Vasovagal responses (VVR) produce symptoms such as faintness, dizziness, weakness, lightheadedness, and possible syncope. VVR are a unique type of stress response, complicating and deterring people from various medical procedures such as blood donation, vaccinations, dental exams, etc. The specific psychological processes involved in VVR have puzzled theorists for decades, given the distinctive stress-related decreases in physiological activity. The psychophysiological processes of VVR continue to be debated. Three studies were conducted to examine the psychophysiology of VVR in both clinical and controlled laboratory settings, including factors related to primary appraisal, secondary appraisal, autonomic, and hemodynamic processes. The first laboratory-based study examined the importance of blood and injection stimuli in provoking VVR. A video of a blood draw led to greater VVR than one of an injection. Sympathetic nervous system activity decreased during both videos but significantly more during the blood-draw video. This decrease in sympathetic activity was reversed by the Applied Tension technique. In Study Two, participants were assigned to have high or low perceived control during exposure to a stimulus video of a mitral valve surgery, known to trigger VVR. Perceived control was manipulated by allowing some participants to choose a break time, though all received equivalent breaks. Low perceived control led to more vasovagal symptoms, higher anxiety, and lower stroke volume, cardiac output, and diastolic blood pressure. The third study examined autonomic and hemodynamic processes associated with the development of naturally occurring VVR. Participants who subsequently experienced vasovagal symptoms experienced lower low-frequency/high-frequency heart rate variability ratios throughout the blood donation process, suggesting lower sympathetic nervous system activity, consistent with Study One. These individuals also showed a greater decrease in total peripheral resistance. In sum, these findings indicate the importance of perceived blood loss (primary appraisal) and perceived control (secondary appraisal) in VVR. The findings from Study Three contribute to knowledge of physiological processes of VVR, providing autonomic and hemodynamic data from clinical blood donation settings. Future research is recommended to examine the salience of blood stimuli and the effectiveness of the manipulation of perceived control on VVR in clinical settings.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2015|