Biological effects of ultrasound

Low-frequency US, such as that used in sonophoresis, has various effects (thermai, cavitationai, acoustic streaming, dermai) on bioiogicai tissues. 

Absorption of US by a medium invariably increases its temperature. Those materials that possess high US absorption coefficients (e.g. bone) experience severe thermal effects compared with, for example, muscle tissue, which has a low absorption coefficient. The increase in temperature upon US exposure at a given frequency varies directly with the US intensity and exposure time. The absorption coefficient of a medium increases with increasing US frequency and so does the temperature as a result. In this context, the time threshold (TT) indicates the time after which a threshold temperature rise is exceeded and hence how long a piece of tissue can be safely exposed to US provided the safe TT is known. 

Collapse of cavitation bubbles releases a shockwave that can cause structural alteration in the surrounding tissue. Tissues contain air pockets that are trapped in the fibrous structures and act as nuclei for cavitation upon US exposure. The cavitation effect varies inversely with US frequency and directly with US intensity. 

The shear stresses developed by streaming velocities may affect the neighbouring tissue structures. Acoustic streaming may be important when the medium has an acoustic impedance different from that of its surroundings, the fluid in the biological medium is free to move or oontinuous waves are applied. 

A study of the effect of US at variable frequenoies and intensities (namely, 1 MHz, 2 W/crrf 48 kHz, 0.5 W/cm and 20 kHz, 12.5-225 mW/cm ) on animal skin revealed that no damage to the epidermis or underlying living tissues occurred provided the application parameters (e.g. application duration, frequency and intensity) were properly controlled. 

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The purpose of this chapter will be to serve as a critical introduction to the nature and origin of the chemical effects of ultrasound. We will focus on organo-transition metal sonochemistry as a case study. There will be no attempt to be comprehensive, since recent, exhaustive reviews on both organometallic sonochemistry Q) and the synthetic applications of ultrasound (2) have been published, and a full monograph on the chemical, physical and biological effects of ultrasound is in press (3). 

The chemical and biological effects of ultrasound were first reported by Loomis more than 50 years ago (4). Within fifteen years of the Loomis papers, widespread industrial applications of ultrasound included welding, soldering, dispersion, emulsification, disinfection, refining, cleaning, extraction, flotation of minerals and the degassing of liquids (5),(6). The use of ultrasound within the chemical community, however, was sporadic. With the recent advent of inexpensive and reliable sources of ultrasound, there has been a resurgence of interest in the chemical applications of ultrasound. 

Biological Effects of Ultrasound Mechanisms and Clinical Implications (1983)... 

In order to understand the mechanisms of sonophoresis, it is important to identify various effects of ultrasound exposure on the human tissue since one or more of these effects may contribute to the mechanism of sonophoresis. A brief description of the various biological effects of ultrasound is provided below. 

Instead, sonochemistry and sonoluminescence derive principally from acoustic cavitation, which serves as an effective means of concentrating the diffuse energy of sound. Compression of a gas generates heat. When the compression of bubbles occurs during cavitation, it is more rapid than thermal transport, which generates a short-lived, localized hot-spot. Rayleigh s early descriptions of a mathematical model for the collapse of cavities in incompressible liquids predicted enormous local temperatures and pressures.13 Ten years later, Richards and Loomis reported the first chemical and biological effects of ultrasound.14... 

NCRP Report No. 74. Biological Effects of Ultrasound Mechanisms and Clinical Applications. National Council on Radiation Protection and Measurements Bethesda, MD, 1983. 

The chemical (3) and biological (4) effects of ultrasound were first reported by Loomis more than 50 years ago. In spite of early work in the area of sonochemistry, interest within the chemical community remained... 

The potential of sonochemistry was identified over sixty years ago in a wide ranging paper entitled The Physical and Biological Effects of High Frequency Sound-Waves of Great Intensity [13]. Over the few years which followed this paper a great deal of pioneering work in sonochemistry was carried out and, as a result of this, two reviews on the applications of ultrasound in polymer and chemical processes were published... 

Biological Effects and Exposure Criteria for Ultrasound Biological Effects of Magnetic Fields Microprocessors in Dosimetry Efficacy Studies... 

Significant attention has thus been given to investigating the effects of ultrasound on biological tissues. Ultrasound affects biological tissues via three main effects thermal, cavita-tional, and acoustic streaming. 

Harley (1985) [Available also in Radioactive Waste, see above] 10 Biological Effects of Non-ionizing Radiations Cellular Properties and Interactions by Herman P. Schwan (1987) [Available also in Nonionizing Electromagnetic Radiations and Ultrasound, see above]... 

For recent reviews on the effect of ultrasound on heterogenous reactions, see (a) P. Boudjouk, in Ultrasound its Chemical, Physical and Biological Effects-, K. S. Suslick (ed.), VCH Publishers, New York, 1988 (b) P. Boudjouk, in High Energy Processes in Organtme-tallic Chemistry ACS Symposium Series No. 333, K. S. Suslick (ed.), American Chemical Society, Washington, DC, 1987 (c) P. Boudjouk, J. Chem Educ., 63, 427 (1986). 

It was shown on model biological systems Enterococcus spp. bacteria) that the destructive effect of ultrasound is enhanced in the presence of nanoparticles. Figure 5 shows scanning electron micrographs of bacteria after the combined action of ultrasound and Theraphthal. 

Analysis of the results shows that the solid-phase inclusion in polymeric and biological structures are effective local amplifiers of thermal and cavitational effects of ultrasound exposure. This can be used in the therapy of cancer. Selection of the optimal method of administration of SPSs in the... 

Researdi into tlie use of ultrasound in environmental protection has received a considerable amount of attention with the majority of investigations focusing on the harnessing of cavitational effects for the destruction of biological and chemical pollutants in water. The field is not restricted to these two topics however, it is much broader (Tab. 4.1), and in this chapter we will review several aspects in addition to the decontamination of water... 

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