Panic attacks during placebo procedures in the laboratory. Physiology and symptomatology.

Heart rate, respiratory measurements, and Acute Panic Inventory symptoms of 17 patients with panic disorder who experienced panic attacks during a placebo infusion (situationally provoked panic) were analyzed and compared with similar data from a group of 19 patients with panic disorder who panicked during lactate infusion. Previously, it was shown that the group with lactate-induced panic attacks exhibited increased minute ventilation compared with normal control subjects and nonpanicking patients with panic disorder during lactate infusion. The group with situationally provoked panic attacks exhibited significant increases in both heart rate and minute ventilation immediately preceding the onset of the panic attack. The increase in minute ventilation appeared to be caused more by increase in tidal volume than in respiratory frequency. The increase in heart rate in the group with situationally provoked panic attacks was very similar to that seen in the group with lactate-induced panic attacks, but the group with situationally provoked panic attacks appeared to have somewhat greater increase in minute ventilation than the group with lactate-induced panic attacks. This suggests that the metabolic alkalosis produced by lactate infusion might actually blunt the full expression of panic-associated respiratory stimulation. These data validate the belief that significant cardiorespiratory stimulation occurring during panic attacks in the laboratory is not simply secondary to the intrinsic physiologic effects of panic-inducing substances such as lactate, yohimbine, and carbon dioxide.