Slow cardiovascular rhythms in tilt and syncope.
The cardiovascular oscillations during orthostasis were analyzed by time-frequency mapping in 23 patients with history of vasodepressor (VD) syncope and in 10 control subjects. Syncope was induced by head-up tilt (80 degrees, 25 min) alone in 11 patients (VD-1). Twelve patients remained asymptomatic (VD-2) during this tilt, but presented VD syncope or presyncope during tilt with an isoproterenol infusion. Data from the first tilt without isoproterenol infusion are presented here. Amplitude of sympathetically-mediated nonrespiratory fluctuations [0.01 Hz-respiratory frequency (Rf)] in blood pressure was greater at the beginning of the tilt in both (VD-1 and VD-2) groups compared to controls. Nonrespiratory oscillations were present throughout the tilt and their amplitude increased toward its end (p < 0.001) in VD-2 and control groups. In contrast, in the VD-1 group, the amplitude of 0.01-0.05 Hz rhythm in blood pressure diminished shortly after the beginning of tilt and continued to decline toward the syncope. Nonrespiratory fluctuations in R-R intervals were greatest in VD-1 group. The slow blood pressure rhythms reflect an integrity of feedback loops, and their disappearance is an early sign of an impending syncope.
Novak
V
V
Department of Neurosciences, Jewish General SMBD Hospital, Montreal, Canada.
Novak
P
P
Kus
T
T
Nadeau
R
R
D000328:Adult; D004562:Electrocardiography; D005260:Female; D006257:Head; D006321:Heart / Q000503:physiopathology; D006801:Humans; D007024:Hypotension, Orthostatic; D007545:Isoproterenol / Q000627:therapeutic use; D008297:Male; D011187:Posture; D012737:Sex Factors; D013575:Syncope / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology
D007545:Isoproterenol