Chapter 15
1

Pain


“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”
—International Association for the Study of Pain
“Pain is whatever the experiencing person says it is, existing whenever he says it does”
—McCaffrey
2
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Pain Theories
 Specificity theory


Amount of pain is related to the amount of tissue injury
Accounts for many types of injuries but does not explain psychological contributions
 Gate control theory
 Developed to explain the complexities of the pain phenomenon
3
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Neuroanatomy of Pain


Nociception
 Perception of pain
Nociceptors


Bare nerve endings in skin, muscle, joints, arteries, and the viscera that respond to chemical, mechanical, and thermal stimuli
Can detect a wide range of stimuli
 Aδ fibers
 Unmyelinated C polymodal fibers
4
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Pathways of Nociception
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Pathways of Nociception
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Pathways of Nociception
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Neuromodulation of Pain
 Segmental inhibition
 Diffuse noxious inhibitory controls
 Integration of:



Peripheral sensory axon terminals
Spinal interneurons
Top-down control pathways
 All converge on the spinal dorsal horns
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Neuromodulation of Pain
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Neuromodulation of Pain
 Chemicals and neurotransmitters




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Pain excitatory
Pain inhibitory
Modulators of pain
Direct excitation
 Threshold depolarization from direct stimuli
Indirect excitation
 Threshold depolarization from inflammatory mediators after tissue injury
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Endorphin Response
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11

Clinical Description of Pain



Pain threshold
 Point at which a stimulus is perceived as pain
Perceptual dominance
 Pain at one location may cause an increase in the threshold in another location
Pain tolerance
 Duration of time or the intensity of pain that a person will endure before initiation of pain responses
12
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Pain Classifications
 Nociceptive pain
 Pain with a cause of normal tissue injury
 Somatic
 Visceral
 Non-nociceptive pain
 Neuropathic pain
 Peripheral and central
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13

Acute Pain
 Protective mechanism
 Alerts an individual to a condition or experience that is immediately harmful to the body
 Manifestations
 Fear and anxiety
 Tachycardia, hypertension, fever, diaphoresis, dilated pupils, outward pain behaviors, elevated blood sugar levels, decreased gastric acid secretion and intestinal motility, and a general decrease in blood flow
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Acute Pain


Acute somatic



Arises from connective tissue, muscle, bone and skin
Aδ fibers—pain is sharp and well localized
C fibers—dull, aching, and poorly localized
Acute visceral


Pain in the internal organs and abdomen
Poorly localized due to the lesser number of nociceptors
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Acute Pain
 Referred pain


Pain that is present in an area removed or distant from its point of origin
The area of referred pain is supplied by the same spinal segment as the actual site
 Myocardial infarction pain
16
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Referred Pain
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Chronic Pain
 A situation; state of existence
 May be sudden or develop insidiously
 Usually defined as lasting at least 3 months
 Response patterns vary
 Produces significant behavior and psychological changes
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Common Types of Chronic Pain
 Myofascial pain syndromes
 Injury to the muscle and fascia
 Spasm, tenderness, and stiffness
 Chronic postoperative pain
 Cancer pain
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Neuropathic Pain
 Result of trauma or disease of nerves
 Most often chronic
 Painful diabetic neuropathy
 Postherpetic neuralgia
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Neuropathic Pain
 Deafferentation pain
 Sympathetically maintained pain
 Complex regional pain syndromes (CRPS)
 Central pain
 Phantom limb pain
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Pediatrics and Pain


Pathways and chemicals associated with pain are functional in preterm and newborn infants
Nociceptor system is functional by 24 weeks’ gestation
 Expressions of pain



Facial expression
Crying
Body language
22
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Pediatrics and Pain
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Aging and Pain
 Increase in pain threshold


Peripheral neuropathies
Skin thickness changes
 Decrease in pain tolerance
 Alteration in metabolism of drugs and metabolites
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Temperature Regulation
 Variable





Location
Activity
Environment
Circadian rhythm
Gender
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Temperature Regulation



Peripheral thermoreceptors
Hypothalamic control
Heat production and conservation





Chemical reactions of metabolism
Skeletal muscle contraction
Chemical thermogenesis
Vasoconstriction
Voluntary mechanisms
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Heat Loss









Radiation
Conduction
Convection
Vasodilation
Decreased muscle tone
Evaporation
Increased respirations
Voluntary measures
Adaptation to warmer climates
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Temperature Regulation


Pediatrics
 Produce sufficient body heat but are unable to conserve heat produced


Small body size and high body surface to weight ratio
Thin subcutaneous layer
Aging


Slow blood circulation, vasoconstrictive response, and metabolic rate
Decreased sweating and perception of heat and cold
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Fever
 Resetting of the hypothalamic thermostat
 Activate heat production and conservation measures to a new “set point”
 Exogenous pyrogens
 Endogenous pyrogens
 Endogenous cryogens
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Fever
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Benefits of Fever





Kills many organisms
Decreases serum levels of iron, zinc, and copper
Deprives bacteria of food
Promotes lysosomal breakdown and autodestruction of cells
Increases lymphocytic transformation and phagocyte motility
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Hyperthermia
 Not mediated by pyrogens



No resetting of the hypothalamic set point
41 o C (105.8
o F): nerve damage produces convulsions
43 o C (109.4
o F): death results
 Forms
 Heat cramps, heat exhaustion, heat stroke
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Heat Cramps




Severe spasmodic cramps in the abdomen and extremities
Following prolonged sweating and associated sodium loss
Common in individuals not accustomed to heat or those performing strenuous work in warm climates
Fever, rapid pulse, and increased blood pressure often accompany the cramps
33
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Heat Exhaustion
 Collapse due to prolonged high core or environmental temperatures
 Prolonged vasodilation and profuse sweating
 Dehydration, depressed plasma volumes, hypotension, decreased cardiac output, tachycardia
 Manifestations
 Dizziness, weakness, nausea, and syncope
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Heatstroke


Potentially lethal result of a breakdown in an overstressed thermoregulatory center
Brain cannot tolerate temperatures >40.5
o C
(104.9
o F)


Temperature maintained by blood flow through the veins in the head and face
Cardiovascular and thermoregulatory centers may cease functioning with higher temperatures
35
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Heatstroke



Manifestations
 Cerebral edema, degeneration of the CNS, swollen dendrites, and renal tubular necrosis
Rapid peripheral cooling will cause peripheral vasoconstriction and limit core cooling
Children are more susceptible



Produce more metabolic heat when exercising
Greater surface area to mass ratio
Sweating capacity is less than adults
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Malignant Hyperthermia


Complication of inherited muscular disorder
Precipitated by the administration of volatile anesthetics and neuromuscular blocking agents


Increased calcium release or decreased calcium uptake with muscle contraction
Causes sustained muscle contractions
 Increased oxygen consumption and lactic acid production
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

Hypothermia

Body temperature less than 35
°
C
Produces:


Vasoconstriction, alterations in the microcirculation, coagulation, and ischemic tissue damage
Ice crystals, which form inside the cells, causing them to rupture and die
Tissue hypothermia slows the rate of chemical reactions; increases blood viscosity and slows blood through the microcirculation; facilitates blood coagulation and stimulates vasoconstriction
38
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Hypothermia
 Accidental hypothermia
 Commonly the result of sudden immersion in cold water or prolonged exposure to cold
 Therapeutic hypothermia


Used to slow metabolism and preserve ischemic tissue during surgery or limb reimplantation
May lead to ventricular fibrillation and cardiac arrest
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Trauma-Induced Temperature
Change
 CNS trauma
 Accidental injuries
 Hemorrhagic shock
 Major surgery
 Thermal burns
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Sleep
 Active, multiphase process
 Hypothalamus is the major sleep center
 Hypocreatins (ovexins)
 Promote wakefulness and rapid eye movement (REM) sleep
 Two phases


Rapid eye movement (REM) sleep
Non–rapid eye movement (NREM) sleep
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EEG Stages of Wakefulness and
Sleep
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NREM Sleep
 75% to 80% of sleep time
 Four stages evaluated by EEG

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Stage I
Stage II
Stage III
Stage IV
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REM Sleep
 20% to 25% of sleep time
 Also known as paradoxic sleep
 Occurs every 90 minutes beginning after 1 to
2 hours of sleep
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Normal Sleep Cycles
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Pediatrics and Sleep
 Newborns sleep 16 to 17 hours per day
 53% of that time is spent in active (REM) sleep
 The infant sleep cycle is about 50 to 60 minutes
 Infants enter REM sleep immediately upon falling asleep
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Aging and Sleep
 Total sleep time is decreased
 Elderly take longer to fall asleep, and awaken more frequently during the night
 Amount of time in stage IV sleep decreases
 Potential causes
 Physical ailments, lack of daily routine, circadian rhythm changes, and medications
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Sleep Disorders
 Four classifications


Disorders initiating sleep
 Insomnia
Sleep-disordered breathing



Upper airway resistance syndrome
Obstructive sleep apnea
Obesity hypoventilation syndrome
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Sleep Disorders

Four classifications (cont’d)


Disorders of sleep/wake cycle
 Parasomnias



Somnambulism
Night terrors
Enuresis
Dysfunctions of sleep, sleep stages, or partial arousals
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Sleep and Disease
 Secondary sleep disorders


Alterations in the quality and/or quantity of sleep due to primary diseases
Depression, pain, sleep apnea syndromes, and alterations in thyroid hormone secretion
 Sleep-provoked disorders
 Sleep stage alterations produced in certain disease states
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Vision




Blepharitis
 Inflammation of the eyelids
Hordeolum (stye)
 Infection of the sebaceous glands of the eyelids
Chalazion
 Infection of the meibomian (oil-secreting) gland
Keratitis
 Infection of the cornea
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Vision
 Conjunctivitis





Inflammation of the conjunctiva
Acute bacterial conjunctivitis (pinkeye)


Highly contagious
Mucopurulent drainage from one or both eyes
Viral conjunctivitis
Allergic conjunctivitis
Trachoma (chlamydial conjunctivitis)
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The Eye
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Visual Field and Neuronal
Pathways
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Vision Changes and Aging
 Cornea
 Anterior chamber
 Lens
 Ciliary muscles
 Retina
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Visual Dysfunctions
 Alterations in ocular movements


Strabismus
 Diplopia
Nystagmus


Pendular nystagmus
Jerk nystagmus
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Visual Dysfunctions
 Alterations in visual acuity




Amblyopia
Scotoma
Retrobulbar neuritis
Cataracts
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Visual Dysfunctions
 Alterations in visual acuity




Papilledema
Dark adaptation
Glaucoma
Age-related macular degeneration (AMD)
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Visual Dysfunctions
 Alterations in accommodation




Accommodation is the process whereby the thickness of the lens changes
Oculomotor nerve changes
Decreased flexibility of the lens
Manifestations:
 Diplopia, blurred vision, and headache
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Visual Dysfunctions
 Alterations in refraction



Myopia (nearsighted)
Hyperopia (farsighted)
Astigmatism
 May coexist with myopia or hyperopia
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Alterations in Refraction
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Visual Dysfunctions
 Alterations in color vision


Age-related yellowing of the lens
Colorblindness
 Generally an X-linked recessive trait
 Commonly red-green colorblindness
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Visual Dysfunctions
 Neurologic disorders



Hemianopia
Injury to the optic chiasm
Homonymous hemianopsia
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Neurologic Disorders Causing
Visual Dysfunction
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The Ear
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The Ear
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Aging and Hearing
 Cochlear hair cell degeneration
 Loss of auditory neurons in spiral ganglia of organ of Corti
 Degeneration of basilar conductive membrane of the cochlea
 Decreased vascularity of cochlea
 Loss of cortical auditory neurons
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Ear Infections
 Otitis externa


Infection of the outer ear
Commonly caused by prolonged moisture exposure (swimmer’s ear)
 Otitis media


Acute otitis media
Otitis media with effusion
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Auditory Dysfunction
 Conductive hearing loss
 Impaired sound conduction
 Sensorineural hearing loss


Impairment of the organ of Corti or its central connections
Presbycusis (age-related hearing loss)
 Mixed hearing loss
 Functional hearing loss
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Olfaction



Cranial nerve I and part of V
Strong relationship between taste and smell
Olfactory stimulants
 Camphoraceous






Musky
Floral
Peppermint
Ethereal
Pungent
Putrid
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Taste
 Cranial nerve VII and part of IX
 Nerves in the tongue, soft palate, uvula, pharynx, and upper esophagus
 Gustatory stimulants




Sour
Sweet
Salty
Bitter
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Age-Related Olfaction and Taste
Changes
 Olfaction



Decline in odor sensitivity
Loss of olfactory sensory neurons and cells in the olfactory bulbs
Causes diminished appetite and food selection
 Taste


Higher concentration of flavors is required
Decline in the number of fungiform papillae
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Olfactory Dysfunction
 Hyposmia
 Anosmia
 Olfactory hallucinations
 Parosmia
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Taste Dysfunction
 Hypogeusia
 Ageusia
 Parageusia
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Somatosensory Function
 Touch


Sensation involves modality, intensity, location, and duration
Receptors are present in the skin
 Proprioception
 Depends on inner ear, vision, and receptors in joints and ligaments
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Proprioceptive Dysfunction
 Vestibular nystagmus


Vertigo
Ménière disease
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