35% CO2 challenge in panic and mood disorders

20 patients with Panic Disorder (PD), 19 patients with Mood Disorder (MD) and 20 healthy controls inhaled one vital capacity of 35% CO2-65% O2 gas mixture and of compressed air in a double-blind, random, cross-over design. Only PD patients showed a strong reaction to 35% CO2 while MD patients and controls did not react significantly. These results support the specificity of the 35% CO2 challenge in PD patients and suggest that PD and MD are separate disorders.