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Biomedical subjects

E L Carstensen

Publications and source records attributed to E L Carstensen.

At least 19 recordsLinked to original sources
PubMed1996

A test for cavitation as a mechanism for intestinal hemorrhage in mice exposed to a piezoelectric lithotripter.

This study tested the hypothesis that intestinal hemorrhage produced by exposure to lithotripter fields depends upon the presence of gas in the intestine. The extent of hemorrhage in the gas-containing intestines of pregnant mice was compared to the amount of hemorrhage in the bubble-free intestines of their fetuses. On day 18 of gestation, the abdominal regions of pregnant C3H mice (n = 6) were exposed to 200 pulses from a piezoelectric lithotripter. Acoustic pulses had a peak pressure amplitude of 10 MPa and were administered at a rate of approximately 1 Hz. All maternal intestines showed hemorrhagic regions extending several centimeters in length. In contrast, only 1 of 43 exposed fetuses showed an intestinal hemorrhage and this one lesion was less than 1 mm in diameter. These results support the hypothesis of the study and are consistent with a cavitation-related mechanism for the production of intestinal hemorrhage by exposure to acoustic fields.

Animals↗
PubMed1995

A test of the hypothesis that a 60-Hz magnetic field affects ornithine decarboxylase activity in mouse L929 cells in vitro.

Four replicate experiments were performed to test the hypothesis that a 4-hr exposure of L929 cells in vitro to a 60 Hz, 10 microT magnetic field results in a large increase in ornithine decarboxylase (ODC) enzyme activity (1-2). A positive control yielded a highly statistically significant increase in ODC activity. However, magnetic field exposure had no statistically significant effect on extractable ODC activity of L929 cells relative to that of sham-exposed cells.

Analysis of Variance↗
PubMed1995

Intestinal hemorrhage from exposure to pulsed ultrasound.

Threshold exposures for producing intestinal hemorrhage in mice were determined using focused sources operating at 0.7, 1.1, 2.4 and 3.6 MHz. The choice of pulse length (10 microseconds) and pulse repetition frequency (100 Hz) made the exposures diagnostically relevant, while at the same time, minimized possible thermal contributions to the mechanism of action of the ultrasound. Each animal was irradiated at four to five abdominal sites for 5 min per site. Suprathreshold lesions ranged from small petechiae to hemorrhagic regions extending 4 mm or more along the intestine, depending upon the exposure levels. Higher frequencies were less effective in producing intestinal hemorrhage than lower frequencies. Thermocouple measurements of temperature rise in the intestine during ultrasound exposure revealed temperature increments between 1 degrees and 2 degrees C at the highest exposure levels. The frequency dependence of the production of intestinal hemorrhage together with the observed limited heating is consistent with a cavitation-related mechanism of action of pulsed ultrasound.

Abdominal Muscles↗
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

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↗
PubMed1994

A test of the influence of cyclotron resonance exposures on diatom motility.

An attempt was made to test the hypothesis (McLeod et al. 1987; Smith et al. 1987) that a certain combination of direct current and alternating current magnetic field exposures at room temperature results in an increase in motility of a marine diatom (Amphora coffeaeformis) to a maximum value. Diatom motility increased as a function of calcium concentration in the medium, as reported by McLeod et al. (1987) and Smith et al. (1987). There was, however, no effect of the magnetic field exposures on diatom motility. The exposures employed 16-Hz magnetic fields with amplitudes of 21 or 29.7 microT (21 microT rms) as well as 21 microT (amplitude) fields at frequencies above and below the reported "resonance" frequency. All experiments were conducted double blindly, and each trial had its own positive control.

Calcium↗
PubMed1993

Characterization of ultrasound-potentiated fibrinolysis in vitro.

We have characterized the effects of ultrasound on fibrinolysis in vitro to investigate the mechanism of ultrasonic potentiation of fibrinolysis and to identify potentially useful ultrasound parameters for therapeutic application. Radiolabeled clots in thin walled tubes were exposed to ultrasound fields in a water bath at 37 degrees C, and lysis was measured by solubilization of radiolabel. Ultrasound accelerated lysis of plasma, whole blood, and purified fibrin clots mediated by recombinant tissue-type plasminogen activator (rt-PA), urokinase, or streptokinase, but ultrasound by itself caused no clot solubilization. The degree of ultrasonic potentiation was dependent on plasminogen activator concentration, increasing from 2.2-fold at a streptokinase concentration of 75 U/mL to 5.5-fold at 250 U/mL in a 1 MHz ultrasound field at 4 W/cm2. Ultrasound exposure resulted in heating due to absorption by the plastic tube, but the temperature increase was insufficient to account for the increase in clot lysis rate, indicating that the primary effect was nonthermal. Ultrasound did not accelerate hydrolysis of a peptide substrate by rt-PA and did not alter the rate of plasmic degradation of fibrinogen, indicating that the augmentation of enzymatic fibrinolysis required the presence of a fibrin gel. The acceleration of fibrinolysis by ultrasound was greater at higher intensities and duty cycles and was maximum at frequencies between 1 and 2.2 MHz, but decreased at 3.4 MHz. These findings suggest that ultrasound accelerates enzymatic fibrinolysis by increasing transport of reactants through a cavitation-related mechanism.

Blood Coagulation↗
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

Effects of pulsed ultrasound on the frog heart: I. Thresholds for changes in cardiac rhythm and aortic pressure.

High intensity pulsed ultrasound at 1.2 MHz is shown to change the cardiac rhythm and aortic pressure of frog hearts in vivo. Threshold levels for these effects occur at acoustic pressure amplitudes of the order of 10 MPa for 5 ms pulse lengths. Depending upon the phase of the heart cycle, a pulse of ultrasound either may cause a premature ventricular contraction, a reduction in the strength of contraction as measured by the aortic pressure, or an enhanced relaxation of the heart muscle. There is an increase in the effectiveness of the ultrasound with increase in pulse length in the range from 1 to 5 ms.

Animals↗
PubMed1993

Effects of pulsed ultrasound on the frog heart: II. An investigation of heating as a potential mechanism.

This study investigated heating as the possible mechanism for the reduction in aortic pressure observed as a result of exposure of frog hearts in vivo to a single, high intensity pulse of ultrasound. The threshold for producing reduced aortic pressure with 5 ms pulses of ultrasound was found to be approximately 5-10 MPa peak positive pressure (ISPPA approximately 350-1000 W/cm2) at both 1.2 MHz and 3.7 MHz. Theoretical estimates and experimental measurements of heating, though, indicate that heating rates at threshold exposures for these two frequencies differ by as much as a factor of 10. As a result, heat alone does not appear to be the primary mechanism responsible for the observed effects on the heart.

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↗
PubMed1992

Enhancement of fibrinolysis in vitro by ultrasound.

The effect of ultrasound on the rate of fibrinolysis has been investigated using an in vitro system. Plasma or blood clots containing a trace label of 125I fibrin were suspended in plasma containing plasminogen activator and intermittently exposed to continuous wave 1-MHz ultrasound at intensities up to 8 W/cm2. Plasma clot lysis at 1 h with 1 microgram/ml recombinant tissue plasminogen activator (rt-PA) was 12.8 +/- 1.2% without ultrasound and was significantly (P = 0.0001) increased by exposure to ultrasound with greater lysis at 1 W/cm2 (18.0 +/- 1.4%), 2 W/cm2 (19.3 +/- 0.7%), 4 W/cm2 (22.8 +/- 1.8%), and 8 W/cm2 (58.7 +/- 7.1%). Significant increases in lysis were also seen with urokinase at ultrasound intensities of 2 W/cm2 and above. Exposure of clots to ultrasound in the absence of plasminogen activator did not increase lysis. Ultrasound exposure resulted in a marked reduction in the rt-PA concentration required to achieve an equivalent degree of lysis to that seen without ultrasound. For example, 15% lysis occurred in 1 h at 1 microgram/ml rt-PA without ultrasound or with 0.2 microgram/ml with ultrasound, a five-fold reduction in concentration. Ultrasound at 1 W/cm2 and above also potentiated lysis of retracted whole blood clots mediated by rt-PA or urokinase. The maximum temperature increase of plasma clots exposed to 4 W/cm2 ultrasound was only 1.7 degrees C, which could not explain the enhancement of fibrinolysis. Ultrasound exposure did not cause mechanical fragmentation of the clot into sedimentable fragments, nor did it alter the sizes of plasmic derivatives as demonstrated by SDS polyacrylamide gel electrophoresis. We conclude that ultrasound at 1 MHz potentiates enzymatic fibrinolysis by a nonthermal mechanism at energies that can potentially be applied and tolerated in vivo to accelerate therapeutic fibrinolysis.

Fibrinolysis↗