Response to 35 % CO2 as a Marker of Panic in Severe Anxiety

One inhalation of 35 % CO2 was administered to each of 32 patients with high anxiety ratings. Only patients with panic disorder had increases in reported anxiety upon CO2 intake. C02-triggered anxiety ap-pears specific for panic disorder and independent of baseline anxiety. (Am J Psychiatry 1990; 145:796-797) T he vulnerability of patients with panic attacks to carbon dioxide (CO2) inhalation has been repeat-edly observed. Whether they breathe a 5 % concentra-tion on take a single inhalation of a 35 % mixture, in panic disorder patients CO2 rapidly increases anxiety to the point of a panic attack. In contrast, healthy control subjects who inhale CO2 usually fail to report significant anxiety, let alone experience panic (1, 2)