Principles of thermal energy: Thermotherapy Flashcards
Thermal regulation
Humans are homeotherms
- we are able to maintain our core temp at a constant
- generally normal core temp is 98.6 degree F
- Can vary due to :
- diurnal changes: lower core temp in am vs pm
- the outside surface of the body can be referred to as shell
Thermal kinetic energy
- the movement of molecules or their components is related to the temp of a substance
- as the temp of a substance increases its molecules move more rapidly
- kinetic energy is thermal energy
- heat- energy in transit from high temp object to low temp object
thermal potential energy
- Energy of position
- molecules are attracted to one another by forces. The energy associated attraction is potential energy
- remains constant so long as the phase of matter doesn’t change
Phase change
- Change from one state to another
- always occur with a change of heat
- solid> liquid
- occurs without a change in temperature
- changes in potential energy
- attraction forces within an object are relaxed
Latent heat of fusion
Amount of heat required to convert a certain unit of a solid into a similar unit of a liquid without changing temperature
First law of thermodynamics
With the exception of nuclear effects energy can be neither created nor destroyed but is transformed from one form to another.
- whenever this transformation occurs some energy is released as heat and is considered thermal energy
Specific heat
- the amount of energy required to raise the temp of a given material by a specific number of degrees
- different materials (thermal agents or body tissues) have different specific heats
- materials with high specific heat require more energy to achieve an equivalent increase in temp than materials with a low specific heat
- material with high specific heat hold more energy than materials with a low specific heat when both are at the same temp
- water has a very large specific heat
Specific heat of paraffin
0.65
specific heat of water
1.0
modes of heat transfer
- conduction
- convection
- conversion
- radiation
- evaporation
Conduction
- exchange of energy between 2 materials at different temps due to the direct collision of molecules of the materials
- the molecules of the higher temp material move faster
- they collide with molecules of the cooler material causing them to accelerate
- heat will continue until speed of molecular movements become equal
- for heat transfer to occur the two materials must be in direct contact with each other
- subcutaneous tissues are heated by conduction of energy through adjacent layers
Rate of heat transfer (ROHT) by conduction depends on:
- temperature difference between materials
- their thermal conductivity
- the area in contact
Rate of heat transfer (ROHT) equation
ROHT= area of contact x thermal conductivity x temp diff/ tissue thickness
Guidelines for heat transfer by conduction
-The greater the temp difference between the two materials the faster the rate of heat transfer (make ice from hot water vs cold)
- materials with high thermal conductivity transfer heat faster than materials with low thermal conductivity
-
Conduction: hot pack
- hot pack kept in water approx 155-165 degree F
- high temp, high specific heat, and moderate thermal conductivity of water allows efficient heat transfer to pt
- but temp difference may be large enough that patient may become uncomfortable or even burned
- dry towels that trap air placed between hot pack and pt will limit the rate of transfer of energy
Conduction modalities application considerations
- metal has high thermal conductivity and may heat rapidly and burn pt
- the larger the area of contact between two materials the greater the heat transfer
- the rate of tissue temp rise decreases in proportion to tissue thickness
Convection
- Transfer of heat as the result of direct contact between circulating medium and another material of a different temp
- thermal agent is in constant motion
- new parts of the thermal agent (@ the initial temp) keep coming in contact with the material to be heated/ cooled
- transfers more heat/time than conduction
Convection examples
- Whirlpool
- Fluidotherapy
- blood: transfers heat by convection to protect local tissue
- oven
- central air conditioning
Conversion
- Converting a non thermal form of energy into heat
- mechanical: ultrasound, friction
- chemical: acid to metal> heat (chem heat pack)
- rate of heat transfer depends upon the power of the energy source
- rub hands together faster> increased heat
- does not require direct contact
- does required a good conductor of energy
Radiation
-Direct transfer of energy without direct contact or intervening medium
radiation rate of temp increase depends on:
- intensity of radiation
- relative size of the radiation source
- relative size of the radiation area
- the distance of the source to the target tissue
- the angle of the radiation source to the target tissue
Radiation examples
- infrared lamp
- ultraviolet light
Evaporation
- A material must absorb energy before it can evaporate
- example: vapocoolant spray
Thermotherapy
- The therapeutic application of heat
- used outside rehab to :
- destroy malignant tissue growth
- treat cold related injuries
- Used in rehab to provide:
- hemodynamic effects
- neuromuscular effects
- metabolic effects
- altered tissue extensibility
Thermotherapy: hemodynamic effects, Vasodilation
-Vasodilation: application of heat increases diameter of BVs and thus increase in rate of blood flow
Thermotherapy: hemodynamic effects, stimulation of cutaneous thermal receptors
- reflex activation of smooth muscles in blood vessels causing dilation (direct)
- increased production and release of histamine, bradykinin, prostaglandins, and nitrous oxide
- vasoactive mediators directly stimulate the smooth muscles in BV wall
- stim of cutaneous thermal receptors project through dorsal root ganglion to synapse on interneurons in dorsal horn of spinal cord
- these interneurons synapse with sympathetic neurons in lateral horn of thoracolumbar segments of spinal cord
- this causes inhibition of sympathetic activity
- causes reduction of smooth muscle contraction
- generally not in skeletal muscle when applied superficially
- acts to protect body from excessive heating and tissue damage
- increased blood flow removes heat via convection
Thermotherapy: neuromuscular effects, increased nerve conduction velocity
- for each 1.8 degree F ( 1 degree C) increase in temp, NCV may increase by approx 2m/sec
- increase muscle temp to 108 degree F (42 C)
- decreased firing rate of type II muscle spindle efferents and gamma efferents
- increased firing rate of type 1b fibers and GTOs
- results in decreased firing rate of alpha motor neurons> decrease in muscle contraction (spasm)
Thermotherapy: neuromuscular effects, increased pain threshold
- directly by activation of spinal gate
- indirectly by reduction in ischemia and muscle spasm and facilitation of tissue healing
Thermotherapy: neuromuscular effects, in demyelinated peripheral nerve
- heat shortens time Na+ channels are opened at node of ranivier
- this decreases conduction time and effects end organ of that nerve
Thermotherapy: neuromuscular effects, changes in muscle strength
- decreases during the first 30 mins after superficial or deep heating
- decreased firing rate of type 1a muscle spindle efferents and gamma efferents
- increased firing rate of type 1b fibers and GTOs
- results in decreased firing rate of alpha motor neurons> decrease in muscle strength
- for next 2 hours strength returns then increases to above preintervention
Metabolic effects
- increases endothermic chemical reaction rate including enzymatic biological reactions
- from 102 degree F to 109 degree F (39-43 C) reaction rate increases 13% for every 18 degree F rise in tissue temp
- beyond 113 degree F enzyme activity begins to decrease and ceases at about 122 degree F
- heat increases oxygen uptake and accelerates healing
- heat increases activity of collagenase which may increase destruction of articular cartilage in RA
- heat shifts oxygen-hemoglobin dissociation curve to right-makes more oxygen available for healing
Thermotherapy: altered tissue extensibility
- decreases fluid viscosity
- decreases joint and muscle stiffness
- relaxes cross-linked collagen fibers
- increase tissue temp to 104 to 113 degree F for 5-10 mins> plastic deformation
Uses for thermotherapy
- pain control
- increased ROM and decreased joint stiffness
- accelerated healing
Types of thermotherapy
- moist hot packs
- paraffin bath
- infrared lamps
Moist Hot packs
Infrared modality emitting electromagnetic radiation
- wavelength is equal to approx 82,457
- frequency= 3.63 x 1012 Hz
Thermal modality used for superficial heating of tissue
- maximum depth of heat penetration= 1 cm
- heat tissues via conduction
* energy exchange by direct collision between molecules of two materials at different temps
Moist hot pack general description
- packs made of canvas and filled with silica gel
- generally heated in hydrocollator to 160 degree F for at least 20 mins prior to heating
- capable of retaining heat for approx 20 minutes
Moist hot pack, paraffin bath, and infrared lamp therapeutic purposes & goals
To heat tissues to therapeutic level
- 105.8 to 113 degree F
- occurs in about 8 to 10 mins
- the bodies physiological response to heat stimulus may be therapeutic
-within 30 mins of superficial heat application the body reaches thermal equilibrium and further heating is not beneficial
primarily used to provide analgesia and reduce pain
increase ROM & decrease joint stiffness ( relax local structures)
accelerate healing
Moist hot pack, paraffin bath, & infrared lamp physiological effects
- Muscle relaxation via effects on muscle spindles and GTOs
- sedation of sensory nerve endings if heat is mild enough
- increased capillary pressure & cell permeability
- increased extensibility of CT with stretching exercises
- increased body temp, pulse rate, & decreased blood pressure (?)
Moist hot pack, paraffin bath, and infrared lamp indications
- impairments associated with sub acute and chronic conditions ( OA, muscle injury, muscle guarding, etc)
- tissue contractures/adhesions
- joint stiffness
- stimulation of perspiration to improve electrical stim
Moist hot pack, Paraffin bath, & infrared lamp contraindications/ cautions
- acute inflammatory disorders (sprains, strains)
- previously existing fever
- malignancies (cancer) in tx area
- active bleeding in tx area
- pts with cardiac insufficiency
- older pts and children under the age of 4
- pts with peripheral vascular disease (PVD)
- previously existing edema
- tissues devitalized by x-ray therapy
Moist hot pack advantages
- relatively safe in that MHPs cool over time
- may effectively treat local areas
Paraffin baths
Infrared modality emitting electromagnetic radiation
- wavelength approx = to 90,187
- frequency approx= to 3.32 x 10^12 Hz
thermal modality used for superficial heating of tissue
- maximum depth of penetration is = to 1 cm
- heats tissues via conduction
Paraffin bath description
- tank containing a mixture of medial paraffin wax and mineral oil
- the two ingredietns are mixed in a ratio of approx 5 lbs of wax to 1 pt of oil
- tanks generally have a heating unit & a thermostat that keeps the melted wax at about 125-127 degree F
- pt areas to be treated are immersed in this heated mixture
- the specific heat of paraffin is low
Paraffin baths advantages
- useful in treating chronic orthopedic conditions of the distal extremities
- aids in softening of the skin
Paraffin bath disadvantages
- provides six times the amount of heat in water thus risk of burn is substantial
- paraffin treatment can be messy
- cleaning of the tank can be difficult
infrared lamp
Infrared modality emitting electromagnetic radiation
- wavelength= to 770 nm to 1mm, IR-A wavelength = 770 to 1400 nm
- frequency= 3.63 x 10^12
Thermal modality used for dry superficial heating
- maximum depth of penetration= 1 cm
- generally absorbed within the first 1-3 mm of tissue
-heats tissues via radiation
* energy exchange by direct collision of molecules of two materials at diff temps
Infrared lamp classification:
IR-A (short or near IR) - most common - wavelengths between 770 to 1400 nm -generated by luminous lamp IR-B (middle IR) - wavelengths between 1400 and 3000 nm -generated by nonluminous lamp IR-C (long or far IR) -wavelengths betweeen 3000 to 10^6 nm -generated by nonluminous lamp
Infrared lamp description
- A lamp or baker that generates infrared radiation that produces heat when absorbed by matter
- TTR proportional to :
- amount of radiation absorbed
- the power and wavelength of the source
- the distance of the source to the tissues (inverse sq law)
- the angle of incidence of the radiation (cosine law)
- the absorption coefficient of the tissue
- most lamps deliver power in range of 50-1500 watts
- clinically used wavelength is 780 to 1500 nm
- absorbed within first 1-3 mm of human tissue
- human skin allows maximal penetration at wavelength of 1200 nm
- IR radiation absorbed best by tissues with high absorption coefficient
- dark skin has higher absorption coefficient therefore will increase in temp greater than light skin
Luminous lamp
- heat produced by resistance to an electric current as it passes through a tungsten or carbon filament surrounded by metal reflectors
- produces visible, bright white light (IR-A)
- power output 60-1500 watts
- no warm up period needed
Infrared lamp advantages
- does not require direct contact with the pt
- can see the area being treated during session
Infrared lamp disadvantages
- ensuring uniform heating is difficult
- glare may irritate pt’s eyes
- hard to localize tx area
Reasons for intervention
- to increase local blood flow
- to relax muscle spasm
- to increase tissue temp
- to increase local tissue extensibility
- to modulate pain
- to promote tissue healing
