by Michael D. Anestis, M.S.
Like any statistical relationship, the connection between experiencing traumatic events and developing post-traumatic stress disorder (PTSD) is not simple - after all, not everyone who experiences something traumatic goes on to experience PTSD. Because of this, scientists spend a lot of time attempting to understand which individuals are most vulnerable to such reactions.
A number of months ago, I wrote a PBB article explaining what is referred to as the diathesis-stress model of mental illness (click here to read about this model). Essentially, what this model says is that some individuals have a vulnerability (diathesis) to a mental illness or set of mental illnesses and that, in the face of the right type/amount of life stress, they are more likely to develop that condition(s). So, for instance, an individual whose parents were both depressed might inherit a genetic vulnerability to mood disorders and, after being fired from is job, may be more vulnerable to developing depression than a colleague with no such genetic vulnerability. The diathesis-stress model thus helps us to understand why two individuals who experience the same thing might not have the same response. It's not that everyone with a genetic vulnerability eventually develops a mental illness or that people without that vulnerability never do. It's simply that the vulnerability increases the probability of that outcome and, as such, helps us understand who is at greater risk.
This brings us back to today's topic. Researchers recognize that not everyone who experiences a traumatic event goes on to develop PTSD, so they want to understand what vulnerabilities make the outcome more likely for particular individuals. In a study published in the most recent issue of the Journal of Abnormal Psychology, Grant Marshall, Jeremy Miles, and Sherry Stewart examined the degree to which anxiety sensitivity is linked to the development of PTSD. You might remember from earlier articles on the topic that anxiety sensitivity is defined as the tendency to fear anxiety and the sensations associated with anxiety (click here for an article on the definition of anxiety sensitivity). In other words, it is not simply that the individual is more anxious but that he or she is more anxious about experiencing anxiety. For some, this is primarily displayed in a fear that visible symptoms of anxiety (e.g., sweating) will result in criticism and judgment from others. For others, this is primarily displayed in a tendency to misinterpret normative bodily experiences (e.g., increased heart rate after sprinting to catch a flight) as catastrophic (e.g., a sign of an impending heart attack). For others, this is primarily displayed as a tendency to believe that the symptoms of anxiety are a sign that he or she is losing control and/or going "crazy."
The authors of this study wanted to test a number of different theories about the relationship between anxiety sensitivity and PTSD symptoms. Specifically, they sought to see which of the following theories is best supported by the data:
- Anxiety sensitivity increases the likelihood that an individual will develop PTSD symptoms after a traumatic event.
- PTSD symptoms increase the likelihood that an individual will develop increased anxiety sensitivity
- Anxiety sensitivity and PTSD both influence one another, such that elevations in one predict subsequent elevations in the other
Marshall and his colleagues are not the first to look at these variables together, but their study offered an opportunity to examine this relationship more closely. 667 survivors of severe physical injuries were assessed immediately post-injury, six months later, and twelve months later. This allowed the authors to check initial levels of both anxiety sensitivity and PTSD symptoms and to track change over a significant amount of time. In many earlier studies, initial PTSD symptoms were not measured and/or measurements were only taken at one time point, which makes it impossible to determine which variable was present first.
What they found was very interesting, although also quite complicated. As it turns out, data indicated that the third theory listed above is the more accurate. Regardless of the severity of an individual's PTSD symptoms immediately following the injury, high levels of anxiety sensitivity predicted increases in PTSD symptoms six months later. Similarly, regardless of PTSD symptom severity at 6-month follow-up, high levels of anxiety sensitivity six months after the injury predicted increases in PTSD symptoms at 12-month follow-up. This sounds simple enough, but it does not end there. Regardless of an individual's level of anxiety sensitivity immediately following the injury, high levels of PTSD symptoms at that point predicted increased anxiety sensitivity six months later. Similarly, regardless of anxiety sensitivity levels at 6-month follow-up, high levels of PTSD symptoms at that point predicted increases in anxiety sensitivity at 12-month follow-up.
The answer, it seems, is that neither the chicken nor the egg always comes first. If an individual is experiencing PTSD symptoms, they are likely to subsequently develop higher levels of anxiety sensitivity. In this sense, the continuous presence of anxiety symptoms due to PTSD might make the individual increasingly sensitive to and uncomfortable with such sensations, so what they were previously able to dismiss as a normal experience becomes more likely to be seen as troubling and aversive. Similarly, if an individual demonstrates initially high levels of anxiety sensitivity, they appear more likely to develop PTSD symptoms in response to a traumatic physical injury. In this sense, anxiety sensitivity appears to serve as one vulnerability to PTSD and a partial explanation as to why some individuals develop PTSD after experiencing trauma and others do not.
These findings are important for a number of reasons. First of all, they highlight that the relationship between variables is not always completely straight forward. Sometimes things are dynamic and bi-directional and, as such, it is important not to oversimplify how we think about these things. Secondly, they highlight the fact that anxiety sensitivity is a potentially strong target for psychological interventions. When Reiss and McNally (1985) first defined this construct, they indicated that they believed it was a stable character trait, resistant to change if it is even subject to change at all. These results, however, indicate otherwise. As such, it appears that treatments that specifically target anxiety sensitivity might offer a substantial amount of promise. Early research on this point is proving to be quite useful. Wald and Taylor (2007) demonstrated that interoceptive exposure - the treatment of choice for panic disorder - can, in fact, reduce anxiety sensitivity. Additionally, multiple research teams have demonstrated that increased levels of physical exercise can also reduce anxiety sensitivity levels (Broman-Fulks & Storey, 2008; Smits et al., 2008).
So, the overall picture presented here by Marshall and colleagues is that, when an individual is fearful of the experience of anxiety and anxiety-related sensations, he or she is more likely to develop PTSD symptoms in response to traumatic physical injuries. Similarly, if an individual develops PTSD symptoms in response to such injuries, he or she is likely to see an increase in their level of anxiety sensitivity. Because anxiety sensitivity appears to change over time in response to environmental events and symptoms of mental illness, it seems to be a valuable target for treatments. Fortunately, research is underway to examine this point and early results indicate that we can, in fact, directly impact this vulnerability both through psychological interventions (e.g., interoceptive exposure) and simple lifestyle changes (e.g., increase physical exercises).
You might recall an earlier PBB article that discussed a fairly similar set of findings by a friend of mine - Katie McLaughlin of Yale University - and her colleague, Mark Hatzenbuehler (click here to read the article). It is not at all uncommon for similar studies to emerge within a close period of time, as different researchers attempt to approach the same issue from slightly different perspectives. Remember, one single study does not tell us everything we need to know about a particular phenomenon, so in order to increase our confidence, we need to see results replicated a number of times by people who do not work with each other. In this sense, the somewhat parallel findings in these two studies offer us a reason to believe that the findings discussed today represent a true relationship and a valuable piece of information with respect to developing treatments for PTSD and understanding who is most vulnerable to developing such symptoms in the first place.
If you would like to learn more about PTSD and its treatment, we recommend the following items, each of which can be found in our online store for scientifically-based psychological resources:
- Prolonged Exposure Therapy for PTSD: Emotional Processing of Traumatic Experiences Therapist Guide by Edna Foa, Elizabeth Hembree, and Barbara Rothbaum
- Cognitive Processing Therapy for Rape Victims: A Treatment Manual by Patricia Resick and Monica Schnicke
- Reclaiming Your Life from a Traumatic Experience: A Prolonged Exposure Treatment Program Workbook by Barbara Rothbaum, Edna Foa, and Elizabeth Hembree