Therapeutic Ultrasound(Part two)

By

Prof.Dr.Gehan Mosaad

At the end of this lecture the student should be able to

Discuss therapeutic effects of US Identify physiological effects of US Understand indications and contraindications of US Know the precautions and adverse effects of US Understand the different techniques of US

application

Therapeutic Effects of US

Ultrasound has a variety of biophysical effects:A-Thermal effects

B- Nonthermal effects The most effect of continuous US is on tissue

temperature; however, nonthermal effects can also occur with the use of continuous ultrasound.

Pulsed US has mainly nonthermal effect, but it also produces a minimal sustained changes in tissues temperature, it probably does have a small brief heating effect during the on time of a pulse

Thermal Effects of US

As the energy within the sound waves is passed and absorbed by the tissues, it will cause oscillation of the molecules of that tissues about their mean position, clearly any increase in the molecular vibration will result in heat generation.

The thermal effects of ultrasound are the same asthose obtained with other heating modalities including: acceleration of metabolic rate reduction or control of pain and muscle spasm alteration of nerve conduction velocity increased circulation increased soft tissue extensibility

Thermal Effects of US (cont.)

The structures heated by US are different from other heating modalities US reaches more deeply and heats smaller areas than most superficial

heating agents. US also heats tissues with high US absorption coefficients more than

those with low absorption coefficients tissues Tissue with high absorption coefficients are generally those with a high

collagen content while tissues with low absorption coefficients generally have a high water content such as muscles.

Thus US is particularly well-suited to heat such as tendons, ligaments joint

capsules and fascia US is generally not the ideal physical agent for heating muscle tissue

because muscle has a relatively low absorption coefficient also, most muscles are much larger than the available ultrasound transducers.

Factors affecting amount of temperature increase

The increase in tissue temperature produced by the absorption of ultrasound varies according to:

Type of tissue (absorption coefficient) Frequency Intensity Duration of the ultrasound. Blood circulating through the tissue Reflection US waves in regions of soft tissue-bone interfaces

Thus, higher temperatures are achieved in tissue with high collagen content with high frequency with high intensity with long duration

Non-Thermal Effects of US

When ultrasound is delivered in a pulsed mode, with a 20% duty cycle, the heat generated during the on time of the cycle is dissipated during the off time, resulting in no measurable net increase in temperature.

Thus, pulsed US is used to produce nonthermal effects that including the following:

increase intracellular calcium, increase skin and cell membrane permeability increase mast cell degranulation, increase histamine release increase macrophage responsiveness, increase the rate of protein synthesis by fibroblast

Non-Thermal Effects of US (cont.)

Nonthermal effects of US are the result of the mechanical events produced by US, including, cavitations, acoustic streaming and micro – massage.

1- Cavitation

The formation of gas filled bubbles within the tissues & body fluids during the phase of relaxation or rarefaction of US waves

There are 2 types of cavitation

Stable and non stables which have very different effects.

Non-Thermal Effects of US (cont.)

Stable cavitation It occurs at therapeutic doses of US. This is the formation &

growth of gas bubbles by accumulation of dissolved gas in the medium. The cavity acts to enhance the acoustic streaming phenomena & as such would appear to be beneficial.

Unstable (transient) cavitation It is the formation of bubbles at the low pressure part of the US

cycle. These bubbles then collapse very quickly releasing a large amount of energy which is detrimental to tissue viability.

This phenomenon occurs at higher US intensities with stationary head.

Pulsing also reduces the risk of damage due to cavitation.

Non-Thermal Effects of US (cont.)2- Acoustic streaming It is a small scale eddying of fluids near a vibrating structure such

as cell membranes & the surface of stable cavitation gas bubble. Or, it is the steady, circular flow of cellular fluid induced by US.

3- Micro-massage (Microstreaming). It is a mechanical effect in which the sound wave traveling

through medium will cause molecules to vibrate, possibly enhancing tissue fluid interchange.

The result of combined effects of stable cavitation and acoustic streaming is the alteration of cell membrane permeability and increased cellular activity which in turn responsible for the therapeutic effect of US.

Physiological Effects of Ultrasound

1 -Effect on blood flow

2 -Pain control

3 -Effect on adhesion and scar tissue

4 -Effect on wound healing

5 -Effect on fracture healing

Physiological Effects of Ultrasound (cont.)

1-Effect on blood flowContinuous US can increase the blood flow up to 45 minutes after treatment because of:

Thermal effect Alteration of cell permeability Histamine release

Physiological Effects of Ultrasound (cont.)

2- Pain controlDirect effect: Increase pain threshold Decrease transmission of pain impulse along nerve fibers produce counterirritant effect (gate theory for pain inhibition)

Indirect effect: It results from the other effect of US which could lead to removing the

source of pain such as: removing waste products and edema reduction, improving tissues healing decrease muscle spasm breaking down adhesion.

Physiological Effects of Ultrasound (cont.)

3-Effect on Adhesion and scar tissues Collagen has high US absorption coefficient The thermal effect of US lead to increasing extensibility

of collagen rich tissues Thus US could be used prior to range of motion exercises

and stretching exercises. Also, US is used to help improving the quality of the

scar, resulting in a slightly stronger & more elastic scar.

Physiological Effects of Ultrasound (cont.)

Effect on wound healingPulsed ultrasound at low intensities (0.8 W/cm²)

enhance healing of wound by stimulating collagen production by fibroblasts, increases the intracellular calcium ion levels improve the local blood supply encourage the growth of new capillaries stimulates the MYOFIBROBLASTS to contract,

giving rapid initial wound strength.

Physiological Effects of Ultrasound (cont.)

Fracture healing The use of ultrasound accelerate the rate of

fracture repair when US delivered at low

intensity (0.03 W/cm²) at 1.5MHz pulsed at a ratio of 1:4. for 20 minutes.

Using higher ultrasound doses(1 – 2 W/cm²) could have an adverse effect on the fracture healing process

Indications of Ultrasound

Muscle spasm Trigger areas Neuroma Scar tissue Joint capsule shortening Acute and chronic soft tissues injuries. Acute and chronic inflammation Wound and ulcers healing. Fracture healing. Neurogenic pain

Contraindications of Ultrasound

Pregnancy when used over the pelvic or lumbar area.

Over areas of acute infection Areas of severely impaired circulation Over malignant tumors Over growing epiphyseal plates Areas around the eyes, heart, and genitals Tissues at risk of haemorrhage Venous thrombosis

Precautions and adverse effects of US applications

It is recommended to avoid using high doses of US or sufficient intensity in the following cases:

Acute inflammation Epiphyseal plates Fractures Breast implantsThe most common adverse effect is a burn, which may

occur in the following conditions: high-intensity, continuous ultrasound is applied. if a stationary application technique is used. in areas with impaired circulation or sensation with superficial bone

Techniques of ultrasound applications

a. Direct contact

b. Water immersion

c. Water bag

d. Solid sterile gel as coupling

a-Direct contact

In this technique, the transducer head is applied directly to the skin with a gel as a conducting coupling media.

Firm constant pressure should be used to hold the sound head in contact with the skin.

It is important to move the US head continuously in a small circular strokes.

a-Direct contact

b. Water immersion application

This technique is used in treating an irregular shapes as extremities.

A water bath may be used. The part to be treated immersed in distilled water which is used as a medium for transmission of US.

The head is placed in the water and moved parallel to the surface of the part which is being treated and as close to the skin as possible.

a-Direct contact

a-Direct contact

Water immersion

c. Water bag application

In this technique, a plastic or rubber bag filled with water and coated with a coupling gel to form a water cushion between US head and the skin is used.

This method is used in treatment of irregular surfaces which cannot be placed in a water bath.

Couplant is used onto the surface of bag, skin and the treatment head.

The bag is held in place over the area to be treated. The US head is moved firmly over the bag.

d. Solid sterile gel as coupling

Ultrasound can't be used over open wounds or injured skin because there is a risk of transmission of infection or moving the treatment head may cause further damage.

So in treatment of such cases, a sterile gel sheet is used as

a couplant instead of regular US gel.

Its benefits: This is a material in sterile packs used for wound dressings

and over skin graft. It is 96% water but impermeable to bacteria. It is better to put a sterile saline with it to ensure that there is

no air bubbles between the sheet and surface of the body.

Also the slightly wetted outside surface of the gel sheet will allow US head to move smoothly over it.

Sterile gel sheet

Ultrasound in conjunction with other physical therapy agents

PhonophoresisIt is the application of ultrasound with a topical drug in

order to facilitate transdermal drug delivery up to 6 cm. In the application of phonophoresis, the medication is in form

of gel or cream. Preheating the area to increase the absorption of the

medication Use only approved ultrasound transmission media. The direct coupling method is recommended Ensure that the skin is well moistened; avoid areas of dry skin. Lower frequency and Pulsed US lead to deeper penetration. High intensity is recommended. The duration depends on the size of the area to be treated.

Case study

Case 1JG is an 80-year-old female with 10 cm² infected pressure ulcer over her left greater trochanter. She is bedridden and completely dependent onto others for feeding and bed mobility as the result of three strokes over the past 5 years.

Case 2

TR is a 60-year-old male,3 months post-open reduction

and internal fixation of a right hip fracture, with placement of a plate and screws. He complains dull pain in the right anteromedial hip and shortening of right anteromedial hip capsule, resulting in limited ambulation and inability to work.

Assignment

Gate control theory of pain

Thank you