| A review of the panic disorder literature strongly suggests subtypes of panic attacks, including a respiratory subtype. This study empirically tested several aspects of Ley?s panic subtype theory, measuring end-tidal carbon dioxide (ETCO2) levels at baseline, during psychologic and respiratory stressors, and at recovery.As predicted, Type 1 (classic or respiratory) panickers had significantly lower resting ETCO2 compared to Type 3 (cognitive) and to controls. Type 3 panickers did not differ from controls. Physiologic findings support the existence of respiratory and other subtypes of panic attacks in panic disorder. More complex measures of respiration and other physiology are likely required to elicit full subtype profiles. Distinguishing between chronic (compensated) hyperventilators and acute hyperventilators will likely be useful in clarifying the subtypes. Recognizing the need for differential diagnosis of panic attacks can facilitate developing more specific treatment plans and interventions (e.g., restoration of normal ETCO2 in Type 1), improving treatment success rates. |