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PubMed1979

[Short-term and average-term automatic control of re-entry arrhythmias].

The AA. described an external stimulator to be utilized instead of invasive pharmacological treatment, as a short and middle-time therapeutic approach to re-entry tachycardia, in Departments of cardiology. The device must be connected with an electrode placed in atrium or in coronary sinus or in ventricle, according to individual request. A frequency discriminant device recognizes tachycardia and activates automatic scanning stimulator, synchronized on R or P waves, with progressive 5 msec stop delay; tachycardia interruption zone is automatically individuated. Stimulation has an automatic stop when tachycardia is interrupted; in case of persistent tachycardia scanning-function cycle will star again automatically. The device, which can be programmed for a simple or a double impulse emission, is equipped with a demand stimulator working if post-tachycardia asystole is present. Frequency discriminant device activates the scanning function beyond a defined threshold which can be varied within a wide range of frequencies.

Arrhythmias, Cardiac↗
PubMed2006

A combined finite element and modal decomposition method to study the interaction of Lamb modes with micro-defects.

This paper presents a combined finite element and modal decomposition method to study the interaction of Lamb waves with damaged area. The finite element mesh is used to describe the region around the defects. On the contrary to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the temporal domain. Then, the modal decomposition method permits to determine the wave reflected and transmitted by the damaged area. Modal analysis allows also identifying the mode conversions induced by the defects. These numerical results agree with previous finite element results concerning the interaction of Lamb modes with a notch. Experiments, carried out with gauged defects on an aluminum plate, are also compared to numerical predictions to validate the simulation. Compared to classical techniques of simulation, this new method allows us to investigate the interaction of Lamb modes generated at high frequency-thickness product with micro-defects as corrosion pitting.

Computer Simulation↗
PubMedDate not supplied

[Radiowave surgery for epibulbar tumor and nontumor masses].

The paper analyzes the results of removal of epibulbar tumor and nontumor masses, by using the radiowave surgical technique. The authors used two basic modes: fulguration and completely rectified and/ or completely filtered wave. Postoperative healing was aseptic and areactive. The duration of reparation depended on the working conditions, the volume of excised tissues, and the individual pattern of reparative processes. No intraoperative and postoperative complications were found. There were no cases of relapses and on-going growth during 9-12-month follow-ups. The authors have concluded that a radiowave knife may be used in surgery for epibulbar tumor and nontumor masses.

Adolescent↗
PubMed2004

Transmembrane voltage induced on altered erythrocyte shapes exposed to RF fields.

In this article, the transmembrane voltage induced on erythrocyte, codocyte, ovalocyte and spherocyte cell models exposed to a linearly polarised electromagnetic plane wave of frequency 1800 MHz is calculated. For this purpose, a finite element (FE) numerical technique with adaptive meshing is used. The results show that the value of the induced voltage on the original erythrocyte shape is higher than the one observed on the rest of the altered cell geometries studied. The erythrocyte shape and the membrane electric permittivity are shown to play a fundamental role on the values of the induced transmembrane voltage.

Animals↗
PubMed1986

The detection of temperature induced structural changes in T4B and T7 bacteriophages by means of high precision acoustic velocity measurements.

High precision measurements of the velocity of 7-7.5 MHz ultrasonic waves in suspensions of both T4B and T7 bacteriophages as a function of temperature revealed the presence of a distinct transition in the physiological range of 35-45 degrees C. Data from acoustic measurements, sedimentation analysis and electron microscopy enabled us to identify this transition as being caused by the protein component of the phage and not the DNA. This transition does not depend on the position of the long tail fibers and may be part of some normal physiological process within the bacteriophage which presumably enhances its recognition and attachment to its host cell.

Acoustics↗
PubMed2006

Effect of millimeter waves on cyclophosphamide induced NF-kappaB.

Antiapoptotic activity of NF-Kappa B (NF-kappaB) in tumors contributes to acquisition of resistance to chemotherapy. The effect of millimeter waves (MMWs) on NF-kappaB activation induced by cyclophosphamide (CPA) was studied in the spleen of mice. CPA, an anticancer drug, caused a marked increase (58.9-fold) in NF-kappaB DNA-binding activity as compared to the control group. No significant enhancement in NF-kappaB activity (0.51-fold) was observed when the CPA group was also irradiated with MMWs. These results suggest that treatment with MMWs can inhibit activation of NF-kappaB induced by chemotherapeutic drugs.

Animals↗
PubMed2004

Clinical S-cone ERG recording with a commercial hand-held full-field stimulator.

Our purpose was to explore S-cone ERG protocols for a commercial full-field hand-held stimulator that contains colored LEDs, and to see whether the test would be useful as a part of routine ERG testing. S-cone responses were elicited by blue flashes over a longer-wavelength background. With the standard stimulator containing blue (461 nm), green (513 nm) and red (652 nm) LEDs, we were unable to obtain satisfactory responses. Reproducible S-cone ERGs were obtained with a stimulator that had been custom-fitted with shorter-wavelength blue (440 nm) LEDs for stimulation, and orange (590 nm) LEDs for background adaptation. S-cone responses took only a few minutes to record, and the typical waveform showed a slow peak at 45-50 ms with amplitude 3-9 microV, but ranging from 0 microV to more than 10 microV. Larger waves appeared in a patient with enhanced S-cone syndrome. S-cone responses could also be obtained with an alternating blue-orange flicker protocol. We added the S-cone response to our regular ERG protocol for a number of months. Although most normal subjects and patients showed recognizable S-cone responses with this stimulator, the amplitudes were small and there was too much variability to make the technique effective for routine clinical testing. In general, the S-cone responses followed the standard cone ERG responses in disease.

Adult↗
PubMed2006

Characterization of the electromagnetic near-field absorption in layered biological tissue in the frequency range from 30 MHz to 6,000 MHz.

Currently, standards for the compliance testing of wireless devices are being extended to cover a wider frequency band and different usage patterns of mobile phones as well as of novel body-worn and handheld devices. As a consequence, not only the head but also strongly varying tissue distributions of the body are exposed to electromagnetic radiation. Several authors have reported changes in the SAR absorption of body tissue due to the presence of a low permittivity fat layer. This paper identifies two different effects which can lead to increased SAR in layered tissue in comparison to the SAR assessed using homogeneous tissue simulating liquid: (1) for larger distances between the tissue and the antenna, standing wave effects occur depending on the frequency and fat layer thickness. (2) In the very close near-field (distances approximately lambda/40), reactive E-field components lead to high local absorption in the skin. The latter effect occurs at lower frequencies and depends on the antenna type. Modification of the parameters of the homogeneous liquids cannot compensate for these effects. However, a conservative exposure estimate can be obtained by applying a multiplication factor between 1 and 3 to the values assessed using current experimental dosimetric techniques.

Absorption↗
PubMed1993

Radiofrequency catheter ablation of Mahaim fibers at the tricuspid annulus.

BACKGROUND: The purpose of this study was to test the feasibility of radiofrequency catheter ablation of Mahaim fibers at the tricuspid annulus. METHODS AND RESULTS: Four patients who fulfilled criteria for having Mahaim fibers and preexcited reciprocating tachycardia underwent radiofrequency catheter ablation. Three patients had atriofascicular connections, and one patient had an atrioventricular connection. The mean age was 27 years (age range, 11-48 years). All patients had highly symptomatic tachycardias, producing syncope in one patient and presyncope in the remaining three patients. Symptoms were present for a mean of 13 years (range, 4-23 years). All pathways conducted only anterogradely, and preexcitation resulted in a left bundle branch block QRS morphology. Adenosine caused block in the accessory pathway in the three patients in whom it was tested. The stimulus to delta interval increased by 75 msec (range, 35-90 msec) during rapid atrial pacing. The atrial insertion of the Mahaim fiber was in the right lateral atrium in one patient, right posterolateral atrium in two patients, and right posterior atrium in one patient. The ventricular insertion was in the distal right bundle branch in three patients and in the posterolateral right ventricle near the tricuspid annulus in the patient with an atrioventricular connection. Stimulus to delta wave mapping was used to help localize the atrial insertion of the atriofascicular connections. A mean of 15 radiofrequency pulses (range, 10-19 pulses) delivered to the tricuspid annulus in the posterior to lateral regions eliminated accessory pathway conduction in all patients. No complications occurred. Tachycardia did not recur during a mean follow-up of 8 months (range, 2-15 months). CONCLUSIONS: Radiofrequency current applied to the tricuspid annulus can safely eliminate tachycardia in patients with Mahaim fibers.

Adolescent↗
PubMed1988

Effects of 2.45-GHz microwave and 100-MHz radiofrequency radiation on liposome permeability at the phase transition temperature.

Large unilamellar dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) liposomes loaded with an aqueous chemotherapeutic drug, cytosine arabinofuranoside (ARA-C), were exposed for 30 min to 60 W/kg continuous-wave (CW) 100-MHz or 2.45-GHz radiation in vitro at temperatures between 37 degrees C and 43 degrees C. Liposomes were exposed in HEPES buffer or in HEPES buffer supplemented with 44% by volume fetal calf serum (FCS). Characteristic phase transition responses were detected in the range of 39 degrees C to 40 degrees C with the presence of FCS, increasing maximum % release of 3H-ARA-C by 20% relative to HEPES suspension. Neither frequency of electromagnetic radiation had any detectable effect on liposome permeability or the location of the phase transition in the presence or absence of FCS.

Cytarabine↗
PubMed2000

Global processing of spectrally complex sounds in macaques (Macaca mullata) and humans.

How nonhuman species perceive the world is a biological question of fundamental importance, and has major significance for establishing the validity and possible limitations of animal models of human sensory function and perception. Studies in comparative hearing have revealed that almost all animals, including monkeys, are worse than humans at discriminating tone frequencies. Less is known, however, about comparative differences in discriminating more spectrally complex sounds. We compared the capacity of macaques and humans to discriminate complex sound patterns by measuring spectral-contrast sensitivity using stimuli having sine-modulated power spectra, analogous to sine-wave gratings used in visual studies. We found that the auditory system of the macaque is far less sensitive than the human system over the sine-profile frequency range tested (0.5-2.0 cycles/octave). These results indicate that rhesus macaques hear at least some spectrally complex sounds with less fidelity than do humans, and demonstrate large differences in primate species' abilities to process low-resolution spectral patterns. These results cannot be accounted for by traditional, narrowband peripheral filter models of spectral analysis, but instead, imply the involvement of a central, frequency integration process that may differ significantly across species.

Animals↗
PubMed1990

An evaluation of radiofrequency exposure from therapeutic diathermy equipment in the light of current recommendations.

Shortwave and microwave diathermy equipment use by physiotherapy departments in Grampian Region has been studied. Stray electric and magnetic fields close to equipment have been measured and compared with exposure levels recommended by the INIRC and the NRPB. Fields above the recommended whole body levels extend to 0.5-1.0 m from the electrodes and cables for continuous wave (cw) shortwave equipment, and up to 0.5 m for microwave units and pulsed shortwave models. Operators were exposed to local fields above these values for 2 - 3 min during cw shortwave treatments, but rarely exceeded the recommended exposure. However, short localised exposures to high fields, which can occur if the operator moves close to the electrodes or cables, could exceed these limits. Physiotherapists are advised to remain at a distance of at least 1 m during cw treatments, and not to approach within 0.5 m of the electrodes and cables even for a short period.

Diathermy↗
PubMed1998

Two-dimensional 220 MHz Fourier transform EPR imaging.

In the last decade radiofrequency continuous-wave EPR spectrometers have been developed to detect and localize free radicals in vivo. Only recently, pulsed radiofrequency EPR spectrometers have been described for imaging applications with small samples. In the present work, we show the first two-dimensional image obtained at 220 MHz on a large phantom (40 ml) that simulates typical conditions of in vivo EPR imaging. This pulsed EPR apparatus has the potential to make the time required for three-dimensional imaging compatible with the biological half-life of normally used paramagnetic probes.

Animals↗
PubMed2002

Angular spectrum method and ray algorithm for the acoustic field of a focusing transducer in an anisotropic solid.

The angular spectrum method is applied to calculating the acoustic field of a liquid-coupled focusing transducer in an anisotropic slab-shaped solid with surfaces normal to the axis of the transducer. The stationary phase approximation (SPA) is used to determine the dominant contributions to this field and calculate the echo signals produced by waves that have been reflected off the rear surface of the solid. The dominant features of this field and of the echoes are reproduced well by a hybrid ray method devised to simulate the finite point-spread function of the lens. Both approaches in the paraxial approximation yield a split focus for each wave polarization branch for a general direction of the surface normal. Echo arrival times and amplitudes calculated by the two methods are in good agreement. The hybrid ray method is shown to be particularly suited to handling multiple stationary phase points within the angular spectrum of the incident field and stationary phase points not associated with the normally incident ray, and should be useful for dealing with scattering from cracks and other defects. Pulse echo calculations for different crystallographic directions in a nickel-based superalloy are shown to be in good agreement with measurements carried out on single crystal specimens of the alloy.

Algorithms↗
PubMed2003

High-frequency acoustic scattering from turbulent oceanic microstructure: the importance of density fluctuations.

Acoustic scattering techniques provide a unique and powerful tool to remotely investigate the physical properties of the ocean interior over large spatial and temporal scales. With high-frequency acoustic scattering it is possible to probe physical processes that occur at the microstructure scale, spanning submillimeter to centimeter scale processes. An acoustic scattering model for turbulent oceanic microstructure is presented in which the current theory, which only accounts for fluctuations in the sound speed, has been extended to include fluctuations in the density as well. The inclusion of density fluctuations results in an expression for the scattering cross section per unit volume, sigma(v), that is explicitly dependent on the scattering angle. By relating the variability in the density and sound speed to random fluctuations in oceanic temperature and salinity, sigma(v) has been expressed in terms of the temperature and salinity wave number spectra, and the temperature-salinity co-spectrum. A Batchelor spectrum for temperature and salinity, which depends on parameters such as the dissipation rates of turbulent kinetic energy and temperature variance, has been used to evaluate sigma(v). Two models for the temperature-salinity co-spectrum have also been used. The predictions indicate that fluctuations in the density could be as important in determining backscattering as fluctuations in the sound speed. Using data obtained in the ocean with a high resolution vertical microstructure profiler, it is predicted that scattering from oceanic microstructure can be as strong as scattering from zooplankton.

Models, Theoretical↗
PubMed1988

[Hyperthermia in gynecological malignancy].

This paper mainly reports our clinical findings so far obtained from thermotherapy performed as part of a multimodality treatment for gynecological malignant tumors. In our thermotherapeutic method, microwaves at 2.45 GHz were applied for superficial tumors and RF waves at 13.56 MHz capable of warming deeper lesions were locally applied, whereas 70-80 MHz radial-type waves were regionally administered when heating of the entire pelvic cavity was required. However, only three of 103 patients were given thermotherapy alone, 47 were given combined chemotherapy, 47 were given radiotherapy and 6 were given both chemotherapy and radiotherapy. The microwave heating was mainly combined with chemotherapy, and when the results obtained from chemotherapy alone were compared with those of thermochemotherapy in the same regimen, the group treated with thermochemotherapy was found to have a more favorable chemotherapeutic effect and prognosis. RF radial-type hyperthermia with radiotherapy was proved to be more effective for reduction of tumor size and histopathological effect than radiotherapy alone.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1979

Normal tissue and solid tumor effects of hyperthermia in animal models and clinical trials.

Localized hyperthermia therapy by high-energy radio-frequency waves was evaluated in malignant and adjacent normal tissue of 30 patients with 10 types of cancer. Hyperthermia was delivered to superficial and deep visceral cancers in awake patients who had refractory disease. Histological and clinical responses were recorded serially. Toxicity tests in dogs, sheep, and pigs showed that progressive necrosis of normal and cancer tissue occurred at temperatures above 45 degrees C (113 degrees F). However, as normal tissues approached this temperature, intrinsic heat dissipation occurred (possibly due to augmented blood flow) so that temperatures below 45 degrees C could be maintained, whereas most solid tumors did not have this adaptive capacity and could be heated to 50 degrees C (122 degrees F) with virtually no injury to normal organs, s.c. tissue, or skin. To date, 69 treatments have been administered to 36 tumors in the 30 patients. Selective heating was observed in both primary and metastatic tumors located in surface tissues and internal organs. Response appeared to be related to tumor size in that differential heating was possible more often in the larger lesions. In tumors successfully heated, moderate to marked necrosis occurred. Radio-frequency hyperthermia appears to be a safe and potentially useful form of therapy for selected cancer patients. While other cancer treatments are more effective for small tumors, hyperthermia may be uniquely beneficial against larger lesions.

Abdominal Neoplasms↗
PubMed2003

Motor cortical and other cortical interneuronal networks that generate very high frequency waves.

A remarkable feature of motor cortical organization in higher mammals is that a brief electrical stimulus elicits in the pyramidal tract and corticospinal tract an unrelayed direct (D) wave followed by multiple indirect (I) waves at frequencies as high as 500-700 Hz. This review presents some conclusions regarding very high frequency synchronous activity in mammalian cortex: (1) Synchrony in repetitive I discharges is extraordinary in humans and monkeys, less in cats and still less in rats, being there represented by a delayed broad wave; such phylogenetic trends have important implications for the suitability of lower mammalian species for studies of high frequency cortical networks in the human brain; (2) The evidence from microstimulation at different cortical depths and pial cooling favors a vertically oriented chain of interneurons that centripetally excite corticospinal neurons as the basis for inter-I wave periodicity and synchrony; (3) Significantly, the I wave periodicity is conserved despite wide changes in stimulus parameters; (4) Synchronous high frequency activity similar to that of I waves can be recorded from other neocortical areas such as visual and somatosensory cortex; however, evidence is still lacking that the output neurons of these cortical regions have synchronized discharges comparable to I waves; (5) In limbic cortices, the frequency of synchronous neural activity is lower than that in motor cortex or related cortices and periodicity is not conserved with changes in stimulus parameters, indicating a lack of the neocortical interneuronal substrate in limbic cortex; (6) We propose that the very high frequency synchronous activity of motor cortical output reflects a computational function such as a "clock," quantizing times at which inputs would interact preferentially yielding synchronous output discharges. Such circuitry, if a general feature of neocortex, would facilitate rapid communication of significant computations between cortical regions.

Animals↗