© 2005 – fa davis therapeutic ultrasound chapter 7

© 2005 – FA Davis

Therapeutic Ultrasound

Chapter 7


Description

• Acoustical energy (sound waves) above the range of human hearing– Therapeutic range: 0.75 to 3.3 MHz

• Effects:– Thermal– Nonthermal (mechanical)


Uses

• Calcific bursitis

• Inflammatory conditions

• Joint contractures

• Pain

• Acute orthopedic injuries (low pulses, low intensity)


Production of Ultrasound

• An alternating current is passed through a crystal

• The current causes the crystal to vibrate– Electropiezo effect

• Vibrating crystal produce high-frequency sound waves


Effective Radiating Area (ERA)

• Area of the crystal that actually produces sound waves– Produces more than 5% of the

energy at 5 mm from the transducer face

• ERA is always smaller than the transducer face

• Energy is concentrated near the center

ERA


Beam Profile

• Multiple waves emerge from the head

• Energy diverges as it moves away from the source

• Energy is uniform close to the head– Near zone (Fresnel zone)

• Becomes less consistent farther away from the head– Spatial peak intensity

Spatial Peak Intensity


Beam Nonuniformity Ratio (BNR)

• Describes the amount of variation in the beam

• Ratio between:– Spatial peak intensity (SPI)– Average intensity (SAI - metered output)– BNR = SPI/SAI

• Perfect beam would have a BNR of 1:1• Minimally acceptable BNR is 8:1• The actual peak output is equal to the

SAI * the BNR– 10 W total output * 6:1 BNR– 60 watt SPI

Spatial Peak Intensity

Spatial Average Intensity(Displayed on the unit)


Modes of Application

Continuous• Ultrasonic energy is constantly produced• Can produce thermal effects based on:

– Output intensity– Treatment duration

Pulsed• Ultrasonic output is regularly interrupted• Produces nonthermal effects


Pulsed Output

• Ultrasonic output is cycled “On” and “Off”– On = Pulse length

– Off = Pulse interval

• Expressed as a Duty Cycle– ON/(ON+OFF) * 100

– 20mSec/(20mSec+10mSec) * 100

– 20/30 * 100

– 67%

Continuous Output (100% Duty Cycle)

Pulsed Output (67% Duty Cycle)


Output Frequency

• Measured in megahertz (MHz)– 1 MHz = 1,000,000 waves per

second• Determines the depth of effects• 1 MHz Output

– Penetrates 5 to 7 cm– Thermal effects last longer– More divergent beam

• 3 MHz Output– Penetrates 2 to 3 cm– Heats 3 times faster than 1 MHz

output– More collimated beam


Power and Intensity

Spatial Average Intensity

Spatial Average Temporal Peak Intensity

Spatial Average Temporal Average Intensity

Half-layer Value


Spatial Average Intensity (SAI)

• Describes the energy per unit of area

• Total output (watts)/area– Watts/effective radiating area (cm2)– W/cm2

• 15 watts being applied with a 10 cm2 ERA – 15 Watts / 10 cm2

– 1.5 W/cm2


Power Measures – Pulsed Output

Spatial Average Temporal Peak Intensity (SATP)

• The average energy delivered during the “On” time of the duty cycle.

Spatial Average Temporal Average Intensity (SATA)

• Energy delivered over time– Spatial Average Intensity * Duty

Cycle• Meaningful only during pulsed

output


Biophysical Effects

Thermal


Thermal Effects

• Increased sensory nerve conduction velocity• Increased motor nerve conduction velocity• Increased extensibility of collagen-rich • Increased vascular permeability structures• Increased collagen deposition• Increased blood flow• Reduction of muscle spasm• Increased macrophage activity• Enhanced adhesion of leukocytes to damaged endothelial

cells


Heating Classifications

Increase Used ForMild 1°C Mild inflammation

Accelerate metabolismModerate 2° – 3°C Decreasing muscle

spasmDecreasing painIncreasing blood flowChronic inflammation

Vigorous 3° – 4°C Tissue elongationScar tissue reduction


Heating Rate

• Heating rate and magnitude is based on:– Duty cycle– Output frequency– Intensity– Target tissues– Size of the treatment area


Thermal Effects

• Same as other heat modalities– Smaller volume of tissue– Shorter duration of effects

• Preheat the skin with a moist heat pack– Decreases the time to reach vigorous heating

• Poorly vascularized, collagen-rich tissues are preferentially heated– Fascia, tendon, scar tissue

• Tissues containing an increased proportion of fluid do not heat as well– Adipose tissue, articular fluid


Biophysical Effects

Nonthermal


Nonthermal Effects

• Increased cell membrane permeability

• Altered rates of diffusion across the cell membrane

• Increased vascular permeability• Secretion of cytokines • Increased blood flow• Increased fibroblastic activity • Stimulation of phagocytosis

• Granulation tissue production• Synthesis of protein• Synthesis of collagen• Reduction of edema• Diffusion of ions• Tissue regeneration• Formation of stronger

deformable connective tissue


Nonthermal Application

• Pulsed output– 20 to 25% duty cycle– Nonthermal output intensity

• Continuous output– 100% duty cycle– Output intensity of less than 0.3 W/cm2


Acoustical Streaming

• Ultrasound causes interstitial fluids to flow

• Fluids strike cell membranes• Produce eddy currents• Eddy currents displace ions and

molecules• Alter:

– Cell membrane permeability– Cellular function


Effect on Injury Response


Cellular Response

• Acoustical streaming:– Increases cell membrane permeability

– Alters cell membrane diffusion rate

– Increased histamine release

– Mast cell degranulation

– Increased rate of protein synthesis

• Thermal effects:– Increased cell metabolism

– Increased rate of inflammation


Inflammation

• May lead to an earlier onset of proliferation– Increased fibroblast proliferation– Release of growth factors and platelets

• Increased macrophage activity

• Leukocytes bind to damaged endothelial cells

• Cell division is increased


Inflammation

Frequency Specificity

• 1 MHz Output– Release of preformed fibroblasts

• 3 MHz Output– Increased synthesis and secretion of fibroblast

precursors• Increased in areas of high collagen concentration


Blood and Fluid Dynamics

• May increase blood flow for 45 minutes– Thermal effects– Decreased vascular tone– Histamine release

• Causes vasodilation

• Moist heat application prior to treatment decreases net increase in blood flow


Pain Control

Direct Pain Reduction• Increased nerve cell sodium permeability• Alters nerve function• Increases pain thresholdIndirect Pain Reduction• Increased blood flow• Increased capillary permeability• Increased oxygen delivery• Decreased muscle spasm


Muscle Spasm

• Reduced secondary to:– Decreased pain– Altered nerve conduction velocity– Increased temperature (counterirritant effect)– Muscle relaxation


Tissue Elasticity

• Ultrasound preferentially heats collagen-rich tissues (tendon, fascia, scar tissue)

• Temperature must be increased 7.2°F• Stretching window lasts approximately 3 minutes

following the treatment– Place tissues on stretch during application– Perform stretching/mobilization immediately following

the treatment

• Multiple treatments are required to gain length


Wound Healing

Tendon Healing• Continuous US application

may:– Increase tensile strength– Increase collagen deposition

Skin Ulcers• 3 MHz, low-intensity pulsed

output may assist the healing process

• Cover the wound with an occlusive dressing


Fracture Healing

• Low-intensity pulsed output• Accelerates rate of fracture

healing for:– Acute fractures– Nonunion fractures– Stress fractures

• Requires specialized unit• Biophysical Effects:

– Mechanical (sound) energy strikes bone

– Microvibration of bone triggers growth (osteogenesis)

PARAMETERSFrequency 1.5 MHzERA 3.88 cm2

Intensity 30 mW/cm2

Treatment Duration 20 minutesDaily


Contraindications

• Acute conditions (thermal mode)

• Ischemic areas• Areas of impaired circulation• Over areas of deep vein

thrombosis• Anesthetic areas• Over cancerous tumors • Sites of active infection or

sepsis• Over the spinal cord or large

nerve plexus in high doses• Exposed penetrating metal (eg,

external fixation devices)

• Around the eyes, heart, skull, or genitals

• Over the thorax in the presence of an implanted pacemaker

• Pregnancy when used over the pelvic or lumbar areas

• Over a fracture site before healing is complete

• Stress fracture sites or sites of osteoporosis

• Over the pelvic or lumbar area in menstruating female patients

© 2005 – fa davis therapeutic ultrasound chapter 7

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