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the human body is converted into heat, with the balance converted into
external work or into tissue growth. The circulatory system, in addition
to circulating blood for its metabolic characteristics also distributes heat,
thus replacing the heat energy lost to the environment, as well as nour-
ishing the tissue. The resultant increase in heat energy delivered by the
blood causes the temperature to rise until the heat energy lost to the
environment again balances with the heat delivered.
It has long been recognized that where there is injury or infection, there
is inflammation, but injury or infection of itself does not create heat
energy. When there is trauma, whether an injury or abnormal stimula-
tion caused by a physical, chemical, or biologic agent, a pathologic
process of reactions occurs in the blood vessels and adjacent tissues
in response to the perturbation. The natural defense mechanism trig-
gered immediately increases the flow of blood to the area of concern,
causing the temperature to rise in proportion to the increase in blood
flow. However, the maximum temperature can be no higher than that
of the core arterial supply to the trauma tissue.
Consider as a simple analogy, the action of washing your hands in a
sink. If the water from the hot faucet were to be trickling in a small
stream, it is likely it would feel only lukewarm. However, if you were to
open that tap full force, the rushing water would feel quite hot. But, no
matter how intense the rush, the water could never be hotter than the
water from its source of heat, the furnace.
The ancient diagnostic technique of feeling for heat over the body is a
longtime indicator of inflammation. While localized temperature eleva-
tions may be felt merely by the touch of the hand, the technique is
highly subjective, and not sufficiently sensitive to detect the subtle
temperature rises indicative of increased cellular or metabolic activity.
With the introduction of infrared techniques, accurate surface tempera-
ture patterns are immediately quantifiable and any changes easily de-
tected. It is this knowledge that enables us to study any disease pro-
cess resulting in a change in heat generation or thermal properties of
the tissue.
Infrared Thermometry
Temperature is a fundamental property of all matter related to its en-
ergy content, and can be described by a numeric value expressed on a
scale of temperature. A human’s touch produces an instinctive sense
of hot or cold to judge the relative temperature of two objects. How-
ever, as a practical matter, clinicians must have a temperature scale
that is independent of the observer, by which unknown temperatures
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