Ultrasound

Description: Ultrasound is a name given to sound waves that are of such high frequency that they are not detectable by the human ear. The frequency band for medical ultrasound is 800,000 to 3,000,000 Hz (0.8 to 3 MHz). Ultrasound waves are produced by means of a piezo-electric crystal . These sound waves are capable of reflection, refraction, penetration, and absorption. When applied to human tissue, they are absorbed by various tissues with the production of heat. Absorption is greatest in tissues with a high proportion of protein and in dense tissues. Because of reflection, heat is greatest at tissue interfaces, especially those of widely different acoustic impedance. For example, much heat is produced between tendon or ligament and overlying muscle and at the periosteum. Penetration is greatest of all heat modalities, with significant heating 5 cm below the surface. There is very little temperature increase in adipose tissue.

Effects of Ultrasound Therapy:

1. Local metabolism is increased.
2. Local perspiration is increased.
3. Local vasodilatation with hyperemia occurs in response o increased demands for nutrients.
4. Muscle relaxation is promoted
5. Sensory nerve endings are sedated if the heat is mild.
6. If applied long enough, there may be increased body temperature, increased respiratory and pulse rates, and decreased blood pressure. These responses act to dissipate the excess heat and maintain core temperature at equilibrium.
7. Separation of collagen fibers with resultant increase in the extensibility of connective tissue, such as in joint capsule, ligament, tendon, adhesions, and scars. While mechanical effects play a role in the increased extensibility, the increase is mostly due to the thermal effects.
8. Increased membrane permeability allowing for increased ionic exchange.