Changes in heart rate variability during fainting.
Studies of heart rate variability in people who faint may yield insights into normal physiologic mechanisms which probably are dynamic. These insights might be gained because fainting appears to be due to a breakdown of these mechanisms. Tilt table testing reliably induces fainting in patients with a history of fainting and can be used to study these mechanisms. During tilt tests ending in fainting heart rate changes markedly, with a loss of high-frequency components on power spectral analysis and a progressive slowing of overall sinus node discharge. These changes appear to be due to changes in efferent vagal nerve traffic. Several possible mechanisms of these changes in heart rate variability are discussed.
Sheldon
Robert
R
Cardiovascular Research Group, University of Calgary, Calgary, Alberta T2E 0A1, CanadaBrady Research Group, Medtronic, Inc., Minneapolis, Minnesota 55401.
Riff
Kenneth
K