Fig. 6.

Assessment of the causal interactions between respiration (RESP), ARI, and SBP. A: possible (theoretical) interactive pathways between all processes. B: for all processes the mean relative power contributions related to all processes (the directed coherence) at the breathing frequency. Black quantifies the contribution of respiration; densely hatched represents SBP and lightly hatched ARI. The directed coherence was measured during control (C), following administration of β-adrenergic blocking (BB), and subsequent addition of atropine (BB + AT). For example, during control, the directed coherence from respiration to ARI (left) is 0.70, indicating that respiration explains 70% of ARI signal power at the breathing frequency. Administration of β-blocker agents significantly reduced the contribution of respiration to respiratory-related oscillations of activation recovery intervals (P < 0.05).