Transcript File

Therapeutic Ultrasound
Chapter 8
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
 Muscle spasm
 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
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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
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ERA
Beam Profile
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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)
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Becomes less consistent
farther away from the head
– Spatial peak intensity
Spatial Peak Intensity
Beam Nonuniformity Ratio (BNR)
Spatial Peak Intensity
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Describes the amount of variation in
the beam
Ratio between:
– Spatial peak intensity (SPI)
– Average intensity (SAI - metered
output)
– BNR = SPI/SAI
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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)
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
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
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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
Mild
Increase
1°C
Moderate
2° – 3°C
Vigorous
3° – 4°C
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
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
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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
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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
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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
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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
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Inflammation
Frequency Specificity
 1 MHz Output
– Release of preformed fibroblasts
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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 threshold
Indirect 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
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– Place tissues on stretch during application
– Perform stretching/mobilization immediately following
the treatment
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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
Electromagnetic Field
In vitro bone deformation produces piezoelectric
currents and streaming potentials
 Electromagnetic (EM) devices are based on
Wolff’s Law that bone responds to mechanical
stress: Exogenous EM fields may simulate
mechanical loading and stimulate bone growth
and repair
 Clinical efficacy very controversial
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Types of EM Devices
Microamperes
 Direct electrical current
 Capacitively coupled electric fields
 Pulsed electromagnetic fields (PEMF)
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PEMF
Approved by the FDA for the treatment of nonunions
 Efficacy of bone stimulation appears to be
frequency dependent
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– Extremely low frequency (ELF) sinusoidal electric
fields in the physiologic range are most effective (15
to 30 Hz range)
– Specifically, PEMF signals in the 20 to 30 Hz range
appear more effective than those below 10 Hz
Ultrasound
Low-intensity ultrasound is approved by
the FDA for stimulating healing of fresh
fractures
 Modulates signal transduction, increases
gene expression, increases blood flow,
enhances bone remodeling and increases
callus torsional strength in animal models
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Ultrasound
Human clinical trials show a decreased
time of healing in fresh fractures
 Has also been shown to decrease the
healing time in smokers potentially
reversing the ill effects of smoking
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Fracture Healing
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Low-intensity pulsed output
Accelerates rate of fracture
healing for:
– Acute fractures
– Nonunion fractures
– Stress fractures
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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
Contraindications
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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)
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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
Where are we going?
Ultrsound
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Ultrasound uses:
– Diagnostic (low intensity)
 Fracture
– Surgical (high intensity)
– Therapeutic

Therapeutic US widely used for
deep heat
Ultrasound
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Primary clinical use:
– Soft tissue repair
– Pain relief (analgesia)
Effective Radiating Area (ERA)

Total area on surface of transducer
producing soundwave
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Ideally ERA should match size of
transducer
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Treatment area should not exceed 2-3
times ERA
Frequency of Ultrasound
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Determined by number of times crystal
deformed/sec.
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2 most common utilized in U.S.
– 1.0 MHz
– 3.0 MHz
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Determines depth of penetration, unlike
ES
Frequency of Ultrasound
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Inverse relationship between frequency and
depth of penetration
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Penetrating depths:
– 1.0 MHz: 2-5 cm
– 3.0 MHz: 1-2 cm
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Absorption rate increases with higher
frequency
Pulsed vs Continuous
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Most new generators produce both
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Both produce thermal & nonthermal
effects
Pulsed vs Continuous
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Continuous:
– Sound intensity remains the same
– Commonly used for thermal effects
Pulsed vs Continuous
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Pulsed:
– Intensity periodically interrupted
– Average intensity reduced over time
Physiological Effects
of Ultrasound
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Thermal effects
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Non-thermal effects
– Cavitation
– Acoustic microstreaming
Thermal Effects
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Clinical effects:
– Increased extensibility of collagen fibers
 tendons
 joint capsule
– Decreased joint stiffness
Thermal Effects
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Clinical effects:
– Reduction in muscle spasm
– Pain modulation
– Increased blood flow
– Increased nerve conduction
Thermal Effects
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Primary advantage of US
– Selective heating of tissues high in
collagen
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– Non-thermal effects are occurring
Non-thermal (Mechanical) Effects
Primary physiological effects
are cavitation and acoustic
microstreaming
 Cavitation:
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– Formation of gas-filled bubbles
in tissue fluids
– Expansion/compression of
bubbles either stable or
unstable
Non-thermal (Mechanical) Effects
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Acoustic microstreaming:
– Unidirectional movement of fluids
along cell membrane boundaries
– Produces high viscous stresses
– Alters membrane structure &
function
– Increased permeability to ionic
influx
Non-thermal (Mechanical) Effects
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Potential therapeutic effects from cavitation &
microstreaming
– Stim. of fibroblast activity increases protein
synthesis & tissue repair
– Increased blood flow
– bone healing & repair of non-union fractures
Ultrasound
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Indications
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Increase deep tissue heat
Decrease inflammation
Decrease muscle spasms
Decrease pain
Increase extensibility of
collagen tissue
– Decrease pain of
neuromas
– Decrease joint adhesions
– Treat myositis ossificans
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Contraindications
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Hemorrhage
Infection
Thrombophlebitis
Suspected malignancy
Impaired circulation or
sensation
– Stress fracture sites
– Epiphyseal growth plates
– Over the Eyes, Heart,
Spine, or genitals
Treatment Frequency
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Ultrasound has cumulative effects
· Daily for 10 days – low irritability and scar
· 3-4 times/week – moderate irritability for 34 weeks
· 2 times /week – high irritability 4-5 weeks
· If no change after 3-4 sessions, change
settings or discontinue.
· Stop after 10-15 treatments
Sound Head Movement
Never stay stationary
 Keep it moving, slow and gentle with
constant pressure.
 This will minimize the risk of creating
unstable cavitation and
 Standing waves that is detrimental
damaging to soft tissue
 1 inch = 1 second
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Movement of the Transducer
4 cm2/sec
 Remaining stationary can cause problems
 Moving too rapidly decreases the total amount
of energy absorbed per unit area
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– May cause clinician to treat larger area and the
desired temps. May not be attained
Slower strokes can be easier maintained
 If patient complains of pain or excessive heat,
then decrease intensity but increase time
 Apply constant pressure – not too much & not
too little
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Coupling Agents
Optimal agent – distilled H20 (.2% reflection)
 Modern units have a shut down mechanism if
sound head becomes too hot (Dynatron beeps;
red lights on Chattanoogas)
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– Improperly coupled head causes  temp.
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Types of agents:
– Direct
– H20 immersion
– Bladder
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Reduce amount of air bubbles
Direct Coupling
Effectiveness is  if body part is hair,
irregular shaped, or unclean
 Must maintain firm, constant pressure
 Various gels utilized
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Water Immersion
Used for odd shaped parts
 Place head approx. 1” away from part
 Operator’s hand should not be immersed
No metal on part or operator’s hand
 Ceramic tub is recommended
 If nondistilled H20 is used, intensity can be
 .5 w/cm2 because of air & minerals
 Don’t touch skin except to briefly sweep
skin when bubbles form
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Bladder
H20 filled balloon or plastic bag coated
with coupling gel
 Use on irregular shape part
 Place gel on skin, then place the bladder
on the part, and then place gel on bladder
 Make sure all air pockets are removed
from bladder
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US Specifics
Burning
 Tissue Density
 Gel application
 Burning the US head with no tissue
contact
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Phonophoresis
Description
Use of therapeutic ultrasound to assist in
diffusion of medication through the skin
 Increases the diameter of skin portals to
allow the medication to pass
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– Pores
– Hair follicles
Biophysical Effects
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Medication is introduced over a large area
– Relative to an injection
Noninvasive
 Medication may not be filtered by the liver
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– Reducing metabolic elimination of the
medicine
Transdermal Application
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Medication must diffuse through:
– Enzymatic barrier of the epidermis
– Stratum corneum
 Rate-limiting barrier to absorption
 Medications must be able to diffuse across this
barrier
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Medication is stored in subcutaneous
tissues for some time before being
diffused deeper
Skin Influences

Medication uptake is improved when the
skin is:
– Well hydrated
– Has a high density of skin portals
– Highly vascularized
– Relatively thin
– “Younger” skin tends to have better diffusion
characteristics than “older” skin.
Ultrasound Influences on Diffusion
Thermal Effects
 Increase kinetic energy
 Increase portal cross-section
 Increase circulation
 Increase capillary permeability
Nonthermal Effects
 Altered cell resting potential
 Increased cell membrane permeability
 Increased molecular permeability
Phonophoresis Medications
Either prescription or nonprescription
 Low molecular size and weight
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– Most medications used can be applied
transdermally without ultrasound
Controlled medications require a
prescription for the patient being treated
 Medication is often mixed in an inert base
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– Base must be able to transmit ultrasonic
energy
Common Medications
Type
Corticosteroid
Indications
Inflammation
Salicylates
Inflammation
Pain
Pain
Trigger points
Anesthetic
Example
Hydrocortisone
Dexamethasone
Lidocaine
Application Tips

Moist heat pack prior to application:
– Increase blood flow
– Increase kinetic energy
– Increase skin portals
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Following treatment
– Leave medication on skin
– Cover with an occlusive dressing
– Moist heat pack re-application may assist in
further absorption
Low-frequency US Phonophoresis
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Parameters:
– 20 kHz output frequency
– 125 mW/cm2
– Pulsed output
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Benefits:
– Allows medications with a larger size and
weight to diffuse
– More efficient medication delivery