Why the study?
Evaluating propensity to postural syncope requires concomitantly characterizing cardiovascular and cerebrovascular controls and disentangling closed-loop relationships and causal links in the frequency domain.
Does Geweke spectral causality analysis of cardiovascular and cerebrovascular oscillations differentiate individuals prone to postural syncope from controls during head-up tilt?
Does Geweke spectral causality analysis of cardiovascular and cerebrovascular oscillations differentiate individuals prone to postural syncope from controls during head-up tilt?
Geweke spectral causality analysis reveals that orthostatic syncope is associated with impaired baroreflex coordination and weak cerebral autoregulation during postural challenge.
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May aid syncope mechanism research via frequency-domain causality; leaves open clinical adoption pending validation.
The evaluation of propensity to postural syncope necessitates the concomitant characterization of the cardiovascular and cerebrovascular controls and a method capable of disentangling closed loop relationships and decomposing causal links in the frequency domain. We applied Geweke spectral causality (GSC) to assess cardiovascular control from heart period and systolic arterial pressure variability and cerebrovascular regulation from mean arterial pressure and mean cerebral blood velocity variability in 13 control subjects and 13 individuals prone to develop orthostatic syncope. Analysis was made at rest in supine position and during head-up tilt at 60°, well before observing presyncope signs. Two different linear model structures were compared, namely bivariate autoregressive and bivariate dynamic adjustment classes. We found that (i) GSC markers did not depend on the model structure; (ii) the concomitant assessment of cardiovascular and cerebrovascular controls was useful for a deeper comprehension of postural disturbances; (iii) orthostatic syncope appeared to be favored by the loss of a coordinated behavior between the baroreflex feedback and mechanical feedforward pathway in the frequency band typical of the baroreflex functioning during the postural challenge, and by a weak cerebral autoregulation as revealed by the increased strength of the pressure-to-flow link in the respiratory band. GSC applied to spontaneous cardiovascular and cerebrovascular oscillations is a promising tool for describing and monitoring disturbances associated with posture modification.
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Porta et al. (2023) studied this question.
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