Test Equipment and Therapeutic Modalities 1 Flashcards

A physical therapist is treating a patient with acute lateral epicondylitis using therapeutic ultrasound. Which duty cycle setting would BEST minimize thermal effects while still delivering mechanical benefits to the tissue?

Answer: 20% pulsed

A 20% pulsed duty cycle (1:4 on:off ratio) minimizes heat accumulation in tissue while still delivering non-thermal mechanical effects such as cavitation and acoustic streaming. Continuous (100%) and higher duty cycles generate significant thermal effects, which are contraindicated during acute inflammation.

During iontophoresis for calcific tendinitis, a physical therapist uses acetic acid (acetate ion, CH₃COO⁻). Under which electrode should the medication be placed?

Answer: Cathode (negative electrode), because like charges repel the ion into tissue

Acetic acid dissociates into the negatively charged acetate ion. In iontophoresis, ions are driven into tissue by repulsion from the same-polarity electrode. Because acetate is negative, it is placed under the cathode (negative electrode), which repels it into the underlying tissue.

A therapist applies interferential current (IFC) using two medium-frequency carrier currents of 4,000 Hz and 4,080 Hz. What beat frequency is produced within the tissue, and which physiological effect does this range BEST target?

Answer: 80 Hz — pain modulation via gate control theory

The beat frequency in IFC equals the arithmetic difference between the two carrier frequencies (4,080 − 4,000 = 80 Hz). Beat frequencies in the 80–150 Hz range activate large-diameter Aβ sensory fibers, producing analgesia through the gate control mechanism.

When applying a commercially prepared moist heat pack to a patient's lumbar spine, what is the recommended minimum number of towel layers between the pack and the patient's skin to prevent burns?

Answer: 6–8 layers

Standard clinical guidelines recommend 6–8 layers of dry toweling between a hydrocollator moist heat pack and the skin. Hydrocollator packs can reach temperatures of 70–75°C (158–167°F), and this layering is necessary to reduce the surface temperature to a therapeutically safe range of approximately 40–45°C.

A physical therapist orders whirlpool hydrotherapy for a patient with peripheral arterial disease (PAD) affecting both lower extremities. Which water temperature is MOST appropriate?

Answer: 96–98°F (35.6–36.7°C) — near neutral warmth

Patients with PAD have impaired arterial perfusion and cannot meet elevated metabolic demands in ischemic tissue. Elevated water temperatures increase local oxygen demand while the compromised vasculature cannot increase supply, risking ischemic injury or ulceration. Near-neutral temperatures (96–98°F) allow gentle débridement benefits without imposing thermal stress.

A therapist uses neuromuscular electrical stimulation (NMES) for quadriceps re-education two weeks after ACL reconstruction. Which on:off time ratio BEST reduces muscle fatigue while still eliciting a training contraction during early rehabilitation?

Answer: 1:5 (one second on, five seconds off)

A 1:5 on:off ratio allows five times more rest than stimulation time, which is critical in early rehabilitation when the quadriceps is deconditioned and fatigues rapidly. As strength and endurance improve, the ratio is progressively advanced toward 1:3 and then 1:1. Ratios with more on-time (2:1 or 1:1) cause rapid fatigue and reduce overall training volume.