Elasticity

Elasticity

the property of a body that tends to return the body to its original shape after the force is removed. If the applied force is too large, the body is distorted beyond its elastic limit, and the original shape is not restored.

ex) twisting your ankle can damage ligaments in your ankle because the ligaments elasticity wasn’t strong enough

Elasticity in the skin allows

movement of joints and facilitates tactile sensory organs.

Cardiovascular System

Allows our blood vessels to function properly. Artery walls stretch when pressure pumps blood away from the heart. Elastic fibers in the walls ensure they keep its shape. Elastic recoil keeps blood moving though the capillaries. Veins have to maintain elasticity so the blood can move properly

Elastic properties change with

age and disease

Arteriosclerosis

a disease in which arteries lose elasticity as their walls became stiff and inflexible; often as a result of high blood pressure exerting excess force against arterial walls. Begins with inflammation and causes arteries to become blocked. decreases blood flow and oxygen caused by elasticity.

*Atonia

Loss of elasticity and muscle strength.

Properties of Sound

Travels in motion, elastics, periodic motion

Periodic Motion

Defined as motion which repeats itself at regular time intervals. Time required to complete one full cycle.

ex) vibration, oscillation, cycles

Frequency

The number of vibrations per unit of time (Mhz). The higher the frequency the less time each vibration takes. Frequency of US wave depends on the thickness of crystal.

Amplitude

Maximum distance moved from the equilibrium point. How intense sound wave is

Transverse Wave

a wave in which the particles are oscillating back and forth perpendicular to the direction of propagation of the wave.

Longitudinal Waves

waves in which the periodic motion of the particles is parallel to the propagation direction.

Ultrasound Pressure Wave

They originate from elastic properties vibrating back and forth. The vibration creates pressure changes within the air and sound will be produced. Energy is transmitted by alternating between compression and rarefying of material. The waves increase blood flow which increases healing.

What is US used for

diagnosis (creates images), treatment (localized increase in temperature), pain control, dermal ulcers, surgical incisions, carpal tunnel syndrome, tendon and ligament injuries, absorbs calcium deposits

What is US

A high frequency sound wave that can enter the body and pass through it while attenuating due to absorption of the sound waves into tissue. Consists of frequencies above human hearing. Greater than 20,000 Hz Increases cellular response and making it happen quicker

Thermal Effects of US

Increases tissue temperature

Reduction of pain, extensibility of tissue, increase circulation, reduce muscle spasms, alter nerve conduction, lengthen soft tissue= lets tissue stretch more

Nonthermal Effects of US

Can alter cellular activity

Micro streaming, acoustic streaming, and cavitation cause mechanical changes in biological tissue and processes.

Inflammation phase of healing, wound healing, blood flow (local area), increase skin permeability to topical medication.

Attenuation

Decrease in intensity as sound waves pass through. Greatest in tissue with high collagen content (tendons, ligaments, cartilage, scar tissue)

Reasons for Attenuation

Absorption, refraction, reflection

Refraction

Redirection of US wave as it continues to enter the tissue.

Reflection

Redirection of US wave opposite to angle of incident. Mostly occurs between tissue interfaces (air-skin, soft tissue-bone). Why it is important to keep middle of transducer head level with skin at all times.

What properties does a crystal in US head have

Pizeoelectric

Transducer crystal

Able to respond to electrical current by contracting and expanding as the electrical current alternates. The contracting causes tissue to compress and rarify. When crystal expands, tissue particles get compressed, when crystal contracts, tissue particles rarify

Transducer

Turns elecrtical waves into sound waves

Power

The amount of watts given out of US machine

Intensity

power per unit area of sound head, how much sound waves going into one area, important in temperature. measured in Wcm²

Acoustic Streaming

Steady, circular flow of cell material caused by US wave

Cavitation

Gas bubbles in tissue are made smaller during compression phase of US and expand during rarefaction phase. If they explode, they cause damage to the cells

Microstreaming

Very small flow of material(gas bubbles from cavitation)

Lithotripsy

If these implode can cause tissue damage

Piezoelectric definition

Able to change shape in response to electrical current

Rarefaction

Decrease in density as US waves pass through. Particles are pulled apart (low density, low pressure)

Effective Radiating Area

the area of the transducer from which US energy radiates. Only half the size of transducer head (middle)

1 Mhz used for tissue ___ cm deep

5

deep within muscle joint, knee, quad

3 Mhz used for tissue ___ cm deep

1-2

elbow

Factors that influence temperature change

Absorption coefficient, average intensity, duration of treatment

Frequency

• higher freq, higher temp

• low Mhz causes higher temp

• less intensity for higher frequency

Clinical uses of US

Soft tissue shortening, pain control, dermal ulcers, surgical skin incisions, absorb calcium deposits, phonophoresis

Ways to maintain elasticity

good diet, exercise, no drugs or smoking

low muscle tone

post seizure, hanging limb, low mobility

high muscle tone

cerebral palsy, arms bent and scrunched to body

what is sound used for

to manipulate tissue