Context The identification of modifiable predeployment vulnerability factors that increase the risk of combat stress reactions among soldiers once deployed to a war zone offers significant potential for the prevention of posttraumatic stress disorder (PTSD) and other combat-related stress disorders. Adults with anxiety disorders display heightened emotional reactivity to a single inhalation of 35% carbon dioxide (CO2); however, data investigating prospective linkages between emotional reactivity to CO2 and susceptibility to war-zone stress reactions are lacking.
Objective To investigate the association of soldiers' predeployment emotional reactivity to 35% CO2 challenge with several indices of subsequent war-zone stress symptoms assessed monthly while deployed in Iraq.
Design, Setting, and Participants Prospective cohort study of 158 soldiers with no history of deployment to a war zone were recruited from the Texas Combat Stress Risk Study between April 2, 2007, and August 28, 2009.
Main Outcome Measures Multilevel regression models were used to investigate the association between emotional reactivity to 35% CO2 challenge (assessed before deployment) and soldiers' reported symptoms of general anxiety/stress, PTSD, and depression while deployed to Iraq.
Results Growth curves of PTSD, depression, and general anxiety/stress symptoms showed a significant curvilinear relationship during the 16-month deployment period. War-zone stressors reported in theater were associated with symptoms of general anxiety/stress, PTSD, and depression. Consistent with the prediction, soldiers' emotional reactivity to a single inhalation of 35% CO2-enriched air before deployment significantly potentiated the effects of war-zone stressors on the subsequent development of PTSD symptoms and general anxiety/stress symptoms but not on the development of depression, even after accounting for the effects of trait anxiety and the presence of past or current Axis I mental disorders.
Conclusion Soldiers' emotional reactivity to a 35% CO2 challenge may serve as a vulnerability factor for increasing soldiers' risk for PTSD and general anxiety/stress symptoms in response to war-zone stressors.