PST 301 Electrotherapy I 2024/25 Session PDF

PST 301
ELECTROTHERPAY I KAJERO O.O. 2024/25 SESSION COURSE OUTLINE Physical principles and procedures governing the use of heating modalities in physiotherapy Heat capacity and specific heat capacity of matter Modes and methods of heat transfer – conduction (h...

PST 301
ELECTROTHERPAY I KAJERO O.O. 2024/25 SESSION COURSE OUTLINE Physical principles and procedures governing the use of heating modalities in physiotherapy Heat capacity and specific heat capacity of matter Modes and methods of heat transfer – conduction (hot/cold pack), convection (whirlpool therapy), conversion (ultrasound, SWD), radiation, evaporation Production, physiological, metabolic, neuromuscular and psychological effects of thermotherapy Indications, therapeutic uses and contraindications of thermotherapy Types of thermotherapy (with examples) Dangers and precautionary safety measures for each of the various heat producing modalities  WHAT IS THERMOTHERAPY? Thermotherapy is the therapeutic application or use of heat In rehabilitation, It is used primarily to control pain, increase circulation, increase soft tissue extensibility and accelerate healing Heat has some role in hemodynamic, neuromuscular and metabolic processes.  PHYSIOLOGICAL EFFECTS OF HEAT  Hemodynamic effects: effects of heat on blood vessels and blood flow Causes vasodilation especially of the cutaneous blood vessel and increased blood flow Vasodilation is caused by direct ref lex activation of the smooth muscles of the blood vessels and indirectly by activation of local spinal cord reflexes by cutaneous thermoreceptors Also in the release of chemical mediators of inflammation  Hemodynamic effects: Direct mechanism Superf icial heating stimulates the cutaneous thermoreceptors and it transmits the impulses from these receptors to the nearby cutaneous blood vessels. This releases bradykinin and nitrous oxide which stimulate relaxation of the smooth muscles and causes vasodialation in the area where heat is applied  Hemodynamic effects: Indirect mechanism Heat stimulates the cutaneous receptors which pass impulses to the dorsal/posterior horn of the gray matter of the spinal cord It synapses with sympathetic neurons in the lateral gray horn of the spinal cord to inhibit their firing and decrease the sympathetic output. This decreased sympathetic activity causes reduced smooth muscle contraction resulting in vasodilatation Hemodynamic effects: Indirect mechanism Increased tissue temperature activates and release vasodilatation promoter such as histamine and prostaglandin which produces vasodilatation.  Effects on blood pressure The peripheral resistance is reduced by the generalized vasodilation and this causes a fall in blood pressure Rise in temperature also reduce the viscosity of the blood which reduces blood pressure  General rise in temperature As blood passes through the heated tissues, it carries heat in to other parts of the body so if heating is extensive and prolonged, a general rise in body temperature occurs  PHYSIOLOGICAL EFFECTS OF HEAT Neuromuscular effects Increase in nerve conduction velocity Decreased nerve conduction latency Increased pain threshold  Neuromuscular effects Increased pain threshold and decreased proprioception of pain through: The pain gating mechanism at the spinal cord Increase blood flow potentially reduce pain from ischaemia Relaxation of muscle spasm  Changes in muscle strength Muscle strength and endurance found to decrease for initial 30minutes following heat application (superf icial/deep heating) Gradually recovers then increases for next 2 hours Measuring muscle strength (before heat application Not after)  GATE CONTROL THEORY OF PAIN a mechanism, in the spinal cord, in which pain signals can be sent up to the brain to be processed to accentuate the possible perceived pain, or attenuate it at the spinal cord itself It is a mechanism where pain is modulated at the level of the spinal cord. The 'gate' is the mechanism where pain signals can be let through or restricted. If the gate is open, pain signals can pass through and will be sent to the brain to perceive the pain. If the gate is closed, pain signals will be restricted from travelling up to the brain, and the sensation of pain won't be perceived d  GATE CONTROL THEORY OF PAIN This mechanism is located in the dorsal horn of the spinal cord specifically n the substantia gelatinosa. Types of primary neurons A-β f ibers: myelinated, large diameter f ibers, have a quick transmission of impulses; activated by non-noxious stimuli, such as light touch, pressure, and hair movement A-δ fibers: thinly myelinated, a smaller diameter fiber, stimulated by noxious stimuli, such as pain and temperature, specifically sharp, intense, tingling sensations. C fibers: unmyelinated; have the slowest transmission of impulse since they are not myelinated, activated by pain and temperature, namely prolonged burning sensations  GATE CONTROL THEORY OF PAIN If the interneurons in the substantia gelatinosa are stimulated by the non- noxious large diameter A-β f ibers, an inhibitory response is produced and there are no pain signals sent to the brain, and in this instance the 'pain gate' is closed GATE CONTROL THEORY OF PAIN When the interneurons are stimulated by the smaller diameter A-δ or C f ibers, an excitatory response is produced. In this case, pain signals are sent to the brain, these can be modulated, sent back down through descending modulation, and perceived as varying amounts of pain.  GATE CONTROL THEORY OF PAIN In the spinal cord, the primary afferent neurons come from the periphery and synapse with the second order neurons in the dorsal horn in the spinal cord, and release respective neurotransmitters or neuropeptides Possible neurotransmitters or neuropeptides released: Glutamate: excitatory Glycine AND GABA: inhibitory Substance P: excitatory Endorphins and serotonin  GATE CONTROL THEORY OF PAIN There are two types of second order neurons: wide dynamic range (WDR) neurons: synapse to A-β, A-δ, and C fibers, and therefore are activated by noxious and non-noxious stimuli nociceptive specific (NS) range neurons: only synapse to A-δ and C fibers, thus are activated by noxious stimuli. Third-order neurons, which are located in the brainstem and diencephalon, transmit the pain signal to the cerebral cortex, where the pain signal, from the A-δ and C fibers, can be further modulated For further reading: https://www.youtube.com/watch?v=M-rL8XdHo6Q  METABOLIC EFFECT Increased metabolic rate Van’t Hoff equation: any chemical change capable of being accelerated is accelerated by a rise in temperature. Heating of tissues accelerates enzymatic activity in the body With rise in temperature, all cell activity increases including cell motility, synthesis cellular interaction such as cell growth The increase in the metabolism is greatest in the region where most heat is produced in the superficial tissue  METABOLIC EFFECT Increased metabolism results in increased demand for oxygen and nutrient, and an increased output of waste productions including metabolites  EFFECT ON GLANDS Increased activity of sweat glands There is a reflex stimulation of the sweat glands in the area exposed to the heat When the heated blood circulates throughout the body, it affects the centers concerned with thermoregulation  ALTERED TISSUE EXTENSIBILITY Increasing the temperature of the soft tissue also increase its extensibility Application of heat before stretching helps to maintain a greater increase in length after the stretching force is applied and also the risk of tissue tearing is reduced. The maintained elongation of the tissues is caused by the changes in the viscoelasticity of the fiber.  INDICATIONS FOR THERMOTHERAPY Subacute and chronic inflammatory condition Subacute or chronic pain Decreased range of motion Facilitate healing Muscle guarding Muscle spasm Myofascial trigger points Subacute muscle strain Subacute ligament sprain  PRECAUTIONS Pregnancy: heating of whole body, abdomen and low back area should be avoided, fetus may be damaged by maternal hyperthermia Impaired Circulation Cardiac Insufficiency: treatment should be discontinued if patient’s heart rate falls or if patient complains of feeling faint Poor Thermal Regulation Edema: heat can increase oedema due to vasodialation and increased circulation CONTRAINDICATIONS Acute musculoskeletal conditions: can aggravate the injury Recent or potential hemorrhage: should not be applied to patient who had bleeding in last 48-72hours; the increased blood flow as a result of heatcan restart or worsen the bleeding Thrombosis: increased rate of circulation can cause a thrombus to be dislodged. Impaired sensation Impaired mentation Malignant tumor: it may increase the rate of metastasis Infrared irradiation of the eyes: can cause optical damage Over an open wound  ADVERSE EFFECTS Burns Fainting: due to low cerebral flow commonly caused by vasodialation and decreased blood pressure Bleeding Skin and eye damage from infrared radiation CHARACTERISTICS OF E-M WAVES Can be transmitted without a medium All radiant energy travels at a constant velocity (300 million meters per second) Can be reflected, refracted, absorbed or transmitted Each operates at specific wavelengths and frequencies Wavelength – distance between the peak of one wave and the peak of the next wave Frequency – the number of waves occurring in 1 second (measured in Hz) Velocity = wavelength x frequency There is an inverse relationship between wavelength and frequency Relationship among wavelength, Frequency & Depth of Penetration Modalities Wavelength Frequency Depth of penetration longest shortest greatest Diathermy 3-5cm IRR/ 1-2cm Conductive thermal 10-15mm LASER 2mm Ultraviolet Shortest highest lowest Laws Governing the Effects of EM Radiations When electromagnetic wavelengths are transmitted into human tissues, they will either be reflected, refracted, absorbed or transmitted Reflected Skin Refracted Fat Muscle Absorbed Laws Governing the Effects of EM Radiations Arndt-Schultz Principle: For physiological changes or reactions to occur within the tissues, sufficient energy must be absorbed by the tissue (similar to the all or none law). Implications – sufficient energy must be absorbed to depolarize a motor nerve - A contact thermal modality must be left on long enough for the effect to be felt Lambert’s Cosine Law: Ray must be applied at a right angle to the area being treated for it to be transmitted to deeper tissues Energy Source Energy Source Laws Governing the Effects of EM Radiations Grothus-Draper law – describes the inverse relationship between energy absorption and depth of penetration. Energy must be absorbed to have an effect. Absorption in superficial tissue α 1/penetration. The lesser the energy absorbed by superficial tissues, the more the depth of penetration Inverse Square Law: The intensity of radiation is inversely proportional to the square of the distance from the source of energy - Intensity of radiation α 1/distance2 - The closer the lamp is to the skin, the greater the intensity of heat TYPES OF MODALITY BASED ON DEPTH OF PENETRATION SUPERFICIAL HEAT MODALITY (0.5 -2CM) DEEP HEATING MODALITY (>2CM) Infra Red Laser Hydrocollator pack Short wave diathermy Whirlpool Microwave diathermy Fluidotherapy ultrasound Paraffin wax  SPECIFIC HEAT This is the amount of energy required to raise the temperature of a given mass of material by a given no of degrees. It is generally expressed in Joules per gram degree Celsius (J/g ºC) Different body tissue has different specific heat Skin > Muscles > Fat > bone Different materials used as thermal agents water > Air  SPECIFIC HEAT Materials with a high specific heat require more energy to achieve the same temperature increase than materials with a low specific heat Materials with a high specific heat hold more energy than materials with a low specific heat energy at the same temperature Therefore, to transfer the same amount of heat to a patient, thermal agents with a high specific heat (e.g. water) are applied than air based thermal agents. Transmission of Thermal Energy Different physical agents transfer heat by different modes Modes of heat transfer include: Conduction Heat transfer by direct contact from a warmer object to a cooler one Caused by direct collision between molecules of two materials at different temperature Heat transfer continues until the temperature and the speed of molecular movement of both materials become equal Transmission of Thermal Energy: Conduction The rate of heat transfer by conduction depends on: The temperature difference between the materials The thermal conductivity of the materials (the rate at which a material transfer heat by conduction) The area of contact between the materials The exposure time Examples of therapeutic agents that transfer heat by conduction: moist hot packs, paraffin wax, ice packs and cold packs Guidelines for transfer of heat by conduction The greater the temperature difference between the two bodies in contact, the faster the rate of heat transfer Materials with high thermal conductivity transfer heat more rapidly than materials with low thermal conductivity Metals have high thermal conductivity, hence metal jewelry and chairs should be removed from any area that will be in contact with conductive thermal agents to mitigate burns Materials with low thermal conductivity can be used as insulators Guidelines for transfer of heat by conduction The larger the area of contact between a thermal agent and the patient, the greater the total heat transfer The rate of temperature rise decreases in proportion to tissue thickness The deeper the tissue, the lesser the temperature increase Mode of Heat transfer - Convection Transfer of heat by direct contact between a circulating medium (f luid and gases) and a material of a different temperature The thermal agent is in motion such that new parts of the agent is in contact with the patient body part Heat transfer by convection in the same period of time > heat transfer by conduction using the same material at the same initial temperature Mode of Heat transfer - Convection The rate of heat transfer depends on: Temperature difference between the medium and the body part Speed of movement of the medium conductivity of the body part Examples of therapeutic agents that transfer heat by convection: whirlpool, hydrotherapy. Mode of Heat transfer - Radiation Transfer of heat from a material with a higher temperature to one with a lower temperature without contact or an intervening medium. Heat transfer through space The rate of temperature increase depends on: The intensity of the radiation The relative sizes of the radiation source and the area being treated The distance from the source of energy to the treatment area The angle of the radiation to the tissue Mode of Heat transfer - Radiation Examples of therapeutic agents that transfer heat by radiation: infrared irradiation, ultraviolet therapy, Shortwave diathermy  Mode of Heat transfer - Conversion Heat transfer by conversion of nonthermal form of energy (sound, electricity or chemical agents) into heat It is not affected by the temperature of the thermal agent Does not require direct contact but requires an intervening material that must be a good transmitter of that type of energy The rate of heat transfer by conversion depends on the power of the energy source  Mode of Heat transfer - Conversion The rate of tissue temperature increase depends on: the size of the area being treated the size of the applicator the efficiency of the transmission from the applicator to the patient the type of tissue being treated Physical agents that heat by conversion may also have other nonthermal effect based on their direct mechanical or electrical effects on tissue Examples of therapeutic agents that transfer heat by conversion are: Ultrasound therapy, Shortwave diathermy  EVAPORATION A material should absorb an energy and thus change its form from a liquid to gas or vapour. In human body, the heat is absorbed by the liquid on the skin surface and cools the skin as it turns in to a gaseous state E.g. vapocoolant spray