Krantz et al - Stress and the Heart
Method: In a laboratory experiment, 39 participants did one of three stress-inducing tasks (a maths test, a Stroop test and public speaking). Their blood pressure and the extent to which the vessels around their heart contracted (low, medium or high myocardial ischaemia) was measured. Participants were instructed not to take any prescribed heart medication prior to the study.
Results: Participants with the greatest myocardial ischaemia showed the highest increases in blood pressure. A small number of participants who showed mild or no mycardial ischaemia only had a very moderate increase in blood pressure.
Conclusion: Stress may have a direct influence on aspects of body functioning, making cardiovascular disorders more likely.
Evaluation: Although the effects were clearly linked to stress, it can't be said that one causes the other. Also it wasn't shown whether the effects also occur at other times. They might sometimes happen even if the person feels relaxed - and therefore couldn't just be linked to feeling stressed. Not everybody showed the same reaction, which suggests that individual differences between the participants may have played a role. The ecological validity of the study was reduces because it took place under laboratory conditions that weren't fully representative.
Brady et al - Stress and the Development of Ulcers
Method: Monkeys were put in pairs and given electric shocks every 20 seconds for 6 hour sessions. One monkey of each pair (the 'executive') could push a lever to postpone each shock. The other could not delay them.
Results: The 'executive' monkeys were more likely to develop illness (ulcers) and later die.
Conclusion: The illnedd and death was not due to the shocks but due to the stress that the executives felt in trying to avoid them. In the long term, this stress reduced the immune system's ability to fight illness.
Evaluation: The experiment has ethical issues - the experiment was very cruel and would not be allowed today. Also, we can't generalise results from monkeys to humans. Furthermore, we know that people with little control over their own lives (such as those with low-level jobs and the long-term unemployed), can experience high levels of stress, which this research cannot explain.
Kiecolt-Glaser et al- Stress and Wound Healing
Method: In a study with an independent measures design, a punch biopsy was used to create a small wound on the arms of 13 women who cared for relatives with Alzheimer's disease (a very stressful responsibility). A control group of 13 people also took part.
Results: Wound healing took an average of 9 days longer for the carers than those in the control group
Conclusion: Long-term stress impairs the effectiveness of the immune system to heal wounds.
Evaluation: Sweeney also found that people caring for relatives with dementia took longer than a control group to heal their wounds. However, for both studies the two groups may have varied in other ways apart from the stress of being a carer. The effects on the carers could be due to poor diet, lack of sleep, etc, and not just the stress they experienced. The study only contained a small number of participants - for more reliable results it should be repeated with a larger number.