title: Physiologic instability in panic disorder and generalized anxiety disorder.
abstract: BACKGROUND
  Because panic attacks can be accompanied by surges in physiologic activation, we tested the hypothesis that panic disorder is characterized by fluctuations of physiologic variables in the absence of external triggers.
  
  
  METHODS
  Sixteen patients with panic disorder, 15 with generalized anxiety disorder, and 19 normal control subjects were asked to sit quietly for 30 min. Electrodermal, cardiovascular, and respiratory measures were analyzed using complex demodulation to quantify variability in physiologic indices.
  
  
  RESULTS
  Both patient groups reported equally more anxiety and cardiac symptoms than control subjects, but certain other somatic symptoms, including breathlessness, were elevated only in panic disorder patients. Mean end-tidal pCO(2) and respiratory rates were lower, and tidal volume and the number of sighs were higher in panic disorder patients than control subjects. Neither cardiovascular (heart rate, arterial pressure, cardiac output), nor electrodermal instability including sighs distinguished the groups; however, tidal volume instability was greater in panic disorder than generalized anxiety disorder patients or control subjects. Several other respiratory measures (pCO(2), respiratory rate, minute volume, duty cycle) showed greater instability in both patient groups than in control subjects.
  
  
  CONCLUSIONS
  Respiration is particularly unstable in panic disorder, underlining the importance of respiratory physiology in understanding this disorder. Whether our findings represent state or trait characteristics is discussed.
authors: Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, California, USA.
authors: F H
authors: FH
authors: Wilhelm
authors: W
authors: W
authors: Trabert
authors: W T
authors: WT
authors: Roth
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001007:Anxiety; D001008:Anxiety Disorders / Q000235:genetics / Q000503:physiopathology*; D001341:Autonomic Nervous System / Q000503:physiopathology*; D002320:Cardiovascular Physiological Phenomena; D016022:Case-Control Studies; D004417:Dyspnea; D005260:Female; D006801:Humans; D007103:Immobilization; D008297:Male; D008875:Middle Aged; D016584:Panic Disorder / Q000235:genetics / Q000503:physiopathology*; D012129:Respiratory Function Tests; D012143:Respiratory Physiological Phenomena