Effects of low-level 50 Hz magnetic fields on the level of host defense and on spleen colony formation.

The results of 3 sets of experiments on the effects of 22 microT sinusoidal 50 Hz magnetic fields (MF), applied for 1 h on 5 successive days (1 h/5 days), on the level of host defense and on spleen colony formation are reported. The first set of experiments shows the effects on the number of colony-forming units (CFUs) on the spleen and on the cellularity of the thymus in mice. The MF exposures resulted in an increase in CFUs which was statistically significant with respect to the controls, but not with respect to the shams. Statistically significant changes in the thymic weight and thymic index with respect to both the controls and the shams were measured 1 h after the last MF exposure. In the second set of experiments, the mice were given a sublethal dose of X-rays (6 Gy), which was followed by exposure 2 h later to the MF. The MF exposure was repeated at the same time of day for 5 days. The number of colonies per spleen showed a consistent, statistically significant increase with MF exposure and the number of CFUs per femur was decreased. In the third set of experiments, bone marrow was taken from mice which had been exposed to 22 microT fields and injected into mice which had been exposed to a lethal dose of X-rays (9 Gy). The number of CFUs per femur in the recipient mice was shown to be reduced by a statistically significant amount at 1 and 4 days after injection.

Combined action of static and alternating magnetic fields on ionic current in aqueous glutamic acid solution.

Combined parallel static and alternating magnetic fields cause a rapid change in the ionic current flowing through an aqueous glutamic acid solution when the alternating field frequency is equal to the cyclotron frequency. The current peak is 20-30% of the background direct current. The peak is observed with slow sweep in the alternating magnetic field frequency from 1 Hz-10 Hz. Only one resonance peak in the current is observed in this frequency range. The frequency corresponding to the peak is directly proportional to the static magnetic field. The above effect only arises at very small alternating field amplitude in the range from 0.02 microT-0.08 microT.

Real-time multichannel computerized electrogastrograph.

The purpose of this study was to develop a real-time multichannel computerized electrogastrograph (EGG) to measure and analyze electrical signals from the human abdominal surface. A soft-contact matrix composed of 25 cutaneous electrodes is embedded evenly in a latex mat. The mat can be firmly attached to the abdominal surface by drawing a vacuum between the matrix and the stomach. Twenty-five high-amplification filter/amplifiers provide a high signal-to-noise ratio and flat amplitude response for a signal between 0.02 and 0.12 Hz (1.2-7.2 cpm). The computer program provides waveform and frequency analysis for any chosen channel and mapping analyses for all 25 channels. A two-dimensional propagation exploration program was also developed. Using four different mapping analysis program subroutines, the optimal points for analyzing the EGG signals can be reliably found and variability of these locations can be observed easily. Results show differences in the EGG mappings of normal and abnormal subjects.

Brief communication: coaxial lines for multiphase power distribution.

A coaxial cable can be used to reduce the magnetic and electric fields that extend into environments in the vicinity of transmission lines and distribution lines and in-house or building wiring for power distribution systems. The use of the coaxial geometry may prove useful in cases where there are environmental concerns with respect to health effects and in cases where there is a need to run high-speed data communications in close proximity to power distribution systems.

Some engineering models for interactions of electric and magnetic fields with biological systems.

The objective of this paper is to review some of the fundamental mechanisms for the interaction of electric and magnetic fields with biological systems at variable levels of field strengths and to examine several possible ways by which weak fields may influence these systems. We begin with a review of the basic equations by which electric or magnetic fields interact with biological fluids and follow it with a look at the effects of inserting a simple cell membrane. The initial starting points are the force equations on charged particles and dipoles. We examine their effects on current flow, the orientation of long-chain molecules, and the forces which can be exerted by particles of magnetite on membranes. This is followed by a very simple model for the effects of a cell membrane on the overall current distribution and a model for current flow through a membrane. Some sources of nonlinearities which might serve as mechanisms for converting weak electrical signals from one frequency to a more biologically significant frequency are described. Additionally, three models by which a biological system may extract weak signals from noise are presented. The first of these is the injection-locking of oscillating processes where the signal-to-noise ratio may be less than unity. The second is parametric amplification which allows the external signal and the biological process to be at different frequencies and where stability requirements on the external pump frequency discriminates against the noise. The third approach is to examine a computer model for a neural network which can be trained to identify a 60 Hz field at signal-to-noise ratios much less than one. The key to each of these models for possible interactions of magnetic fields with biological systems is the long-term coherence of the signal with respect to the noise. Finally, we briefly examine the possibility of using scanning force and tunneling microscopes to give a better description of the characteristics of the cell surface.

Temporally-specific modification of myelinated axon excitability in vitro following a single ultrasound pulse.

Single, short-duration, low-energy pulses of ultrasound were found to elicit distinct modifications of the electrical excitability of myelinated frog sciatic nerve in vitro in a window extending 40-50 ms after pulse termination. These modifications include both enhancement and suppression of relative excitability, the sequence of which generally follows one of two distinct temporal response patterns. The ultrasound pulses were focused, 2-7 MHz, of 500-microseconds duration, and of peak intensities of 100-800 W/cm2. Total absorbed pulse energies were generally less than 100 mJ/g, corresponding to local temperature rises of the nerve trunk of no more than 0.025 degrees C per pulse, thereby precluding bulk heating as a basis of this effect. The observed effects cannot be elicited using either a subthreshold square wave or RF electrical prestimulus, suggesting a unique form of receptivity of the nerve trunk to mechanical perturbation. We present evidence that the low-frequency radiation pressure transient accompanying the envelope of the acoustic pulse is the active parameter in this phenomenon, and postulate that it may act by the gating of stretch-sensitive channels, which have been recently reported in a variety of cell membranes. These results may demonstrate that stretch-sensitive channels in neural membrane can serve to functionally modulate neuro-electric signals normally mediated by voltage-dependent channels, a finding which could suggest new clinical applications of high peak-power, low-total-energy pulsed ultrasound.

Transient modification of nerve excitability in vitro by single ultrasound pulses.

Single pulses of focused ultrasound have been observed to significantly modify neuronal excitability in vitro for a period of 40-50 ms following pulse termination. This window of transient modification includes periods of both relative suppression and enhancement of excitability, the sequences of which generally follow distinct temporal patterns. The ultrasound pulses were focused, 2-7 MHz, nominally of 500 microseconds duration, and of peak intensities of 100-800 W/cm2. Specific absorbed energies were less than 100 mJ/gm, which strongly precludes bulk thermal mechanisms as a basis of this effect. Our current evidence suggests that the low-frequency radiation pressure transient accompanying the envelope of the acoustic pulse is the proximal effector in this phenomenon, acting by the gating of relatively slow stretch-sensitive channels in the neuronal membrane. These observations demonstrate the potential for high peak-power, low total-energy pulses of ultrasound to functionally modulate neuroelectric signals, a finding which could suggest new prosthetic, analgesic, or therapeutic clinical applications.

Radio-microwave interactions with biological materials.

There are a variety of ways in which a microwave field can affect a biological system. The best understood are those associated with heating, which, in turn, lead to changes in chemical reaction rates and current flows. At high levels, forces associated with the field gradients have been observed, as well as nonlinearities, including the destruction of membranes. At low levels, we discuss the possibility of quantum effects and some limits set by noise.

Cell membrane temperature rate sensitivity predicted from the Nernst equation.

A hyperpolarized current is predicted from the Nernst equation for conditions of positive temperature derivatives with respect to time. This ion current, coupled with changes in membrane channel conductivities, is expected to contribute to a transient potential shift across the cell membrane for silent cells and to a change in firing rate for pacemaker cells.

Improved phonocardiogram system based on acoustic impedance matching.

We considered that phonocardiographic recording could be improved 1) by minimizing the acoustic impedance mismatch between the precordial tissue and transducer, 2) by optimizing the configuration of the impedance-matching medium and transducer design, and 3) by storing signals in digital form through analog-to-digital conversion of analog recordings made at the bedside. The use of an aqueous coupling medium to improve energy transmission increased signal voltage approximately 100-fold over presently used commercial devices. Further match to the crystal was achieved by a concentrating horn configuration for the aqueous medium. Measured frequency response of the device in the range 1 Hz to 1 kHz was better than two other commercially tested microphones. Inspection of comparative phonocardiograms showed more information from the new device than from the two other commercial devices. Unfiltered digitized signals, using our microphone in normal subjects, demonstrated good beat-to-beat repeatability, but analog filtering to obtain the conventional phonocardiogram showed significant loss of information. The new instrument appears to be superior to those commercial devices tested in recording heart sounds.

A simplified theory of pearl chain effects.

Many biological particles immersed in liquid media will align themselves and form pearl chains under an applied electric field. The alignment is independent of the frequency of the applied field, has a time delay, and can occur only when the field strength is greater than a certain minimum value. Also, at certain frequencies the particles will turn 90 degrees in space (turn-over phenomenon). In this paper we propose a simple theory explaining these phenomena and suggest further experimental checks and a possible application.