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Foundations of Therapeutic
Modalities
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What is Physiotherapy?
•
Physiotherapy is the utilization of physical agents (Electrotherapy Modalities)and
techniques(Therapeutic Exercises) in the diagnosis and treatment of disabilities and
impairments
FACTS about physical agents modalities
•
All physical agents modalities involve the introduction of some physical energy into a
biologic system.
•
This energy brings about the one or more Physiological changes, which are used for
Therapeutic benefit.
•
In the Clinical environment, firstly to select the most appropriate dose & secondly to
apply the treatment.
•
The mechanism of action of each therapeutic modality depends on which form of energy
is utilized during its application. Different forms of energy are generated and transferred
by different mechanisms.
o Electromagnetic energy is typically generated by a high energy source and is
transmitted by the movement of photons.
o Thermal energy can be transferred by conduction, which involves the flow of
thermal energy between objects that are in contact with each other.
o Electrical energy is stored in electric fields and delivered by the movement of
charged particles.
o Acoustic vibrations produce sound waves that can pass through a medium. Each
form of energy and the mechanism of its transfer will be discussed in more detail
to provide the scientific basis for understanding the therapeutic modalities.
How do we classify the physical agent Modalities?
The most popular classification of physical agent Modalities is Classification of Therapeutic
Modalities under the Various Forms of Energy
Energy is defined as the capacity of a system for doing work and exists in various forms.
Energy is not ordinarily created or destroyed, but it is oft en transformed from one form to
another or transferred from one location to another.
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According to the types of energy, Therapeutic Modalities Used By physical therapists can Be
Classified As being…
ELECTROMAGNETIC ENERGY MODALITIES
• Shortwave diathermy
• Microwave diathermy
• Infrared lamps
• Ultraviolet therapy
• Low-power laser
THERMAL ENERGY MODALITIES
• Thermotherapy
• Cryotherapy
ELECTRICAL ENERGY MODALITIES
• Electrical stimulating currents
• Biofeedback
• Iontophoresis
SOUND ENERGY MODALITIES
• Ultrasound
• Extracorporal shockwave therapy
MECHANICAL ENERGY MODALITIES
• Intermittent compression
ELECTROMAGNETIC ENERGY
Radiation is a process by which electromagnetic energy travels from its source outward
through space.
Electromagnetic radiation
 Electromagnetic radiation (often abbreviated E-M radiation or EMR) is a
phenomenon that takes the form of self-propagating waves in a vacuum or in
matter.
 Electromagnetic Radiation: Electromagnetic waves are produced by the motion of
electrically charged particles. These waves are also called "electromagnetic
radiation" because they radiate from the electrically charged particles. They travel
through empty space as well as through air and other substances.
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 It consists of electric and magnetic field components which oscillate in phase
perpendicular to each other and perpendicular to the direction of energy
propagation.
Fig 1. Electromagnetic Waves and Their Propagation through the Atmosphere
Sunlight Is A Form Of Radiant Energy
Sunlight is a visible type of radiant energy, and we know that it not only makes
objects visible but also produces heat.
If a ray of sunlight is passed through a prism, it will be broken down into various regions of
colors. Each of these colors represents a different form of radiant energy.
Fig 2. Visible light
In Addition, Other Forms Of Radiation Beyond Infrared And Ultraviolet Regions May Be
Produced When An Electrical Force Is Applied
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These Radiations Have Different Wavelengths And Frequencies Than Those In The Visible
Light Spectrum
All of these various classifications of radiations collectively constitute the electromagnetic
spectrum .
 The electromagnetic spectrum is the entire range of electromagnetic waves arranged
according to their frequencies or wavelengths.
Fig 3. Electromagnetic spectrum
All the electromagnetic radiations lying within this spectrum have several theoretical
characteristics in common
1. They may be produced when sufficiently intense electrical or chemical forces are applied to
any material.
2. They all travel readily through space at an equal velocity.
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3. Their direction of travel is always in a straight line.
4. They may be reflected, refracted, absorbed, or transmitted, depending on the specific medium
that they strike.
Laws Governing the Effects of Electromagnetic Energy
When electromagnetic radiation strikes or comes in contact with various objects, it can be
reflected, transmitted, refracted, or absorbed, depending on the type of radiation and the nature
of the object it interacts with.
Reflection
Reflection is the return of the electromagnetic wave from a surface. When
electromagnetic radiations strike a surface, part of the energy is reflected back in the same plane
of the incident angle [Incident angle = reflected angle], see figure (4).
The amount of reflection depends on the:
1-nature of the radiation
2-angle of incidence
3-nature of the surface
Refraction
Refraction is the change of direction of radiation when it passes from one medium to
another of a different optical density. It depends on the media involved and the angle of
incidence of the rays. So rays striking the surface at right angle continue in the same straight
lines, see figure (4).
Absorption:When electromagnetic rays strike a new medium they may be absorbed and thus produce an
effect.
The proportion of rays absorbed depends on:Wave length
Frequency.
Angle of incidence.
Nature of the medium.
The intensity of radiation.
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Fig 4. When electromagnetic radiations contact human tissues, they may be reflected,
refracted, or absorbed. Energy that is transmitted through the tissues must be absorbed before
any physiological changes can take place.
Arndt–Schultz Principle
The Arndt–Schultz principle states that no reactions or changes can occur in the body tissues if
the amount of energy absorbed is insufficient to stimulate the absorbing tissues. The goal of the
clinician should be to deliver sufficient energy to stimulate the tissues to perform their normal
function.
Clinical consideration An example would be using an electrical stimulating current to create a
muscle contraction. To achieve the depolarization of a motor nerve, the intensity of the current
must be increased until enough energy is made available and is absorbed by that nerve to
facilitate a depolarization. The clinician should also realize that too much energy absorbed in a
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given period of time may seriously impair normal function and, if severe enough, may cause
irreparable damage.
Law of Grotthus–Draper
It describes an inverse relationship between the penetration and absorption of energy. If the
therapeutic energy is not absorbed by the superficial tissues, it will penetrate to deeper tissues.
Clinical consideration An example showing application of the Law of Grotthus–Draper is the use
of ultrasound treatment to increase tissue temperature in the deeper portions of the gluteus
maximus muscle. A clinician could use ultrasound at a frequency of either 1 MHz (long
wavelength) or 3 MHz (short wavelength). Using ultrasound treatment at a frequency of 1 MHz
would be more effective at penetrating the deeper tissues than ultrasound treatment at 3 MHz,
since less energy would be absorbed superficially for the longer wavelength.
Cosine Law
This law states that the intensity of radiation varies with the cosine of the angle of incidence,
see figure (6).
Effective energy= energy X cosine of the angle of incidence
So, electromagnetic energy is most efficiently transmitted to the tissue when it strikes the body
at right angle. As the angle of incidence deviates away from 90o, the intensity of radiation
affecting the tissue decreases.
Clinical consideration An example showing the application of the cosine law could be that, when
doing an ultrasound treatment, the surface of the applicator should be kept as flat on the skin
surface as possible. This allows the acoustic energy coming from the applicator to strike the
surface as close to 90 degrees as possible, thus minimizing the amount of energy reflected.
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Fig 5. The cosine law states that the smaller the angle between the propagating ray
and the right angle, the less the radiation reflected and the greater the radiation absorbed.
Thus the energy absorbed would be greater in a than in b.
Inverse Square Law
This law states that the intensity of radiation from a source is inversely proportional to the square
of the distance from that source.
I α 1/d2
Where I= intensity and d= distance from the source to the target
Clinical consideration doubling the distance between the source and the surface will reduce the
intensity to one-quarter, as the area over which the energy is distributed is four times larger as
illustrated in figure ( ). For example, when using an infrared heating lamp to heat the low back
region, the intensity of heat energy at the skin surface with the lamp positioned at a distance of
10 inches will be four times greater than if the lamp is placed at a 20-inch distance so modalities
are most effective when placed as close to the body as possible.
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Fig 6: Inverse Square Law
Example of Electromagnetic modalities
• Shortwave diathermy
• Microwave diathermy
• Infrared lamps
• Ultraviolet therapy
• Low-power laser
THERMAL ENERGY
Thermal energy is the energy a substance or system has related to its temperature, i.e., the energy
of moving or vibrating molecules. Atoms and molecules, the smallest particles of any substance,
are always in motion. The motion of thermal energy is usually not visible, but we can feel or see
its effects. We use thermal energy to cook our food and heat our homes, and we use it to
generate electricity.
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Thermal energy is not the same as heat.
Heat is the form of energy which is transferred from one body, region or thermodynamic system
to another due to thermal contact or thermal radiation when the system are at different
temperature whereas thermal energy is the energy of a body that increases with the increase in its
temperature.
The amount of heat transferred by a substance depends on the speed and number of atoms or
molecules in motion. The faster the atoms or molecules move, the higher the temperature, and
the more atoms or molecules that are in motion, the greater the quantity of heat they transfer
Thermal Energy Modalities
Thermotherapy
Thermotherapy techniques are used primarily to produce a tissue temperature increase for a
variety of therapeutic purposes. The modalities classified as thermotherapy modalities include
warm whirlpool, warm hydrocollator packs, paraffin baths, and fluidotherapy. The specific
procedures for applying these techniques will be discussed in the hydrotherapy subject
Cryotherapy
Cryotherapy techniques are used primarily to produce a tissue temperature decrease for a variety
of therapeutic purposes. The modalities classified as cryotherapy modalities include ice massage,
cold hydrocollator packs, cold whirlpool, cold spray, contrast baths, ice immersion, cryo-cuff ,
and cryokinetics. The specific procedures for applying these techniques will be discussed in the
hydrotherapy subject
ELECTRICAL ENERGY
In general, electricity is a form of energy that can effect chemical and thermal changes on tissue.
Electrical energy is associated with the flow of electrons or other charged particles through an
electric field. Electrons are particles of matter that have a negative electrical charge and revolve
around the core, or nucleus, of an atom. An electrical current refers to the flow of charged
particles that pass along a conductor such as a nerve or wire. Electrotherapeutic devices generate
current, which, when introduced into biologic tissue, are capable of producing specific
physiological changes. An electrical current applied to nerve tissue at a sufficient intensity and
duration to reach that tissue’s excitability threshold will result in a membrane depolarization or
firing of that nerve. Electrical stimulating currents affect nerve and muscle tissue in various
ways, based on the action of electricity on tissues.
SOUND ENERGY
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Acoustic energy and electromagnetic energy have very different physical characteristics. Sound
energy consists of pressure waves due to the mechanical vibration of particles, whereas
electromagnetic radiation is carried by photons. The relationship between velocity, wavelength,
and frequency is the same for sound energy and electromagnetic energy, but the speeds of the
two types of waves are diff erent. Acoustical waves travel at the speed of sound. Electromagnetic
waves travel at the speed of light. Since sound travels more slowly than light, wavelengths are
considerably shorter for acoustic vibrations than for electromagnetic radiations at any given
frequency.
Electromagnetic radiations are capable of traveling through space or vacuum. As the
density of the transmitting medium is increased, the velocity of electromagnetic radiation
decreases.
Acoustic vibrations (sound) will not be transmitted at all through vacuum, since they propagate
through molecular collisions. The more rigid the transmitting medium, the greater the velocity of
sound will be.
Example of Sound Energy Modalities
Ultrasound
Extracorporeal Shock Wave Therapy
MECHANICAL ENERGY
Mechanical energy is the energy possessed by an object due to its motion or position.
Mechanical energy can be either
kinetic energy (energy of motion)
or potential energy (stored energy of position).
Objects have kinetic energy if they are in motion. Potential energy is stored by an object and has
the potential to be created when that objected is stretched or bent or squeezed. The kinetic energy
created by a clinician’s hands moves to apply a force that can stretch, bend, or compress skin,
muscles, ligaments, and the like. The stretched, bent, or compressed structure possesses potential
energy that can be released when the force is removed.
Example of Mechanical Energy Modalities
Intermittent compression, traction techniques, and massage each use mechanical energy
involving
a force applied to some soft -tissue structure to create a therapeutic effect.
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Physiological background
Organization of the Nervous System
Sensory Receptors
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Two principal divisions of the nervous system:
1. Central nervous system (CNS) consists of the brain and spinal cord. Within the CNS,
various sorts of incoming sensory information are integrated and correlated. The
CNS is connected to sensory receptors, muscles, and glands in peripheral parts of the
body by the PNS
2. Peripheral nervous system (PNS) includes 12 pairs of cranial nerves that arise from
the brain and 31 pairs of spinal nerves that emerge from the spinal cord. Portions of
these nerves carry nerve impulses into the CNS while portions carry impulses out of
the CNS. Input component of the PNS consists of nerve cells called (sensory or
afferent) neurons. They conduct nerve impulses from sensory receptors in various
parts of the body to the CNS. Output component consists of nerve cells called (motor
or efferent) neurons. They originate within the CNS and conduct nerve impulses from
the CNS to muscles and glands.
PNS subdivided into two parts: (based on body area response)
 Somatic: body
 Autonomic: smooth muscle, cardiac muscle, glands
Somatic consists of sensory neurons that convey information from cutaneous and
special sense receptors primarily in the head, body wall, and extremities to the CNS and
motor neurons from the CNS that conduct impulses to skeletal muscles only.
Autonomic nervous system consists of sensory neurons that convey information from
receptors primarily in the viscera (internal organs) to the CNS and motor neurons from the
CNS that conduct impulses to smooth muscles, cardiac muscle, and glands.
Motor portion of the ANS consists of two branches:
 Sympathetic
 Parasympathetic
Neurons are the basic unit of the nervous system. They carry information or impulses as
electrical signals from one place to another in the body. There are 3 types of neurons:
Sensory Neurons- Sensory neurons carry electrical signals (impulses) from receptors or sense organs
to the CNS. Sensory neurons are also called afferent neurons. The cell body of sensory neurons is outside
the CNS in ganglia.
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Fig 1. Sensory neuron
Motor Neurons- Motor neurons carry impulses from the CNS to effector organs Motor
neurons are also called efferent neurons. The cell bodies of motor neurons are inside the CNS.
Fig 2. Motor neuron
Interneurons- These are also called intermediate, relay, or associative neurons. They carry information
between sensory and motor neurons. They are found in the CNS.
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Fig 3 .interneurons
Neuron potential
When a neuron is not carrying an impulse the inside of the axon has a negative charge and the
outside has a positive charge.
The threshold is the minimum stimulus needed to cause an impulse to be carried. It must
be of sufficient strength. Not all stimuli cause an impulse. A stimulus below the threshold has no
effect on the neuron. Some people have higher thresholds for pain, heat or other stimuli. This
means they can tolerate a stronger stimulus before their nervous system reacts with an impulse.
The mechanisms responsible for the membrane having a net positive charge on its outer surface
and a net negative charge on its inner surface are as follows:
1. Asodium-potassium pump actively transports sodium ions (Na+) to the outside and
potassium ions (K+) to the inside, with three Na+ moved out for every two K+ moved in.
2. The cell membrane is more permeable to K+ than to Na+, so that the K+ , which is more
concentrated inside the cell, diffuses outward faster than the Na+, which is more
concentrated outside the cell, diffuses inward. Na+ and K+ move through the membrane
using different channels.
3. The cell membrane is essentially impermeable to the large (negatively charged) anions
that are present inside the neuron, therefore fewer negatively charged particles move out
than positively charged particles.
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Fig 4. Resting membrane potential
Nerve impulses carry information from one point of the body to another by progression along the
neuron membrane of an abrupt change in the resting potential. This "traveling disturbance,"
called an action potential, is described below.
1. A stimulus (chemical-electrical-mechanical) is sufficient to alter the resting membrane
potential of a region of the membrane.
Fig 5. Action potential
2. The membrane's permeability to sodium ions (Na+) increases at the point of stimulation.
3. Na+ rapidly moves into the cell through the membrane; the membrane becomes locally
depolarized (membrane potential = 0).
4. Na+ continues to move inward; the inside of the membrane becomes positively charged
relative to the outside (reverse polarization).
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5. Reverse polarization at the original site of stimulation results in a local current that acts
as a stimulus to the adjacent region of the membrane.
6. At the point originally stimulated, the membrane's permeability to sodium decreases, and
its permeability to K+ increases.
7. K+ rapidly moves outward, again making the outside of the membrane positive in
relation to the inside (repolarization).
8. N+ and K+ pumps transport Na+ back out of, and K+ back into the cell. The cycle
repeats itself, traveling in this manner along the neuron membrane.
Fig 6. Action potential
Skin Anatomy and somatosensory system
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The skin is composed of several layers.
The very top layer is the epidermis and is the layer of skin you can see. In Latin, the prefix
"epi-" means "upon" or "over." So the epidermis is the layer upon the dermis (the dermis is the
second layer of skin). Made of dead skin cells,
Function : the epidermis is waterproof and serves as a protective wrap for the underlying skin
layers and the rest of the body.
Structures:


It contains melanin, which protects against the sun's harmful rays and also gives skin its
color. When you are in the sun, the melanin builds up to increase its protective properties,
which also causes the skin to darken.
The epidermis also contains very sensitive cells called touch receptors that give the brain
a variety of information about the environment the body is in.
The second layer of skin is the dermis.
Function:


Its primary function is to sustain and support the epidermis by diffusing nutrients to it and
replacing the skin cells that are shed off the upper layer of the epidermis. New cells are
formed at the junction between the dermis and epidermis, and they slowly push their way
towards the surface of the skin so that they can replace the dead skin cells that are shed.
Oil and sweat glands eliminate waste produced at the dermis level of the skin by opening
their pores at the surface of the epidermis and releasing the waste.
Structures:
The dermis contains hair follicles, sweat glands, sebaceous (oil) glands, blood vessels, nerve
endings, and a variety of touch receptors.
The bottom layer is the subcutaneous
tissue
Function:

The layer of fat acts as an insulator and helps regulate body temperature.
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
It also acts as a cushion to protect underlying tissue from damage when you bump into
things. The connective tissue keeps the skin attached to the muscles and tendons
underneath.
Structures: This layer is composed of fat and connective tissue.
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Somatosensory System: The Ability To Sense Touch
The skin contains numerous sensory receptors (Cutaneous receptors) which receive information from the
outside environment.
What is a sensory receptor?
A sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or
external environment of an organism. In response to stimuli the sensory receptor initiates sensory
transduction by creating graded potentials or action potentials in the same cell or in an adjacent
one.
What is a cutaneous receptor?
Cutaneous receptors are sensory receptors located in the dermis or epidermis, which is a layers of
the skin. These receptors are responsible for sensations of touch, pressure, heat, cold, and pain.
They are classified as mechanoreceptors which are associated with pressure, thermoreceptors
which are associated with temperature, and nociceptors which are associated with pain.
The following Table shows where each receptor is located, what their function is in detecting a
stimulus, and lastly what their rate of adaptation is
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Pain Physiology
A detailed understanding of sensory perception and the experience of pain is
fundamental to the practice of physiotherapy.
Definition of pain (old vs. recent definition):
In the past, pain was often regarded as a simple response by the brain to a noxious
stimulus in the periphery. The biologic processes involved in pain perception are,
however, no longer viewed as a simple system with a pure ‘stimulus–response’
relationship. The International Association for the Study of Pain has defined pain as
‘…an unpleasant sensory and emotional experience associated with actual or potential
tissue damage’. Thus pain has objective, physiologic sensory aspects as well as
subjective emotional and psychological components In consequence, the perception of
pain and its threshold are the result of complex interactions between sensory, emotional,
and behavioral factors.
What is the purpose or function of pain?
Protective function:
A withdrawal reflex response to an acute noxious stimulus is an understandable
and necessary reaction that has an obvious protective function even in the absence of
conscious perception.
Biological function:
More importantly, the experience of pain may lead to the avoidance of potentially
harmful situations and possible injury. Immobility and withdrawal due to pain may serve
to provide an environment in which healing and restoration of function can occur.
Nociceptive Processing
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The physiologic component of pain is termed nociception, which consists of the
following processes:




Transduction
Transmission,
Modulation of neural signals generated in response to an external noxious stimulus.
Perception
Transduction
Transduction is the process by which afferent nerve endings participate in
translating noxious stimuli (e.g., a pinprick) into nociceptive impulses.
Nociceptors are receptors that are sensitive to noxious or painful stimuli. Nociceptors
are further classified into four types.
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



The first type is termed high threshold mechanonociceptors or specific nociceptors.
These nociceptors respond only to intense mechanical stimulation such as pinching,
cutting or stretching.
The second type is the thermal nociceptors, which respond to the intense heat and
cold.
The third type is chemical nociceptors, which respond only to chemical substances.
A fourth type is known as polymodal nociceptors, which respond to high intensity
stimuli such as mechanical, thermal and to chemical substances like the previous
three types.
Transduction begins when the free nerve endings (nociceptors) of C fibres and A-delta fibres of
primary afferent neurones respond to noxious stimuli. More specifically, Following tissue
injury, chemical mediators such as (substance P, cholecystokinin , acetylcholine,
prostaglandin, and bradykinin) are released to the vicinity of nociceptors that may be
activated and sensitized. The resultant "soup" of chemical mediators also changes the
transduction sensitivity of nociceptors, resulting in reduction of threshold for activation
and increased response to suprathreshold stimulus, i.e., peripheral sensitization.
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Figure . Soap of chemical mediators.
Transmission
Transmission is the process by which impulses are sent to the dorsal horn of the
spinal cord, and then along the sensory tracts to the brain.
The transmission process occurs in three stages. The pain impulse is transmitted:
1- from the site of transduction along the nociceptor fibres to the dorsal horn in the spinal
cord;
 Pain impulses are transmitted by two fiber systems. The presence of two
pain pathways explains the existence of two components of pain: fast,
sharp and well localized sensation (first pain) which is conducted by Aδ
fibers; and a duller slower onset and often poorly localized sensation
(second pain) which is conducted by C fibers.
 Aδ fibers are myelinated, 2 – 5 μm in diameter and conduct at rates of 12 –
30 m/s,
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 Whereas C fibers are unmyelinated, 0.4 – 1.2 μm in diameter and conduct
at rates of 0.5 to 2 m/s.
2- from the spinal cord to the brain stem; via the anterolateral system which actually
contains at least two pathways:
 The first is called the spinothalamic pathway. Because it is the newest
component of the system, and the most direct route to the thalamus, it is also
known as the neospinothalamic or direct pathway.
 The second is known as the spinoreticular pathway - also called the
paleospinothalamic or indirect path. (Recently, other components of
anterlolateral system may be added as Spinomesencephalic,
Spinohypothalamic and Spinotectal pathways).
3- through connections between the thalamus, cortex and higher levels of the brain.
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Perception:
Perception of pain is the end result of the neuronal activity of pain transmission and where pain
becomes a conscious multidimensional experience. The multidimensional experience of pain has
affective-motivational, sensory-discriminative, emotional and behavioural components.
When the painful stimuli are transmitted to the brain stem and thalamus, multiple cortical areas
are activated and responses are elicited.
Modulation: This modulation can either inhibit or facilitate pain.
MODULATION AT A SPINAL LEVEL
Let's go through the theory step by step:
1. Without any stimulation, both large and small nerve fibers are quiet and the inhibitory
interneuron (I) blocks the signal in the projection neuron (P) that connects to the brain.
The "gate is closed" and therefore NO PAIN.
2. With non-painful stimulation, large nerve fibers are activated primarily. This activates the
projection neuron (P), BUT it ALSO activates the inhibitory interneuron (I) which then
BLOCKS the signal in the projection neuron (P) that connects to the brain. The "gate is
closed" and therefore NO PAIN.
With pain stimulation, small nerve fibers become active. They activate the projection neurons (P)
and BLOCK the inhibitory interneuron (I). Because activity of the inhibitory interneuron is
blocked, it CANNOT block the output of the projection neuron that connects with the brain. The
"gate is open", therefore, PAIN!!
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Supraspinal modulation (Descending modulation)
Just as there are ascending pain pathways from the body to the brain, there are also descending pain
pathways communicating from the brain to the body which inhibit pain. The most important descending
pathways begin in the periaqueductal gray (PAG).
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Heat unit
Physical, physiological, and therapeutic effects of heat
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Heat unit
PHYSICAL EFFECTS OF HEAT
HEAT – INTRODUCTION
Every living organism produces heat.
 In man’s natural environment the predominant form of radiation is THERMAL.
 Heat is continually produced in the body as a by-product of METABOLISM.
LATENT & SPECIFIC HEAT
 LATENT HEAT: A specific amount of energy is required to change the solid form of a particular substances
into a LIQUID or the liquid into a GAS. This energy is called LATENT HEAT & is the energy
required for a CHANGE OF STATE.
 SPECIFIC HEAT CAPACITY:Specific heat capacity of a material is the quantity of heat in JOULES that must by supplied to 1
GRAM of material to raise its temperature by 1 DEGREE of CELCIUS. The units are J/G/C˚.
PHYSICAL EFFECTS OF HEAT
1.
EXPANSION: It is the result of increased kinetic energy producing a greater vibration of
molecules, which thus move further apart.
2.
CHANGE OF STATE: One form of state (Solid) to the other form of state (Liquid)
3.
ACCELERATION OF CHEMICAL ACTION: Van’t Hoff’s Law states that “Any chemical action
capable of being accelerated is accelerated by a rise in temperature”.
4.
THERMOCOUPLE PRINCIPLE: If the junction of two dissimilar metals is heated, a potential
difference is produced between their free ends.
5.
PRODUCTION OF ELECTROMAGNETIC WAVES: If energy is added to an atom by heat, this can
cause electron to move out to a HIGHER-ENERGY electron shell. It is then said to be in a EXCITED
STATE. When the electron returns to its normal level, energy is released as a PULSE of electromagnetic
energy (A PHOTON).
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6.
THERMIONIC EMISSION: The heating of molecules of some materials (e.g.) TUNGSTEN may
cause such molecular AGITATION that some electrons leave their atoms.
7.
REDUCED VISCOSITY OF FLUIDS: The molecules in viscous fluids are fairly strongly attracted to
one another. Heating increases the KINETIC MOVEMENT of these molecules & reduces their COHESIVE
MUTUAL ATTRACTION; this makes the fluid less viscous.
THERAPEUTIC HEAT
 Several THERMAL AGENTS are available for heat application to tissues.
 Types of therapeutic heating agents are classified as follows;
SUPERFICIAL HEATING
DEEP HEATING AGENT AGENTS
SUPERFICIAL HEATING AGENTS:
1. Heat from outside or external source transferred to skin by conduction, convection or
radiation – DOES NOT PASS THROUGH the THERMAL BARRIER.
Note:- Adipose tissue acts as insulation (THERMAL BARRIER) to the underlying tissues, thus
limiting the degree of temperature change.
EXAMPLES OF SUPERFICIAL HEATING / MODALITIES PRODUCING HEAT
1. Hot water bottle
2. Hot packs
3. Hydro collator unit
4. Hot water bath
5. Hot mud's
6. Wax Bath
7. Electric heat pad
8. Fluido therapy
9. Hydrotherapy
10. I.R.R.
2. DEEP HEATING AGENTS
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 One form of energy is converted to heat in the tissues – can PASS THE THERMAL BARRIER.
EXAMPLES OF DEEP HEATING AGENTS ARE:
1. Ultrasound therapy (U.S.T)
2. Shortwave Diathermy (S.W.D)
3. Microwave Diathermy (M.W.D)
MECHANISM/MODES OF HEAT EXCHANGE
 The means by which therapeutic heat is delivered to the target tissues is attributed to the
following physical mechanisms;
1.
CONDUCTION
2.
CONVECTION
3.
RADIATION
4.
CONVERSION
5.
EVAPORATION
1.
CONDUCTION:1. Heat is transferred through a material by being passed from one particle to the next.
2. Particles at the warm end move faster and this then causes the next particles to move faster
and so on.
3. In
this
the HOT end
way
→
heat
in
the cold end
an
object
travels
from:
Heat gain or loss through DIRECT CONTACT between materials with DIFFERENT TEMPERATURE
is called conduction.
E.g. Heat is absorbed by the body tissues when using a HEATING PAD – heat exchange by
conduction.
 Can happen in solids, liquids and gases. Happens best in solids-particles very close together.
 Conduction does not occur very quickly in liquids or gases
2. CONVECTION: It is defined as the transference of heat to a body by the MOVEMENT OF AIR, MATTER OR
LIQUID around or past the body.
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The heat is carried by the particles themselves moving →
Convection currents
e.g. Warm or cool whirlpool in which movement of the water around a body part results in a
temperature change.
Hot liquids and gases expand and rise while the cooler liquid or gas falls
3. RADIATION: Transfer of heat directly form the source to the object by a wave, travelling as rays. It
transfers heat (usually through air) from a warmer source to a cooler source.
 Heat radiation is also known as INFRARED RADIATION.
 All objects that are hotter than their surroundings give out heat as infra-red radiation
e.g. Infra red radiation lamp (I.R.R.)
4. CONVERSION:It refers to the temperature change that results when energy is transformed from one form to
another such as the conversion from
MECHANICAL or ELECTRICAL ENERGY to THERMAL ENERGY.
e.g. Ultrasound Therapy (U.S.T.)
5. EVAPORATION:It is defined as the transformation from a liquid state to a gas state.
Heat is given off when liquids transform to gases.
e.g. Sweating results from heat production within the body. Cooling occurs as the perspiration
evaporates from the surface of the skin.
PHYSIOLOGICAL EFFECTS OF HEAT –
UNIT –4A
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PHYSIOLOGICAL EFFECTS OF HEAT – INTRODUCTION
 Any form of local body tissue heating will lead to a complicated set of physiological changes
which interact to produce still further complex responses.
local body tissue heating →complicated set of physiological changes →complex responses.
 Heating is MILD when less than 40˚C.
 VIGOROUS heating occurs when tissue temperature reaches 40˚ - 45˚C
 At these temperatures HYPEREMIA or READNESS is noted which indicates an INCREASE BLOOD
FLOW.
 Temperature increase greater than 45˚C may potentially result in THERMAL (HEAT) PAIN &
IRREVESIBLE TISSUE DAMAGE – BURNS.
 Living tissues appear to be affected by temperature changes in two fundamental ways, from
which further changes emanate. These are
1. HYPEREMIA or READNESS indicates → INCREASE BLOOD FLOW.
2. Temperature increase > 45˚C →THERMAL (HEAT) PAIN & IRREVESIBLE TISSUE DAMAGE –
BURNS.
METABOLIC ACTIVITY:Metabolism being a series of chemical reactions, will INCREASE with a RISE & DECREASE with a
FALL of temperature. (Van’t Hoff’s Law)
 In the living organism increase in temperature tends to DENATURE PROTEINS & thus interfere
with the enzyme (Protein) – controlled metabolic processes.
1.
Metabolism →
series of chemical reactions, will INCREASE with a RISE of temperature &
DECREASE with a FALL of temperature. (Van’t Hoff’s Law)
2.
Increase in temperature →LIVING TISSUES→DENATURE PROTEINS
3.
Temperatures > 45˚C →protein damage occurs → destruction of cells & tissues.
4.
With appropriate rise in temperature;
 all CELL ACTIVITY INCREASE, INCLUDING CELL MOTILITY &
 the synthesis & release of CHEMICAL MEDIATORS.
 The rate of cellular interactions such as PHAGOCYTOSIS or GROWTH is ACCELERATED.
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 At temperatures above 45˚C so much protein damage occurs that there is destruction of cells
& tissues.
 With appropriate rise in temperature all CELL ACTIVITY INCREASE, INCLUDING CELL MOTILITY
& the synthesis & release of CHEMICAL MEDIATORS.
 The rate of cellular interactions such as PHAGOCYTOSIS or GROWTH is ACCELERATED.
VISCOSITY:The resistance to flow in a blood vessel depends directly on the viscosity of the fluid &
inversely on the 4th power of the radius of the vessels.
 It is temperature dependent, so raising the temperature in the liquids lowers the viscosity.
 Viscosity changes affect not only the fluids in narrow vessels (Blood & Lymph), but also fluid
movement within & throughout the tissue spaces.
 Viscosity is a measure of the resistance of a fluid. It describes a fluid's internal resistance to
flow .
 e.g. water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity.
 INCREASING the temperature in the liquids → lowers the viscosity. (not only the fluids in
narrow vessels (Blood & Lymph), but also fluid movement within & throughout the tissue
spaces.)
COLLAGENOUS TISSUE:1. It is the most abundant protein in mammal’s → making up about 25% to 35% of the whole-body
protein content.
2. Collagen constitutes →
strong, tendinous muscles.
1% to 2% of muscle tissue, and accounts for 6% of the weight of
3. At normal tissue temperatures, collagen primarily exhibits elastic properties & only minimal
viscous flow. E.g. Cooking of meat.
4. At temperatures within the range (40 – 45˚C), the extensibility of collagen tissue INCREASE.
5. Collagen melts at temperature above 50˚C.
 At normal tissue temperatures, collagen primarily exhibits elastic properties & only minimal
viscous flow. E.g. Cooking of meat.
 At temperatures within the range (40 – 45˚C), the extensibility of collagen tissue INCREASE.
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 Collagen melts at temperature above 50˚C.
 Joint stiffness is often associated with changes in the visco-elastic properties of joints.
 Heat can RELIEVE joint stiffness.
NERVE STIMULATION:Heat stimulates the sensory receptor of the skin & these receptors pass information to the
heat regulating centers, contributing to the control of body temperatures.
 Afferent nerves stimulated by heat may have an ANALGESIC EFFECT by acting on the GATE
CONTROL MECHANISM.
 1.
Heat → stimulate the sensory receptor of the skin →heat regulating centers → control
of
body
temperatures
→
ANALGESIC
EFFECT
→
GATE
CONTROL
MECHANISM.
 HYPERALGESIA occurs in the area of heated region & remains only for a few minutes after the
cessation of heating.
 It is suggested that heating the SECONDARY afferent MUSCLE SPINDLE NERVE ENDINGS &
GOLGI TENDON ENDINGS could be the way in which MUSCLE SPASM is DECREASED by
heating.

Heating the SECONDARY afferent NERVES →i.e. MUSCLE SPINDLE NERVE ENDINGS & GOLGI
TENDON ENDINGS → MUSCLE SPASM DECREASE.
BLOOD VESSEL CHANGES:1. Heating the skin surface →REDNESS – an ERYTHEMA
2. Vasodilatation occurs to → distribute the additional heat around the body –(compensatory
heat loss), but also to protect the heated skin.
3. With heating the skin surface REDNESS – an ERYTHEMA is produced.
4. Vasodilatation occurs not only to distribute the additional heat around the body –
compensatory heat loss, but also to protect the heated skin.
MECHANISM OF VASODILATION DUE TO HEAT:1. Direct effect on CAPILLARIES, ARTERIOLES & VENULES causing them all to dilate – due to the
release of HISTAMINE like & other vaso-active substances which activate capillary dilatation.
2. An AXON REFLEX triggered by stimulation of POLYMODAL RECEPTORS is an important cause of
the vasodilatation.
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3. Increased metabolism will lead to further release of carbon di-oxide & lactic acid, leading to
greater acidity of the heated tissues which tends to provoke dilatation.
PHYSIOLOGICAL - GENERALISED EFFECTS OF HEAT
1. Increasing sweating - owing to the stimulation of ANTERIOR HYPOTHALAMUS.
2. Increased PULSE RATE.
3. Lowering of BLOOD PRESSURE due to decrease in sodium concentration, loss of urea & other
nitrogenous substance.
4. Increased rate of BREATHING.
5. Increased elimination through KIDNEYS.
NOTE: - Heat therapy is most commonly used for rehabilitation purposes. The therapeutic effects of
heat include increasing the extensibility of collagen tissues; decreasing joint stiffness; reducing pain;
relieving muscle spasms; reducing inflammation, oedema, and aids in the post-acute phase of healing;
and increasing blood flow. The increased blood flow to the affected area provides proteins, nutrients,
and oxygen for better healing.
THERAPEUTIC EFFECTS OF HEAT –
1. ENCOURAGEMENT OF HEALING:38
It is evident that any condition in which increased metabolic rate, cell activity & local blood
flow were beneficial could be appropriately treated by MILD HEATING.
Note:- The application of heat to INFLAMMATORY injuries on the EARLY STAGES is NOT BENEFICIAL.
 Chronic inflammatory stages, the stages of repair & regeneration are all appropriately treated
with MILD HEATING.
 All forms of therapeutic heating are applied to a wide range of CHRONIC & POST-TRAUMATIC
CONDITIONS including the ARTHROSES, SOFT TISSUE LESIONS & POST SURGICAL HEATING.
2. RELIEF OF PAIN:Therapeutic heat is widely used for the RELIEF OF PAIN. It was found that heat is the most
effective NON-ANALGESIC method of pain control.
 Much therapeutic heating is of the skin. It is therefore reasonable to assume that the major
pain relieving effects are mainly REFLEX as far as SUBCUTANEOUS structures are concerned.
 Stimulation of SENSORY HEAT RECEPTORS may activate PAIN GATE MECHANISM.
 Vascular changes could also decrease LOCAL PAIN.(The increased blood flow that has been
observed could WASH OUT some of the pain provoking metabolites resulting from tissue
injury.) (PROSTAGLANDINS & BRADYKININ)
3. REDUCTION OF MUSCLE SPASM:It has been suggested that heating the secondary afferent muscle spindle nerve endings &
Golgi tendon organs could be a way in which an INHIBITORY INFLUENCE is applied to the MOTOR
NEURON POOL to DIMNISH MUSCLE EXCITATION.
 The pain & muscle spasm are interdependent – A reduction in one will cause a reduction in
the other.
4. SEDATIVE EFFECT:During & after heat treatments patients have been found to sleep more readily.
 This might be simply a consequence of pain relief.
 This sedative effect of superficial heat could be a REFLEX PHENOMENON.
5. INCREASE OF RANGE OF JOINT MOTION:
(A) The analgesic effect of heat allows greater tolerance of stretching.
(B)The viscosity of tissues will be decreased which partly account for the REDUCTION OF JOINT
STIFFNESS that occurs with heating.
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©Increased COLLAGEN EXTENSIBILITY occurs at higher temperatures.
Note:- Heat is used PRIOR to passive stretching & exercise to increase joint movement or lengthen
scars or contractures.
6. PROPHYLAXIS (PREVENTION) OF PRESSURE SORES:Heat applied to areas of skin subjected to prolonged pressure or friction has been suggested in
order to promote a greater BLOOD FLOW in the skin & thus decrease the risk of skin breakdown.
7. OEDEMA OF EXTREMITIES – REDUCTION:
Heat has been recommended for the treatment of CHRONIC OEDEMA of the hand & foot.
This must be given with the part in ELEVATION since the application of superficial heating will
tend to increase oedema if the part is dependent.
 Vessel dilatation induced by heating will allow increased rates of fluid exchange & thus may
help to increase the reabsorption of exudates.
 To be successful, the modality used would need to encompass the whole swollen region. Such
heating arrangements coupled with active ex’s are valuable in the treatment of hand injuries
in general.
8. RESOLUTION OF SOME SKIN DISEASES:Fungal infections which are difficult to control & thrive in moist conditions are sometimes
treated with regular I.R.R. therapy. (PARONYCHIA)
IMPORTANT THINGs TO NOTE
1. Due to heat there is increased capillary permeability & Increased capillary dilatation causes –
REDNESS OEDEMA.
2. The skin temperatures over 45˚C causes tissue damage. Further rise in temperature will lead to
DENATURATION & DEATH OF CELLS & TISSUES.
3. The dosage of heat treatment can only be guided by the FEELING OF WARMTH on the part of the
patient.
Degrees of heat sensation can be categorized AS FOLLOWS;
a) MINIMAL WARMTH:- Threshold value, Gentle comforting warmth.
b) MEDIUM WARMTH:- Distinct feeling of agreeable warmth.
c) MAXIMUM WARMTH:- Intense feeling of heat, maximum heat tolerance is exercised.
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d) DANGER LEVEL:- Intolerable heat, Burning sensation.
TESTING OF THERMAL SENSATION
1. Apply 2 test tubes of water at 40 – 45˚C & 15 -20˚C randomly to the treatment area.
2. Ask the patient to identify which is hot & cold with the eyes closed.
3. The patient should actually discriminate between only a few degrees of Celsius.
4. Temperature over 45˚C or much below 15˚C should not be used. (Because they may test PAIN
instead of THERMAL SENSATION)
Indications and Contraindications for Thermotherapy
Indications
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
Subacute and chronic inflammatory conditions
Subacute or chronic pain
Subacute edema removal
Decreased ROM
Resolution of swelling
Myofascial trigger points
Muscle guarding
Muscle spasm
Subacute muscle strain
Subacute ligament sprain
Subacute contusion Infection
Contraindications
a.
b.
c.
d.
e.
f.
Acute musculoskeletal conditions
Impaired circulation
Peripheral vascular disease
Skin anesthesia
Open wounds or skin conditions (cold whirlpools and contrast baths)
Primary goals of thermotherapy include increased blood flow and increased muscle
temperature to stimulate analgesia, increased nutrition to the cellular level,
reduction of edema, and removal of metabolites and other products of the
inflammatory process.
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