Menstrual cycle-related sensitivity to 35% CO2 in panic patients

In a double blind, random, cross-over design, 10 patients and seven controls inhaled one vital capacity of 35% CO2-65% O2 during their early-follicular and midluteal phases. Anxiety after CO2 intake was significantly stronger in the early-follicular phase than in the midluteal phase for patients. Controls had no anxiety reactions.