The effect of anxiety sensitivity and expectancy manipulation on panic-like response to the 35% CO2 challenge

The Anxiety Sensitivity (AS) theory, developed by Reiss and McNally, refers to the fear of anxiety related bodily sensation, due to the belief that they are psychologically, physiologically, and socially harmful. In this field several researches established the relationship between AS and panic: subjects with High AS (HAS), compared to Low AS (LAS), had greater panic-like responses when the carbon-dioxide (CO2) challenge was administered. Telch and colleagues suggested that the standardized instructions for the CO2 challenge might influence the anxiety response to the test in healthy subjects. Surprisingly, they found that HAS subjects (versus LAS), randomized to Expected Relaxation instructions (ER) (versus standard Expected Arousal instructions - EA) had higher panic response to the 35% CO2 challenge compared to room air inhalation. Thus, the aim of the present research was to replicate Telch and colleagues’ study in order to overcome some methodological limitations and verify if AS, and the manipulation of expectations, might affect the psychological and physiological responses to the 35% CO2 challenge. Sixty-eight healthy subjects, matched for sex, age, and opposite level of AS (HAS versus LAS), as measure by the Anxiety Sensitivity Index - 3 (ASI-3), were randomized to one of two instructional set (ER versus EA). Immediately before and after the 35% CO2 challenge and room air inhalation, they filled the Visual Analogue Scale of Anxiety (VAAS), of Fear (VAS-F), of Discomfort (VAS-D), and the Panic Symptom List (PSL). Physiological parameters (i.e., systolic and diastolic blood pressure, heart rate) were also measured. Hierarchical multiple regression showed greater psychological responses at VAAS, VAS-F, VAS-D, and PSL, and higher systolic blood pressure under CO2 compared to room air. The psychological and physiological response to the test was not affected by the level of AS (HAS versus LAS) or the instructional set (Expected Arousal versus Expected Relaxation). The present study confirmed the psychological effect of CO2 challenge on emotional responses of healthy subjects and strengthens the goodness of the standardized instructions used to administer it.