cardiovascular stress testing in the laboratory. good general reference kamarck & lovallo (2003)...
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Cardiovascular Stress Testing in the
Laboratory
Good general reference
Kamarck & Lovallo (2003)
Psychosomatic Medicine, 65, 9-21
Discusses;
CV reactivity stability over time
CV reactivity over different tasks
Types of tasks that are useful
Laboratory – Real life
Ideally we would measure cardiovascular reactions to stress in real life…..
However, this approach come with a number of problems
1.How do we know when people will experience stress?
2.What if we choose people under a lot of stress (e.g. caregivers)?
3.Will chronically stressed people be stressed all the time?
4.Why not recruit people who were stressed in the past?
5.Most importantly, CV measures still quite difficult to use in the field
•Portable or “ambulatory” BP and HR monitors
•Often bulky
•Visible to others
•For BP usually record periodically not continuously
Best option for real world events;
• Events that are stressful but not too upsetting
• Events that occur at predictable times
E.g. exams, driving tests, etc
• Standardised / timed
However, still problems;
• Limited in measures we can use
e.g. blood pressure cuff
• Critical not to distract people
• Still lots of confounds – e.g. smoking, caffeine
So what are your options?
•Aim -> Look at CV reactivity during stress
•Use an artificial laboratory stress task
Advantages;
• Complete experimental control
• Standardisation
• Task mixing (if interested in effects of stress on X)
• Can make sure CV measures working OK
What kind of tasks?
• Ethical considerations
• Demanding not traumatic
Ten most common lab stressors (in no order)
Reaction Time tasks
Respond to tone as fast as possible
Simple or choice versions
Public Speaking
Short period to prepare a speech
Typically fake job talk, defendant in court, etc
Audience / video camera
Mirror Tracing
Trace a complex shape
Using only mirror image
Usually distance / number correct in time allowed
Mental Arithmetic
Either backwards counting with large numbers
Or mentally solving rapidly presented maths problems
Stroop Task
Colour – word task
Name ink colours
Speeded test
RED
BLUE
YELLOW
GREEN
Cold Pressor Task
Hand /foot in iced water
1-2 mins (as long as possible)
Often painful
Distress Recall
Relive stressful event
Usually frustrating past events
Describing all the details
Video games
Tracking a target
Responding quickly
Parts requiring good hand-eye co-ordination
Raven’s Matrices
Visual logic puzzles
Must choose next in series
Often timed
Distressing Films
Passively watching nasty films
Car crashes, autopsy, childbirth, industrial accidents, horror films, etc
One of the best lab tasks
Combines public speaking and mental arithmatic;
The ‘Trier Social Stress Test’
Kirschbaum, Pirke, & Hellhammer (1993)
• Trier Social Stress Test
Part 1
Prepare
“Imagine you’ve applied for a job as a psychologist. In 5-10 minutes you will give a speech to the selection committee about why you would be good for this job.
You must speak for 5 minutes without notes and you will be audio and video-taped so we can analyse your body language.”
• Trier Social Stress Test
Part 2
Speech
‘The committee’ – 2-3 people
Microphone and video camera (switched on in silence).
Begin speech
Silence for >20 secs = “you still have time, please continue”
Further silence = questions
• Trier Social Stress Test
Part 3
Counting
“Thank you – we will now move onto a second task”
Count backwards (out loud) from 1687 in 13s
Quickly & accurately as possible
Mistake= start again
Committee still present
Camera / microphone still on
•Control task depends on your measure (BP, HR, cortisol, etc)
•Cortisol – quiet period at the start (before they know the nature of the task)
•BP/HR – quiet task at end (after a break) with similar demands but no stress
Debrief
•Participants told no recordings made
•Told task designed to elicit stress response and committee instructed to appear formal / unfriendly
Data from the lab (n=24)
BPM
50
60
70
80
90
100
110
120
130
Preparation Speech Maths Control
Individuals Average
BPM
50
60
70
80
90
100
110
120
130
Preparation Speech Maths Control
Data from the lab (n=24)
BPM
50
60
70
80
90
100
110
120
130
Preparation Speech Maths Control
Individuals Average
BPM
80
90
100
Preparation Speech Maths Control
Data from the lab (n=1)
High Speech Reactor High Maths Reactor
BPM
80
90
100
110
120
Preparation Speech Maths Control
BPM
80
90
100
110
120
Preparation Speech Maths Control
Data from the lab (n=1)
Non-Reactor
BPM
80
90
100
110
120
Preparation Speech Maths Control
The Trier task has been shown to elicit significant stress responses in
•Both males and females•Both children and adults•Both younger and older adults
•Kudielka, Buske-Kirschbaum, Hellhammer, & Kirschbaum. (2004) Psychoneuroendocrinology, 29, 83-98.
•NB – This paper is quite complicated – the main point to note is that they showed the Trier’s effectiveness in both genders, and all age groups.
Trier task = most effective laboratory task for inducing stress reactions (measured with cortisol)
Dickerson, S.S. & Kemeny, M.E. (2004) Psychological Bulletin, 130, 355-391 – READ ONLY ABSTRACT & DISCUSSION
Dickerson & Kemeny (2004) conclude Trier type tasks = effective because they include;
1.Social-evaluative threat (when other people may make negative judgements about the participant, or when poor performance would reveal a lack of ability)
2.Uncontrollability (when participant’s best efforts are not sufficient to prevent negative outcome)
To understand these last 2 references – need to know what the “HPA axis” is
HPA axis = Hypothalamic Pituitary-Adrenal Axis
Major part of the neuroendocrine system which controls the release of stress hormones
Under Stress, the HPA axis;
•Hypothalamus produces corticotrophin releasing hormone (CRH)
•CRH causes the Pituitary gland to release adrenocorticotrophin (ACTH)
•ACTH causes the Adrenal glands to release epinephrine (adrenaline), norepinephrine (noradrenaline) and cortisol (amongst other things)
These stress hormones help the body respond to threat by increasing HR and BP, diverting blood to muscles, speeding reaction time, releasing sugar to use as fuel, etc.
Worth remembering;
•Lab tasks aren’t perfect;
•Artificial
•Therefore lab reactivity may not relate directly to reactivity in real life (DJ to discuss)
In Summary
Measuring stress during real life events = sacrificing experimental control
Measuring stress in the laboratory = sacrificing ecological validity
Best strategy
•Combine both lab and field measures
•Use lab tasks with ecologically valid characteristics like the Trier
