Respiration drives phase synchronization between blood pressure and RR interval following loss of cardiovagal baroreflex during vasovagal syncope

Abstract

Ocon AJ, Medow MS, Taneja I, Stewart JM. Respiration drives phase synchronization between blood pressure and RR interval following loss of cardiovagal baroreflex during vasovagal syncope. Am J Physiol Heart Circ Physiol 300: H527-H540, 2011. First published November 12, 2010 doi:10.1152/ajpheart.00257.2010.-Loss of the cardiovagal baroreflex (CVB), thoracic hypovolemia, and hyperpnea contribute to the nonlinear time-dependent hemodynamic instability of vasovagal syncope. We used a nonlinear phase synchronization index (PhSI) to describe the extent of coupling between cardiorespiratory parameters, systolic blood pressure (SBP) or arterial pressure (AP), RR interval (RR), and ventilation, and a directional index (DI) measuring the direction of coupling. We also examined phase differences directly. We hypothesized that AP-RR interval PhSI would be normal during early upright tilt, indicating intact CVB, but would progressively decrease as faint approached and CVB failed. Continuous measurements of AP, RR interval, respiratory plethysomography, and end-tidal CO 2 were recorded supine and during 70-degree head-up tilt in 15 control subjects and 15 fainters. Data were evaluated during five distinct times: baseline, early tilt, late tilt, faint, and recovery. During late tilt to faint, fainters exhibited a biphasic change in SBP-RR interval PhSI. Initially in fainters during late tilt, SBP-RR interval PhSI decreased (fainters, from 0.65 Ϯ 0.04 to 0.24 Ϯ 0.03 vs. control subjects, from 0.51 Ϯ 0.03 to 0.48 Ϯ 0.03; P Ͻ 0.01) but then increased at the time of faint (fainters ϭ 0.80 Ϯ 0.03 vs. control subjects ϭ 0.42 Ϯ 0.04; P Ͻ 0.001) coinciding with a change in phase difference from positive to negative. Starting in late tilt and continuing through faint, fainters exhibited increasing phase coupling between respiration and AP PhSI (fainters ϭ 0.54 Ϯ 0.06 vs. control subjects ϭ 0.27 Ϯ 0.03; P Ͻ 0.001) and between respiration and RR interval (fainters ϭ 0.54 Ϯ 0.05 vs. control subjects ϭ 0.37 Ϯ 0.04; P Ͻ 0.01). DI indicated respiratory driven AP (fainters ϭ 0.84 Ϯ 0.04 vs. control subjects ϭ 0.39 Ϯ 0.09; P Ͻ 0.01) and RR interval (fainters ϭ 0.73 Ϯ 0.10 vs. control subjects ϭ 0.23 Ϯ 0.11; P Ͻ 0.001) in fainters. The initial drop in the SBP-RR interval PhSI and directional change of phase difference at late tilt indicates loss of cardiovagal baroreflex. The subsequent increase in SBP-RR interval PhSI is due to a respiratory synchronization and drive on both AP and RR interval. Cardiovagal baroreflex is lost before syncope and supplanted by respiratory reflexes, producing hypotension and bradycardia. orthostatsis; nonlinear; fainting THE 2009 GUIDELINES FOR THE diagnosis and management of syncope define syncope as a transient loss of consciousness due to transient global cerebral hypoperfusion characterized by rapid onset, short duration, and spontaneous complete recovery (22). Vasovagal syncope, also known as simple faint, often occurs in young people following prolonged orthostasis. As illustrated in Fig. 1, loss of consci...

Disruption of phase synchronization between blood pressure and muscle sympathetic nerve activity in postural vasovagal syncope

“…Additionally, although MSNA does not completely disappear, as has been previously suggested (26,48), the disruption of the MSNA-AP relationship may represent a loss of sympathetic baroreflex control of cardiovascular regulation (15,21). This determination would be consistent with our previous findings of a loss in the cardiovagal baroreflex during faint (32).…”

“…The phase synchronization index (PhSI) was analyzed using previously described methods (32). Briefly, nonlinear coupling of two autonomously oscillating signals, such as MSNA and DAP, results in phase synchronization during a period of time in which there is a nearly fixed phase difference between the signals and they are therefore oscillating at the same frequency.…”

“…Based on these findings, it remains unclear how persistent MSNA may be involved in the loss of vasoconstriction during syncope. We (32) have recently shown that the functional phase relationship between blood pressure and HR becomes deficient before the rapid decrease of blood pressure in VVS during upright tilt, and this may account for the accompanying bradycardia. We hypothesized that a similar loss in the functional relationship between MSNA and blood pressure occurs during VVS and accounts for the lack of blood pressure regulation despite persistence of MSNA.…”

Dynamic Cerebral Autoregulation Is Acutely Impaired During Maximal Apnoea In Trained Divers

“…This filtering approach also had the effect of removing variability in each time-series due to respiration and the cardiac cycle. The intrinsic phases of the filtered MAP and CBFV time series, W MAP (t) and W CBFV (t), were extracted using the Hilbert transform [23,30]. The distribution of phase differences between MAP and CBFV was then determined as: DW(t)~W MAP (t){W CBFV (t).…”

Detection of Artifacts and Brain Responses Using Instantaneous Phase Statistics in Independent Components

“…Especially the research on physiological oscillators and their mutual synchronization has a long tradition (Holst, 1937) and phase based methods for synchronization analysis have contributed a lot to this field of research (Glass, 2001;Mosekilde et al, 2002;Schiek et al, 1998;P. Tass, 1999), while the improvement of these methods still continues (Ocon et al, 2011;Wacker & Witte, 2011;Wagner et al, 2010).…”