Hyperventilation is not diagnostically specific to panic patients

It has been claimed that hyperventilation is a cause of panic attacks in patients suffering from panic disorder (PD), and various studies have, in fact, documented low resting CO2 in PD patients. However, most comparisons have been made using non-psychiatric controls. Since increased ventilation is a common concomitant of distress, the relevance of using healthy/non-anxious control groups may be questioned. Respiratory peculiarities of PD patients may actually just reflect background anxiety rather than a diagnostically specific feature. In order to explore the possible diagnostic specificity of hyperventilation, as well as increased respiratory rate and respiratory variability, to PD patients, capnographic patterns were analyzed from PD patients, non-panic disorder anxiety patients, and healthy controls. Capnographic data were obtained while subjects were resting, watching an exciting film, relaxing, and being exposed to idiosyncratically relevant fearful imagery. Findings were robust. As found in most studies, PD patients had lower resting CO2 than healthy controls; however, that of non-panic disorder anxiety patients was just as low as PD patients. The exciting film and fearful imagery produced consistent increases in distress and concomitant increases in respiratory rate, variability of end-tidal CO2, and decreases in end-tidal CO2. However, this was similar in all three groups. Data suggest that hyperventilation is not specific to PD patients.