title: Do unexpected panic attacks occur spontaneously?
abstract: BACKGROUND
  Spontaneous or unexpected panic attacks, per definition, occur "out of the blue," in the absence of cues or triggers. Accordingly, physiological arousal or instability should occur at the onset of, or during, the attack, but not preceding it. To test this hypothesis, we examined if points of significant autonomic changes preceded the onset of spontaneous panic attacks.
  
  
  METHODS
  Forty-three panic disorder patients underwent repeated 24-hour ambulatory monitoring. Thirteen natural panic attacks were recorded during 1960 hours of monitoring. Minute-by-minute epochs beginning 60 minutes before and continuing to 10 minutes after the onset of individual attacks were examined for respiration, heart rate, and skin conductance level. Measures were controlled for physical activity and vocalization and compared with time matched control periods within the same person.
  
  
  RESULTS
  Significant patterns of instability across a number of autonomic and respiratory variables were detected as early as 47 minutes before panic onset. The final minutes before onset were dominated by respiratory changes, with significant decreases in tidal volume followed by abrupt carbon dioxide partial pressure increases. Panic attack onset was characterized by heart rate and tidal volume increases and a drop in carbon dioxide partial pressure. Symptom report was consistent with these changes. Skin conductance levels were generally elevated in the hour before, and during, the attacks. Changes in the matched control periods were largely absent.
  
  
  CONCLUSIONS
  Significant autonomic irregularities preceded the onset of attacks that were reported as abrupt and unexpected. The findings invite reconsideration of the current diagnostic distinction between uncued and cued panic attacks.
authors.affiliation: Department of Psychology, Southern Methodist University, Dallas, Texas, USA. ameuret@smu.edu
authors.forename: Alicia E
authors.initials: AE
authors.lastname: Meuret
authors.forename: David
authors.initials: D
authors.lastname: Rosenfield
authors.forename: Frank H
authors.initials: FH
authors.lastname: Wilhelm
authors.forename: Enlu
authors.initials: E
authors.lastname: Zhou
authors.forename: Ansgar
authors.initials: A
authors.lastname: Conrad
authors.forename: Thomas
authors.initials: T
authors.lastname: Ritz
authors.forename: Walton T
authors.initials: WT
authors.lastname: Roth
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D001794:Blood Pressure; D005260:Female; D006339:Heart Rate; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000379:methods; D016584:Panic Disorder / Q000175:diagnosis* / Q000503:physiopathology*; D010808:Physical Examination; D010991:Plethysmography; D056152:Respiratory Rate; D057566:Self Report; D055815:Young Adult