الفهرس 
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Abstract
INTRODUCTION
Pain:
Definition of pain:
Mountcastle in 1968~wrote simply ”pain is that sensory experience
evoked by stimuli that injure”. The taxonomy committee of the
International Association for the study of pain chaired by Merskey in
1979 defined Pain as ”an unpleasant sensory and emotional experience
associated with actual or potential tissue damage”. They added crucial
notes to this sentence:
Pain is always subjective. Each individual learns the application of
the word through experiences related to injury in early life (Wall ,1984).
In attempting to understand the patient’s complaint, a
comprehension of factors that influence the perception as well as the
cause of pain is essential. Learned behavior, ethnic, religious, and cultural
factors, the context of the painful situation, social influences, and
psychologic factors all contribute to the complexity of pain. (Warfield
and Stien 1991).
Function of pain:
Pain in its acute form, especially when it is caused by disease,
plays a biologic role; it warns the patient that something is wrong and
prompts him to seek help. (Dwaracanath ,1991). Its aversive nature
strongly motivates the patient to avoid noxious stimuli. Moreover, pain
may help to promote healing by motivating the patient to avoid contact or
motion of an injured area. (Raja et al., 1988).
However, if not treated adequately, pain persists beyond”its useful
purpose and results in profound behavioral disturbances, (Dwaracanatb
,1991), and produce serious abnormal physiological and psychological
reactions, which in turn can cause complications that prolong disability.
Pain, when it outlasts the natural course of disease or injury, or when it
accompanies a chronic disorder, loses its biologic importance, serves no
useful function and does not permit the organism to escape harm.
(Sternbach ,1984).
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Types of pain acute or chronic:
There seems to be a quite significant difference between acute and
chronic pain. Whereas acute pain may promote survival, chronic pain is
usually destructive, physically, psychologically and socially. (Sternbach
,1984).
Acute pain:
Patients with acute pain are characterized by a well- defined
temporal pattern of pain onset, usually associated with subjective and
objective physical signs. These signs are commonly associated with
hyperactivity of the autonomic nervous system. Acute pain is relatively
easy to recognize and is more amenable to many of the therapeutic
approaches available (Foley ,1982).
Chronic pain:
In contrast, chronic pain is the persistence of pain with a less welldefined
temporal onset, in which the signs of autonomic nervous system
hyperactivity are absent. With patients in chronic pain, the persistent pain
has usually failed to respond to those modalities directed at the treatment
of the cause of pain (Foley ,1982). In general, these patients respond
poorly to the use of analgesic agents and have developed significant
changes in personality, lifestyle and functional ability. (Abram, 1989).
Visceral versus somatic pain:
Somatic pain sensation is much more precise in its localization. It
is concerned with our relationship to external factors. Visceral pain, on
the other hand, is often poorly localized due to the relative paucity of
nerve endings, the threshold of sensation is higher and the infrequency of
the challenging stimuli from the internal environment. (MaDani et at,
1984). Visceral pain is described as dull aching boring, cramping or
colicy squeezing, pulling and appears to come from deep inside the body
and in most instances overlying the general area of the viscera involved,
(Haugen ,1968). While superficial somatic pain has been classified into
pricking pain, burning pain and aching pain. (Alauuhta et aI., 1990).
Another difference between the two systems is that many of the
stimuli, which activate somatic sensory nerves, do not elicit pain response
when applied to viscera. If the abdominal wall is infiltrated with a local
anaesthetic, the abdomen can be opened and the intestine can be handled,
cut and even burned without eliciting any discomfort. Visceral pain
receptors are present in the viscera, however, and although they are more
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sparsely distributed than in somatic structures, certain types of stimuli
cause severe pain, such as ischemia, chemical stimuli, and spasm and
over distension ofa hollow viscus. (Guyton ,1991).
Referred pain:
At times the sensation of pain arising form viscera is referred to an
area of the body distant from the point where the stimulus originates. In
addition to pain, hyperalgesia of the skin and muscle spasm may be noted
in the area of referral. Figure 1- illustrates the most likely mechanism by
which most pain is referred. In the figure branches of visceral pain fibers
are shown to synapse in the spinal cord with some of the same secondorder
neurons that receive pain fibers form the skin. When the visceral
pain fibers are stimulated, pain signals from the viscera are then
conducted through, at least, some of the same neurons that conduct pain
signals from the skin, and the person bas feeling that the sensations
actually originate in the skin itself (Guyton ,1991)