Midterm 2 Flashcards
Pain Threshold and Tolerance
Threshold: when you feel pain
Tolerance: when you can’t take it anymore
Measuring this is still subjective because actually measuring motivation (doesn’t tell us about their actual pain)
Rating scales
- VRS Verbal Intensity scale
- VAS Visual analogue scale
- NRS Numeric pain intensity scale
- Faces scale
VAS better than NRS because in NRS you remember the previous number you used
FACES scales are problematic because they start happy instead of neutral
Problems with these scales: hard to say when we are measuring, context matters (could be in pissy mood), “pegs” people don’t understand the worse and use 10 too much (to send a message) (people have different ideas of what worse pain looks like), is is useful for WITHIN but not BETWEEN patients.
We always imagine pain as worse than it really is
Clinical pain score
Combines:
- ongoing pain
- allodynia
- hyperalgesia
- functionning
The score you give actually is a lot of things that have nothing to do with what we assign the score to (not just nociceptors)
FACS
By Paul Ekman
Facial Action Coding System
Encodes for facial muscle movements associated with pain expression
Melzack
Came up with:
- Pain descriptors by intensity
- Peak intensity diagram (sprained ankle to causalgia)
- MPQ McGill pain questionnaire (20 categories, pick 1 of each. Splitting attempt between inflammatory/neuropathic). Made a shorter version with descriptors + PPI + visual analog
DN4
Short pain questionnaire
10 questions, 1 point per question, need 6+ to be neuropathic pain
Owestry Disability Index
Test if your pills are working
Come up with a disability score
10 sections
Pain Catastrophizing
Catastrophizing = rumination + magnification + helplessness
High catastrophizing = more likely to get chronic pain, and to not get better
WOMAC questionnaire (3 sections)
Western and MacMaster
3 sections: pain, stiffness, disability
QST Quantitive Sensory Testing
Detect threshold and tolerance
Use mechanical/thermal stimuli and have method to measure it
Psychophysics: go up and down around threshold until 50% chance to find exact
German way: do series of QST, express patient values in z-scores, how many SD away you are from average. Try and split patients into categories based on symptoms ( need an average and everyone trained the exact same)
Biomarkers of pain
Don’t actually have any but:
tissue damage, cardiovascular (heart rate, BP), stress (cortisol), neural (EEG, imaging (best biomarker)), chemical (don’t work), molecular (DNA variant, mRNA levels) (don’t work because DNA doesn’t change with pain, and mRNA would need spinal tissue but can’t)
fMRI as biomarker?
YES:
- only one accepted
- differences in brain activity (brain agrees with the ratings so don’t need ratings)
NO:
- Found big overlap with imagined/pretend pain suggesting brain can be tricked, and so people could fake it
Why we use animals
Pain uses rats
Science in general uses mice
- Causation experiments (can’t in humans)
- can lesion any tissue
- can record or extract any tissue
- can give unapproved drugs
- can alter gene expression
- can be precise at turning neurons on/off
- can control environmental pre-exposures
- cheaper, faster, less regulated
- they don’t have fake motivations (ie macho)
Challenges to using animals
- wrong species
- they don’t talk
- they’re prey (could hide pain)
- lot tougher than we are (stoic compared to us)
- ethical issues (no consent)
Different animal ethics
Deontological: rule is the only to decide if something is right or wrong (and animal research is against the consent rules)
Consequentialist (utilitarianism): end justify the means
Thermal Assays
- Hot plate test: wait for reaction (lick paw, jump off,…) and stop times to compare thresholds. 50 degrees, no pain at first cause takes time for skin temperature to adjust. This measures conscious decision
- Tail-Flick test: measure threshold with time to flick out of water, this measures spinal reflex
- Hargreaves test: radiant heat paw withdrawal, toe-toaster. Apply heat on either side
Mechanical Assays
- Von Frey Filaments: apply to different body parts. Not sure if measure pain or annoyance
- Randall-selitto test: pinch paw, measure how much pressure it takes for them to pull away
- Weight bearing, grip force, gait changes,…
Chemical assays
- Writhing test: give chemical and measure how many belly contractions
- Formalin test: can measure up to one hour (early acute phase / interphase quiescent period / late tonic phase)
Inflammatory Assays
Inject inflammogens and then do mechanical or thermal stimulus. Can cause allodynia and hyperalgesia
Neuropathic assays
Surgery, cut a nerve in the foot and then measure thermal or mechanical
Axotomy (complete denervation) vs Partial denervation. Measure Autotomy (bite off own foot) when feels like phantom limb and count how many phallenges left in the morning
3 big criticisms for Status Quo (animal modelling)
- Reflexive vs Conditioned measures: need to condition the animal to pain to avoid reflexes. Behavior could be caused by personality or thirst rather than just pain. Use motivational conflict (inflame cheek and have to press cheek to get reward solution). Use Conditioned place preference
- Pain-affected measures: ignore comorbidities (sleep, anxiety, attention) that develop after some time.
- Symptom epidemiology vs dependent measure use: we are not measuring the main problem in humans (least humans complain about is thermal but what we measure most in animals)
Individual differences in pain perception
Real question isn’t what causes pain but why pain in some people but not others?
Only 7% of surgical patients get chronic post-surgical pain (which is a lot of people still)
Morphine does for sufficient analegesia is 2-80mg/kg which is a 40 fold (huge difference)
Reasons:
- Organismic: nature, about you, genetic background, sex, age, psychological traits,…
- Environmental: nurture, what happens to you, past experiences, gender, psychological states, diet,…
Biopsychosocial model
Disease better explained by interplay of 3:
biologival, sociocultural, psychological