rats. During the conditioning phase (12 days), three groups of rats were placed in a sensory cue-defined environment paired with morphine (10mg/kg, i.p.) following exposure to either 20 Hz (1.80 mT) or 50 Hz (2.20 mT) or sham electromagnetic fields for 60 min/day, respectively, and were placed in another sensory cue-defined environment paired with physiological saline (1 ml/kg, i.p.) without exposure to electromagnetic fields. After finishing 12 days of conditioning, preference tests for the morphine-paired place were performed during a 10-day withdrawal period. The exposure to electromagnetic fields substantially potentiated morphine-induced place preferences in rodents, suggesting that ELF electromagnetic fields can increase the propensity for morphine-induced conditioned behaviors.     

Effects of 50-Hz magnetic field on the cardiovascular system in rats

AIM: The 50-Hz magnetic field( MF) is a potential health-risk factor. Its effects on the cardiovascular system have not been fully investigated. This study was conducted to explore the effects of long-term exposure to 50-Hz MF on the cardiovascular system.METHODS: In the study,an exposure system was constructed and the distribution of 50-Hz MF was detected. Sixty-four SpragueDawley( SD) rats were exposed to 50-Hz MF at 100 μT for 24 weeks,20 hours per day,while another 64 rats were sham exposed.During the exposure,blood pressure was measured every 4 weeks,and 24 weeks later,echocardiography,cardiac catheterisation and electrocardiography were performed. Moreover,heart and body weight were recorded,while haematoxylin-eosin staining and real-time PCR were conducted. RESULTS: The results showed that compared with the sham group,exposure to 50-Hz MF did not exert any effect on blood pressure,pulse rate,heart rate and cardiac rhythm. Further,echocardiography and cardiac catheterisation showed that there were no significant differences in the cardiac morphology and haemodynamics. In addition,histopathological examination showed that 50-Hz MF exposure had no effect on the structure of hearts. Finally,the expression of the cardiac hypertrophic relative genes did not show any significant differences between 50-Hz MF exposure group and the sham group. CONCLUSION: Taken together,in SD rats,exposure to 50-Hz /100-μT MF for 24 weeks did not show any obvious effects on the cardiovascular system.