Physiological Clues to an Unexpected Panic Attack

Panic attack is a type of psychological disorder in which a person experiences intense fear and anxiety. This reaction can be for a trivial reason or sometimes even without any reason. The latter type, which occur out of the blue, is called an unexpected panic attack. Panic attacks produce several changes in physiological parameters (autonomic irregularities) such as increase in heart rate. Unexpected panic attacks, as against the predisposed ones, are expected to be spontaneous, unaccompanied by prior changes in physiological parameters. The present study was undertaken to learn whether there are any changes in physiological parameters before the onset of an unexpected panic attack.

Panic attacks occur as a paroxysmal episode with several changes in the body, which reach a maximum limit within 10 minutes. Panic attacks produce an enormous amount of discomfort to the patient and increase the chances of committing suicide. Irregularities in autonomic functions can be measured by assessing the heart rate, respiratory rate, and conductance in skin.  In the present study, people suffering from panic disorder were continuously monitored to identify the changes in their autonomic functions before the onset of an unexpected panic attack. If there were any detectable changes, it would prove that the unexpected panic attacks are not spontaneous in the true sense; rather the physiological changes are not perceived by the mind.

* The study involved 43 patients who were diagnosed with panic disorder. All of them were asked to wear an ambulatory recording devise continuously for 24 hours and were told to perform their usual routine activities. Eighty-four recordings of 24-hour monitoring were available for analysis.
* Participants were asked to report the occurrence of panic attack, severity of the symptoms on a scale of 10, duration of the attack and whether it was expected or unexpected.
* The ambulatory recording devise measured the respiratory rate, partial pressure of carbon dioxide, heart rate, skin conductance, and physical activity of the patient.
* Changes in these parameters were assessed from 60 minutes before the onset of panic attack until 10 minutes after the occurrence of the attack. This data was compared with the recordings obtained in the non-attack period.

* In total, 13 incidents of panic attack were recorded, the mean duration of which was eight minutes. An equal number of them, i.e. 38 percent each, occurred when the participants were alone and with family. In 69 percent of the cases, the panic attacks were unexpected.
* An hour before the onset of a panic attack, there were significant changes in the cardio and respiratory parameters. There was a significant increase in the heart rate and decrease in the respiratory rate. There was steep rise in the levels of partial pressure of carbon dioxide. These changes were more pronounced in the last minute before the onset of the panic attack.
* Evaluation of physiological parameters in the control period, i.e. in the absence of a panic attack, did not reveal any such changes.

Shortcomings/Next steps
Changes in the physiological parameters and their timings were not uniform in all the participants. However, synchronization of the data was done during statistical analysis. The onset of panic attack was self reported by the participant. This is subject to uncertainty. Moreover, this study included only 13 panic attacks. Further studies involving more number of patients, with more number of panic attacks are necessary to confirm the findings of the present study.

According to the authors of this study, “Significant patterns of instability across a number of autonomic and respiratory variables were detected before the onset of panic attack.” Such changes were not seen in the periods when there was no panic attack. Premier textbooks of psychiatry mention that a panic attack is spontaneous and occurs as “an instantaneous alarm reaction, both subjectively and physiologically peaking within 3 to 5min”. The present study has proved that this definition is only partially correct. Although subjective changes occur in a paroxysmal manner, the changes in physiological parameters start occurring as early as one hour before the onset of a panic attack. Nevertheless, these changes are probably not perceived by the patient.

For More Information:
Do Unexpected Panic Attacks Occur Spontaneously?

Publication Journal: Biological Psychiatry, 2011
By Alicia E. Meuret; David Rosenfield; Sothern Methodist University, Dallas, Texas

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