A contactless electromagnetic implantable middle ear device for sensorineural hearing loss

Following basic science experiments, improvement of precision micromechanics and electronics design, and development of different prototypes, a contactless electromagnetic hearing device has been successfully implanted in cats (acute experiments). Chronic animal experiments using the cat as well as the rabbit are ongoing to test the components of the device. A highly efficient air core coil is used to vibrate a neodymium-iron-boron magnet cemented to the body of the incus. The parts of the system, including implanted electronics (hybrid circuit, solid state), are laser welded and hermetically sealed. The system allows for the generation of enough force which vibrates the magnet implanted on the incus. It would be suitable for the treatment of moderate to severe sensorineural hearing loss.

Implantation of electromagnetic ossicular replacement device

Semi-implantable hearing aids consisting of permanent middle ear implanted magnet, either partial ossicular replacement prostheses (PORP's) or total ossicular replacement prostheses (TORP's) driven by an electromagnet placed in the ear canal have been tested on six patients undergoing surgery for chronic otitis. The surgical and audiological problems are described. The audiological results were excellent in all six cases. A functional gain of 40-70 dB can be obtained for entire frequency range of the audiogram.

Effect of tonic voluntary activity on the excitability of human motor cortex

1. The threshold for obtaining EMG responses after transcranial magnetic stimulation of the brain is reduced by voluntary contraction of the target muscle. The present experiments tested whether some of this effect is due to increased cortical, as opposed to spinal, excitability during the contraction. 2. Magnetic stimulation was delivered with a figure-of-eight coil oriented with the junction region along the interaural line and also (in 4 of 7 subjects) with a circular coil centred at the vertex. The intensity of the conditioning stimulus was subthreshold for evoking a motor response in the relaxed wrist flexor muscles of the forearm. The presence of a small descending corticospinal volley in both the relaxed and active conditions was detected by measuring the facilitation of test H reflexes elicited in the flexor muscles of the forearm. 3. In all subjects, magnetic stimulation with either coil facilitated the H reflex at conditioning-test intervals of -1 to -3 ms (median nerve stimulus before magnetic). This was followed by a long-lasting facilitation. In three of the seven subjects stimulation with the figure-of-eight coil elicited an additional, earlier peak of facilitation at a conditioning-test interval of -3 to -5 ms. 4. In all subjects, the threshold for obtaining facilitation of the H reflex using a conditioning-test interval of -1 to -3 ms was reduced, and the amount of facilitation was larger, if subjects performed a weak tonic voluntary contraction. In contrast, with a conditioning-test interval of -3 to -5 ms voluntary contraction had no effect on the threshold. 5. It is suggested that H reflex facilitation at the conditioning-test interval of -1 to -3 ms was produced by indirect activation of corticospinal neurones by the magnetic stimulus, whereas at -3 to -5 ms, the facilitation was produced by direct activation of corticospinal axons. It is concluded that tonic voluntary contraction of a target muscle decreases the threshold for indirect activation of corticospinal neurones but not for direct stimulation of their axons.

Power frequency magnetic field exposures among nurses in a neonatal intensive care unit and a normal newborn nursery

Given the current interest in potential carcinogenic and developmental effects of exposure to extremely-low-frequency electromagnetic fields, there is a need to identify cohorts of exposed female workers for future epidemiologic investigations. This study was designed to test the hypothesis that nurses working in neonatal intensive care units (NICU) may be significantly exposed to power-frequency magnetic fields. An electromagnetic field monitor was used to measure magnetic fields at distances of 5, 15, 30, and 60 cm from the surfaces of each device used in the NICU. Six female nurses assigned to the NICU (the "exposed" group) and six female nurses working in the normal newborn nursery (the "referent" group) wore EMDEX dosimeters for the entire duration of their 12 h shifts. An investigator kept a detailed log of each NICU subject's whereabouts for the first one-third of her shift. Magnetic fields at 5 cm from the front (defined by the nurses' usual work area) of the NICU devices ranged from less than 0.1 to 114 microT and in all cases decreased considerably with increasing distance. The geometric mean of the shift-time-weighted average exposure of the NICU nurses was 0.17 microT compared with 0.11 microT for the normal newborn nurses. The percentage of time when subjects were exposed to magnetic fields of 0.4 microT or greater ranged from 5.8% to 15.6% for the NICU nurses, 0.4% to 2.9% for five of the comparison group nurses, and was 9.4% for one of the normal newborn nurses with unidentified aberrantly high exposures. Log data revealed that the vast majority of observed peaks among NICU nurses occurred while subjects were in close proximity to infant bed units. We conclude that NICU nurses represent one female-intensive job sector with intermittent high exposures to ELF magnetic fields and encourage larger exposure studies of nurses in a variety of medical settings.

[Effect of low intensity and ultra high frequency electromagnetic irradiation on memory functions]

The experiments on rats proved that low intensity electromagnetic waves result in retrograde amnesia due to benzodiazepine, gamma-aminobutyric acid and cholinergic mechanisms. Nootropic drug pyracethamum was proved to reduce the pathologic effect.

[Non-contact, biologically adequate, electromagnetic stimulation of reparative regeneration of osseous, cartilagenous and muscular tissues in children]

The authors analyse the results of using a Kaskad electromagnetic apparatus in 508 children with long-term ununited fractures, false joints, contractures, sluggish wounds, decubituses, trophical ulcers, osteochondropathies, Pertes' disease, and crush syndrome. The efficiency of the therapy was 75-90%, depending on the type of an abnormality. The authors had developed and put into practice a Kaskad-synchro electromagnetic apparatus synchronized with the pulse of a patient's arterial vessel. Such a high efficiency of the electromagnetic therapy bioadequate to man is likely to be explained by the exposure of electromagnetic waves directly to the areas of bone marrow hemopoiesis. To elucidate this, the authors made an experiment on dogs. The results of this experiment are being processed.

Photoacoustic ultrasound

Differential absorption has been detected and localized in three-dimensions by recording the photoacoustic pulses that were produced when short-duration (approximately 1 microsecond) pulses of electromagnetic energy were absorbed regionally within a turbid medium. These absorption sites were localized with a spatial resolution of approximately 6 mm within a 20 x 20 x 7.5-cm3 volume of 0.3% Liposyn solution, a highly scattering medium. A Xenon flashlamp, delivering a nominal 1 microsecond pulse of broadband light, was used to irradiate the Liposyn solution. Photoacoustic echoes were recorded with a focused, ultrasonic transducer, tuned to a nominal frequency of 0.5 MHz. The spatial resolution that was demonstrated is consistent with the expected ultrasonic properties of the transducer. Improved spatial resolution can be expected with shorter-duration radiation exposure and higher-frequency transducer designs. The technique is generalizable to any electromagnetic energy range (including long-wavelength microwaves) that penetrates the medium and produces differential, regional absorption of energy.

Ureteral stone. Treatment using the Modulith SL 20 and Lithostar plus

The treatment of ureteric calculi by extra-corporeal shock waves was found to have an 80% success rate by Mannheim authors, regardless of the site of the calculus. The authors compared two 3rd generation apparatuses: 1--the Siemens Lithostar Plus, in which waves are produced by a electromagnetic cylinder and focussed by a parabolic electromagnetic cylinder and focussed by a parabolic reflector: 2--the Storz Medical Modulith SL 10, in which waves produced by an electromagnetic coil are focussed by acoustic lenses. Both apparatuses are based upon image-intensification and ultrasonography concepts. No difference in efficacy was found between the two apparatuses. A second shock wave session was necessary in 16% of cases and some other type of additional treatment in 7% of cases.

Cross section parameterizations for cosmic-ray nuclei. II. Double nucleon removal

Parameterizations of double nucleon removal from the electromagnetic and strong interactions of cosmic rays with nuclei are presented. These parameterizations are an extension of previous single nucleon removal parameterizations and combined they represent the dominant part of the electromagnetic dissociation encountered by a cosmic ray on its traversal through matter. Such parameterizations should be very useful in studying cosmic-ray transport through the interstellar medium, the Earth's atmosphere, spacecraft walls, and extraterrestrial matter.

Injectate port selection affects accuracy and reproducibility of cardiac output measurements with multiport thermodilution pulmonary artery catheters

OBJECTIVE

To compare the accuracy and reproducibility of thermodilution cardiac output measurements obtained from the injectate and infusion ports of a multilumen pulmonary artery catheter. The thermodilution results were compared with an independent measure of flow obtained from an electromagnetic flow meter.

METHODS

In an experimental study conducted at an animal research laboratory of a health sciences university, two virgin western breed ewes were surgically instrumented with an inferior vena cava occluder, which reduced venous return and thus lowered cardiac output, and an ascending aortic electromagnetic flow probe, which provided an independent reference measure of cardiac output. On the day of study, a multilumen pulmonary artery catheter was inserted. Cardiac output was manipulated over a range of 2.9 to 12.1 L/min with i.v. isoproterenol or inferior vena cava occlusion. Approximately 30 simultaneous thermodilution and electromagnetic flow meter measurements of cardiac output were obtained from both the infusion and injectate ports in each of the two subjects.

RESULTS

Correlation coefficients were lower and standard error of the estimates was higher for the infusion port (r = .83; SEE = 1.19 L/min) vs the injectate port (r = .94; SEE = .74 L/min), indicating reduced reproducibility with infusion port thermodilution cardiac output determinations. Accuracy was also adversely influenced in the infusion port results. The linear regression for the infusion port data intercepted the Y axis at +2.64 L/min, indicating significant overestimation of cardiac output at flows of less than 5 L/min and underestimation of flow when cardiac output exceeded 8 L/min.

CONCLUSIONS

The use of the infusion port for the measurement of thermodilution cardiac output measurements may result in nonreproducible and inaccurate results.

Circularly polarized, sinusoidal, 50 Hz magnetic field exposure does not influence plasma testosterone levels of rats

We exposed rats to circularly polarized 50 Hz magnetic fields to determine if plasma testosterone concentration was affected. Previous experiments indicate that magnetic fields suppress the nighttime rise in melatonin, suggesting that other neuroendocrine changes might occur as well. Male Wistar-King rats were exposed almost continuously for 6 weeks to magnetic flux densities of 1, 5, or 50 microT. Blood samples were obtained by decapitation at 12:00 h and 24:00 h. Plasma testosterone concentration showed a significant day-night difference, with a higher level at 12:00 h when studied in July and December, but night difference, with a higher level at 12:00 h when studied in July and December, but the day-night difference disappeared when concentrations were studied in April. In three experiments, magnetic field exposure had no statistically significant effect on plasma testosterone levels compared with the sham-exposed groups. These findings indicate that 6 weeks of nearly continuous exposure to circularly polarized, 50 Hz magnetic fields did not change plasma testosterone concentration in rats.

Human exposure to magnetic fields: a comparative assessment of two dosimeters

Two types of dosimeters for measuring human exposure to 60 Hz magnetic fields were compared. Fifty adults wore the single-axis, wrist model AMEX (average magnetic field exposure system) and the triple axis, hip-pocket or pouch model AMEX-3D meters for 2 days. Ninety-six percent of the tests were accomplished without apparent dosimeter failure. The average root mean square magnetic flux density measurements with the AMEX-3D (mean = 0.10 microT, S.D. = 0.07, range = 0.03-0.31) were significantly higher than with the AMEX meter (mean = 0.07 microT, S.D. 0.05, range = 0.02-0.27 microT) (t test, P < 0.01). There was substantial correlation between the AMEX and the AMEX-3D measurements (Pearson's correlation coefficient = 0.65, P < 0.01) but poor concordance (Intraclass correlation coefficient = -0.25). These results suggest that there is a wide variation in exposure to extremely low frequency magnetic fields in the population. Magnetic field measurements with the AMEX-3D are nearly always higher than with the AMEX dosimeters. Caution is advised when comparing magnetic field measurements made with different types of dosimeters.

Idiopathic generalized epilepsy: magnetic stimulation of motor cortex time-locked and unlocked to 3-Hz spike-and-wave discharges

In 20 patients with idiopathic generalized epilepsy who showed typical 3-Hz spike-and-wave (SW) EEG complexes, we studied the corticospinal motor output with a transcranial electromagnetic stimulator. First we measured the corticospinal discharge threshold for both hemispheres in the patient group and compared it with that of 10 age- and sex-matched volunteers. Threshold was significantly higher in the patient group, regardless of whether subjects were treated with antiepileptic drugs (AEDs). In 4 patients with very frequent SW paroxysms, we were able to study motor evoked potential (MEP) changes time-locked to epileptic EEG transients. The EEG signal was recorded bipolarly (C3-P3, C4-P4) by scalp needle-electrodes. For a given stimulus intensity, we collected and measured MEPs occurring during the spike or the wave portion of the SW complexes. Data were compared with those of MEPs obtained time-locked to normal EEG segments. MEP size was significantly decreased when the cortical stimulus was time-locked to the wave component, and was decreased or unchanged when the stimulus was time-locked to the spike. Magnetic stimulation never produced remarkable side effects.

Limitations of electromyography and magnetic stimulation for assessing laryngeal muscle control

The development of new phonosurgical techniques has increased the level of interest in the field of neurolaryngology. This field requires valid techniques for determining if muscle activation is normal. Laryngeal electromyography is being used more frequently to assess muscle innervation and synkinesis. Further, magnetic stimulation has been introduced as a noninvasive technique for nerve stimulation. Technical limitations that affect the clinical utility of both these techniques are reviewed: 1) difficulties obtaining selective and accurate electromyographic laryngeal muscle recordings, 2) normal variation in movement and muscle activation patterns within and between normal individuals when producing the same speech syllables, and 3) variation in laryngeal muscle response latencies between and within normal subjects during peripheral magnetic stimulation. Given the normal variation in laryngeal electromyography and magnetic stimulation response latencies, these techniques may not yet be reliable or accurate for assessing reinnervation or synkinesis following recurrent laryngeal nerve injury.

Multi-applicator hyperthermia system description using scattering parameters

Hyperthermia systems using electromagnetic phased arrays have often been investigated from a SAR distribution point of view. One of the problems in these systems is that the achieved SAR distribution is different from the intended one because of changes in the generator signals due to mutual coupling between applications. The use of circuit theory and S-parameters in the description of an N-applicator phased array system is introduced in this paper, and a compact matrix equation giving excitation as a function of generator signals is derived. Measurement of the S-parameters is discussed using a phased array deep heating system (Danish Hyperthermia Foundation (DHF)) as an example. In a phantom experiment a significant improvement in the SAR distribution is demonstrated when the developed method is applied.

Optimal steady-state temperature distribution for a phased array hyperthermia system

A method is presented for the evaluation of optimal amplitude and phase excitations for the radiating elements of a phased array hyperthermia system, in order to achieve desired steady-state temperature distributions inside and outside of malignant tissues. Use is made of a detailed electromagnetic and thermal model of the heated tissue in order to predict the steady-state temperature at any point in tissue. Optimal excitations are obtained by minimizing the squared error between desired and model predicted temperatures inside the tumor volume, subject to the constraint that temperatures do not exceed an upper bound outside the tumor. The penalty function technique is used to solve the constrained optimization problem. Sequential unconstrained minima are obtained by a modified Newton method. Numerical results for a four element phased array hyperthermia system are presented.

Interactions of cAMP-mediated vasodilators with angiotensin II in rat kidney during hypertension

In previous studies [C. Chatziantoniou and W.J. Arendshorst. Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32): F573-F580, 1992], we reported that vasodilator prostaglandins (PGs) are defective in buffering the angiotensin II (ANG II)-induced vasoconstriction in the renal vasculature of spontaneously hypertensive rats (SHR). The purpose of the present study was to determine whether this defect in SHR kidneys is specific to PGs or generalized to the action of vasodilators and to gain insight into which intracellular signal(s) mediates this abnormality. Renal blood flow (RBF; electromagnetic flowmetry) was measured in 7 wk-old anesthetized, euvolemic SHR and normotensive Wistar-Kyoto (WKY) rats pretreated with indomethacin to avoid interactions with endogenous PGs. ANG II (2 ng) was injected into the renal artery before and during continuous intrarenal infusion of fenoldopam [DA1 receptor agonist and G protein-dependent stimulator of adenosine 3',5'-cyclic monophosphate (cAMP)], forskolin (G protein-independent stimulator of cAMP), dibutyryl-cAMP (soluble cAMP), and acetylcholine (cGMP stimulator). Each vasodilator was infused at a low dose that did not affect baseline arterial pressure or RBF. In the control period, ANG II reduced RBF by 50% in both strains. Infusion of fenoldopam significantly blunted the ANG II-induced vasoconstriction in WKY, but not in SHR. In contrast, forskolin, dibutyryl-cAMP, and acetylcholine effectively buffered the vasoconstriction due to ANG II in both SHR and WKY. These results suggest that renal vasodilators acting through receptor binding to stimulate the cAMP signaling pathway are ineffective in counteracting the ANG II-induced vasoconstriction in SHR kidneys. (ABSTRACT TRUNCATED AT 250 WORDS)

Optical imaging of shock waves produced by a high-energy electromagnetic transducer

An electromagnetic acoustic transducer (EMAT) and acoustic lens have been constructed to provide reproducible and well characterized acoustic shock waves in water. The peak pressure amplitude variation for the unfocused and focused shock waves was found to be within +/- 5%. The focal region has been characterized both optically and by conventional piezoelectric pressure measurements. Optical investigations centre around ruby laser illuminated Schlieren and focused shadow imaging. The temporal resolution of the optical technique was determined by the ruby laser pulse length of 20 ns, giving a spatial resolution of 30 microns for a shock front in water.

The effect of hyperosmotic solutions on the hepatic blood flow

The present study was undertaken in order to measure the effect of hyperosmotic solutions on portal and hepatic blood flow. In five anaesthetized pigs without arterial blood supply to the liver, portal blood flow rate was measured (electromagnetic flowmeter) during 5 min lasting intravenous infusions of hyperosmotic galactose (50%, 84-100 ml) and mannitol (25%, 100 ml), with physiological saline (100 ml) as control. Portal blood flow increased to a peak value of (39% [P = 0.06] galactose and 37%, [P = 0.06], mannitol) soon after stop of the hyperosmotic infusion. For galactose the change ended somewhat earlier than for mannitol. Saline induced a minor increase (15%). Similarly, increments of, on average, 144% of the hepatic blood flow rate was seen in six patients with cirrhosis, following infusion of hyperosmotic galactose, the increase being more pronounced than in the pigs. The causes for these osmotic effects are not known, but they have to be taken into consideration in studies of the portal and hepatic blood flow.

Neurobiological effects of extensive transcranial electromagnetic stimulation in an animal model

The effects of transcranial electromagnetic stimulation (TEMS) on the cellular morphology of the cortex, cerebellum, and brain-stem were systematically investigated in rabbits exposed to 1000 pulsed stimuli at 100% maximum stimulation level (2.0 Tesla at the skull) over a 12 month period with a 5 cm circular magnetic coil positioned over the cranium. Also, the acute effects of TEMS on heart rate and respiration were examined. (1) T1 and T2 weighted magnetic resonance images (MRI) of 1-3 mm sections in both sagittal and axial planes revealed no evidence of gross morphological changes or subtler tissue damage to the cerebrum, cerebellum, or brain-stem. (2) Light microscopic examination of 60 microns hematoxylin-eosin/Cresyl Violet Luxol Fast Blue stained sections of the brain-stem, cerebellum, and cerebral cortex showed no TEMS-related changes in cellular organization or histological damage. (3) Autonomic activity as reflected by heart rate was also unaffected by high intensity TEMS. Normal heart rate was maintained during repeated TEMS at 100% of maximum. (4) Respiration rate was briefly altered at the time of the stimulus, but returned to normal immediately after the stimulus. These findings in experimental animals revealed no biohazardous effects on the brain following extensive exposure to high intensity, low frequency time-varying magnetic field stimulation from the coil of a clinical instrument.

Noise enhancement of information transfer in crayfish mechanoreceptors by stochastic resonance

In linear information theory, electrical engineering and neurobiology, random noise has traditionally been viewed as a detriment to information transmission. Stochastic resonance (SR) is a nonlinear, statistical dynamics whereby information flow in a multi-state system is enhanced by the presence of optimized, random noise. A major consequence of SR for signal reception is that it makes possible substantial improvements in the detection of weak periodic signals. Although SR has recently been demonstrated in several artificial physical systems, it may also occur naturally, and an intriguing possibility is that biological systems have evolved the capability to exploit SR by optimizing endogenous sources of noise. Sensory systems are an obvious place to look for SR, as they excel at detecting weak signals in a noisy environment. Here we demonstrate SR using external noise applied to crayfish mechanoreceptor cells. Our results show that individual neurons can provide a physiological substrate for SR in sensory systems.

On-line estimation of changes in left ventricular stroke volume by transesophageal echocardiographic automated border detection in patients undergoing coronary artery bypass grafting

Echocardiographic automated border detection can determine the interface between blood and myocardial tissue and calculate left ventricular (LV) cavity area in real-time. The objective was to determine if on-line measurements of LV cavity area by transesophageal automated border detection could be used to determine beat-to-beat changes in stroke volume in humans. Studies were attempted on 9 consecutive patients, aged 66 +/- 8 years, undergoing coronary bypass surgery. Stroke volume was measured by electromagnetic flow from the ascending aorta, and LV cavity area was measured at the midventricular short-axis level. Simultaneous area and flow data were recorded on a computer workstation through a customized interface with the ultrasound system. Recordings were performed during baseline apnea and rapid alterations induced by inferior vena caval occlusions before and after cardiopulmonary bypass. Measurements of stroke area (maximal area-minimal area) were correlated with stroke volume for matched beats. Data were available for analysis on 8 of 9 patients before and on 5 patients after cardiopulmonary bypass for 644 beats. Stroke area was closely correlated with stroke volume both before (mean R = 0.94 +/- 0.03, SEE = 0.33 +/- 0.12 cm2) and after (mean R = 0.92 +/- 0.05, SEE = 0.59 +/- 0.81 cm2) cardiopulmonary bypass. The slopes of these stroke area-stroke volume relations were quite reproducible from before to after cardiopulmonary bypass in the same patient but varied between individual patients. Transesophageal automated border detection has potential for on-line estimation of changes in stroke volume in selected patients.