A Systems Theory of Cardiac-Autonomic Trajectories and Equilibria

STATE shows that, for isotropic linear autonomic dynamics, sympathetic and parasympathetic coordinates are not separately identifiable from a scalar RR signal, but distinct time scales or coupling restore observability.

• Why it matters: Static HRV indices miss how autonomic regulation persists, transitions, responds to perturbation, and recovers, leaving uncertainty about what can be inferred from RR intervals alone.
• What they did: The authors model autonomic regulation as a low-dimensional latent stochastic dynamical system observed through RR intervals, proving identifiability limits for isotropic linear dynamics and deriving exact properties for a minimal bistable system.
• The result: In Monte Carlo tests, simulated mean escape time matched the exact value within 6%, and in 2000 simulated replicates sustained return after an identical pulse was 100% versus 7%, enabling falsifiable resilience hypotheses.

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