Vasovagal fainting consistently demonstrated a diphasic response across 23 observed instances, with an initial hyperdynamic phase followed by hypotension and bradycardia.
Observational (n=23)
What are the physiological phases of vasovagal fainting?
Vasovagal fainting is characterized by a diphasic physiological response, starting with a hyperdynamic phase reflecting anxiety, followed by sudden bradycardia and hypotension.
Vasovagal (vasodepressor) fainting was studied in three different situations: in persons donating blood, in persons having a simple venipuncture, and in patients undergoing pneumoencephalography. Ten faints were observed in the first situation, 7 in the second and 6 in the third. In all instances, the faint itself, characterized by low blood pressure and bradycardia, was the second phase of a diphasic response; the first phase was characterized by rapid or rising heart rate, and by rising blood pressure, especially diastolic. The data are compatible with the view that the first (hyperdynamic) phase is a reflection of anxiety, while the second phase begins with the sudden cessation of anxiety. It is suggested that physiologically the faint reflects the action of reflex mechanisms activated by the first phase, and then left suddenly unopposed. The other psychobiological interpretations exhibit inconsistencies because they fail to recognize the diphasic nature of this response. Fainting and dying resemble each other closely, and there is reason to think that some vasovagal faints are fatal. Cardiac asystole is not rare in faints and is often associated with convulsions. Apnea was observed in 2 of our subjects. Disturbances of cardiac rhythm, including A. V. nodal rhythm, interference dissociation, and asystole (in 1 instance for 18 sec.) were observed. Generalized convulsions were seen on four occasions, always in association with asystole.
Graham et al. (Wed,) conducted a observational in Vasovagal fainting (n=23). Blood donation, venipuncture, or pneumoencephalography was evaluated on Physiological characteristics of the fainting response. Vasovagal fainting consistently demonstrated a diphasic response across 23 observed instances, with an initial hyperdynamic phase followed by hypotension and bradycardia.