Key study: Telch and Harrington (2011)

Telch and Harrington (2011) wanted to see the role that one's sense of control would play in panic attacks.

For the study, they used a sample of 79 introductory psychology students, 45 men and 34 women between the ages of 18 and 29, who participated for partial class credit at the University of Texas at Austin. None of the participants had a history of panic attacks.

The participants were labeled as "high" or "low" risk for panic attacks based on their scores on the Anxiety Sensitivity test. The test measures their self-reported anxiety as a response to physical symptoms - eg. heart beating rapidly or feeling faint.

The study was a 2 x 2 factorial design.  That means that there were two independent variables manipulated by the researchers. First, participants for both the high and the low anxiety groups were randomly allocated to either the "relaxation" group or the "arousal" group. In each of those groups, participants would be asked to breathe in a gas. In one case, they breathed room air and in the other, they breathed air with a 35% concentration of carbon dioxide.  Each group was exposed to both gasses.  The experiment was counter-balanced.

In the relaxation condition, they were read the same instructions as in the other condition, except they were told that they may experience various physical feelings of relaxation, such as lightheadedness, a slight tingling in the extremities, or a sense of floating or being detached from your body.

The arousal condition was told that they may experience rapid breathing, heart rate acceleration, sweating, and dizziness or lightheadedness.

They were told to breathe in and then hold their breath for five seconds while the experimenter counted - and then exhale.  They were then asked to fill in two forms - the API and SUDS.

The API is a 17-item inventory for assessing symptoms associated with panic attacks.  Examples include, “Do you feel faint?”, “Are you afraid of dying?”, “Do you feel detached from part or all of your body?”, and “Do you have palpitations?”

The SUDS is a Likert scale ranging from 0 (not disturbed at all) to 100 (the worst imaginable experience) used to measure self-reported fear, anxiety, and breathlessness. 

In addition, during the experiment, the participants' heart rate was monitored through the use of a wrist monitor microcomputer.

Figure 1 Percentage of panic attacks (Telch and Harrington, 2011)

You can see in the graph on the left that when arousal was expected - that is, the individuals could prepare for the feelings of arousal from the carbon dioxide, in both the low and the high anxiety participants the frequency of panic symptoms was relatively low.  However, in the case where they were expecting to relax and were then experiencing unexpected symptoms, those with high levels of anxiety started to panic.  It was the lack of control over their situation which is believed to have led to their panic response.