Estimation of Time Characteristics of Baroreflex Resetting During Orthostatic Stress

To estimate time characteristics of baroreflex resetting process, 9 young subjects participated in “dynamic” tilt tests, during which their body position was periodically changed from supine position to 60° orthostasis and back, periods of “swings” were 24, 12, 6, 4 and 2 min. Baroreflex activity was estimated by phase synchronization index (PSI) of arterial pressure and heart rate fluctuations in frequency range of baroreflex waves (~0.1 Hz). A transition to orthostasis was accompanied by an increase in the PSI. Orthostatic change in the PSI was significantly reduced when the “swing” period decreased to 4 min. These results suggest that the resetting of baroreflex HR control takes about several tens of seconds.