Cardiovascular dynamics in blood phobia: evidence for a key role of sympathetic activity in vulnerability to syncope.

This study was aimed at clarifying the mechanism predisposing people with blood phobia to syncope by investigating the complete hemodynamic response pattern and the underlying autonomic control. Blood phobics and controls were shown 3 film-clips: phobia-related, phobia-unrelated, and neutral. Hemodynamic responses were recorded using impedance cardiography and Finapres. Preejection period and respiratory sinus arrhythmia were employed as indices of cardiac sympathetic and parasympathetic activity. Self-ratings of emotion were also collected. Blood phobics displayed global heart rate and cardiac output increases to the phobic film, mediated by augmented cardiac sympathetic activity. Systolic blood pressure and total peripheral resistance markedly declined, with no evidence of diphasic reaction or parasympathetic activation. An impaired vasomotor response under sympathetic control might be the key mechanism underlying the phobic dysfunctional response.