Journal of anxiety disorders vol:7 issue:1 pages:61-73
Predictability of type of symptoms and perceived control were manipulated during placebo-controlled inhalation of 5.5 % CO2-enriched air in a group of high and low trait anxious subjects. Overall, high anxious subjects had more complaints, more state anxiety, and breathed faster than low anxious subjects. CO2 inhalation produced more complaints, more state anxiety, faster breathing, and larger minute ventilation than placebo. Perceived control increased the level of complaints during CO2 inhalation compared to placebo and raised the respiration frequency of low anxious subjects. Across high and low anxious subjects, control raised the respiration frequency to a CO2 challenge, but only when this came first and not when placebo had preceded the CO2 inhalation. High anxious subjects tend to respond strongly in terms of minute ventilation in conditions of minimal information and control, when they were first challenged with a CO2 mixture. Moreover, they tend to continue this breathing pattern when subsequently breathing regular air. On the other hand, with placebo first, and/or with sufficient information and control, their minute ventilation dropped considerably, even below the level of low anxious subjects.