Categorizing the Role of Respiration in Cardiovascular and Cerebrovascular Variability Interactions

Objective:
Respiration disturbs cardiovascular and cerebrovascular controls but its role is not fully elucidated.
Methods:
Respiration can be classified as a confounder if its observation reduces the strength of the causal relationship from source to target. Respiration is a suppressor if the opposite situation holds. We prove that a confounding/suppression (C/S) test can be accomplished by evaluating the sign of net redundancy/synergy balance in the predictability framework based on multivariate autoregressive modelling. In addition, we suggest that, under the hypothesis of Gaussian processes, the C/S test can be given in the transfer entropy decomposition framework as well.
Experimental protocols:
We applied the C/S test to variability series of respiratory movements, heart period, systolic arterial pressure, mean arterial pressure, and mean cerebral blood flow recorded in 17 pathological individuals (age: 64±8 yrs; 17 males) before and after induction of propofol-based general anesthesia prior to coronary artery bypass grafting, and in 13 healthy subjects (age: 27±8 yrs; 5 males) at rest in supine position and during head-up tilt with a table inclination of 60°.
Results:
Respiration behaved systematically as a confounder for cardiovascular and cerebrovascular controls. In addition, its role was affected by propofol-based general anesthesia but not by a postural stimulus of limited intensity.
Conclusion:
The C/S test can be fruitfully exploited to categorize the role of respiration over causal variability interactions.
Significance:
The application of the C/S test could favor the comprehension of the role of respiration in cardiovascular and cerebrovascular regulations.