Diathermy (week 3)

Diathermy

application of shortwave or microwave electromagnetic energy to increase tissue temperature, particularly in deep tissues.

Two forms:

• Shortwave diathermy (SWD)

• Microwave diathermy

How it works

Energy from electromagnetic waves increases tissue temperature.

• Diathermy has the ability to heat tissues more deeply than hot packs and a larger area than ultrasound.

• SWD is not reflected by bones (which means it doesn’t concentrate in the periosteum and cause burning in this area)

• MWD reflects at tissue interfaces (air:skin, skin:subcutaneous fat, soft tissue:superficial bone – which can lead to hot spots)

Types of Applicators

Inductive Coil and Capacitive Plates can be used to apply SWD.

Magnetron (Condensor)

Inductive Coil

An alternating electrical current flows through a coil

The alternating current in the coil creates a magnetic field perpendicular to the coil

This magnetic field creates an electrical eddy in the tissues

This results in oscillation of charged particles in the tissues.

The friction caused by the oscillation results in an elevation in tissue temperature

The amount of heat that reaches the tissues is dependent on:

Strength of the magnetic field that reaches the tissues

• Decreases as the distances of the tissue increases

• Is not affected by the type of the tissue

Strength and density of the induced eddy currents (electrical)

• Is affected by the conductivity of the tissue

  • (muscles and tissue with high water content have high conductivity, but fat and bone have low conductivity)

Inductive coil diathermy applicators can heat deep and superficial tissue, but produce the MOST heat in tissues that have high electrical conductivity and that are closest to the applicators

Cables

Plastic coated wires that are wrapped around the patient’s limb

Drums

Flat spiral coil is contained within plastic housing

May have 1-2 drums

Capacitive Plates

Metal plates encased in plastic housing or carbon rubber electrodes that are between felt pads

High frequency alternating current flows between one plate to another through the patient

Same mechanism of action (oscillation  friction  heat) as the inductive coil

Most heating occurs in tissues with highest conductivity

Doesn’t penetrate to deepest tissue as much, esp. if excessive fat tissue

Magnetron (Condenser)

Creates a high-frequency- short wavelength radiation.

Delivers microwave diathermy by producing a high-frequency alternating current in an antenna which in turn produces an electromagnetic field

Used only to treat a small defined area

Generate the most heat in tissues with high-electrical conductivity and superficial tissues

Has a higher risk of burns because of standing waves

Thermal Effects

Vasodilation

Increased rates of nerve conduction

Elevation of pain threshold

Alteration of muscle strength

Alteration of enzymatic activity

Increased soft tissue extensibility

Nonthermal effects

Increased microvascular perfusion

• This results in increased local circulation, increased tissue oxygenation, increased nutrient availability and phagocytosis

Altered cell membrane function and cellular activity

• Affect ion binding to the cell membrane

• Accelerate cell growth and division where it is too slow and inhibit it when it is too fast

Indications Thermal US

• Decrease pain

• Accelerate tissue healing

• Decrease joint stiffness

• Increase joint range of motion (if combined with stretching)

Indications Nonthermal Pulsed Shortwave Diathermy

Control of Pain and Edema

Pain Control

Soft Tissue Healing

Nerve Healing

Bone Healing

Osteoarthritis Symptoms

Contraindications General

Implanted or transcutaneous neural stimulators, including cardiac pacemakers

Pregnancy

Contraindications For Nonthermal Pulsed Shortwave Diathermy

Deep tissue such as internal organs

Substitute for conventional therapy for edema and pain

Contraindications For Thermal Diathermy

Metal implants

Malignancy

Eyes

Testes

Growing Epiphyses

Precautions General

Near electronic or magnetic equipment

Obesity

Copper-bearing inter-uterine contraceptive device

Skeletal immaturity

Precautions for the PT/PTA

• Therapists stay 1-2 m away from all continuous diathermy applicators

• Therapists stay 30-50 cm away from PSWD

• Therapists stay out of the direct beam of any MWD

Adverse Effects

Fat tissue is the most likely to be burned, especially with capacitive plate applicators

To avoid burns during the application of diathermy, the patient’s skin must be kept dry by wrapping with towels.

Cables application

Cable is wrapped around the towel-covered limb with the cable at least 3 cm from the next wrap/segment

Cable can be coiled on top of 6-8 layers of toweling over a flat surface

Drum placed directly over the area. Slight gap to allow for heat dissipation. (Consistent distance maintained)

Capacitive application

Two plates placed at an equal distance (2-10 cm) on either side of the area to be treated

Magnetron Microwave Applicator

Applicator placed a few inches from the area to be treated and the beam directed perpendicular to the patient’s skin.