Voluntary hyperventilation: the influence of duration and depth on the development of symptoms.

Hyperventilation is considered an important factor in the development of somatic symptoms or even panic attacks, though its role has recently been disputed. Arguments are often based on findings from the so-called Hyperventilation Provocation Test (HVPT), which is a procedure consisting of voluntarily overbreathing. The HVPT has been widely used for diagnosing Hyperventilation Syndrome and for experimentally eliciting panic attacks. Almost no attention, however, has been paid to standardizing the test and determining critical values with respect to depth and duration of hyperventilation. In the present study, symptom development was examined in 16 healthy subjects who underwent four HVPTs that differed in depth of hyperventilation (end-tidal PCO2 < 2.4 kPa or < 1.9 kPa), as well as duration of hyperventilation (2 or 5 min). Both depth and duration appeared to have an independent effect on the development of symptoms. In the 5-min condition, symptoms appeared mainly within the first 3 min. To be sure that the HVPT is long enough and deep enough to elicit symptoms in most people, a minimum duration of 3 min is advised, with end-tidal PCO2 decreasing to at least 1.9 kPa or dropping well over 50% of baseline.