Confrontation with blood and disgust stimuli precipitates respiratory dysregulation in blood–injection–injury phobia

Blood–injection–injury (BII) phobia patients sometimes faint during exposure to relevant stimuli. However, mechanisms and timing of physiological adjustments in BII phobia remain poorly understood. In a larger sample of 60 patients and 20 controls, we sought to replicate findings of a prior study demonstrating the role of hyperventilation in the phobic response. We also investigated the timing of respiratory adjustment across an extended exposure recovery period. In addition, because intense disgust is commonly reported by patients, responses to surgery films were compared to a pure disgust film. End-tidal PCO2 dropped significantly while volume and flow increased during the surgery film in patients compared to controls and to other emotional films except disgust. Patients recovered quickly following the disgust film but not the surgery film. PCO2, volume, and flow parameters showed robust associations with anxiety, disgust, and physical symptoms. Findings suggest that respiratory adjustments during and after phobic exposure may provide a critical missing link in the understanding of the psychophysiology of this singular disorder, including why fainting often occurs after the stimulus is removed.