title: Observations on the arterial baroreflex in neurally mediated vasodepressor syncope.
abstract: The arterial baroreflex was studied in subjects who had recently had an episode of vasodepressor syncope. This was determined using 2-3 mcg/kg intravenous boluses of phenylephrine and assessing the bradycardic response. The values were measured in ms/mmHg and expressed as the angular coefficient of the regression line between the increase in R-R interval on the electrocardiograph and the systolic arterial pressure. In subjects examined immediately after the vasodepressor syncope episode the bradycardic response was much more marked than in controls (p < 0.01) and in the subjects themselves 6 months after the episode, provided that they were symptom-free (p < 0.01). It is concluded that in vasodepressor syncope there is a phase in which the baroreflex is highly sensitive and that this is due not to a lowering of the stimulation threshold but to a gain in the efferent arc, which explains a 'vagotonic' response.
authors.affiliation: Department of Internal Medicine, S. Maria Nuova Hospital, Firenze, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Lagi
authors.forename: M
authors.initials: M
authors.lastname: Cipriani
authors.forename: L
authors.initials: L
authors.lastname: Fattorini
authors.forename: C
authors.initials: C
authors.lastname: Paggetti
authors.forename: A
authors.initials: A
authors.lastname: Macerata
mesh_terms: D000293:Adolescent; D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001919:Bradycardia / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D009474:Neurons / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology; D012044:Regression Analysis; D013575:Syncope / Q000503:physiopathology*; D013997:Time Factors; D014655:Vascular Resistance / Q000502:physiology