Epinephrine and fear of bodily sensations in panic disorder and social phobia

Development of a theoretically-derived human anxiety syndrome biomarker

“Anxiety disorders” are extremely common; and are a major source of health costs and lost work days. Their diagnosis is currently based on clinical symptom check lists and there are no biological markers to diagnose specific syndromal causes. This paper describes: 1) a detailed theory of the brain systems controlling anxiolytic-insensitive threat-avoidance and anxiolytic-sensitive threat-approach — where, in specific brain structures, activity generates specific normal behaviours, hyperactivity generates abnormal behaviours, and hyper-reactivity (hypersensitivity to input) generates specific clinical syndromes; 2) a rodent model of systemic anxiolytic action (rhythmical slow activity), linked to the theory, that over a period of 40 years has shown predictive validity with no false positives or false negatives — and which is likely to assay the sensitivity of endogenous systems that control anxiety; and, 3) derivation from this rodent-based theory of a specific non-invasive biomarker (goal-conflict-specific rhythmicity) for the threat-approach system in humans. This new biomarker should allow division of untreated “anxiety” patients, with superficially similar clusters of symptoms, into distinct high scoring (syndromal) and low scoring groups with different treatment-responses. This would be the first theoretically-derived biomarker for any mental disorder and should: 1) predict treatment efficacy better than current symptom-based diagnoses; 2) provide a human single dose test of novel anxiolytics; 3) provide a starting point for developing biomarkers for other “anxiety” syndromes; and so, 4) greatly improve treatment outcomes and cost-effectiveness.

Role of epinephrine in acute stress

This article presents the likely pathway of stimuli generated by the recognition of high-intensity stressors to ultimately produce a fight-or-flight response. A key element is the recognition that psychological stressors that do not directly alter the internal environment represent the most important etiology of a fight-or-flight response. Adrenomedullary secretion is a critical component of that response; impromptu stimulation of the adrenal medulla can produce plasma epinephrine concentrations greater than 10,000 pg/mL. When these plasma levels reach the hypothalamus to act on the CNS, the result is facilitation of the decision making, and decision execution processes (fight-or-flight), and perhaps further sympathetic stimulation and vasopressin release. Subjects with underlying cardiovascular and/or metabolic pathology may be particularly susceptible to potentially lethal reactions to this neuroendocrine response. Additionally, since this biological reaction may be triggered by sudden changes in the social environment, the coordinated actions of epinephrine, sympathetic stimulation and vasopressin must be directed at not only optimizing the chances for survival, but also at attaining maximal preservation of the individual environmental and social domains.

Epinephrine-induced panic attacks and hyperventilation

To assess the effects of epinephrine on ventilation in patients with panic disorder and in social phobics, analyses were performed on pooled data from two previous infusion studies. Throughout the infusion, changes in transcutaneous PCO2 (tcPCO2), subjective anxiety, heart rate and blood pressure were recorded continuously. Twenty-nine patients received epinephrine, ten patients received placebo. Thirteen patients (45%) had a panic attack during epinephrine. The fall in tcPCO2 and the cardiovascular response was greater in panicking patients than patients who did not panic. Although the fall in tcPCO2 associated with panic was not substantial and did not indicate clinically significant acute hyperventilation, it appears to be a sensitive index for epinephrine-induced panic. The fall in tcPCO2 was predicted rather by the frequency of occurrence of anxiety-related somatic symptoms than by the fear of these symptoms. These findings further reduce a role for fear of bodily sensations in epinephrine-induced panic attacks and favor a biological sensitivity to sympathetic stimulation.

Predictability, controllability, and fear of symptoms of anxiety in epinephrine-induced panic

BACKGROUND

Psychological manipulations (supplied information, safety cues) may influence panic rates during pharmacologic challenge tests in subjects with panic disorder (PD). Psychological panic models assume that fear of stress-related bodily sensations is central to the etiology of PD.

METHODS

Prior to infusion of epinephrine, 50 subjects with PD were randomly assigned to one out of four experimental conditions: with or without extensive information and with or without external control, according to a 2 x 2 design. The panic rate was hypothesized to be lower in subgroups possessing extensive information and/or control. Fear of bodily sensations was used as a predictor.

RESULTS

Thirty-four out of 50 patients (68%) panicked during the infusion. Subjects who received extensive information were marginally less likely to panic, but manipulation of control did not influence panic rates. Panickers did not differ from nonpanickers in measures of fear of fear. Anxiety sensitivity best predicted baseline anxiety and cognitive symptom scores, but was not associated with other outcome measures in panickers. Only baseline partial pressure of CO2 discriminated between panickers and nonpanickers.

CONCLUSIONS

Manipulating external safety cues appears to be of limited value in modulating responses to epinephrine challenge. Together with our finding that fear of anxiety symptoms does not predict panic rates, these data argue against "fear of fear" as a key mechanism in epinephrine-induced panic.