Effects of low pulmonary CO₂ on panic anxiety

In order to investigate the possible role of hyperventilation in the pathogenesis of panic, 11 panic patients and eight normal controls underwent a hyperventilation provocation test. The word "hyperventilation" itself was not used; the subjects were told the test was meant to measure the amount of carbon dioxide in their expired air. End tidal pCO₂ was reduced to less than half of its initial value, resulting in a significant increase in physical symptoms, both in patients and controls. However, there proved to be no significant increase in subjective anxiety. It is suggested, that hypocarbia alone is not sufficient to provoke anxiety in panic disorder patients.