SLOW CARDIOVASCULAR RHYTHMS IN TILT AND SYNCOPE

The cardiovascular oscillations during orthostasis were analyzed by ti me-frequency mapping in 23 patients with history of vasodepressor (VD) syncope and in 10 control subjects. Syncope was induced by head-up ti lt(80 degrees, 25 min) alone in 11 patients (VD-1). Twelve patients re mained asymptomatic (VD-2) during this tilt, but presented VD syncope or presyncope during tilt with an isoproterenol infusion. Data from th e first tilt without isoproterenol infusion are presented here. Amplit ude of sympathetically-mediated nonrespiratory fluctuations [0.01 Hz-r espiratory frequency (Rf)] in blood pressure was greater at the beginn ing of the tilt in both (VD-1 and VD-2) groups compared to controls. N onrespiratory oscillations were present throughout the tilt and their amplitude increased toward its end (p < 0.001) in VD-2 and control gro ups. In contrast, in the VD-1 group, the amplitude of 0.01-0.05 Hz rhy thm in blood pressure diminished shortly after the beginning of tilt a nd continued to decline toward the syncope. Nonrespiratory fluctuation s in R-R intervals were greatest in VD-1 group. The slow blood pressur e rhythms reflect an integrity of feedback loops, and their disappeara nce is an early sign of an impending syncope.