Howard Wachtel

Distance-weighted traffic density in proximity to a home is a risk factor for leukemia and other childhood cancers

ABSTRACT Occupational exposure to elevated concentrations of benzene is a known cause of leukemia in adults. Concentrations of benzene from motor vehicle exhaust could be elevated along highly trafficked streets. Several studies have reported significant associations between proximity to highly trafficked streets and the occurrence of childhood cancers and childhood leukemia. These associations may be due to chronic exposure to benzene or other carcinogenic components of vehicle exhaust from these nearby streets or to some other factor (e.g., noise, increased light exposure, or some unaccounted-for socioeconomic variable). We used data for homes studied in an earlier childhood cancer study conducted in Denver, CO, in the 1980s. No air pollution measurements were made in the original study. We identified the highest trafficked street near each study home and obtained the traffic density in 1979 and 1990. Traffic density was weighted for the distance from the street to the home using 3 different widths of Gaussian curves to approximate the decay of the emissions into the surrounding neighborhoods. The associations between the 750-ft-wide distance-weighted traffic density metrics and all childhood cancers and childhood leukemia are strongest in the highest traffic density category (≥ 20,000 vehicles per day [VPD]). The odds ratio is 5.90 (95% confidence interval [CI] 1.69-20.56) for all cancers and 8.28 (95% CI 2.09-32.80) for leukemia. The results are suggestive of an association between proximal high traffic streets with traffic counts ≥ 20,000 VPD and childhood cancer, including leukemia.

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.

Effects of Pulsed Acoustic and Mechanical Stimuli on the Excitability of Isolated Neuronal and Cardiac Cells

Abstract This article presents the final results of a series of investigations conducted on the interaction of two specific forms of mechanical stimuli with isolated neuronal and cardiac cells: short bursts of focused, high peak-power ultrasound (1 to 7 MHz, 0.5 ms, 50 to 800 W/cm2 spatial-peak, pulse-average intensity, 3-mm half-power spot) and 0.5-ms direct pressure pulses applied with a transducer-driven glass stylus with a 1- to 6-μm peak displacement. The current study has investigated the effects of these stimuli on the mouse sciatic nerve trunk and cardiac preparations of the leopard frog. They are compared to those observed with the leopard frog sciatic nerve trunk and lobster axon, reported previously. These studies have revealed that each of these preparations exhibits brief and fully reversible modifications of cellular excitability within a 10- to 30-ms window following both single, submillisecond ultrasound bursts and appropriately applied direct mechanical stimuli. The high peak-power ultras...

Comparison of the efficacy of pulsed versus CW microwave fields in evoking body movements

Short bursts of 1250-MHz microwave pulses (2-4 pulses of 10 ms duration leading to a midbrain peak-pulse specific absorption rate of 20 MW/kg) have been shown to be effective in evoking body movements in mice. This exposure translates to a specific absorption of 0.2 to 0.4 J/gm for achieving 50% response frequency. Separate experiments using continuous wave (CW) had previously indicated that about twice as much energy was required to elicit similar movements. In recent experiments in which CW and pulsed wave (PW) exposures were carried out on the same mice this result was confirmed. The midbrain bulk temperature rises resulting from these exposures (in the range of 0.1 degrees C) and the comparable efficacy of pulsed versus CW modes suggest that these evoked responses may be based on microthermal effects on the central nervous system.<<ETX>>

Single microwave pulses can suppress startle reflexes in mice

Modification of the acoustic startle reflex (ASR) exhibited by mice was used as a basis for determining the neural effectiveness of single microwave pulses (1 to 10 mu s, 1250 MHz). The authors utilized a tail clamp body motion detector to monitor the ASR while the mice were constrained within an exposure chamber which focused microwave energy selectively in the head and neck region. Complete suppression of the ASR was seen when single microwave pulses yielding absorbed energies of 0.2 J/kg or more were applied anywhere from 500 to 5 ms before the sound burst. Partial suppression of the ASR could be seen with even lower energy pulses or with pulses delivered over a wider range of prestimulus delays. These results cannot be attributed to bulk thermal effects, but may be due to thermoelastic or microthermal phenomena leading to neural intervention acting at the cochlea or within the CNS.<<ETX>>

Synchronization of Neural Firing Patterns by Relatively Weak ELF Fields

Usually, when the effects of ELF fields on neural activity are discussed it is pointed out that current densities of the order of 10−3 A/cm2 are required to produce direct excitation of quiescent neural tissue. By contrast, we have shown that spontaneously firing (pacemaker) neurons can be affected by ELF current densities down to 10−6 A/cm2. This effect takes the form of “phase-locking” wherein the neural firing rate is synchronized to the ELF frequency or a multiple of it. In this paper we review the evidence for this ELF synchronization phenomenon including recent extension of our findings by Sheppard et al[2]. We also propose a model to show how phase-locking of individual nerve cell firing rates could lead to “population synchrony” among large numbers of neurons. The possible relevance of this phenomenon to other reported low level ELF effects on the nervous system as well as its relevance to human ELF exposure conditions is discussed.

An Exposure System for Variable Electromagnetic-Field Orientation Electrophysiological Studies

A TEM system for exposing isolated nerve cells at 2 GHz is described. The system allows for monitoring of transmembrane potentials by means of microelectrodes and variation of the angle between the electric-field vector and the cell. An S-parameter characterization of the system is included along with temperature profile measurements for the energy distribution within the exposure chamber. Additional data on the transient electrical characteristics of microelectrodes upon exposure to microwave pulses in this system are included along with a few examples of the response of Aplysis pacemaker neurons to microwave fields.

Magnetic space shuttle experiments

Applications of magnetic fields in separation science, biotechnology and gravitational biology as studied in the low-gravity environment of space flight are reviewed. Ferromagnetism, ferrimagnetism, paramagnetism and diamagnetism have been applied in studies of collagen gel formation, bacterial growth and mixing in the free-fall condition of orbital space flight.

Transient Modification Of Membrane Potential And Conductance By Single Ultrasound Bursts Modulates Neuronal Excitability

The effect of short ultrasound bursts on the electrochemical characteristics of both myelinated and unmyelinated nerves was studied in vitro. These studies have revealed excitability changes occurring in a window of 40-50 ms following a single submillisecond exposure, which include periods of both relative enhancement and suppression of excitability. These modulations of excitability have now been associated with changes of membrane rest potential and conductance, as measured with intracellular electrodes. It is postulated that the radiation pressure transient accompanying the envelope of the acoustic pulse is the effective field parameter in this phenomenon, and may act by the gating of stretchsensitive channels in the membrane.