Breathing retraining: a rational placebo?

Breathing retraining of patients with Hyperventilation Syndrome (HVS) and/or panic disorder is discussed to evaluate its clinical effectiveness and to examine the mechanism that mediates its effect. In relation to this theoretical question, the validity of HVS as a scientific model is discussed and is deemed insufficient. It is concluded that breathing retraining and related procedures are therapeutically effective, but probably due to principles other than originally proposed, namely decreasing the tendency to hyperventilate. An alternative principle is the induction of a relaxation response, presenting a credible explanation for the threatening symptoms, giving a distracting task to practice when panic may occur, and promoting a feeling of control.