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) © 2005 – FA Davis

Uses Calcific bursitis Inflammatory conditions Joint contractures Pain Muscle spasm Acute orthopedic injuries (low pulses, low intensity) © 2005 – FA Davis

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 © 2005 – FA Davis

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 © 2005 – FA Davis

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 © 2005 – FA Davis

Beam Nonuniformity Ratio (BNR) Spatial Peak Intensity 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 Average Intensity (Displayed on the unit) © 2005 – FA Davis

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 © 2005 – FA Davis

Continuous Output (100% Duty Cycle) Pulsed Output (67% Duty Cycle) 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) © 2005 – FA Davis

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 © 2005 – FA Davis

Power and Intensity Spatial Average Intensity Spatial Average Temporal Peak Intensity Spatial Average Temporal Average Intensity

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 © 2005 – FA Davis

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 © 2005 – FA Davis

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 © 2005 – FA Davis

Heating Classifications Increase Used For Mild 1°C Mild inflammation Accelerate metabolism Moderate 2° – 3°C Decreasing muscle spasm Decreasing pain Increasing blood flow Chronic inflammation Vigorous 3° – 4°C Tissue elongation Scar tissue reduction © 2005 – FA Davis

Heating Rate Heating rate and magnitude is based on: Duty cycle Output frequency Intensity Target tissues Size of the treatment area © 2005 – FA Davis

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 © 2005 – FA Davis

Biophysical Effects Nonthermal

Nonthermal Effects Granulation tissue production Synthesis of protein 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 © 2005 – FA Davis

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 © 2005 – FA Davis

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 © 2005 – FA Davis

Effect on Injury Response

Cellular Response Acoustical streaming: Thermal effects: 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 © 2005 – FA Davis

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 © 2005 – FA Davis

Inflammation Frequency Specificity 1 MHz Output 3 MHz Output Release of preformed fibroblasts 3 MHz Output Increased synthesis and secretion of fibroblast precursors Increased in areas of high collagen concentration © 2005 – FA Davis

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 © 2005 – FA Davis

Pain Control Direct Pain Reduction Increased nerve cell sodium permeability Alters nerve function Increases pain threshold Indirect Pain Reduction Increased blood flow Increased capillary permeability Increased oxygen delivery Decreased muscle spasm © 2005 – FA Davis

Muscle Spasm Reduced secondary to: Decreased pain Altered nerve conduction velocity Increased temperature (counterirritant effect) Muscle relaxation © 2005 – FA Davis

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 © 2005 – FA Davis

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 © 2005 – FA Davis

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) PARAMETERS Frequency 1.5 MHz ERA 3.88 cm2 Intensity 30 mW/cm2 Treatment Duration 20 minutes Daily © 2005 – FA Davis

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