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Topic 4: General Effects of Heat

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natalia m zameri

on 9 April 2018

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Transcript of Topic 4: General Effects of Heat

Temperature Regulation
occurs to maintain homeostasis
hypothalamus (body's thermostat) maintain normal range of human body temp (36 - 38'C)
temperature regulating mechanism
changes in circulation(vasodilate/contrict b/vessels)
shivering (maintain/generate)
sweating (lose heat)
Topic 4: General Effects of Heat
Physiologal Effects of Heat
Hot & Cold Test
Test for temperature sensation
use test tubes filled with cold & hot water each
Borders of the thermal loss may be determined by rolling the tube over the skin from affected to normal areas.
These borders will often coincide with the margins of pain sensibility.
This test is not routinely tested.
Learning Objectives
At the end of this topic, students should be able to acquire & apply knowledge of:
types of heat
conduction of heat, physiological effects of heat
sensation test regarding heat
in treating patients
Types of Heat Reaction
Physical Mechanisms of Heat Exchange
Intervention Goals
Pathways of Heat Loss
Deep Heat
Superficial Heat
(major pathway)
Respiratory Tract
(secondary pathway)
body heats evaporates water from respiratory mucosa & water vapor exhaled
Urinary Tract
(Minor Pathway)
urine is at body temperature when eliminated
Digestive Tract
(minor pathway)
feces are at body temperature when eliminated
loss/gain through direct contact between materias w/ different temperatures
eg.: heat absorb by body when using h/pack
transference of heat to a body by movt of air, matter @ liquid around or past the body
eg: hot-air furnace, fluidotherapy
transfer heat through air from warmer source to cooler source
eg.: glowing coals on open fire, IRR
temperature change that results from energy transformed from one form to another
eg.: conversion from mechanical/electrical energy to heat energy
therapeutic u/sound - sound waves (mechanical e.) transform to heat (thermal e.) as absrobed by tissue
transformation from liquid state to gas state
this requires energy exchange
heat is given off when liquid transform to gases
eg.: sweating, vapocoolant
Pain Reduction
Reduction of Muscle
Guarding or Spasm
heat decrease viscosity & increase elastic properties of connective tissue (esp ms, tendon & jt capsule)
sufficient load must be applied to reproduce residual elongation of tissue over long time
temperature range needed for residual length changes = 40 to 45'C
decrease potential for irritation & tissue damage when applied during stretching procedure
residual elongation of conn tissue depends on
sufficient increase in tissue temp
timing of application - best during heat appl, @ immediate after removal
type of stretch applied - low-load prolonged stretch = less tissue damage & greaer increase ROM
Athritis - heat increase elastic prop of jt capsule, reduce assoc pain = increased ROM
Tissue Extensibility
may occur d/t
trauma - protective mech
painful stimulus - pain-spasm-pain cycle
ms temp elevate
firing rate of ms spindle afferents is decreased, Golgi tendon organs increased
decrease in alpha motor neuron = decrease tonic ms activity
decrease ms guarding from decrease stimuli to ms
Local Effects
Vasodilatation of local blood vessels occurs due to:
Stimulation of cutaneous thermoreceptors by heat leads to reflex vasodilatation of blood vessels
Increase local release of chemical mediators of inflammation as histamine like substance, bradykinins.
Vasodilatation causes increase in blood flow to the heated area which will lead to
increase supply of oxygen and nutrients to the heated area.
Increase antibodies to the heated area.
Hemodynamic Effects
Increase fluid dynamics
Heating and increase in blood flow will increase the capillary pressure and permeability which forces edema and metabolites from the area, then these wastes can be drained into the venous and lymphatic systems.
SO, heat leads to increase venous and lymphatic drainage which aids removal of wastes and re-absorption of edema.
Neuromuscular Effects
Local application of heat increases the pain threshold by the following mechanisms:
Direct mechanism
Activation of spinal gating mechanism through stimulation of free nerve ending (A-beta) leads to blocking the transmission of pain at level of spinal cord.
Indirect mechanism:
Heat leads to vasodilatation and increase blood flow resulting in reducing pain through:
Increase the oxygen and nutrition supply
Removal of irritant waste products
Re-absorption of edema
Decrease muscle spasm
Improving tissue healing

Increased pain threshold
Increased temperature increase nerve conduction velocity of both sensory and motor nerves.
Elevation of muscle temperature 42 °C has been shown to result in:
decreased firing rate of type II fiber of muscle spindle and gamma efferent fibers which reducing afferent firing from the spindles
increased firing rate of type Ib fibers from Golgi tendon organ that leads to reflex inhibitory effect of the respective muscles.
These changes in nerve firing rates lead to a reduction in the activities of alpha motor neurons and thus to reduction in muscle spasm and relaxation of muscle  
Changes in nerve conduction
velocity and firing rate
Muscle strength and endurance decrease during the initial 30 minutes after the application of deep or superficial heating agents as a result of change in the firing rate of type II fibers, gamma efferent and Ib fibers from Golgi tendon organ.
Beyond 30 minutes after the application of heat, and for the next 2 hours, muscle strength gradually recovers and then increases to above pretreatment levels.
Change in the muscle strength
Increased Metabolic Rate
Increase tissue temperature leads to increase rate of cell metabolism as a result of increase enzymatic activities and biological reactions.
Increase in the cell metabolic rate leads to the followings:
1- Increase demand for oxygen and nutrients.
2- Increase amount of wastes excreted from the cell.
For each increase of 10'C in skin temperature, the cell metabolic rate increase by a factor of two to three.
Enzymatic activities increase with increase temperature up to 45'C. Above this level, increase temperature leads to de-naturation of enzymes and proteins and destruction process begins.
Increased Tissue Extensibility
Increase temperature leads to increase extensibility of collagen and soft tissue.
So, heating is indicated before stretching or range of motion exercises.
Systemic Effects
occurs when large area / whole body exposed to heat
generalized skin vasodilation
generalized sweating
increased pulse rate
increase respiratory rate
decrease blood pressure
Melzack & Wall - gate control theory of pain
therap heat used - thermal stimuli provide input - spinal gate mech - overrides painful stimuli
Gammon & Starr - thermal stimuli produce counterirritation
thermal input "counter" painful stimuli
may explain rubbing @ pressure common rx
heat - elevate pain threshold & increased nerve conduction velocity
elevated pain threshold - delay onset & perception pain
change in nerve conduction velocity has not been demonstrated
Deep heating is thought to
lessen nerve sensitivity,
increase blood flow,
increase tissue metabolism and decrease muscle spindle activity to stretch,
cause muscle relaxation and
increase tissue flexibility
Superficial heat increases joint mobility by
increasing connective tissue extensibility,
reducing pain and
tissue viscosity
applied to the skin over the involved area.
The depth of heat depends on types of tissue
ranges from 0.5 cm to 1–2 cm
amount of fat in the area (insulator)
example of modalities:
hot pack
example of modalities:
application of modalities that cause a tissue temperature rise in deeper tissue (3-4cm).
the application of heat in the treatment of deep body tissues, particularly muscles and tendons.
Deep heat treatments direct heat toward specific inner tissues through ultrasound or by electric current.
application of modalities to surface of body that primarily heat surface tissue (<1cm).
Superficial heat treatments apply heat to the outside of the body.
skin & subcutaneous tissue
increase 5 - 6'C after 6 min, maintain 30 min
jt capsule
increase 9'C at 20 min
* heat should be applied 15 - 30 min for max benefit
radiation & conduction - heat lost from body to cooler air/objects
convection - air currents move warm air away from skin
sweating - excess body heat evaporates sweat on skin surface
Electrotherapy I HJS 1032 Sem 2 2015/16
Diploma in Physiotherapy (UniSZA)
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