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P D Edmonds

Publications and source records attributed to P D Edmonds.

29 records · Page 2Linked to original sources
PubMed1979

Postpartum survival of mice exposed in utero to ultrasound.

We found no credible enhancement of neonatal mortality in mice exposed in utero on Day 8 of gestation to ultrasound at 0.44 W/cm2 (+/- 20%) spatial average intensity, 2 MHz, continuous wave, for 60--180 s in a 37 degrees C water bath. This result is compared with the adverse effect on neonatal survival reported by Curto [in Ultrasound in Medicine (Plenum, New York, 1976), Vol. 2, pp. 535--536] for exposure on Day 14 of gestation at about 0.125 to 0.5 W/cm2, 1MHz, continuous wave, for 180 s in a 30 degrees C bath. It is concluded that a temporary reduction in fetal viability, lasting from 4 days to less than 10 days after exposure, could account for both sets of data. It is also evident from these data that improved methods of determining intensities within mammalian tissues are highly desirable.

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PubMedDate not supplied

Evidence for free radical production by ultrasonic cavitation in biological media.

The statement is often made that free radicals will be produced during the violent collapse of transient cavities in liquids, that may result from the passage of ultrasonic waves in the low megahertz frequency range. Evidence for such free radicals is mostly indirect. We have insonated some argon-saturated aqueous solutions of biological molecules (trypsin, Dulbecco's Minimum Essential Medium, fetal bovine serum, and human blood plasma) and whole human blood, all containing a spin trapping compound, at 1 MHz, continuous wave, 6.6 W/cm2 (SPTA) for 15 min at 4-8 degrees C. Electron spin resonance spectra of the samples were recorded 10 and 30 min. after cessation of insonation. The spectra included those of spin adducts formed with .OH and .H radicals, which were absent in the cases of the sham treated controls. Thus, we have demonstrated the formation of the highly reactive .OH and .H radicals in the insonated media, even in the presence of natural radical scavengers in the mammalian derived products.

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PubMedDate not supplied

Flow dependence of 2-D temperature distributions induced in the perfused canine kidney by ultrasound.

The influence of perfusate flow rate on the two-dimensional (2-D) temperature distributions induced by hyperthermia in the canine kidney was evaluated. Localized hyperthermia was induced by ultrasound (frequency 2.040 MHz, transducer diameter 6.7 cm) in the ex-vivo perfused kidney. Temperatures were mapped using shielded copper/constantan thermocouple sensors. The 2-D temperature distribution of the kidney was obtained by pulling these sensors through a planar array of eight stainless-steel trocars inserted along its longitudinal axis. The perfusion system allowed for the control of internal/external organ temperature and type of perfusate, and it simulated vasodilation and vasoconstriction by changing the arterial volume flow rate. The temperature data obtained at flow rates ranging from 0 to 570 ml/min and power levels from 0 to 150 W showed that acoustic power densities in excess of 1.5 W/cm2 were required to maintain therapeutic temperatures in this system. Contour maps for characterizing the 2-D temperature distributions induced in this system were analysed with the introduction of a quantitative measure based on the area within a given isotherm. They show the effects of tissue heterogeneity, flow rate, and non-uniform power deposition. Time constants computed from the exponentially decaying temperatures measured following power off ranged from 5 to 555 s. These findings provide a basis for comparison with temperature measurements being acquired in the in-vivo kidney system. Information acquired from this system may facilitate the process of developing tissue-equivalent dynamic phantoms for ultrasound-induced hyperthermia. The ex-vivo model presented in this paper might be used to study the performance of alternative heating applicators, the effect of haematocrit, blood viscosity, and the use of vasoactive drugs.

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