UNSTEADINESS OF BREATHING IN PATIENTS WITH HYPERVENTILATION SYNDROME AND ANXIETY DISORDERS

The breathing pattern of 399 patients with hyper-ventilation syndrome (HVS) and/or with anxiety disorders and that of 347 normal controls wa s investigated during a 5 min period of quiet breathing and after a 3 min period of voluntary hyperventilation. The diagnosis of HVS was bas ed on the presence of several suggestive complaints occurring in the c ontext of stress, and reproduced by voluntary hyperventilation. Organi c diseases as a cause of the symptoms were excluded. The anxiety disor ders were diagnosed by means of an abbreviated version of the Anxiety Disorders Interview Schedule (ADIS). There was a large overlap between the two diagnoses. Simply breathing via a mouthpiece and pneumotachog raph made end-tidal CO2 fractional concentration (FET,CO2) decrease pr ogressively both in hyperventilators and in patients with anxiety diso rders, but not in normals. At the start of the measurement the FET,CO2 was not different between patients and healthy subjects. In patients less than or equal to 28 yrs, the decrease of FET,CO2 resulted from a higher tidal volume, and in patients greater than or equal to 29 years from an increase in frequency. After voluntary hyperventilation, the recovery of FET,CO2 was delayed in patients, due to a slower normaliza tion of respiratory frequency in females and in older males, and of ti dal volume in younger males, and also due to less frequent end-expirat ory pauses. When breathing was recorded first by means of inductive pl ethysmography (Respitrace), the progressive decline of FET,CO2 seen in patients was not observed: from the onset of the recording, FET,CO2 w as reduced in patients. It did not change further when, immediately af ter ards, the subject switched to mouthpiece breathing. The finding th at breathing through a mouthpiece induces hyperventilation in patients and that recovery of FET,CO2 is delayed after voluntary hyperventilat ion, suggests that the respiratory control system is less resistant to challenges (mouthpiece or voluntary hyperventilation) in those patien ts. On the other hand, the lower values of FET,CO2 measured during rec ording by means of a Respitrace probably result from a challenge, prio r to the recordings, induced by the fitting of the measuring device to the patient. This unsteadiness of breathing characterizes patients wi th hyperventilation syndrome end those with anxiety disorders, but is not sufficiently sensitive to be used for individual diagnosis.