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College of Medicine/Babylon University
Medical Physics Module
Session 2
Lecture 3:
Heat and Cold In Medicine
Objectives: after the end of this lecture, the student must know:
1- Different methods available to measure body temperature
2- How heat and cold can be used in medicine
1- The most common way to measure temperature is with glass thermometer,
containing mercury or alcohol. For the thermometer to measure fractions of
temperature degree, it requires capillary diameter to be so small (<0.1 mm).
It has restriction just above the bulb.
2- Thermistor : special resistor changes its resistance rapidly with temperature
~ ( 5% ) Cº
Resistance are equal the bridge is balance.
This used in medicine because of its sensitivity (0.01 Cº). Thermistor is placed in the
nose to monitor breathing rate by showing temperature change between inspired and
expired air and this type called pneumograph.
3- Thermocouple : consist of two junction different metals, if the two junctions
are different temperature, voltage is produced. This can be made small
enough to measure the temperature of individual cells.
4- Thermograph – mapping the body temperature.
Measurements of body surface temperature indicate that it varies from point to point
depending upon metabolic and circulatory processes near the skin. In 1950 it’s found
that most of breast cancers characterized by an elevated skin temperature in the
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College of Medicine/Babylon University
Medical Physics Module
region of the cancer. The surface temperature above tumor ~1 Cº higher than
normal surrounding tissue.
If the temperature is sufficiently high (red hot), the radiation is visible. At body
temperature the emitted radiation is in the infrared (IR) region.
Boltzman law : for the total radiated power per surface area ( W )
W= e
Ϭ T
4
T = temperature
Ϭ =Steven boltzman constant = 5.7 X 10
- 12
w / cm
2
K
4
, e = 1 for radiation body
Example : what is power radiated per square centimeter from the skin temperature of
300 Kº ~ 33 Cº
W = 5.7 X 10
-12
( 300 )
4
What power radiated from a nod body 1.75 m
2
( 1.75 X 10
4
cm
2
in area
W = 0.05 X 1.75 X10
4
cm
2
= 875 w
Heat therapy
two primary therapeutic effects take placed in a heated area:
1- increase in metabolism → relaxation of capillary → vasodilatation.
2- increase blood flow as blood moves to cool the heated area.
There are many methods of producing heat in the body:
1- conductive heating
2- infrared heating
3- radio wave heating (diathermy)
4- ultrasonic wave heating
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College of Medicine/Babylon University
Medical Physics Module
Heat from diathermy used in treatment of inflammatory diseases of the joints
(arthritis), bursitis & neuralgia.
Short wave diathermy used in reliving muscle spasm & bursitis.
Microwave diathermy is used for fractures, sprains, strain bursitis & injuries to
tendon.
Ultrasound used to relieving tightness & scarring occurs in joint diseases.
Use Of cold In Medicine
Cryogenic methods used to destroy cells & this applications called cryosurgery
Cryosurgery has several advantages:
1- There is minimal bleeding.
2- The volume of tissue destroyed can be controlled.
3- There is little pain sensation.
One of first use of cryosurgery was in treatment of Parkinson disease (shaking
palsy).
Parkinson disease causes uncontrolled tremors in the arms and legs, it is possible to
stop tremors by destroying the parts of thalamus in the brain that control the
transmission of nerve impulses to other parts of nervous system.
Cryogenic method also used in several types of eye surgery we discuss two:
1- The repair of detached retina and cataract surgery ( the removal of darkened
lens )
2- In surgical extraction of the lens, a cooled probe is touched to the front
surface of the lens, the probe sticks to the lens making lens easy to remove.
Caution should be taken, when cryogenic liquid or cooled gasses are used, because
any contact between this materials and the eyes or skin results in freeze burns. The
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College of Medicine/Babylon University
Medical Physics Module
most care is required when oxygen is used because many materials do not burn in air
will burn in pure oxygen.
Much interest has been aroused by the idea of using cryogenic methods to cool the
body into state of suspended animation so that it can pass time without aging. This
science is called Cryonics
One goal of cryonics is to preserve at law temperature people with fatal diseases
with hope that in future by could be revived and their disease cured.
Some simpler human biological system such as blood, semen and tissue have
successfully been cooled, stored and revived.
The results of using thermography as a screening technique for breast cancer have
been disappointing . If 1000 random women of age 45 are studied, about one third
will have abnormal thermograms of the breast although far fewer than 1% have
cancer.
Most of the false positive findings are due to different blood flow patterns in the two
breasts. As general rule x-ray studies are much more reliable than thermography for
detection of breast cancer they detect of 80% of known cancers.
Thermography has been used to detect other types of cancers and is also used to
study circulation of blood in the head, differences in temperature between left and
right sides can indicate circulatory problem.
Thermography has increases in reducing leg amputations in diabetics. The blood
supply in diabetic leg is usually inadequate, but if the tissue break down and an ulcer
is formed , the need of blood in the leg may double , the circulatory problems of
diabetic then become evident, the ulcer does not heal and often becomes infected.
The presence of hot spots of the foot can be determined before an ulcer forms.
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College of Medicine/Babylon University
Medical Physics Module
The physician can then use preventive measures such as having the patient wear
special foot wear to try to eliminate the hot spot and avoid formation of ulcer.
Preliminary studies resulted in a reduction of about 20% in limb amputations of
diabetic in 1975.