Heat Flashcards
What 5 things do the biophysical effects of temperature elevation depend on?
- the extent of temperature rise
- rate energy is added to tissue
- volume of tissue exposed
- composition of absorbing tissue
- capacity of tissue to dissipate heat
What temp do you have to get tissue at or above in order to reach therapeutic levels?
100 degrees F (40 degrees C)
what is skin temp typically?
98
want to get above that
what skin temp is “feeling cool”
96 or below
signs of heating
redness
swelling
sweating
what is one of the mechanisms that rises skin temperature?
- blood flow
when skin is getting warm, what does blood do?
starts flowing with cooler blood
what occurs if you add heat too fast
the blood cant keep up with cooler blood and results in a burn
do all tissues have the same rate of warming?
nope
what makes a difference in heating
the rate of application
the larger the area you heat…
the more likely you are going to get a systemic effect
Composition of absorbing tissue
- how much fat is there? it will be a barrier to getting heat down to muscle
- what is composition of that area of tissue
capacity of tissue to dissipate heat
- heat on people with peripheral vascular disease or arterial disease should be used with caution
4 physiologic responses to heat
- metabolic reactions
- hemodynamic techniques
- neuromuscular response
- connective tissue effects
how much does metabolic reaction increase for each ten degrees Celsius?
2-3 times
at what temperature is increased enzymatic activity observed?
40 degrees Celsius / 102-109 F
lend to therapeutic significance
what temp is scalding
120 F
why does tissue burn occur
due to metabolic activity required to repair
tissue not being capable of matching protein denaturation
what increases with heat, promoting tissue healing?
oxygen uptake
even with mild temperatures
happens greater with higher elevations
take home message for metabolic reactions
if you dont have enough heat, it won’t increase the metabolic activity enough to make a change BUT dont increase it too much or too fast
what hemodynamic effect does heat cause?
vasodilation –> increased blood flow
Direct Axonal Reflex (neural)
Heat applied to skin stimulates cutaneous
thermoreceptors
These sensory afferents carry impulses to the
spinal cord
Some of these afferents are carried toward the
skin blood vessels, causing release of a
vasoactive mediator
Leads to vasodilation through an axon reflex
Spinal Cord Reflex
- decreased sympathetic nerve activity to smooth muscle of blood vessels
- probably the biggest thing that is happening
- Most things that are happening are going up to the spinal cord saying “open up, we need cold blood to the area”
chemical mediators released from heat
histamine and prostaglandins
what does sweat secretion produce
an enzyme called Killikren
does what killikren do?
- acts on globulin and kininogen to release Bradykinin and nitrous oxide which then acts on smooth muscle and endothelial cells of
contractile structures
what occurs to permeability with heat?
here is an increase in permeability in capillary and post capillary venule due to the action of the chemical mediators on the endothelial cells
what occurs due to increase in capillary pressure?
- outward fluid filtration from vascular to extravascular space can occur
- Mild inflammation –> little bit is normal but sweating occurs first
shunting
When overheating occurs, branches of the
peripheral system which were bringing blood to the
area may constrict shunting the blood to the
periphery
clinical implication for hemodynamic effects?
- due to increased blood flow, there should be some redness and possible mild swelling
- when moving blood out, there could be some inflammation in the periphery (be careful!)
neuromuscular response to heat
Heat can elevate the pain threshold, alter nerve conduction velocity and change muscle spindle firing rate
How does heat affect pain?
Decrease underlying muscle spasms
Counterirritant
Gate theory (maybe stimulating aBetas)
Still under investigation –> heat is rarely getting to the muscle yet we’re still seeing changes
How does heat affect muscle spasms?
Type II afferent firing decreases and firing of Ib fibers increases
Decrease firing of alpha motorneruons leading to decreased extrafusal fiber activity (1b fibers coming off GTOs) CANT PRODUCE AS MUCH STRENGTH
DONT PUT HEAT ON FIRST
another theory on how heat affects muscle spasms
gamma Efferents: heat decreases the firing of the muscle spindle via gamma efferents
DOMS
Moist heat more effective than heat wraps and chemical wraps
Heat wrap PRIOR to exercise 45%-52% decrease pain, disability and improvement in self-reported physical function
138% greater pain relief for 24 hours postexercise
Neural Clinical Implications
- positives: pain threshold is addressed; promotes relaxation
- use of heat to resolve pain is not well understood
- nonetheless, heat does appear to alter pain perceptions
- multiple ways to decrease muscle spasm via changes in nerve conduction velocity
- potential downside: can effect strength
what occurs to collagen at 50 C
collagen shrinks and dematerializes
what occurs to tendons at 41-50 C?
they show a different behavior
450C, water properties become dominate
If temperature is elevated, but no load applied there is no residual elongation (have to heat AND stretch)
- changes the structural soundness of tissue (stress/strain curve)
- stiffness is decreased
As far as the stress/strain curve goes, heating the tissue =
less force, more elongation
(more deformation with less load)
Clinical implications of connective tissue affects of heat?
- superficial tendons and scar tissue most likely tissues affected
- if you want to maintain the stiffness of the tissue, heat is a bad choice (dont heat ligaments)
- tissue needs to be stretched WHILE heat is applied
therapeutic effects of heat
Increases the extensibility of collagen tissues
Decreases joint stiffness
Produces pain relief
Relieves muscle spasms
Assists in resolution of inflammatory infiltrates, edema, and exudates
how long should you apply heat
8-10 minutes
not much change after that
Factors that influence heat exchange
- Conductivity of material
- Intensity of Heat Supply*
- Time of Exposure*
- Gradient between thermal agent and material being heated
conduction
Kinetic motion of atoms and molecules of one object get
passed to another
Total heat transfer with conduction is dependent on: time of flow, temperature gradient, treatment area, and thermal conductivity (all directly proportional)
Convection
Bulk movement of moving molecules, in liquid or gaseous form, from one place to another
- transfer of heat by movement of air or liquid around the object to be heated
- little bit more heat transfer with this rather than conduction
- contact is not constant like conduction
- ask Daniela the last bullet here
Radiation
Conversion of heat energy to electromagnetic radiation
All objects above –2730C (absolute 0) emit and absorb radiant energy
- not the biggest form of transfer but always there
Superficial heating agents
Hot Packs
Paraffin Wax
Fluidotherapy
Hydrotherapy
Radiant Heat
Moistaire Cabinets
what is a hot pack
Canvas or nylon case filled with hydrophilic silicate or sand
what temp of water is a hot pack kept in?
158-167 F (70-75 C)
when is greatest tissue temp increase seen with a hot pack?
after 8 minutes with reduction after that time secondary to increase in blood flow and cooling of the hot pack
what occurs if you repeat the application of a hot pack (change the pack)
may increase the time of heating effects, but does not significantly change tissue temperature
are deep tissues affected from hot packs?
usually not affected secondary to heat transfer
from skin to the deep tissue is inhibited by subcutaneous fat
clinical implications of hot pack- Advantages
- easy prep and application
- variety of sizes
- positioning
- home applications
clinical implications of hot pack - disadvantages
- no temp control (poor heat retention)
- poor conformity
- hard to secure sometimes
- passive patient environment
- tank maintenance
what is paraffin wax mixed with?
paraffin oil or mineral oil (5-7:1)
what does oil do to the wax
Oil decreases its melting point (54 C); wax remains molten between 45-54C
what does molten state of wax allow?
even distribution of wax around area
being treated
somethings about wax
Wax has a low specific heat and therefore feels less hot than water at the same temperature; also decreases risk of burn with greater temperature
Conducts heat more slowly than water, allowing more gradual buildup of heat lending to decreased risk of burn; also tolerated better by patient
Heat is conducted from the layer of solid wax on the skin
types of application of paraffin wax
- dip wrap
- dip re-immersion
dip wrap
multiple layers of wax wrapped with insulated towels (is it 8 times??)
dip re-immersion
dip 1-2 times for a protective later then leave the body part in the wax mixture for remaining treatment
advantages of paraffin wrap
- apply at a higher temperature without burn
- contours to body part
- increase skin moisture
- home use
disadvantages of paraffin wrap
- only useful on distal parts of extremities
- no temp control
- passive
- some wax reusable
Fluidotherapy
A bed of finely divided solids (glass beads with an avg diameter of .0165”, or finely ground corn cob called “cellex”) through which thermostatically controlled heated air is blown to produce a warm semifluid mixture to which the body can be exposed
The solid particles become suspended when air is blown into them, and the particles behave as a liquid
Permits movement of the body part due to the low viscosity
temperature ranges of fluidotherapy
38.3 - 47.8 C
clinical applications of fluidotherapy- advantages
heat control
can have activity
desensitization
disadvantages of fluidotherapy
claustrophobia
no home application
$$$
advantages of hydrotherapy
- conformity
- exercise
- desensitization
- other principles of water
disadvantages of hydrotherapy
- $$$
- positioning
- possible systemic reactions
- fear of water
