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End-Tidal pCO₂ in Blood Phobics During Viewing of Emotion- and Disease-Related Films

From the Psychological Institute III, University of Hamburg, Germany (T.R., A.K.); the Department of Psychology, University of Basel, Basel, Switzerland (F.H.W.); the Department of Psychology, University of Münster, Münster, Germany (A.L.G.); and the Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, California, and the VA Palo Alto Health Care System, Palo Alto, California (W.T.R.).

Address correspondence and reprint requests to Thomas Ritz, PhD, Psychological Institute III, University of Hamburg, Von-Melle-Park 5, D-20146 Hamburg, Germany. E-mail: thomas.ritz{at}uni-hamburg.de

Objective: Many patients with blood, injection, and injury (BII) phobia respond to specific stimuli with vasovagal dysregulation and fainting. However, little is known about the role of hyperventilation in the distress of these patients. Hyperventilation, defined by subnormal arterial pCO₂ levels, induces anxiety and may promote the development of fainting. We studied end-tidal pCO₂ in 12 patients with BII phobia and 14 nonanxious controls during presentation of emotional films.

Method: Ten film clips were shown, two in each of 5 categories: pleasant, unpleasant, neutral, BII-related (surgery), and asthma-related (portraying labored breathing). For each subject, two subsets were created, each containing one clip from each category. For one subset, the instruction was simply to view the film, and for the other subset, to view the film while tensing the leg muscles. PCO₂, heart rate, blood pressure, and leg electromyogram were recorded continuously during viewing, and self-report of symptoms and emotion was collected after each film.

Results: Patients reported the greatest anxiety and disgust during surgery films. PCO₂ was relatively stable throughout all categories except surgery films, during which minima were below 30 mm Hg, indicating significant hypocapnia. Cardiovascular variables suggested biphasic patterns in two patients with BII phobia. These patients, together with one additional patient and one control who were close to fainting after or during one surgery film, also showed a marked fall in pCO_2. Leg muscle tension raised heart rate and systolic blood pressure for all films, but was not related to near-fainting or endurance in surgery film viewing.

Conclusion: Hyperventilation is part of the fear response of patients with BII phobia, but was transitory in experimental fear induction using surgery films. Its role in real-life exposure and fainting deserves further study.

Key Words: blood–injection–injury phobia • anxiety • respiration • hyperventilation • fainting • vasovagal response

Abbreviations: BII = blood, injection, and injury; HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; EMG = electromyogram; MFS = Medical Fear Survey.

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