EFFECT OF ANTIPANIC TREATMENT ON RESPONSE TO CARBON-DIOXIDE

Background: Disordered breathing among patients,vith panic disorder, i ncluding hyperventilation during attacks and increased anxiogenic resp onse to carbon dioxide (CO2) inhalation, is well established We wished to assess whether there is a change in the physiological response to CO2 after patients have undergone antipanic therapy with either tricyc lic antidepressants or cognitive behavioral therapy (CBT). Methods: Tw enty-nine patients with panic disorder underwent baseline CO2 sensitiv ity testing using the traditional Read rebreathing method and then rec eived either antidepressant treatment (n = 21) or CBT (n = 8). After c ompleting treatment, CO2 testing was repeated. A comparison sample of 14 normal volunteers also had two CO2 sensitivity tests, separated by an average of 21.6 (SD = 8.8) weeks. Results: Using a liberal standard , in which all CO2 sensitivity tests whose correlations between minute ventilation and end-tidal CO2 were at least .75 were used, patients, but not controls, demonstrated a significant reduction in CO2 sensitiv ity between the first and second rest. Using a more conservative .90 c orrelation standard reduced the sample size available and resulted in trend reduction in patients but no significant change in controls. The re was a suggestion that the change was most pronounced in treatment r esponders, although the number of patient nonresponders is extremely s mall in this sample, Conclusions: These data indicate that treatment r educes CO2 sensitivity in patients with panic disorder, We speculate t hat manipulation of the serotonergic and noradrenergic neurotransmissi on systems, both known to play a role in the control of respiration ma y have a specific effect in reducing respiratory hype, activity in pan ic disorder. (C) 1997 Society of Biological Psychiatry.