Respiratory and hemodynamic contributions to emotion-related pre-syncopal vasovagal symptoms.

Vasovagal reactions are conventionally understood as resulting from systemic changes in cardiovascular activity; however, there exists a complementary perspective focused on specific changes in cerebral vasoconstriction associated with hyperventilation-induced hypocapnia. The present study investigated the role of cardiovascular and respiratory activity in self-reported pre-syncopal vasovagal reactions to a surgery video in a sample of 49 healthy women. Participants who indicated more previous real-life episodes of dizziness reported experiencing significantly more symptoms in the laboratory consistent with a vasovagal response. They also showed lower total peripheral resistance and higher pre-ejection period in general, suggesting lower sympathetic nervous system activity. Significant decreases in end-tidal carbon dioxide (P _ET CO ₂ ) occurred during the surgery video among susceptible participants, without significant increases in respiration rate. Further, participants who experienced reductions from the neutral video in P _ET CO ₂ , systolic blood pressure, or both, reported vasovagal symptoms during the surgery video. The results suggest that patterns of respiration associated with decreases in P _ET CO ₂ may contribute to vasovagal symptoms reported in non-clinical groups as well as those with blood-injection-injury phobia and are associated with susceptibility to dizziness.
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