electromagnetics

diathermy

application of electromagnetic waves (radio frequency range)

most common diathermy

short wave diathermy (SWD)

types of diathermy

PSWD, CSWD, MWD

physical properties of diathermy

absorption of energy by tissues causes heating (deep tissues)

shortwave: 1.8-30 MHz

microwave: 300 Mhz-300 GHz

diathermy parameters: shortwave frequency bands

13.56, 27.12, and 40.68 MHz

diathermy parameters: microwave frequency

2450 MHz

diathermy parameters: mode

continuous or pulsed

types of diathermy devices

capacitive, inductive, microwave, pulsed shortwave, pulsed electromagnetic

capacitive method

aka electric field method

tissues are part of the dielectric of a capacitor

subcutaneous fatty tissue heated greater than muscle

electrodes placed 1-3 in away from skin

contraplanar or coplanar set-up

inductive method

aka magnetic field method

eddy currents produce in tissues w/ lowest impedance

drum or sleeve applicators

monode or diplode drums

pulsed electromagnetic fields/PEMF

deliver very low intensity electromagnetic waves that do not heat tissues

selection of proper dosage

pt’s subjectivity important for dosing

dose I

<38 W mean power, acute injury stage

dose II

38-80 W mean power, subacute injury stage

dose III

80-300 W mean power, late subacute injury stage

dose IV

>300 W mean power, chronic injury stage

types of applicators

inductive coils—SWD

capacitive plates—SWD

magnetron—MWD “MASER”

capacitive diathermy advantages over inductive SWD

ease of depolarization of polarizable material—dielectric constant

high dielectric constant—muscle and skin

low dielectric constant—fat and bone

heating of fat greater

microwave diathermy (MWD)

use magnetron device similar to those used in microwave ovens

applicator positioned perpendicular to skin’s surface

less penetration depth than SWD

uncommon in USA

pulsed shortwave diathermy (PWSD)

most modern devices are this or a combo w/ CSWD

easier set-up

portable

inductive sleeves

PSWD parameters

high pulse rate (~800 pps), short pulse duration (~400 microseconds)

duty cycle=(pulse duration/(pulse duration+interpulse interval))

example parameters for PSWD

pulse duration 0.4 msec

pulse freq 200 pps

peak pulse power 800 W

physiological effects of diathermy

deeper heating than superficial modalities

larger area treated compared to US

does not require constant attention

cannot depolarize motor nn.

thermal effects

deeper heating than superficial modalities

affect tissue extensibility, muscle strength, pain, healing

factors to consider of diathermy thermal effects

continuous or pulsed

distance btwn applicator and skin

duration of treatment

intensity

effects on tissue extensibility

combo of prolonged low load stretch and heat shown to effectively increase tissue flexibility

effects on pain

analgesic effects—SWD may be more effective than moist heat for deeper tissues

possible non thermal mechanisms of relief

effects on tissue healing

promotes soft tissue and bone healing

what is temperature determined by?

field intensity

tissue type

duty cycle

distance from pt

nonthermal effects of diathermy

increased microvascular perfusion

altered cell membrane function and cellular activity

clinical applications

thermal: pain control, tissue healing, decreased stiffness, increase ROM

nonthermal: pain & edema control; soft tissue, nerve, bone healing; improvement of osteoarthritis symptoms

indications

mostly the same as regular thermotherapy

greater depth of heating than superficial modalities and larger area than US

muscle spasms, joint stiffness

mild heating for inflammation

PEMF: superficial wound and bone healing

general contraindications for all diathermy

implanted or transcutaneous stimulators, including pacemakers; pregnancy

thermal diathermy contraindications

metal, malignancy, eyes, testes, growing epiphyses

nonthermal diathermy contraindications

deep tissue/internal organs

substitute for conventional therapy for edema and pain

pacemakers, electronic devices, metal implants

precautions for all types of diathermy

near electronic or magnetic equipment

obesity

copper bearing IUD

burns—particularly fat layers, keep skin dry

precautions for nonthermal diathermy

pregnancy, skeletal immaturity

application technique (after preparation etc)

tune device

select parameters

turn on machine

assess at 5 min for adverse effects

document

when do you use US over diathermy?

smaller areas of dense collagen tissue—ligaments, tendons, joint capsules

when to use diathermy instead of US

tissues with high fluid content, large areas (muscles)

why is diathermy more common in other countries?

practitioner bias, high cost, reimbursement issues