title: Physiological changes during carbon dioxide inhalation in patients with panic disorder, major depression, and premenstrual dysphoric disorder: evidence for a central fear mechanism.
abstract: BACKGROUND
  Inhalation of carbon dioxide (CO(2)) has been shown to produce more anxiety in patients with panic disorder (PD) than in healthy comparison subjects or patients with most other psychiatric illnesses tested, although premenstrual dysphoric disorder (PMDD) may be an exception. Several reasons have been proposed to explain CO(2) breathing effects in PD. We examined differences in respiratory response to CO(2) breathing in 4 groups to address these issues.
  
  
  METHODS
  Patients with PD (n = 52), healthy controls (n = 32), patients with PMDD (n = 10), and patients with major depression without panic (n = 21) were asked to breathe 5% and 7% CO(2). Continuous measures of respiratory physiological indices were made.
  
  
  RESULTS
  Carbon dioxide breathing produced the expected increases in all 4 respiratory variables measured. More patients with PD and PMDD had panic attacks than did controls or patients with major depression. Subjects who experienced panic during 5% or 7% CO(2) inhalation had the most extreme increases regardless of diagnostic group. Among patients with PD, baseline end-tidal carbon dioxide levels were significantly lower in those who subsequently had a panic attack during 5% CO(2) breathing than those who did not.
  
  
  CONCLUSIONS
  Although CO(2) breathing causes a higher rate of panic attacks in patients with PD than other groups (except PMDD), the physiological features of a panic attack appear similar across groups. Once a panic attack is triggered, minute ventilation and respiratory rate increase regardless of whether the subject carries a PD diagnosis. These findings are compatible with preclinical fear conditioning models of anxiogenesis.
authors.affiliation: Department of Psychiatry, Columbia University, 1051 Riverside Dr, Unit 32, New York, NY 10032, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Gorman
authors.forename: J
authors.initials: J
authors.lastname: Kent
authors.forename: J
authors.initials: J
authors.lastname: Martinez
authors.forename: S
authors.initials: S
authors.lastname: Browne
authors.forename: J
authors.initials: J
authors.lastname: Coplan
authors.forename: L A
authors.initials: LA
authors.lastname: Papp
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000494:pharmacology; D003866:Depressive Disorder / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D016584:Panic Disorder / Q000139:chemically induced / Q000175:diagnosis* / Q000503:physiopathology*; D011293:Premenstrual Syndrome / Q000175:diagnosis*; D012143:Respiratory Physiological Phenomena / Q000187:drug effects
chemical_list: D002245:Carbon Dioxide