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.

Copyright © 2011 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Illustration of the ambulatory set-up for 24-h monitoring. Ambulatory recorder [1], thoracic and abdominal plethysmography bands [2], capnometry device [3] with attached nasal cannula [4], EKG electrodes [5], electrodermal activity [6],sound sensor [7], accelerometers [8], external and finger temperature sensors [9], and event marker button [10].

Figure 2

Bold black and red lines reflect average levels of the measure and significant changes in those average levels. The time of the reported PAs (or corresponding NPA time periods) is marked as a vertical dashed red line at time point 1. The red box encloses CPs occurring at PA onset, the blue box CPs during min −47 to −42, the yellow box CPs during min −30 to −27, and the green box CPs during min −19 to −9.

Figure 3

Variables with no CPs and control variables

Figure 4

Illustration of single case (Pt #41) example of heart rate in the hour prior to, during, and the first 10 min following the PA.The time of the reported PAs (or corresponding NPA time periods) is marked as a vertical dashed red line at time point 1. The dotted line reflects missing data which was interpolated in the analysis.