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Biomedical subjects

S Z Child

Publications and source records attributed to S Z Child.

At least 19 recordsLinked to original sources
PubMed1995

Tactile perception of ultrasound.

In this investigation, acoustic radiation force was used as a stimulus to determine the threshold for tactile perception in the human finger and upper forearm as a function of frequency and pulse duration. Initially, a small (1.8-cm2) acoustically reflecting disk was affixed to the anatomical exposure site to maximize the delivered radiation force. Exposures were performed using a 2.2-MHz unfocused source modulated to produce square waves at 50, 100, 200, 500, and 1000 Hz. For the finger, maximum tactile sensitivity occurred at 200 Hz with a threshold radiation force of approximately 0.4 mN. For single pulses of 1 to 100 ms at 2.2 MHz, the threshold forces were an order of magnitude greater than for continuous exposure modulated at 200 Hz. Thresholds for pulse durations of 0.1 ms were somewhat greater than for pulses longer than 1 ms. Subsequently, thresholds of tactile perception were determined for direct exposure of the upper forearm (avoiding bone) to single pulses of 2.2-MHz ultrasound. Comparison of perception thresholds with and without a reflecting material over the tissue were consistent with the hypothesis that the tactile sensation experienced when tissue is exposed to ultrasound is its response to the radiation force associated with the transfer of momentum from the sound field to the tissue medium.

Acoustics↗
PubMed1994

Feasibility of recanalization of human coronary arteries using high-intensity ultrasound.

To investigate the feasibility of ultrasonic recanalization of obstructed human coronary arteries in vitro, high-intensity ultrasound was applied to 16 coronary arteries obtained at autopsy, using a prototype instrument enabling insonification through a catheter tip. It was a 119 cm long, 0.95 mm thick wire in an 8Fr catheter connected to an external ultrasonic transformer and power generator. A 5 MHz phased-array 2-dimensional echocardiography instrument was used to determine minimal luminal diameter and percent diameter narrowing before and after ultrasound application. The ultrasonic energy was delivered at 21.5 kHz and with a 52 +/- 19 micrometer average amplitude of tip displacement. The mean percent luminal diameter narrowing, flow rate and mean pressure gradient before ultrasound exposure were 74 +/- 11%, 97 +/- 61 ml/min, and 92 +/- 18 mm Hg, respectively. After recanalization, the mean percent luminal diameter narrowing decreased to 45 +/- 17% (p < 0.001), the mean flow rate increased to 84 +/- 92 ml/min (p < 0.001), and the mean pressure gradient was reduced to 45 +/- 24 mm Hg (p < 0.001). Of the debris particles, 95% had a diameter < 9 microns (range 5 to 12). Arterial perforation occurred in 5 of 16 arteries (31%) and all 5 occurred due to stiff wire manipulation and without ultrasound application. Mechanical fracture of the wire occurred in 8 cases (50%). No signs of thermal injury were found on histology. Thus, ultrasonic recanalization of human coronary arteries in vitro is feasible. It may reduce obstruction and improve blood flow. Debris sizes are sufficiently small to minimize the hazard of peripheral embolization.

Adult↗
PubMed1994

A test of the hypothesis that diagnostic ultrasound disrupts myelination in neonatal rats.

Neonatal rats were exposed or sham exposed for 30 min to pulsed ultrasound [2.25 MHz carrier frequency, 1 microsecond pulse length, 50 Hz pulse repetition frequency (PRF), 50 W/cm2 Imax, 2 mW/cm2 ITA], euthanised and prepared for electron microscopic analysis of the nodes of Ranvier of the dorsal and ventral roots of the spinal cord. There was also a cage control. All materials were processed and scored blindly, evaluating whether perinodal myelin was normal. Rats from all regimens had areas of disrupted myelination. There was no statistically significant difference among the regimens for absence of myelination. The results did not confirm an earlier report that diagnostic ultrasound disrupts myelination in neonatal rats.

Animals↗
PubMed1994

Damage to murine kidney and intestine from exposure to the fields of a piezoelectric lithotripter.

Earlier studies, in which murine kidneys were exposed to spherically diverging, spark-generated shock waves, demonstrated extensive hemorrhage in the interior of the organ at peak positive pressures somewhat less than 10 MPa. With comparable pulse numbers, this investigation, using the focal fields of a piezoelectric lithotripter, found no damage to murine kidneys at peak positive pressures as high as 40 MPa. Comparison of these cases and earlier bioeffects studies using pulsed, focused ultrasound leads to the conclusion that damage to murine kidneys is not simply correlated with peak positive pressure or peak negative pressure, nor is spectral content of the wave able to explain the striking differences in damage from these sources. With 200 individual shock waves from the piezoelectric lithotripter applied ventrally, 20-30% of the animals suffered superficial kidney damage (bleeding into the capsule), but the same exposure conditions produced severe intestinal hemorrhage in more than 80% of the animals.

Animals↗
PubMed1993

Morphological effects of pulsed ultrasound in the lung.

We have previously described the induction of subcapsular hemorrhage in the murine lung by extracorporeal shock wave lithotripsy at exposures of 2 MPa (Hartman et al. 1990) and pulsed ultrasound (Child et al. 1990). Since extravasation of erythrocytes and alveolar flooding are prominent, we proposed to determine whether or not the injury was progressive, by continuing to develop following termination of exposure, and by localizing where the injury was developing. Mice were exposed to 10 microsecond impulses at 1.6 MPa for 3 min and sacrificed either immediately or 5 min following exposure. When observed with both light and transmission electron microscopy, there was no gradation in lung injury, with a sharp demarcation of the hemorrhagic area. Moreover, both type I pneumocytes and capillary endothelial cells were injured, causing direct continuities between vessel lumina and alveolar spaces. In the absence of extravasation, the tissue appeared normal. There was no evidence that injury increased in severity during the first 5 min after exposure.

Animals↗
PubMed1993

Lysis of erythrocytes by exposure to CW ultrasound.

The threshold for lysis of erythrocytes suspended at concentrations of 0.5-1% in saline or plasma in rotating cylindrical exposure vessels is approximately spatial peak intensities of 2 W/cm2 at 1 MHz continuous wave (CW). Results of a series of experiments in which cell concentration, viscosity and gas composition of the suspending medium and rotation speed of the exposure vessel were varied combined with observations of sonoluminescence are all consistent with a hypothesis that cells are lysed by inertial (transient) acoustic cavitation. For the proposed mechanism to operate in cell suspensions, it is necessary that bubbles be brought into contact with the cells. Rotation of the chamber recycles bubbles that are driven by radiation forces to the far wall of the chamber in a matter of milliseconds. The physical and chemical properties of the wall of the chamber appear to be important as stabilizing sites for nuclei that serve as seeds for cavitation events.

Animals↗
PubMed1993

Timing of exposures in ultrasonic hemorrhage of murine lung.

Pressure thresholds for lung hemorrhage by exposure to low-temporal-average-intensity, pulsed ultrasound are of the order of 1 MPa. Earlier evidence suggested that ultrasound modifies the tissue over short periods of time in such a way that the nonthermal action of ultrasound is enhanced. Measurements of thresholds (1) for hemorrhage and (2) for penetration of the hemorrhage through the murine lung in which a given "on-time" was presented to the tissue over periods of time up to 3 min support the hypothesis.

Animals↗
PubMed1993

A test for teratological effects of power frequency magnetic fields on chick embryos.

An analysis of 13 studies of the teratological effects of pulsed magnetic fields on chick embryos from ten independent laboratories permits no clear conclusions. Comparatively little has been done to follow up on the reports by Juutilainen and coworkers on the effects of extremely low-frequency, sinusoidal magnetic fields on the malformation rate in chick embryos. Our attempt to follow up on their results using similar but not identical exposures of 10 microT, 50 Hz magnetic fields produced negative results.

Animals↗
PubMed1992

The sensitivity of Drosophila larvae to continuous-wave ultrasound.

The threshold for killing of freshly hatched Drosophila larvae exposed to continuous-wave (CW) ultrasound shows a minimum at approximately 0.3 MHz. This suggests that the stiffness of the material surrounding the gas bodies in the organism is comparable to water. From this, it is apparent that the gas bodies in three-day-old larvae that we have used in earlier studies are far larger than resonance size at the frequencies (1-5 MHz) used. Yet, these larvae were killed by short exposures to low-temporal-average-intensity pulsed ultrasound with peak intensities of the order of 10 W/cm2. Hence, it appears that "large" bubbles cannot be ignored in considerations of the biological effects of pulsed ultrasound and lithotripsy.

Animals↗
PubMed1992

Ultrasonic heating of lung tissue.

Tests with mice show that lung tissue is not selectively heated in comparison with other soft tissues and that lung has an efficient mechanism for dissipating that heat which is produced. Temperatures measured with a fine thermocouple placed at the outer surface of the mouse lung show approximately 1 degree C total rise in temperature in the living animal for an incident intensity of 1 W/cm2 (4 MHz, unfocused sound field).

Animals↗
PubMed1991

Pulsed ultrasound and the hyperbarically exposed mouse fetus.

To enhance the likelihood of cavitation, pregnant mice were subjected to hyperbaric conditions and quickly returned to atmospheric pressure. Following this treatment, they were exposed to spatial average, pulse average intensities of 100 W/cm2 (2.2-MHz, 20-microseconds pulses with a duty cycle of 1/1000 or a temporal average spatial average intensity of 0.1 W/cm2). Fetal weights, deaths and malformations were scored. No statistically significant effects were observed in the offspring.

Animals↗
PubMed1990

Effects of lithotripter fields on development of chick embryos.

Chick embryos at 72 h incubation were subjected to three double shock waves from a Wolf Model 2137.50 Electrohydraulic Lithotripter. The pressure amplitude at the embryo was adjusted by variation of the distance from the source to the embryo. After a total of 120 h of incubation, they were assessed for developmental abnormalities. Early deaths, delayed deaths and malformations were all significantly increased at pressures of 10 MPa with suggestions of possible effects at lower pressure levels.

Animals↗
PubMed1990

Lung damage from exposure to pulsed ultrasound.

Motivated by a recent finding that threshold pressures for hemorrhage in mouse lung exposed to the fields of an electrohydraulic lithotripter were less than 2 MPa, we extended the exposures to pulsed ultrasound. Sharply defined thresholds of the order of 1 MPa were found with 10 microseconds length pulses and roughly twice that value for 1 microsecond pulses. The thresholds at 4 MHz are greater than at 1 MHz. The thresholds are comparable for focused and unfocused fields. As would be expected for a cavitation-like phenomenon, temporal average intensity is a very poor predictor of this effect. In the extreme case, lesions were found at temporal average intensities on the order of 1 mW/cm2.

Animals↗
PubMed1990

Lung damage from exposure to the fields of an electrohydraulic lithotripter.

Threshold pressures for hemorrhage in mouse lung exposed to the fields of an electrohydraulic lithotripter appear to be less than 2 MPa with as few as 10 pulses and with severe damage occurring at levels between 5 and 6 MPa. This is very much smaller than the fields required to fragment kidney and gallstones and smaller than the thresholds for damage to kidney tissues. Fetal lung, in contrast, did not show signs of damage at 20 MPa. The lower sensitivity of fetal lung is consistent with a cavitation-related mechanism for lung damage by shock waves. Since the pressures in these exposures are almost entirely positive, it suggests that the value of negative pressures as predictors of the behavior of gas bodies in tissues should be reconsidered.

Animals↗
PubMed1990

Test for kidney hemorrhage following exposure to intense, pulsed ultrasound.

A recent study has found that the threshold for extravasation in mouse kidney tissues by exposure to a spark-generated shock wave is of the order of 3-5 MPa (peak positive pressure). Since the mode pressure used by commercial pulsed Doppler ultrasound units is approximately 5 MPa, it is essential to determine whether these observations are relevant to diagnostic ultrasound. Hence, a comparable study has been completed using the same pathological endpoints but with exposure to pulsed ultrasound (10 microseconds pulse length) at 1.2 MHz and 3.8 MHz in which peak positive pressures exceeded 10 MPa. At these levels the focal waves are in shock because of the nonlinear properties of the propagating medium. The results of the pulsed ultrasound study were negative. Although this finding is encouraging for the use of diagnostic ultrasound, the two studies eventually must be integrated into a single mechanistic picture before the limits of safety will be known.

Animals↗
PubMed1990

Killing of Drosophila larvae by the fields of an electrohydraulic lithotripter.

Drosophila larvae contain small gas bodies stabilized within their respiratory system. Because these bubbles are inhibited in their capacity to expand by the surrounding tissues, it is probable that they do not respond to acoustic fields in the manner described by classical cavitation theory that assumes a spherical bubble in an infinite fluid. However, just because of this inhibited expansion, they may serve as reasonable models for the gas bodies in mammalian tissues. Approximately one half of a population of Drosophila larvae is killed by exposure to 3 to 10 double lithotripter shocks with a positive pressure of 2-3 MPa. In contrast with the predictions of classical cavitation theory, adding a negative pressure to the exposure has little influence on the killing rate or its threshold pressure. The available evidence suggests that interaction of gas bodies in tissues with pressure fields and the resultant biological effects may be qualitatively different than predicted by classical cavitation theory and that positive rather than negative pressure may be a predictor of these effects.

Animals↗
PubMed1990

Lysis of cells in Elodea leaves by pulsed and continuous wave ultrasound.

Resonance lysis of the cells in the leaves of the aquatic plant Elodea originally reported by Miller have thresholds at intensities of a few W/cm2. With pulsed ultrasound, the resonance behavior vanishes and the thresholds are at much higher amplitudes. This is similar to the characteristics of the thresholds for killing of Drosophila larvae by pulsed ultrasound. Both organisms contain small gas bodies within the tissues which may serve as nuclei for a cavitation related phenomenon. The results suggest that the response of these bubbles to continuous wave fields and very short pulses is qualitatively different.

Cell Survival↗