Results from a study at the University of Texas at Austin indicate that how a person responds to inhaling carbon dioxide (CO2) could predict how well he or she will cope with some of the stresses of combat. The study follows in the steps of prior research that examined emotional responsiveness to CO2 as a litmus test for disordered anxiety. The university study engaged 158 soldiers who had never been deployed. The soldiers were exposed to 35 percent CO2 enhanced air and their responses were recorded. Reactions varied. About one-third of the soldiers showed zero emotional reaction to the inhalation although 99 percent reported feeling dizzy and faint as a result. But 11 percent of the soldiers said they felt alarmed and panicky when breathing in the enriched air. During their 16-month deployment to Iraq, all of the soldiers were asked to complete monthly reports on stress factors as well as symptoms related to depression, anxiety and post-traumatic stress disorder. By the end of the study, researchers found that soldiers with the greatest degree of emotional reactivity to CO2 were also those who reported the highest level of PTSD symptoms during duty. Emotional CO2 responsiveness did not appear to predict anxiety or depression during deployment. "The highest CO2 reactors were most likely to experience an amplification effect related to war zone anxiety, including more stress that was experienced and the greater the chance for PTSD in relation to the war zone stressors," said lead author Michael J. Telch, PhD, of the University of Texas at Austin. "This evidence supports our hypothesis that an emotional response to CO2 really could potentiate the effects of war zone stressors and the subsequent emergence of PTSD anxiety symptoms, but not depression." It could be that the CO2 test reveals a person\u2019s inherent sensitivity to their own suffocation alarm. In other words, some people are biologically more anxious under stress and the CO2 test reveals this. If the person becomes panicked when there is a stress and he or she begins to hyperventilate, the kind of stress combat is likely to cause, they may become more anxious in the same situation compared to the person whose body does not react as severely to tightness of breath.