Poincaré plot descriptors of heart rate variability as markers of persistent pain expression in freely moving rats

► Time domain analysis of heart rate variability (HRV) as an autonomic index of pain expression. ► Pain expression is associated with high HRV parameters (SD1, pNN18) measured by radiotelemetry. ► Pain symptoms correlate well with elevated SD1 and pNN18 but poorly with mean heart rate in two inflammatory pain models.