August 2, 2011 — Panic attacks do not come "out of the blue" but are preceded by physiological changes similar to those that precede seizures, stroke, and even manic episodes, a new study suggests.
"There is reason to believe that waves of physiological instability occur for a substantial period of time before the attack is reported by patients," Alicia E. Meuret, PhD, an assistant professor from the Department of Psychology, Southern Methodist University, in Dallas, Texas, who led the study, told Medscape Medical News.
The finding may have relevance for other medical disorders where symptoms seemingly happen "out of the blue," such as seizures, strokes, and even manic episodes, the researchers note.
There is speculation that panic attacks are triggered by marked changes in physiology, in particular breathing, Dr. Meuret explained. However, until now, very little is known on the physiological functioning of those with panic attacks outside the laboratory.
In the current study, 43 patients with panic disorder underwent repeated 24-hour ambulatory monitoring of various physiological indices, including respiration, heart rate, and skin conductance level. During 1960 hours of monitoring, 13 natural panic attacks were recorded.
"We managed to capture spontaneously occurring attacks in these recordings, which we were able to examine closer. The study marks the first to gain an in-depth look into what occurs in early stages before a panic attack occurs," Dr. Meuret said. The investigators specifically analyzed the 60 minutes before panic onset and during the panic attack.
Early Warning System?
The researchers say they detected significant patterns of instability across a number of autonomic and respiratory variables as early as 47 minutes before panic onset. The final minutes preceding the attack were dominated by respiratory changes, with significant decreases in tidal volume followed by abrupt carbon dioxide partial pressure increases, they report.
With the onset of a panic attack, heart rate and tidal volume increased and carbon dioxide partial pressure decreased. Skin conductance levels were generally elevated in the hour preceding an attack and during an attack. "These changes were largely absent in the control periods," the investigators write.
Because most patients report panic attacks as being unexpected, "it appears that they do not 'feel' these instabilities," Dr. Meuret noted.
"From a patient's point of view, our study may be upsetting news, since it is hard to control something that one does not sense.
"However, it would be fascinating to explore whether it is possible to monitor such changes and train the patient to become aware of them, similar to patients who have auras before a migraine or an epileptic attack strikes," Dr. Meuret said.
"Likewise, the extent to which therapies that alter physiological responding (such as pharmacotherapy or respiratory therapy) can help to combat such instabilities remains to be tested," she noted.
Reached for comment, Alexander Bystritsky, MD, PhD, professor of psychiatry and biobehavioral sciences and director of the Anxiety Disorder Program at the David Geffen School of Medicine, University of California, Los Angeles, said this study provides "new evidence that [unexpected] panic attacks are not so unexpected.
"The dynamic changes in some physiological parameters may be detected by the brain and trigger the response. This is important for behavioral treatments of panic," Dr. Bystritsky added.
The study was funded by the National Institutes of Mental Health, Department of Veterans Affairs, and the Beth and Russell Siegelman Foundation. The study authors and Dr. Bystritsky have disclosed no relevant financial relationships.
Biol Psychiatry. Published online July 21, 2011. Abstract
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Cite this: Panic Attacks Don't Come Out of the Blue After All - Medscape - Aug 02, 2011.