Hyperventilation and panic disorder: a psychophysiological connection

Hyperventilation is probably the most frequently discussed correlate of panic attacks. Although some authors see it as the main or even unique cause of panic attacks, there have been numerous reviews with contradictory conclusions. Recent research, however, provides some more clarity. After a short overview of the characteristics of hyperventilation, the present article discusses (1) indirect measures of the overlap between panic and hyperventilation, (2) direct measures of hyperventilation at rest and during naturally occurring panic, (3) the influence of cognitive variables, and (4) the major theories attempting to explain the relationship between hyperventilation and panic. The results indicate a substantial overlap between panic and hyperventilation, but by far no one-to-one relationship and no chronic hyperventilation in panic patients if anticipatory anxiety is ruled out. In addition, cognitive studies firmly support the relevance of perceptive and associative processes. Theories that consider hyperventilation as a necessary or sufficient condition for panic attacks are clearly discarded by the imperfect relationship between the two phenomena. The central chemoreceptor sensitivity theory of panic is consistent with the physiologic effects of both hyperventilation and CO₂ inhalation but has to face inconsistent results on ventilatory characteristics of panic patients. Furthermore, it can neither explain the weak responses to hyperventilation or CO₂ in some panic patients nor the influence of cognitive variables. Only a psychophysiological theory that takes cognitive, conditioning and physiologic factors into account is consistent with the total body of research accumulated to date. According to this approach, hyperventilation is related to panic in two ways: First, it is one of many processes that can lead to the perception of bodily sensations which may trigger positive feedback loops between sensations and anxiety responses. Second, because of the circular nature of such feedback processes, hyperventilation can also be a response to anxiety. In conclusion, hyperventilation is not uniquely relevant for panic, but the degree of overlap between the two phenomena gives it a prominent role as a trigger for panic and a vehicle for successful psychological treatment.