An objective marker of lactate-induced panic

There are a number of agents claimed effective in provoking panic attacks in the laboratory. For each case, however, the determination of whether an attack has occurred is largely subjective. An objective index of panic would be of great benefit in standardizing laboratory provocation studies. Using heart rate (HR) recordings during sodium lactate infusion, we developed a formula--the heart rate index (HRI)--which appears to correlate well with the subjective experience of panic. Of note is the fact that the HRI was most powerful in identifying attacks that occurred in the first 15 min of the 20-min infusions. In an accompanying study, we examined HR variability during the infusions using the successive difference mean square statistic. HR variability did not change during lactate-induced panic attacks. Therefore, tachycardia during lactate-induced panic probably does not result from decreased vagal tone to the heart.