Waves of significant physiological instability occur at least 60 minutes before patients become aware of a panic attack, according to a new study.

Researchers at Southern Methodist University (Dallas, TX, USA), the University of Salzburg (Austria), and other institutions monitored 43 panic disorder patients during repeated 24-hour ambulatory periods to examine if points of significant autonomic changes preceded the onset of spontaneous panic attacks. In all, 13 natural panic attacks were recorded during 1,960 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 were compared with time matched control periods within the same person.

The results showed that 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 (CO2) partial pressure increases. Panic attack onset was characterized by heart rate and tidal volume increases, and a drop in CO2 partial pressure; symptom report was consistent with these changes. Skin conductance levels were generally elevated in the hour before, and during, the attacks, but changes in the matched control periods were largely absent. The study was published ahead of print on July 21, 2011, in Biological Psychiatry.

“The changes don't seem to enter the patient's awareness. What they report is what happens at the end of the 60 minutes - that they're having an out of the blue panic attack with a lot of intense physical sensations,” said lead author psychologist Alicia Meuret, PhD, of Southern Methodist University. “They would say they were sitting watching TV when they were suddenly hit by a rush of symptoms, and there wasn't anything that made it predictable.”

Panic attacks are periods of intense fear or apprehension that are of sudden onset and of relatively brief duration. Panic attacks usually begin abruptly, reach a peak within 10 minutes, and subside over the next several hours. The effects of a panic attack vary; many, who experience a panic attack, mostly for the first time, fear they are having a heart attack or a nervous breakdown. Repeated panic attacks are considered a syndrome of panic disorder; screening tools such as the Panic Disorder Severity Scale can be used to detect possible cases of disorder, and suggest the need for a formal diagnostic assessment.

Guangzhou Jia Yu medical equipment Limited