LECTURE 1

Intro to Pain

Pain is…

1. a perception
2. an emotion
3. a strong motivator

Inguinal hernia

occurs when intestines are poking through abdominal wall

Henry Beecher

a physician who studied the comparison of the use of narcotics in 2 situations: war veterans and civilian surgical wounds

Findings of Henry Beecher

War veterans were less likely to ask for narcotics than civilians with surgical wounds

Possible confounds in Henry Beecher’s study

1. war veterans were younger than the civilians
2. war veterans under a lot more stress\*\* (stress plays a role on inhibition of pain)

osteoarthritis

joint space is narrowing which leads to bones touching each other

Bedson and Croft Study

Their study shows that not everyone with an injury experiences pain.

What magnifies the experience of pain?

rumination and pain catastrophizing

top 10 reasons to seek health care

1. **cough****
2. **back pain****
3. **abdominal pain****
4. sore throat
5. **dermatitis (itch)****
6. fever
7. **headache****
8. leg pain
9. respiratory
10. fatigue

explanation of pain can kill

* pain can kill indirectly.
* individuals with chronic pain have a shorter life span.
* pain highly contributes to morbidity hence the quote of Albert Schweitzer: “*Pain is a more terrible lord of mankind*

*than even death itself.”*“

morbidity

suffering; everything that is bad that is not mortality

morbidity affects the quality of life

prevalence of pain

prevalence = how common

pain is ubiquitous i.e. it is everywhere

prevalence of chronic pain

out of the whole population

→ about 50% = lifetime prevalence of having chronic pain (once in your lifetime, you have a 1/2 of experiencing chronic pain)

→ about 20% = individuals experiencing chronic pain at this moment

epidemiologist’s bathtub

prevalence: how much water there is in the bathtub

incidence: how fast the faucet is dripping (new cases of something in a time period)

how much of the bathtub is filled depends on how fast the faucet is going (under normal circumstances)

variables that influence prevalence

1. death
2. recovery

prevalence of pain and the difference in men and women

huge difference of prevalence of pain in migraine, back pain and arthritis

prevalence vs incidence

prevalence: how much

incidence: new cases over a time span

why do women suffer more from chronic pain?

* stigma (men are less prone to notifying about pain)
* women outlive men

out-patients vs in-patients

out-patients: patients prescribed medication (no stay in hospital)

in-patients: patients that were hospitalized (stay in hospital)

epidemiology

***Epidemiology*** is the study of how often diseases occur in different groups of people and why.

Migraine Epidemiology: Lipton and Bigal

* prevalence of headache and migraine in children
* children are defined in different way
* headaches are defined in different ways

→ different definitions allow for different numbers

prevalence of pain in women vs men

* women have higher prevalence in pain which increases as they age

why does the prevalence in chronic pain for men peak at \[70-74\] range and then decrease?

men with chronic pain die (men have a lower life expectancy than women)

prevalence of pain by education level

why is pain more prevalent among people with lower levels of education?

* Having chronic pain might not allow you to pursue higher education.
* People with lower levels of education might have jobs requiring more physical effort leading to injury
* High SES is protective against chronic pain (to some degree)
* Better lifestyle
* Access to better healthcare
* Access to health insurance

why is prevalence of pain in lower back the highest?

The vertebrae that are at the bottom take on more pressure due to gravity

effect and burden of chronic pain

chronic pain can have an effect on the following:

* functional activities i.e. sleep, leisure activities, household chores
* social consequence i.e. marital relations, intimacy, etc.
* socioeconomic consequences i.e. heath-care cost, lost productivity
* emotional functioning i.e. irritable, angry, depression, anxiety

pain and disability

* low back pain is highly associated with disability
* knee pain is second highest

definition of disability

having difficulty and limitations in doing things

global burden of disease

The Global Burden of Disease (GBD) provides a tool to **quantify health loss** from hundreds of **diseases, injuries, and risk factors**, so that health systems can be improved and disparities can be eliminated.

GBD research incorporates both the ***prevalence*** of a given disease or risk factor and the ***relative harm*** it causes, in addition to just estimating disease prevalence

effect of pain on social functions (study by Roy)

pain comorbodities

==Co-morbidity== = if you have 1 condition, what other conditions are you more likely to have

* can also be correlational => you might not be able to sleep because of your back pain or you may get back pain due to not getting a good night’s sleep

comorbidity

* The condition of having two or more diseases at the same time.
* can be correlational i.e. difficulty sleeping can be a cause or a consequence of pain

3 types of suicide risk

1. thoughts
2. suicide plans
3. suicide attempts

chronic pain and suicide risk (study by Campbell)

table shows us that having chronic pain puts you at a greater risk for suicide risk

Kaplan-Meier plot

shows us survival function: it graphically displays the probability that a subject will survive up to time t

effect of chronic pain on lifespan

20% of those with widespread pain died vs 10% in control group

=> people w/ more pain have a lower probability of surviving

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economic burden of pain

pain can have direct and indirect burden on the economy

which service has the most economic burden

listed high to low

* employment-related cost (inability to come to work due to pain)
* community care cost
* cost of private services
* inpatient care

pain in Abrahamic religions

1. pain as atonement
2. pain for sin
3. pain as redemption

pain in philosophy (AGAD)

Aristotle (384-322 BCE) → pain is an emotion in the heart (partially right, pain has a duality)

Galen (130-201) → pain is a sensation in the brain

Avicenna (980-1037) → pain is an independent sensation different from touch/temperature

Descartes (1596-1650) → presence of pain pathway from body to brain (the actual pathway is wrong but the concept is correct)

Aristotle

Galen

Avicenna

Descartes

theodicy

the job of theodicy is to demonstrate the justice of God in ordaining or allowing the existence of moral and physical evil.

i.e. why is God allowing pain is God = good/protector?

Pain and utilitarianism

Classic utilitarianism rests on 3 propositions


1. Actions are to be judged right/wrong solely in virtue of their consequences → right actions are those that have the best consequences (stealing from the rich to give to the poor would maximize happiness)
2. In assessing consequences, the only matter is the amount of (un)happiness caused → right actions are those that produce the greatest balance of happiness over unhappiness
3. No one person’s happiness is to be counted as more important than another’s → everyone counts equally, everyone’s welfare is important

principle of utility

* term honed by Jeremy Bentham (1748-1832)


* **Principle of utility** then approves/disapproves of every action according to the ability to promote or oppose the happiness/interest of the person/group →  by utility he means something the produces benefit, advantage, pleasure good or happiness while at the same time preventing pain, evil or mischief

the mind-body problem

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the problem of understanding what the relation between the mind and body is, or more precisely

→ are mental phenomena a subset of physical phenomena or not?

i.e. phantom-limb pain

Phantom limb-pain

* limb can be amputated but the individual can still experience pain
* evidence for a soul (wrong); if pain can be perceived without a body part, then what does the body have to do with pain? pain has to do with the soul
* supports dualism

dualism

* theory to explain the mind-body problem
* mind and body are seperate

monism

* mind is simply an output of the body (more specifically, output of the brain)
* mental and corporeal phenomena are merely different manifestations of what is really one and the same Reality.

pain and the problem of other minds

I exist, but I can not say for sure you exist”, the same is for pain → I don’t know what kind of pain you are experiencing because I can not leave my mind to get into yours.

pain and human rights

* the ends justify the means: is used to suggest that any activity, whether or not that activity could be considered ethically or morally bad, is worth doing so long as a desired end result is achieved.
* peter singer: philosopher + advocate for animal rights

declaration of montreal (2010)

declaration that access to pain management is a fundamental human right

the 3 human rights in Declaration of Montreal

__**Article 1.**__ The right of all people to have access to pain management without discrimination.

__**Article 2.**__ The right of people in pain to an acknowledgment of their pain and to be informed about how it can be assessed and managed.

__**Article 3.**__ The right of all people with pain to have access to appropriate assessment and

treatment of the pain by adequately trained health care professionals.

opioid consumption by country

* opioid consumption is high in industrialized countries
* no opioids in developing countries

Broken Column by Frida Kahlo: painting representing her pain following her bus accident

old definition of pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

new definition of pain

An unpleasant sensory and emotional experience associated with, or __resembling__ that associated with, actual or potential tissue damage.

pain and unpleasantness

* pain has a negative valence
* **Masochism**: masochists don’t find pain unpleasant, to some degree they find pain pleasant (this would make the definition not applicable) vs for biological/ environmental, ppl find pain stimulating, the trade-off is worth making (pain to achieve orgasm)
* self-harm
* exercise: another example of a trade-off (no pain, no gain)
* spicy food
* itch

Sensory and emotional part of pain

* Sensations = energy in env, that turn into electrical signals so that your brain can interpret it
* sensations habituate (when entering a kitchen for the first time, you will hear the fridge hum, 5 mins later, you don’t “hear the humming” because brain becomes habituated), pain does not


* Pain does not habituate, the longer the pain lasts, the more you will feel it
* Stimulus of same intensity, you will have a higher perception = problem with chronic pain
* Pain sensitizes instead of habituates
* pain = emotion

pain is a drive state (homeostatic emotion)

* drive state – something that compels action i.e. thirst (it compels you to drink liquid); you don’t need to do something about rage, fear, sadness
* hunger compels you to eat
* thirst compels you to drink
* Pain trumps all other drive states (not necessarily true as a little amount of pain might not trump a lot of hunger/thirst)

Actual or potential tissue damage and pain

Injury is minimized with the “potential tissue damage”

i.e. Cut skin with knife, individuals will experience pain before you actually damage tissue

adequate stimulus for pain

* noxious cold temperatures
* inflammation
* mechanical pressure
* heat
* natural compounds i.e. chili
* cell rupture

why does surgery hurt after patient wakes?

* inflammation
* actual tissue damage

__Described in terms of such damage__ (old definition of pain)

* phrase is here because of neuropathic pain (nerve damage; people with nerve damage still experience pain w/o actually having tissue damage)
* nerves are not tissue damage

neuropathic pain

pain due to damage of the nervous system (usually peripheral nervous system)

tissue damage

damage to skin, muscle, organs or joints (nerves not included)

issue with the old definition of pain

* The issue with the old definition → **“described” implies verbal communication.**
* implies babies don’t feel pain, mutes don’t feel pain

pain is not

* somatosensation (touch)
* emotional pain (exceptions)
* social rejection causes inflammation → example of cyber ball
* social suffering (via cyber ball or rejection by romantic partner) activates “pain matrix“
* acetaminophen (administered to those who just experiences social rejection) reduces social pain and fear of death
* pain is not suffering
* pain is not disability
* pain behaviour (moaning, stooping, etc.)
* nociception (workings of the nervous system that eventually lead to the perception of pain)

difference between anesthesia vs. analgesia

o   Anesthesia (local): mouth frozen for a tooth extraction, no sensation felt (no touch, no vibration, no cold, no heat) \*no sensory information transmitted\*

o   Analgesia refers to pain, specifically

o   All anesthetics are analgesics, but the opposite isn’t true

nociception

working of nervous system that eventually lead to the notion of pain/ firing of neurons => the biology behind the pain; pain is the sensation at the end

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Nociception refers to the central nervous system (CNS) and peripheral nervous system (PNS) processing of noxious stimuli which activate nociceptors and their pathways.

thermal grill

* example of how perception of pain can be created in the brain w/o the actual presence of noxious stimulants
* each tube either cool or warm temperatured water
* hand over multiple tubes causes pain

Fordyce’s behavioural model of pain

pain behavior reflects the influence of three important factors:


1. suffering
2. pain
3. nociception

three types of pain

1. acute pain
2. tonic pain
3. chronic pain

acute pain

seconds to minutes

o   Acute pain enables us to avoid tissue damage or minimize it

o   It’s a teaching signal (allows to learn physical limitations of limbs)

tonic pain

hours to weeks

o   To enforce us to rest i.e. when we break a bone

o   Casts enforces mobility

o   DOMS: delayed onset muscle soreness (pain after workout)

chronic pain

o   Classic reason: no reason; it’s pathological => something has gone wrong with your body. Like a broken smoke alarm that is stuck in the on position

congenital insensitivity to pain

no feeling of pain

* short life span
* Most common cause of death: keep fracturing hip over and over, which increases the likelihood of infection (sepsis)

congenital insensitivity to pain with anhidrosis

anhidrosis = inability to sweat

pain and the lumping vs splitting problem

* lumping and splitting are both problematic


* Splitting is complicated and so is lumping (we don’t know if pain is multiple things or whether its one big lump)

how long does an individual have to experience pain in order for it to be considered chronic?

3 months

etiology

the underlying cause of a disease

etiology of pain

\*reminder\*

nociceptive pain: pain from tissue damage

what is nociceptive pain

* not neuropathic (no nerve damage)


* inflammation

2 types of ^^neuropathic^^ pain

1. damage to the nerves of the central nervous system (^^CNS^^)
2. damage to the nerves of the peripheral nervous system (^^PNS^^)

central nervous system

CNS is composed of the brain and spinal cord

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peripheral nervous system

PNS is composed of all the nerves branching out from the spinal cord and extending to the different body parts

4 types of chronic pain

1. neuropathic
2. nociceptive
3. visceral
4. mixed

causes of acute pain

1. injury
2. post-operative flare

different ways to split up pain

1. time duration (acute vs tonic vs chronic)
2. causes of pain
3. pain location

cause of nociceptive chronic pain

* rheumatoid arthritis
* osteoarthritis (more common)

causes of central neuropathic pain

* post-stroke
* multiple sclerosis
* spinal cord injury
* migraine (most common)
* HIV related pain

causes of peripheral neuropathic pain

* post-herpetic neuralgia
* diabetic neuropathy

causes of visceral chronic pain

1. internal organ
2. pancreatitis
3. inflammatory bowel syndrome (IBS)

causes of mixed chronic pain

* lower back (most common)
* cancer
* fibromyalgia

Pain etiologies (Costigan et al)

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4 types of pain in Costigan’s pain etiologies

1. nociceptive (no nervous system lesion + no inflammation i.e. light punch)
2. inflammatory (active inflammation)
3. dysfunctional ()
4. neuropathic (nervous system lesion)

the 4 different symptom profile in Costigan’s study

1. no stimulus
2. non-noxious stimulus
3. noxious stimulus
4. highly noxious stimulus