Disorders of Synchronization of Blood Pressure and Heart Rate Precede the Development of Vasovagal Syncope during Orthostasis

The goal of the present study was to identify the possible disturbances in the synchronization of spontaneous fluctuations in arterial pressure (AP) and heart rate (HR) at the frequency of baroreflex waves (~0.1 Hz) in patients prone to vasovagal fainting. In healthy volunteers and patients diagnosed with vasovagal syncope, AP (photo-compensation method) and ECG were continuously recorded, first in a horizontal position, and then during a passive orthostatic test (60°) lasting for 40 min. According to the results of the test, all patients were divided into two groups: subjects with a positive (development of the presyncopal or syncopal states) and a negative result of the orthostatic test. These groups of patients did not differ from each other and from the control group in terms of baseline AP and HR. The values of the phase synchronization index (PSI) of AP and HR were calculated in the frequency range from 0.02 to 0.8 Hz within 10-min recording intervals in the horizontal position and at the initial stage of orthostasis (starting from the second minute after the transition to the vertical position). Initially, all three groups had a distinct peak at the frequency of ~0.1 Hz in the PSI spectra. In the control group and in patients with a negative orthostatic result, a transition to the state of orthostasis was accompanied by an increase in the PSI in this frequency domain, in contrast to the patients with a positive orthostatic test, in which the PSI did not increase. Thus, the lack of amplification of phase synchronization of AP and HR at the early stage of orthostatic test is associated with the subsequent decompensation of hemodynamics and the development of syncope.