Carbon Dioxide Challenge May Predict PTSD Risk
Carbon Dioxide Challenge May Predict PTSD Risk
LA JOLLA, California — A panicked reaction to a single inhalation of 35% carbon dioxide (CO2) may predict risk for anxiety and subsequent posttraumatic stress disorder (PTSD) in military personnel, new research suggests.
"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."
The findings were presented here at the Anxiety and Depression Association of America (ADAA) 33rd Annual Conference.
Although an emotional reaction to CO2 has previously been shown to be associated with a greater risk for anxiety disorders, the role of CO2 reactivity in war zone anxiety and the development of PTSD has not been well evaluated.
For the longitudinal study, 158 soldiers were administered a single inhalation of 35% CO2-enriched air prior to a 16-month deployment in Iraq. The soldiers had not previously been deployed in a war zone.
Suffocation Alarm?
Nearly all (99%) of the soldiers experienced the most common symptom of dizziness and feeling faint related to the inhalation. However, only 11% experienced panic and alarm. Thirty-two percent had no response to the inhalation.
All soldiers were then asked to submit Web-based monthly reports of combat stressors, such as incoming fire, along with PTSD symptoms, depression, and anxiety symptoms during their deployment.
Soldiers exhibiting greater anxiety in response to the CO2 inhalation were among those most likely to experience PTSD related to the combat stressors.
The CO2 reaction was not found to be associated with generalized anxiety symptoms or depression. However, after adjustment for trait anxiety and comorbidities, soldiers exhibiting high CO2 reactivity and exposure to more combat stressors in a given month showed a greater risk for PTSD and general anxiety symptoms.
Several possible mechanisms could explain the association between the CO2 response and subsequent anxiety or panic, Dr. Telch said.
"One possibility is that CO2 reactivity is a behavioral marker for a neurobiological hypersensitivity of one's suffocation alarm, which could be triggered under times of heightened stress exposure," he added.
"In addition, reactivity to CO2 may function more as a specific vulnerability to respond fearfully to respiratory distress. If you're the type of person who has a fear of a shortness of breath, then it only makes sense that in a war zone environment, you would start to hyperventilate and feel that suffocating sensation, and it could hence trigger an alarm reaction," said Dr. Telch.
Potential Implications
The findings add to the growing understanding of the underpinnings of anxiety, said psychologist Sonya B. Norman, PhD, an assistant professor with the University of California, San Diego, School of Medicine.
"There has been research showing people with highly elevated heart rates or high pain after the stress may be more likely to experience PTSD, and there are some other predictors, but we don't really know what to do with them yet," Dr. Norman said.
"But I think this study is part of a really important body of research because any evidence we can get to help with early intervention, we could potentially prevent a great deal of suffering and cost to society."
The idea of a biological means for assessing the risk for PTSD could be particularly valuable in a military setting, said Spencer Eth, MD, a professor of psychiatry at the University of Miami, in Florida.
"It would be very nice if there could be a way to identify soldiers who are at risk for PTSD before they are deployed," he told Medscape Medical News.
"There have been susceptibility and vulnerability factors that have been identified, but not biologic factors."
Although the challenge itself could be easily implemented, its use would be subject to a host of ethical issues, he noted.
"It's not a hard or dangerous procedure, so in terms of the battery of exams and inoculations that soldiers already go through, it wouldn't be hard to add this to the menu. The question is, what do you do with the data once you get it?"
"Would it mean you are not going to deploy a soldier to a war zone? Would it mean he will be discharged? It raises some interesting clinical and ethical questions."
Dr. Telch, Dr. Norman, and Dr. Eth report no relevant financial relationships.
Anxiety and Depression Association of America (ADAA) 33rd Annual Conference. Abstract 493. Presented April 6, 2013.
LA JOLLA, California — A panicked reaction to a single inhalation of 35% carbon dioxide (CO2) may predict risk for anxiety and subsequent posttraumatic stress disorder (PTSD) in military personnel, new research suggests.
"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."
The findings were presented here at the Anxiety and Depression Association of America (ADAA) 33rd Annual Conference.
Although an emotional reaction to CO2 has previously been shown to be associated with a greater risk for anxiety disorders, the role of CO2 reactivity in war zone anxiety and the development of PTSD has not been well evaluated.
For the longitudinal study, 158 soldiers were administered a single inhalation of 35% CO2-enriched air prior to a 16-month deployment in Iraq. The soldiers had not previously been deployed in a war zone.
Suffocation Alarm?
Nearly all (99%) of the soldiers experienced the most common symptom of dizziness and feeling faint related to the inhalation. However, only 11% experienced panic and alarm. Thirty-two percent had no response to the inhalation.
All soldiers were then asked to submit Web-based monthly reports of combat stressors, such as incoming fire, along with PTSD symptoms, depression, and anxiety symptoms during their deployment.
Soldiers exhibiting greater anxiety in response to the CO2 inhalation were among those most likely to experience PTSD related to the combat stressors.
The CO2 reaction was not found to be associated with generalized anxiety symptoms or depression. However, after adjustment for trait anxiety and comorbidities, soldiers exhibiting high CO2 reactivity and exposure to more combat stressors in a given month showed a greater risk for PTSD and general anxiety symptoms.
Several possible mechanisms could explain the association between the CO2 response and subsequent anxiety or panic, Dr. Telch said.
"One possibility is that CO2 reactivity is a behavioral marker for a neurobiological hypersensitivity of one's suffocation alarm, which could be triggered under times of heightened stress exposure," he added.
"In addition, reactivity to CO2 may function more as a specific vulnerability to respond fearfully to respiratory distress. If you're the type of person who has a fear of a shortness of breath, then it only makes sense that in a war zone environment, you would start to hyperventilate and feel that suffocating sensation, and it could hence trigger an alarm reaction," said Dr. Telch.
Potential Implications
The findings add to the growing understanding of the underpinnings of anxiety, said psychologist Sonya B. Norman, PhD, an assistant professor with the University of California, San Diego, School of Medicine.
"There has been research showing people with highly elevated heart rates or high pain after the stress may be more likely to experience PTSD, and there are some other predictors, but we don't really know what to do with them yet," Dr. Norman said.
"But I think this study is part of a really important body of research because any evidence we can get to help with early intervention, we could potentially prevent a great deal of suffering and cost to society."
The idea of a biological means for assessing the risk for PTSD could be particularly valuable in a military setting, said Spencer Eth, MD, a professor of psychiatry at the University of Miami, in Florida.
"It would be very nice if there could be a way to identify soldiers who are at risk for PTSD before they are deployed," he told Medscape Medical News.
"There have been susceptibility and vulnerability factors that have been identified, but not biologic factors."
Although the challenge itself could be easily implemented, its use would be subject to a host of ethical issues, he noted.
"It's not a hard or dangerous procedure, so in terms of the battery of exams and inoculations that soldiers already go through, it wouldn't be hard to add this to the menu. The question is, what do you do with the data once you get it?"
"Would it mean you are not going to deploy a soldier to a war zone? Would it mean he will be discharged? It raises some interesting clinical and ethical questions."
Dr. Telch, Dr. Norman, and Dr. Eth report no relevant financial relationships.
Anxiety and Depression Association of America (ADAA) 33rd Annual Conference. Abstract 493. Presented April 6, 2013.
Source...