Opposing breathing therapies for panic disorder: a randomized controlled trial of lowering vs raising end-tidal P(CO₂).

Background: Teaching anxious clients to stop hyperventilating is a popular therapeutic intervention for panic. However, evidence for the theory behind this approach is tenuous, and this theory is contradicted by an opposing theory of panic, the false-suffocation alarm theory, which can be interpreted to imply that the opposite would be helpful.

Objective: To test these opposing approaches by investigating whether either, both, or neither of the 2 breathing therapies is effective in treating patients with panic disorder.

Method: We randomly assigned 74 consecutive patients with DSM-IV-diagnosed panic disorder (mean age at onset = 33.0 years) to 1 of 3 groups in the setting of an academic research clinic. One group was trained to raise its end-tidal P(CO₂) (partial pressure of carbon dioxide, mm Hg) to counteract hyperventilation by using feedback from a hand-held capnometer, a second group was trained to lower its end-tidal P(CO₂) in the same way, and a third group received 1 of these treatments after a delay (wait-list). We assessed patients physiologically and psychologically before treatment began and at 1 and 6 months after treatment. The study was conducted from September 2005 through November 2009.

Results: Using the Panic Disorder Severity Scale as a primary outcome measure, we found that both breathing training methods effectively reduced the severity of panic disorder 1 month after treatment and that treatment effects were maintained at 6-month follow-up (effect sizes at 1-month follow-up were 1.34 for the raise-CO(2) group and 1.53 for the lower-CO(2) group; P < .01). Physiologic measurements of respiration at follow-up showed that patients had learned to alter their P(CO₂) levels and respiration rates as they had been taught in therapy.

Conclusions: Clinical improvement must have depended on elements common to both breathing therapies rather than on the effect of the therapies themselves on CO(2) levels. These elements may have been changed beliefs and expectancies, exposure to ominous bodily sensations, and attention to regular and slow breathing.

Trial Registration: ClinicalTrials.gov identifier: NCT00183521.