DPT Electrotherapy & Modalities 5 — Questions and Answers
Question 1: A patient has a demand-type cardiac pacemaker. Which electrotherapy modality poses the GREATEST risk of interference?
- Infrared lamp
- TENS with conventional mode (80–150 Hz) (Correct answer)
- Therapeutic ultrasound at 1 MHz
- Photobiomodulation (low-level laser)
Correct answer: TENS with conventional mode (80–150 Hz)
TENS, especially at higher frequencies, can produce electrical signals that mimic cardiac activity, potentially inhibiting a demand pacemaker and causing arrhythmia.
Question 2: The beam non-uniformity ratio (BNR) of an ultrasound transducer indicates:
- The percentage of energy reflected at the skin surface
- The ratio of peak to average spatial intensity within the beam, where lower is safer (Correct answer)
- The depth of penetration in centimeters per MHz
- The frequency stability across the treatment session
Correct answer: The ratio of peak to average spatial intensity within the beam, where lower is safer
BNR is the ratio of peak spatial intensity to average spatial intensity; values closer to 1:1 indicate a more uniform beam, reducing risk of hot spots.
Question 3: Which waveform is classified as monophasic and is most commonly used for wound healing in HVPC?
- Symmetrical biphasic
- Twin-peak monophasic (Correct answer)
- Russian current (medium-frequency AC)
- Interferential current
Correct answer: Twin-peak monophasic
HVPC uses a twin-peak monophasic waveform with very short pulse durations (< 200 µs) and high peak voltages (> 100 V), producing minimal electrochemical effects at the electrodes.
Question 4: During fluidotherapy treatment, the active ingredient that provides therapeutic benefit is:
- Heated water providing hydrotherapy
- Cellulose particles suspended in warm dry air providing convective heat and sensory stimulation (Correct answer)
- Infrared radiation from the heated particles
- Ultrasonic vibration from particle movement
Correct answer: Cellulose particles suspended in warm dry air providing convective heat and sensory stimulation
Fluidotherapy uses finely divided cellulose particles agitated in a stream of warm air, delivering dry heat via convection and providing desensitization through sensory bombardment.
Question 5: A therapist is using neuromuscular electrical stimulation (NMES) for quadriceps strengthening post-ACL reconstruction. The optimal on:off ratio to minimize fatigue while building strength is:
- 1:1 (equal on and off time)
- 1:5 (short on, long off) (Correct answer)
- 5:1 (long on, short off)
- 2:1 (twice as much on as off)
Correct answer: 1:5 (short on, long off)
A 1:5 on:off ratio (e.g., 10 s on, 50 s off) allows adequate recovery between contractions to minimize fatigue and maintain contraction quality during early rehabilitation.
Question 6: Transcranial direct current stimulation (tDCS) in neurological rehabilitation uses which current characteristic to modulate cortical excitability?
- High-frequency alternating current to depolarize neurons
- Weak direct current (1–2 mA) to subthreshold polarize cortical neurons (Correct answer)
- Pulsed current to create action potentials in motor cortex
- Interferential beats at delta frequency (0.5–4 Hz)
Correct answer: Weak direct current (1–2 mA) to subthreshold polarize cortical neurons
tDCS delivers subthreshold DC (1–2 mA) that modulates resting membrane potential without directly generating action potentials; anodal stimulation increases excitability, cathodal decreases it.
Question 7: When selecting ultrasound duty cycle for an acute injury with significant edema, which setting is most appropriate and why?
- Continuous (100%) to maximize thermal effects and accelerate healing
- 20% pulsed to minimize heat while delivering mechanical effects (Correct answer)
- 50% pulsed as a compromise between thermal and mechanical effects
- 10% pulsed at maximum intensity to reach deep tissue
Correct answer: 20% pulsed to minimize heat while delivering mechanical effects
A 20% duty cycle (pulsed mode) minimizes thermal accumulation in acutely inflamed tissue while still delivering non-thermal mechanical effects that promote healing.
DPT Electrotherapy & Modalities 5
A patient has a demand-type cardiac pacemaker.
Which electrotherapy modality poses the GREATEST risk of interference?