DPT Electrotherapy & Modalities 3 — Questions and Answers
Question 1: Which pulse characteristic of TENS is most responsible for determining comfortable sensory versus motor recruitment?
- Pulse frequency (Hz)
- Pulse duration (µs) (Correct answer)
- Amplitude (mA)
- Waveform symmetry
Correct answer: Pulse duration (µs)
Pulse duration (width) determines which fiber types are recruited; longer durations recruit larger motor fibers, while shorter durations preferentially stimulate sensory Aβ fibers.
Question 2: A patient reports increased pain 24 hours after ultrasound treatment to the Achilles tendon. The most likely cause is:
- Excessive thermal effects from continuous mode at high intensity (Correct answer)
- Mechanical cavitation from pulsed mode
- Electrode contact dermatitis
- Phonophoresis drug reaction
Correct answer: Excessive thermal effects from continuous mode at high intensity
Continuous ultrasound at high intensity over a superficial tendon can generate excessive heat, causing delayed inflammatory pain flare-up.
Question 3: Acupuncture-like TENS (AL-TENS) is characterized by:
- High frequency (80–150 Hz), low intensity producing paresthesia
- Low frequency (1–10 Hz), high intensity producing visible muscle twitching (Correct answer)
- Medium frequency (50 Hz), medium intensity producing no visible response
- Variable frequency bursts at patient-controlled amplitude
Correct answer: Low frequency (1–10 Hz), high intensity producing visible muscle twitching
AL-TENS uses low frequencies (1–10 Hz) and high intensity sufficient to elicit rhythmic muscle twitching, theorized to release endorphins via motor fiber stimulation.
Question 4: For a patient with lymphedema, which electrophysical agent should be AVOIDED?
- Compression pump
- Low-level laser therapy
- Thermal ultrasound over the affected limb (Correct answer)
- Manual lymphatic drainage
Correct answer: Thermal ultrasound over the affected limb
Thermal ultrasound increases local blood flow and capillary permeability, potentially worsening edema formation in lymphedematous tissue.
Question 5: The inverse square law applies to which modality and explains why treatment distance is critical?
- Ultrasound
- TENS
- Infrared radiation (Correct answer)
- Iontophoresis
Correct answer: Infrared radiation
Infrared radiation intensity is inversely proportional to the square of the distance from the source, so doubling distance reduces intensity by 75%.
Question 6: During pelvic floor electrical stimulation for stress urinary incontinence, which frequency range is most appropriate to strengthen the external urethral sphincter?
- 1–10 Hz (low frequency for endurance)
- 35–50 Hz (medium frequency for fast-twitch recruitment) (Correct answer)
- 80–100 Hz (high frequency for pain inhibition)
- 200 Hz (ultra-high for deep penetration)
Correct answer: 35–50 Hz (medium frequency for fast-twitch recruitment)
Frequencies of 35–50 Hz effectively recruit fast-twitch (type II) sphincter muscle fibers responsible for rapid closure during stress maneuvers.
Question 7: Which biophysical effect of therapeutic ultrasound is responsible for increasing collagen extensibility prior to stretching?
- Cavitation disrupting cell membranes
- Acoustic streaming altering membrane permeability
- Thermal effect raising tissue temperature to 40–45°C (Correct answer)
- Piezoelectric effect generating secondary currents
Correct answer: Thermal effect raising tissue temperature to 40–45°C
Raising tissue temperature to 40–45°C via continuous ultrasound reduces the viscous resistance of collagen cross-links, allowing greater elongation during concurrent stretching.
DPT Electrotherapy & Modalities 3
Which pulse characteristic of TENS is most responsible for determining comfortable sensory versus motor recruitment?