DPT Electrotherapy & Modalities 2 — Questions and Answers
Question 1: Which parameter distinguishes interferential current (IFC) from traditional TENS?
- IFC uses direct current; TENS uses alternating current
- IFC uses two medium-frequency currents that interfere to produce a low-frequency beat; TENS applies low-frequency current directly (Correct answer)
- IFC requires a water bath; TENS uses surface electrodes
- IFC penetrates only superficial tissue; TENS reaches deep muscle
Correct answer: IFC uses two medium-frequency currents that interfere to produce a low-frequency beat; TENS applies low-frequency current directly
IFC crosses two medium-frequency (4,000 Hz) currents whose amplitude modulation creates a low-frequency beat frequency (1–150 Hz) within deeper tissue.
Question 2: A patient with a fresh third-degree burn is referred for wound care. Which thermal modality is CONTRAINDICATED?
- Pulsed ultrasound at low intensity
- Infrared lamp (dry heat) (Correct answer)
- Cold pack application
- Pulsed electromagnetic field (PEMF)
Correct answer: Infrared lamp (dry heat)
Infrared (dry heat) over a third-degree burn is contraindicated because destroyed sensory nerves eliminate protective pain sensation and heat can worsen tissue damage.
Question 3: The Arndt-Schulz law as applied to laser therapy states:
- Higher doses always produce greater therapeutic effects
- Weak stimuli excite physiological activity; very strong stimuli inhibit or abolish activity (Correct answer)
- Laser wavelength determines depth of penetration exclusively
- Red and infrared lasers are equally effective for all conditions
Correct answer: Weak stimuli excite physiological activity; very strong stimuli inhibit or abolish activity
The Arndt-Schulz law holds that weak stimuli increase biological activity while excessively strong stimuli suppress it, guiding dose selection in photobiomodulation.
Question 4: During iontophoresis with dexamethasone for lateral epicondylitis, the drug is placed under which electrode?
- Anode (positive)
- Cathode (negative) (Correct answer)
- Either electrode; polarity is irrelevant
- The dispersive electrode
Correct answer: Cathode (negative)
Dexamethasone carries a negative charge, so it is driven into tissue from the cathode (negative pole) by electrostatic repulsion.
Question 5: What is the primary mechanism by which moist heat packs (hydrocollator) relieve pain?
- Direct inhibition of prostaglandin synthesis
- Decreased nerve conduction velocity of pain fibers
- Gate control via thermal mechanoreceptor stimulation and increased local circulation (Correct answer)
- Ultrasound cavitation at the cellular level
Correct answer: Gate control via thermal mechanoreceptor stimulation and increased local circulation
Heat activates thermoreceptors that compete with nociceptive input at the dorsal horn (gate control) and increases local blood flow, reducing ischemic pain.
Question 6: A PT selects 3 MHz ultrasound instead of 1 MHz for a patient with superficial scar tissue 1 cm deep. What is the rationale?
- 3 MHz penetrates deeper than 1 MHz
- 3 MHz is absorbed more superficially, making it more effective for shallow tissues (Correct answer)
- 3 MHz produces cavitation; 1 MHz does not
- Frequency has no effect on depth of penetration
Correct answer: 3 MHz is absorbed more superficially, making it more effective for shallow tissues
Higher ultrasound frequencies (3 MHz) are attenuated more rapidly and are therefore most effective in superficial tissues (0.5–2 cm), while 1 MHz reaches 3–5 cm depth.
Question 7: Which electrode placement configuration for neuromuscular electrical stimulation (NMES) produces the strongest muscle contraction with the least current?
- Both electrodes over the muscle belly
- One electrode over the motor point; one electrode over the distal tendon (Correct answer)
- Bipolar placement with equal electrode sizes
- Monopolar with large active electrode over the motor point
Correct answer: One electrode over the motor point; one electrode over the distal tendon
Placing the active electrode precisely over the motor point minimizes impedance and directly depolarizes the motor nerve, producing maximal contraction at lowest current.
DPT Electrotherapy & Modalities 2
Which parameter distinguishes interferential current (IFC) from traditional TENS?