Physical Agents & Electrotherapy
Understanding thermal modalities, ultrasound, electrical stimulation, and other physical agents used in rehabilitation and pain management.
Table of Contents
1. Thermotherapy (Heat)
Physiological Effects of Heat
- Vasodilation: Increased blood flow to area
- Decreased pain: Gate control mechanism, endorphin release
- Decreased muscle spasm: Relaxation of muscle fibers
- Increased tissue extensibility: Collagen becomes more pliable
- Increased metabolic rate: Enhanced healing (chronic conditions)
- Increased nerve conduction velocity: Can increase spasticity
Heat Transfer Mechanisms
Conduction
Direct contact between objects
Examples: Hot packs, paraffin, ice packs
Convection
Heat transfer through fluid medium
Examples: Hydrotherapy, fluidotherapy
Radiation
Electromagnetic energy transfer
Examples: Infrared lamp, UV therapy
Conversion
Energy converted to heat in tissues
Examples: Ultrasound, diathermy
Superficial vs. Deep Heating
| Type | Modalities | Depth |
|---|---|---|
| Superficial Heat | Hot packs, paraffin, infrared, fluidotherapy, warm whirlpool | 1-2 cm (skin, subcutaneous) |
| Deep Heat | Ultrasound, shortwave diathermy, microwave diathermy | 3-5 cm (muscle, joint) |
Common Heat Modalities
Hot Packs (Hydrocollator)
- • Temperature: 70-75°C (158-167°F) in tank
- • Duration: 20-30 minutes
- • Use 6-8 layers of toweling
- • Check skin after 5 minutes
Paraffin Bath
- • Temperature: 52-54°C (126-130°F)
- • Best for: Hands, feet (irregular surfaces)
- • Methods: Dip-wrap, dip-immersion
- • Duration: 15-20 minutes
Contraindications for Heat
- • Acute inflammation/trauma (first 24-48 hours)
- • Impaired sensation
- • Impaired circulation
- • Malignancy
- • Over ischemic areas
- • Bleeding disorders
- • Pregnancy (over abdomen/pelvis)
- • Fever
2. Cryotherapy (Cold)
Physiological Effects of Cold
- Vasoconstriction: Decreased blood flow (initial response)
- Decreased pain: Slowed nerve conduction, numbing
- Decreased muscle spasm: Reduced spindle sensitivity
- Decreased inflammation: Reduced metabolic rate, edema
- Decreased nerve conduction velocity: Helpful for spasticity
- Hunting response: Alternating vasoconstriction/vasodilation (15-30 min)
Stages of Cold Application
CBAN Sequence:
- Cold sensation (0-3 minutes)
- Burning/aching (3-7 minutes)
- Aching (7-12 minutes)
- Numbness (12-15 minutes) - therapeutic goal
Cryotherapy Methods
Ice Packs
- • Duration: 15-20 minutes
- • Use towel barrier
- • Crushed ice conforms better
Ice Massage
- • Duration: 5-10 minutes
- • Direct application
- • Good for small areas, trigger points
Cold Bath/Immersion
- • Temperature: 10-15°C (50-59°F)
- • Duration: 15-20 minutes
- • Good for distal extremities
Vapocoolant Sprays
- • Ethyl chloride, Fluori-Methane
- • Quick cooling
- • Spray-and-stretch technique
Contraindications for Cold
- • Raynaud's disease/phenomenon
- • Cryoglobulinemia
- • Cold urticaria (cold allergy)
- • Impaired sensation
- • Over regenerating peripheral nerves
- • Cold intolerance
- • Over open wounds
PRICE/POLICE Protocol
- Protection
- Rest / Optimal Loading
- Ice
- Compression
- Elevation
3. Therapeutic Ultrasound
Therapeutic ultrasound uses high-frequency sound waves (beyond human hearing >20,000 Hz) to produce thermal and mechanical effects in tissues.
Parameters
| Parameter | Options | Application |
|---|---|---|
| Frequency | 1 MHz vs 3 MHz | 1 MHz: Deep tissues (3-5 cm) 3 MHz: Superficial tissues (1-2 cm) |
| Intensity | 0.5-2.0 W/cm² | Lower for acute; Higher for chronic Reduce over bony prominences |
| Mode | Continuous vs Pulsed | Continuous: Thermal effects (chronic) Pulsed: Non-thermal effects (acute) |
| Duty Cycle | 10-50% (pulsed) | 20% = mostly mechanical 50% = some thermal |
| Duration | 5-10 minutes | Based on treatment area size |
Effects of Ultrasound
Thermal Effects
- • Increased tissue temperature
- • Increased blood flow
- • Increased collagen extensibility
- • Decreased muscle spasm
- • Altered nerve conduction
Non-thermal (Mechanical)
- • Cavitation (microbubble formation)
- • Acoustic streaming
- • Microstreaming
- • Increased cell membrane permeability
- • Enhanced tissue healing
Application Technique
- • Apply coupling medium (gel or water)
- • Move soundhead in overlapping circles or strokes
- • Speed: 4 cm/second
- • Keep soundhead moving (prevents hot spots)
- • Treatment area: 2-3x ERA (Effective Radiating Area)
- • Full contact with skin
Contraindications for Ultrasound
- • Over eyes, heart, brain, reproductive organs
- • Over pregnant uterus
- • Over epiphyseal plates (growth plates) in children
- • Over malignancy
- • Over thrombophlebitis
- • Over implanted devices (pacemakers, metal implants)
- • Over spinal cord after laminectomy
- • Acute inflammation (use pulsed only)
Phonophoresis
Use of ultrasound to drive medication through skin (transdermal delivery).
- • Common drugs: Hydrocortisone, dexamethasone, lidocaine
- • Medication mixed with coupling gel
- • Controversial effectiveness
4. TENS (Transcutaneous Electrical Nerve Stimulation)
TENS uses electrical stimulation for pain management. It does not cause muscle contraction at standard settings - it stimulates sensory nerves.
TENS Types
| Type | Frequency | Pulse Duration | Intensity | Mechanism |
|---|---|---|---|---|
| Conventional (High-Rate) | 50-150 Hz | 50-100 µs | Sensory level (tingling) | Gate Control Theory |
| Acupuncture-like (Low-Rate) | 1-10 Hz | 200-300 µs | Motor level (twitch) | Endorphin Release |
| Brief Intense | 100-150 Hz | 150-250 µs | Highest tolerable | Both mechanisms |
| Burst Mode | 70-100 Hz in bursts | Variable | Motor level | Endorphin Release |
Pain Gate Theory (Melzack & Wall)
Large diameter afferent fibers (Aβ) activated by TENS can inhibit ("close the gate") transmission of pain signals from small diameter fibers (Aδ, C) at the spinal cord level.
- • High frequency TENS activates large Aβ fibers
- • Inhibits pain transmission in dorsal horn
- • Fast onset, short duration relief
Electrode Placement
- • Over painful area: Direct stimulation
- • Along nerve pathway: Proximal to pain
- • Dermatomal placement: Based on nerve root
- • Trigger points: Over myofascial trigger points
- • Acupuncture points: Traditional points
Contraindications for TENS
- • Pacemaker/implanted devices (relative - check with cardiologist)
- • Over carotid sinus (anterior neck)
- • Over eyes
- • Over pregnant uterus
- • On areas with impaired sensation
- • Over malignancy
- • Over thrombophlebitis
5. NMES & FES
NMES (Neuromuscular Electrical Stimulation)
NMES uses electrical current to produce muscle contraction for strengthening, re-education, or preventing atrophy.
- Frequency: 20-50 Hz (tetanic contraction)
- Pulse duration: 200-400 µs
- Intensity: Motor level (visible contraction)
- On:Off ratio: 1:3 to 1:5 (allows recovery)
Applications of NMES
Muscle Strengthening
- • Post-surgical weakness (ACL reconstruction)
- • Quadriceps inhibition
- • Athletic training
Muscle Re-education
- • Post-stroke
- • Peripheral nerve injury
- • Facilitate voluntary control
Atrophy Prevention
- • Immobilization
- • Spinal cord injury
- • Prolonged bed rest
Spasticity Management
- • Stimulate antagonist
- • Reciprocal inhibition
- • Post-stroke, SCI
FES (Functional Electrical Stimulation)
FES uses electrical stimulation to produce functional movement during activity.
- • Foot drop: Stimulate peroneal nerve during swing phase
- • Hand function: Grasp and release in SCI
- • FES cycling: Lower extremity exercise
Russian Current
Medium frequency AC (2500 Hz) with 50 bursts/second. Originally developed for strength training. High intensity, less comfortable.
6. Iontophoresis
Iontophoresis uses direct current (DC) to drive ionized medication through the skin (transdermal drug delivery). Based on principle that like charges repel.
Common Medications
| Drug | Polarity | Indication |
|---|---|---|
| Dexamethasone | Negative (-) | Inflammation, tendinitis |
| Lidocaine | Positive (+) | Local anesthesia, pain |
| Acetic Acid | Negative (-) | Calcium deposits |
| Tap Water | Either | Hyperhidrosis (excessive sweating) |
Parameters
- • Current: 1-4 mA (based on tolerance)
- • Duration: 10-20 minutes
- • Dose: 40-80 mA-minutes (current × time)
- • Place drug electrode at treatment site
7. Interferential Current (IFC)
IFC uses two medium-frequency currents (typically 4000 Hz) that interfere to produce a beat frequency (0-150 Hz) deep in tissues. Better penetration with less discomfort.
How IFC Works
- • Two channels cross at treatment area
- • Channel 1: 4000 Hz (fixed)
- • Channel 2: 4000-4150 Hz (adjustable)
- • Beat frequency = difference between channels
- • Example: 4000 Hz - 4100 Hz = 100 Hz beat
Electrode Placements
Quadripolar (4 electrodes)
Two channels cross at 90°; interference at depth
Bipolar (Premodulated)
Two electrodes; beat created in machine
Applications
- • Pain relief (similar to TENS)
- • Muscle stimulation
- • Edema reduction
- • Good for deep tissues
8. Other Modalities
Hydrotherapy
- Whirlpool: Warm (36-40°C) or cold; debridement, ROM
- Contrast bath: Alternating hot/cold; vascular exercise
- Aquatic therapy: Buoyancy reduces joint loading; resistance
- Hubbard tank: Full body immersion
Shortwave Diathermy
- • Deep heating using electromagnetic energy
- • Frequency: 27.12 MHz
- • Heats tissues rich in water/electrolytes
- • Contraindicated with metal implants, pacemakers
Laser Therapy (LLLT/Photobiomodulation)
- • Low-level laser or LED light
- • Wavelength: 600-1000 nm (red to near-infrared)
- • Proposed effects: Pain reduction, wound healing, inflammation
- • Non-thermal mechanism (photochemical)
Traction
- Cervical traction: 10-30 lbs; neck flexion 20-30°
- Lumbar traction: 25-50% body weight
- Effects: Disc separation, muscle relaxation, nerve root decompression
- Types: Sustained, intermittent, manual, positional
Key Takeaways for the Board Exam
Ultrasound
- • 1 MHz = deep (3-5 cm)
- • 3 MHz = superficial (1-2 cm)
- • Continuous = thermal; Pulsed = non-thermal
TENS
- • High frequency = Gate control (sensory level)
- • Low frequency = Endorphins (motor level)
- • Pain management, no muscle contraction
Heat vs Cold
- • Heat: Chronic conditions, tissue extensibility
- • Cold: Acute injury, inflammation (PRICE)
- • Cold sequence: CBAN
Iontophoresis
- • Dexamethasone = negative pole
- • Lidocaine = positive pole
- • DC current drives medication
PT Study Notes
- Anatomy & Physiology
- Kinesiology & Biomechanics
- Therapeutic Exercises
- → Physical Agents & Electrotherapy
- Clinical Conditions