Transcript Light Modalities

Therapeutic Ultrasound
Chapter 7
© 2005 – FA Davis
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
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
© 2005 – FA Davis
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
© 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
© 2005 – FA Davis
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
© 2005 – FA Davis
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%
© 2005 – FA Davis
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
© 2005 – FA Davis
Power and Intensity
Spatial Average Intensity
Spatial Average Temporal Peak Intensity
Spatial Average Temporal Average Intensity
Half-layer Value
© 2005 – FA Davis
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
© 2005 – FA Davis
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
Mild
Increase
1°C
Moderate
2° – 3°C
Vigorous
3° – 4°C
© 2005 – FA Davis
Used For
Mild inflammation
Accelerate metabolism
Decreasing muscle spasm
Decreasing pain
Increasing blood flow
Chronic inflammation
Tissue elongation
Scar tissue reduction
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
© 2005 – FA Davis
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
© 2005 – FA Davis
•
•
•
•
•
•
•
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
© 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
© 2005 – FA Davis
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
© 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
– 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)
© 2005 – FA Davis
PARAMETERS
Frequency
1.5 MHz
ERA
3.88 cm2
Intensity
30 mW/cm2
Treatment Duration
20 minutes
Daily
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)
© 2005 – FA Davis
• 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