You may qualify for this study if you meet the following criteria.

Key Criteria:

• Ages 18+
• A primary DSM-5 diagnosis of panic disorder (with or without an agoraphobia diagnosis), social anxiety disorder, obsessive compulsive disorder, or post traumatic stress disorder (we will target equal representation across these disorders)
• Score of 8 or greater on the Overall Anxiety Severity and Impairment Scale
• No lifetime history of bipolar or psychotic disorders, substance abuse or dependence (other than nicotine) or eating disorder in the past 6 months; organic brain syndrome, mental retardation or other potentially interfering cognitive dysfunction
• No suicidal behaviors within the past 6 months
• No medical conditions contraindicating CO2 inhalation or VH (e.g., cardiac arrhythmia, cardiac failure, asthma, lung fibrosis, high blood pressure, epilepsy, or stroke
• No pregnancy or lactation
• No ongoing psychotherapy directed toward the primary disorder
• No pharmacological treatment started within 8 weeks prior to the screen (patients “stable” on their medication regimen will be included and their medication status will be included as a variable in the model)