3) Deep Heating Agents: Ultrasound & Diathermy Flashcards
Ultrasound
- Deep-penetrating agent
- Mechanical or sound energy
- Changes produces in tissue
- Thermal
- Non-thermal (mechanical)
Ultrasound is produced by
- An alternating current flowing through a piezoelectric crystal housed in a transducer
Piezoelectric crystals
- Produce positive and negative electrical charges when they contract or expand
The reverse piezoelectric effect (electropiezo effect)
- Used to produce therapeutic ultrasound
- AC current is passed through a piezoelectric crystal resulting in contraction and expansion
Coupling method
- Requires a coupling medium for energy to pass from the transducer to the tissues
Treatment area
- Effectively exposed to the ultrasonic energy
- Limited to an area slightly larger than the diameter of the sound head
Near field (Fresnel zone)
- Portion of the ultrasound beam used for therapeutic purposes
Ultrasonic output is described in terms of
- Power
- Frequency of the waves
- Area that produces the power
- Time
Frequency
- Measured in megahertz (MHz)
- Most commercial therapeutic ultrasound units offer 1- and/or 3-MHz outputs
Low-frequency (1-MHz)
- Divergent beam – deeper penetration ≈ 5 cm
High-frequency (3-MHz)
- Collimated/focused beam – superficial ≈ 2.5 to 3 cm
- Energy is rapidly absorbed and heats three times faster than 1-MHz ultrasound
Power and intensity
- Power is measured in watts (W)
- Intensity describes the strength of the sound waves at a given location within the tissues being treated
Spatial average intensity
- Amount of energy passing through the sound head’s effective radiating area (W/cm2)
- SAI = Total watts (W)/Effective radiating area (cm2) = W/cm2
Biophysical effects
- The physiological changes within the tissues can be grouped into two classifications
- Nonthermal
- Thermal
Nonthermal biophysical effects
- Changes within the tissues resulting from the mechanical effect of ultrasonic energy
- Acute injuries
Thermal biophysical effects
- Changes within the tissues as a direct result of ultrasound’s elevation of the tissue temperature
- When thermal effects are desired
Duty cycle continuous output
- Primarily thermal effects
- Used for tissues 5 cm or more deep
Duty cycle pulsed output (20%, 25%, or 50%)
- Primarily nonthermal (mechanical) effects
- Superficial (2-3cm)
- ↓ the temporal average intensity, ↓ the thermal effects, and ↑ the proportion of nonthermal effects
Biophysical nonthermal effects
- Interrelated events that produce the nonthermal effects (acoustical streaming, cavitation, microstreaming)
- Increased fibroblastic activity and protein synthesis
- Tissue regeneration
- Reduction of edema
- Bone healing
- Pain modulation
Cavitation (non-thermal)
- Formation of gas filled bubbles that expand & compress due to change in fluid pressure
- Stable Cavitation (pulsating, results in an increased fluid flow around those bubbles/provides therapeutic benefits)
Microstreaming (non-thermal)
- Unidirectional movement of fluid along the cell membrane causing mechanical pressure waves in an ultrasonic field
- Produces viscous stresses altering cell membrane permeability to sodium and calcium ions (important in healing process)
Baseline muscle temperature
- 36-37 C (98.6 F)
Mild heating
- +1 C
- Accelerates metabolic rate in tissue
Moderate heating
- +2-3 C
- Decreased muscle spasm, pain, and chronic inflammation
- Increased blood flow
Vigorous heating
- 3-4 C
- Decrease viscoelastic properties of collagen
- Increased tissue elongation
- Scar tissue reduction
Continuous ultrasound indications
- Acute and post-acute conditions (non-thermal)
- Soft tissue healing and repair
- Scar tissue
- Joint contracture
- Chronic inflammation
- Increase extensibility of collagen
- Decrease muscle spasms
- Pain modulation
- Increase blood flow
- Increase protein synthesis
- Tissue regeneration
- Bone healing
- Repair of nonunion fx
- Decrease Inflammation (associated with myositis ossificans)
- Myofascial trigger points
Continuous ultrasound effects on the injury response process
- Mode of application (continuous or pulsed)
- Frequency of the sound
- Size of the area treated
- Vascularity and density of the target
Acoustical streaming and cavitation
- ↑ cell membrane permeability = changing the diffusion rate across the cell membrane
Cellular responses to ultrasound
- ↑ histamine release
- ↑ intracellular calcium
- Mast cell degranulation
- ↑ rate of protein synthesis
Thermal effects of continuous ultrasound
- ↑ cell metabolism
- ↑ rate of inflammation
Changes in cell membrane permeability with continuous ultrasound
- Degranulation and the release of growth factors and platelets that stimulate fibroblast proliferation
- Continuous ultrasound has been shown to positively influence macrophage activity and to increase the adhesion of leukocytes to the damaged endothelial cells
Ultrasound stimulates cell division during
- Proliferation phase
Continuous ultrasound effects on blood and fluid dynamics
- ↑ blood flow
dilation of the blood vessels - ↑histamine release
Continuous ultrasound effects on nerve conduction and pain control
- ↑ nerve conduction velocity resulting from the thermal effects (cell membrane permeability to sodium ions is affected, altering the nerve’s electrical activity and elevating the pain threshold)
- ↓ the activity of chemosensitive pain receptors
- ↑ blood flow
- ↑ capillary permeability
Continuous ultrasound effects on muscle spasm
- ↓ the mechanical and chemical triggers that continue the pain-spasm-pain cycle
- Relaxation of muscle tension
- ↑ blood flow
- ↑ delivery of oxygen
- Aiding in the elongation of muscle fibers
Continuous ulstrasound effects on tissue elasticity
- Heats collagen-rich tissues, especially tendon, ligament, fascia, and scar tissue
- Vigorous heating
- Not effective for large areas of muscle
Vigorous heating with continuous ultrasound
- 3 MHz, have an effective stretching time of just over 3 minutes after the end of the treatment
- May be slightly longer when 1-MHz ultrasound is used
- Not effective for large areas of muscle
Continuous ultrasound effects on muscle and tendon healing
- 1-MHz of continuous output ultrasound enhances the release of preformed fibroblasts
- 3-MHz of continuous output ultrasound increases the cells’ ability to synthesize and secrete the building blocks of fibroblasts (localized to areas with a high collagen content, especially tendons and may be a more effective treatment for tendinopathies than phonophoresis)
Continuous ultrasound effects on wound healing
- Some superficial wounds have responded favorably to ultrasound application
- Continuous ultrasound (100%) delivered at 1.5 W/cm2 x 5-minute treatment over a 1-week period can increase the breaking strength of incisional wounds
Continuous ultrasound effects on fracture healing
- Low-intensity pulsed ultrasound (LIPUS) applied in one 20-minute session per day has demonstrated an improved healing rate for acute and nonunion fractures
- Results unclear for stress fractures
- Less effective when applied late in the healing process
- When applied early in the healing stage, cavitation and acoustical streaming increase the quality and strength of the bony callus
Phonophoresis
- Use of therapeutic ultrasound to assist in the diffusion of medication through the skin
- Delivers medication over a larger area than an injection
- Cavitation is believed to cause small openings in the stratum corneum and increase in pore size
Phonophoresis preheating
- Preheating the treatment area with a moist hot pack to increase local blood flow and kinetic energy can further enhance delivery of the medication into the tissues
Commonly used medications with phonophoresis
- Anti-inflammatory (cortisol, salicylates, dexamethasone, hydrocortisone)
- Analgesic (lidocaine)
Contraindications to therapeutic ultrasound
- Impaired circulation
- Ischemic areas
- Areas having sensory deficit
- Deep vein thrombosis or thrombophlebitis
- Cancerous tumors
- Over–fluid-filled cavities
- Over implanted pacemaker
- Pregnancy/menstruating women (over the pelvic area)
- Active fractures or stress fractures
- Metal or bony implants
- Joint replacements
- Caution over the vertebral column, nerve roots, or large nerve plexus
Shortwave diathermy
- Late 1800s
- High-frequency alternating current flowing through a coil creates an electromagnetic field (EMF) that radiates away from the cable producing deep tissue heating
- Larger treatment area (approximately the size of a cereal bowl)
Indications for shortwave diathermy
- Post-acute musculoskeletal injuries
- Increase blood flow
- Increase Vasodilation
- Increase metabolism
- Increase collagen extensibility
- Increase nerve growth
- Improved joint range of motion
- Changes in some enzyme reactions
- Muscle relaxation
- Muscle guarding
- Decrease pain threshold
- Joint contractures
- Myofascial trigger points
- Decrease subacute and chronic pain
- Re-absorption of hematoma
- Decrease joint stiffness
Continuous shortwave diathermy
- ↑ subcutaneous tissue temperature
- Generally limited to chronic conditions
Pulsed shortwave diathermy
- Some acute and subacute conditions can be treated
- Prevents tissue temperature from raising too fast or too high
- Pulsed output can be used to produce thermal effects -not to be confuse “pulsed” with “nonthermal”
- ↑the pulse frequency = the ↑ the amount of tissue heating
Nonthermal effects of shortwave diathermy
- Tissue healing
- ↑ microvascular perfusion
- Activation of fibroblast growth factors
- Increased macrophage activity
Shortwave diathermy nonthermal indications
- Acute trauma
- Post-surgical treatment
Thermal effects of shortwave diathermy
- Can ↑ intramuscular temperatures in the level of 4 to 5C
- Heating characteristics of SWD are similar to those of ultrasound, but because of the larger amount of tissue heated, the heat is retained three times longer
Nonthermal effects of SWD on injury response
- Alter the rate of diffusion across the cell membrane
Thermal effects of SWD on injury response
- ↑ the rate of cell metabolism
Cellular level effects of SWD combined with increased blood flow
- ↑ delivery and concentration of white blood cells and improved chondrocyte proliferation
- Increased cell membrane permeability assists in the removal of cellular debris and metabolic toxins
SWD and nerve conduction/pain control
- Primary pain relief is associated with:
- ↓ muscle spasm
- Reduction of adhesions and contractures
- ↑ blood flow
SWD blood and fluid dynamics
- Vasodilation
- Increases blood flow
- Capillary filtration
- Capillary pressure
- Oxygen perfusion
SWD deep-heating characteristics
- Increased blood flow
- Increased fibroblastic activity
- Increased collagen deposition
- New capillary growth are stimulated deeper
Tissue elongation with SWD is obtained by
- Altering the viscoelastic properties of deep, collagen-rich fibrous tissues by increasing the temperature and applying an external force to elongate the tissues
Wound healing and SWD
- Pulsed SWD
- ↑ white blood cell infiltration and ↑ rate of phagocytosis = more rapid healing time and ↓ need for pain medications
- ↑ number and quality of collagen bundles
- ↓ proportion of necrosed muscle fibers
Contraindications and precautions of SWD
- Acute inflammation
- Ischemia
- Hemorrhage
- Sensory impairment
- Pregnancy
- Cardiac pacemaker (or other electronic devices)
- Metal jewelry and implants
- Deep vein thrombosis or thrombophlebitis
- Cancerous tumors
- Plastic implants
- Bone cement
- Precautions
- Contact lenses (remove)
- Unfused epiphyseal plates (with caution)
- Moist dressings, adhesive tapes, skin creams (remove)
