WK11: Electromagnetic Radiation

What does it mean that therapeutic electromagnetic (EM) radiation is nonionizing?

Nonionizing energy means it does not have enough energy to alter the chemical structure of body tissue cells. However, it still interacts with tissue to stimulate biological responses and promote tissue healing.

How do wavelength, frequency, and energy relate to each other in the electromagnetic spectrum?

"Wavelength and frequency/energy have an inverse relationship:

• Long wavelength = Low frequency = Low energy

• Short wavelength = High frequency = High energy"

What are the four primary electromagnetic modalities used in physical therapy?

"1. Short Wave Diathermy (SWD)

2. Ultraviolet Light (UV)

3. Low-Level Laser Therapy (LLLT)

4. Infrared Lamp / Therapy"

How does Short Wave Diathermy (SWD) generate heat differently than traditional surface heating packs?

Hot packs and infrared lamps apply heat externally (conduction or radiation), whereas SWD generates thermal energy internally within target body tissues by converting high-frequency electromagnetic energy into heat.

What radio frequency is most commonly used for Short Wave Diathermy (SWD), and how deep can it heat?

SWD operates at a standard radio frequency of 27.12 MHz. It can heat deep tissues 3 to 5 cm below the skin surface without overheating the superficial skin or subcutaneous fat layer.

How does an Inductive Short Wave Diathermy (SWD) unit generate heat in target tissue?

Inductive SWD uses magnetic field coils (inside flexible cables or a rigid drum applicator) to project a magnetic field into the body. This creates circular, high-frequency electrical currents called eddy currents within the tissue.

Which tissue type absorbs more heat during Inductive SWD application?

Tissues with high electrical conductivity and water content (such as deep skeletal muscle and internal organs) absorb more energy and heat up more than low-conductivity tissues like fat.

A therapist placing an inductive drum applicator (monode) over a patient's lower back Why is the patient's sensation of warming delayed when using an inductive SWD drum electrode?

Inductive fields heat deep muscle tissues directly while sparing superficial skin thermal receptors. Because the warmth builds up deep inside before traveling outward, therapists should start at a lower power setting and gradually increase intensity in increments.

How does a Capacitive Short Wave Diathermy (SWD) unit generate heat?

Capacitive SWD places the body part between two insulated condenser plates, forming a capacitor. High-frequency electric field oscillations pass between the plates, storing and releasing charge to produce localized tissue heating.

Capacitive SWD setup showing two insulated condenser plate electrodes positioned on opposite sides of a patient's shoulder Which tissue layer absorbs the most heat during Capacitive SWD application?

Capacitive SWD heats fat (adipose) tissue more effectively than muscle. For patients with thick subcutaneous fat, a larger Electrode-Skin Distance (ESD) must be used to ensure heat reaches deeper joint and muscle structures.

What is the key difference between Continuous Shortwave Diathermy (CSWD) and Pulsed Shortwave Diathermy (PSWD)?

"• CSWD delivers uninterrupted energy, producing maximum thermal effects (with higher risk of burns if concentrated).

• PSWD interrupts the energy stream into periodic pulses, allowing heat to dissipate during off-times for lower thermal or primarily non-thermal effects."

In Pulsed Short Wave Diathermy (PSWD), how does interpulse interval affect heat production?

The interpulse interval is the off-time between pulses. The longer the off-time relative to the on-time (pulse duration), the lower the overall thermal effect in the target tissue.

What are the primary thermal physiological effects of Short Wave Diathermy (SWD)?

"• Increased deep tissue temperature (up to 3-5 cm deep)

• Accelerated cellular metabolism and oxygen uptake

• Vasodilation (increased local blood flow)

• Muscle relaxation and reduced stiffness (via muscle spindle and Golgi tendon organ modulation)

• Increased connective tissue extensibility"

What are the non-thermal (athermal) cellular effects of Short Wave Diathermy (SWD)?

Non-thermal SWD alters semipermeable cell membrane permeability, increases cellular metabolic pathways, enhances adenosine triphosphate (ATP) production, and stimulates membrane-bound protein activity.

What are the main clinical indications for applying therapeutic Short Wave Diathermy (SWD)?

"• Pain relief and muscle spasm reduction

• Decreasing joint stiffness and joint contractures

• Increasing blood flow

• Chronic inflammatory conditions (e.g., bursitis, tenosynovitis, synovitis, chronic pelvic inflammatory disease)"

Why are cardiac pacemakers and metal implants strict contraindications for Continuous Short Wave Diathermy (CSWD)?

Diathermy produces a broad electromagnetic field extending beyond the applicator. This field can disrupt electronic pacemakers/implants or rapidly heat internal metal hardware, risking severe tissue burns and internal damage.

What red flag action must a therapist take if a patient receiving SWD reports that the treatment area is becoming excessively warm or hot?

Excess warmth indicates localized tissue overheating (often due to high water/perspiration content or poor local blood circulation to clear heat). The clinician must immediately stop or decrease intensity, dry accumulated sweat from the skin, and add extra toweling barrier layers.

How are the three bands of Ultraviolet (UV) light categorized by wavelength?

"• UV-A: 320 to 400 nm (longest wavelength, lowest frequency)

• UV-B: 280 to 320 nm (intermediate wavelength/frequency)

• UV-C: 100 to 280 nm (shortest wavelength, highest frequency; artificial sources only)"

How does UV light wavelength affect skin layer penetration depth?

"Diagram showing UVA penetrating deeply into the dermis layer, while UVB and UVC only penetrate into the superficial epidermis Lower frequency/longer wavelengths penetrate deeper:

• UV-A penetrates deep into the dermis layer.

• UV-B and UV-C are absorbed superficially within the epidermis layer."

What latent period characteristic is unique to UV radiation tissue responses?

All biological effects of UV light (such as skin reddening or cell changes) have a latent period of at least 1 hour before visible symptoms appear.

What three primary physiological skin reactions occur following UV radiation exposure?

"1. Erythema: Inflammatory vasodilation (reddening of skin)

2. Epidermal Hyperplasia: Increased cell production causing skin thickening

3. Desquamation: Peeling/shedding of epidermal skin cells due to intercellular edema"

Why is UV-C light specifically selected for clinical wound bed management?

UV-C (250 nm wavelength) provides bactericidal effects (killing pathogens like MRSA), promotes necrotic tissue debridement, increases localized tissue blood flow, and accelerates cell regeneration without thermal burning risks.

A clinician holding a cold quartz UV-C handheld lamp near an open ulcer wound on a patient's heel When should UV-C lamp treatment for infected open wounds be discontinued?

UV-C wound treatments should be stopped as soon as clinical infection clears and bacterial pathogens are no longer present within the wound bed.

What is the Minimal Erythemal Dose (MED) in UV light therapy?

The MED is the shortest UV exposure duration that produces uniform skin erythema (redness) within 1 to 6 hours and completely disappears within 24 hours.

How is a Cold Quartz generator MED test performed on a patient?

Position the generator lamp approximately 1 inch (2.5 cm) from test cutout holes on the skin. Uncover one hole every 15 seconds. Have the patient observe the site every 2 hours to note which exposed area turns red and when it fades.

What key medical conditions contraindicate the use of therapeutic UV light?

"• Photosensitivity (easy sunburn)

• Systemic Lupus Erythematosus (SLE dermatitis)

• Pellagra (niacin deficiency dermatitis)

• Active tuberculosis

• High fever or acute active diabetes"

What essential safety protection must be worn during UV light administration?

Both the patient and clinician MUST wear protective eye goggles equipped with UV-blocking safety filters to prevent retinal damage and severe corneal burns.

What does the acronym L.A.S.E.R. stand for?

Light Amplification by the Stimulated Emission of Radiation

Why is Low-Level Laser Therapy (LLLT) often referred to as 'cold laser'?

LLLT uses low-power laser diodes whose energy outputs are insufficient to generate a macro thermal (heating) response in biological tissue.

What does it mean that laser light is monochromatic?

Monochromatic means the emitted light consists of one single, specific wavelength and color.

What are coherence and beam divergence in laser physics?

"• Coherence: Photons travel in phase with synchronized peaks and troughs.

• Beam Divergence (Collimation): Photons remain parallel with minimal spreading apart, concentrating high light energy into a small target area."

How do Helium-Neon (HeNe) and Gallium-Arsenide (GaAs) lasers differ in wavelength and visibility?

"• Helium-Neon (HeNe): Wavelength of 632.8 nm (visible brilliant red light).

• Gallium-Arsenide (GaAs): Wavelength of 910 nm (non-visible infrared light range)."

What is the typical depth of penetration for Low-Level Laser Therapy (LLLT)?

LLLT penetrates tissue between 5 mm and 10 mm (0.5 to 1 cm). Shorter visible wavelengths are absorbed superficially in the skin, while longer near-infrared wavelengths penetrate deeper.

Why is protective eyewear required when operating clinical Class 3B lasers?

Class 3B clinical lasers emit sufficient energy to cause permanent retinal damage if direct or reflected light enters the eye.

How does laser photon absorption in cellular cytochromes and porphyrins stimulate biological repair?

Light photons absorbed by cell cytochromes increase mitochondrial ATP production. Photons absorbed by endogenous porphyrins increase hemoglobin synthesis, enhancing cellular energy and oxygen delivery.

What cellular and tissue changes occur during Low-Level Laser Therapy (LLLT)?

"• Stimulates fibroblast and nerve growth factor synthesis

• Increases collagen production and lesion tensile strength

• Enhances cell membrane transport ($Ca^{2+}$, $Na^+$, $K^+$)

• Increases cellular DNA and RNA synthesis"

Through what mechanisms does Low-Level Laser Therapy (LLLT) reduce pain and inflammation?

"• Increases pain-inhibiting endorphins and serotonin

• Decreases nociceptive C-fiber firing and bradykinin activity

• Downregulates inflammatory mediators like prostaglandin E2 ($PGE_2$)

• Enhances macrophage/mast cell immune activity"

What pulse frequency ranges (Hz) are selected in LLLT for pain, edema, and inflammation?

"• Low Range (1–100 Hz): Targeted for Pain management

• Medium Range (500–1000 Hz): Targeted for Edema reduction

• High Range (2500–5000 Hz): Targeted for Acute Inflammation control"

What are the primary contraindications for applying Low-Level Laser Therapy (LLLT)?

"• Direct application over cancerous lesions / active malignancy

• Directly over unclosed pediatric skull fontanels

• Directly over endocrine glands (e.g., thyroid)

• Directly over the eyes

• Directly over photosensitive skin or active hemorrhaging"

What red flag symptom indicates that LLLT treatment must be stopped immediately?

If a patient reports a burning sensation during LLLT, treatment must stop immediately. This indicates heightened skin sensitivity to laser radiation that could cause skin irritation or chemical burns.

What is the wavelength spectrum range for Infrared radiation?

Infrared light occupies the spectrum band between red visible light and microwaves, ranging from 780 nm to 1 mm.

How does an Infrared lamp transfer heat to body tissue?

Infrared lamps transfer thermal energy via radiant electromagnetic waves through the air to heat the superficial skin layer.

How does superficial heating from Infrared lamps help reduce muscle spasms?

Elevating skin temperature decreases the firing rate of primary Type Ia and secondary Type II afferent sensory nerves in muscle spindles, relaxing involuntary skeletal muscle guarding.

What is Monochromatic Infrared Energy (MIRE)?

MIRE is infrared light delivered through light-emitting diode (LED) or supra-luminous light-emitting diode (SLED) arrays built directly into flexible application pads.

A flexible Monochromatic Infrared Energy pad with lit red light-emitting diodes Why is placing MIRE pads in direct contact with skin advantageous?

Direct skin contact eliminates the air gap, minimizing light reflection and refraction off the skin surface so that maximum photon energy is absorbed into underlying tissues.

By what biochemical mechanism does 890 nm MIRE restore sensation in patients with diabetic peripheral neuropathy?

Absorption of 890 nm infrared energy causes hemoglobin to release Nitric Oxide (NO), a potent vasodilator. NO increases local blood circulation to ischemic peripheral nerve endings, supporting nerve recovery and restoring lost cutaneous sensation.

What clinical conditions benefit from Infrared light therapy?

"• Chronic low back pain and myofascial trigger points

• Diabetic peripheral neuropathy sensory loss

• Joint osteoarthritis, rheumatoid arthritis, and frozen shoulder

• Tendinitis and delayed skeletal muscle fatigue"