Cardiac-neurovascular crosstalk: Cardiac rhythms reveal maladaptive cerebral autoregulation and constrained ventilatory status

In the context of brain-heart interactions, several pathways have been proposed to mediate feedback loops between neurophysiological oscillations. However, the role of cerebrovascular dynamics in shaping this interplay remains poorly understood. In particular, the interaction between cardiac autonomic control, ventilation mechanisms, and cerebral autoregulation is not well characterized, especially in ageing and post-stroke conditions, where cerebral perfusion is often compromised. In a cohort of 57 elderly participants, including 30 stroke survivors, we investigated the relationship between cardiac sympathetic activity and both, cerebral blood flow regulation and ventilatory status. Sympathetic reflexes, assessed via cardiac sympathetic index (CSI) during sit-to-stand transitions, were preserved across all participants, with no significant group differences between stroke and non-stroke populations. However, among individuals with constrained ventilation, indexed by reduced end-tidal CO ₂ (EtCO ₂ ) at baseline, we identified a more elevated CSI following postural change, scaling with the degree of CO ₂ dysregulation. Furthermore, transcranial Doppler measurements revealed exaggerated changes in mean flow velocity (MFV) within the right middle cerebral artery in most participants. These MFV shifts significantly correlated with the magnitude of cardiac sympathetic change under orthostatic stress, suggesting that CSI can capture maladaptive neurovascular responses. Together, these findings highlight a distinct cardiac-neurovascular crosstalk in elderly individuals, revealing a potential mechanism of compensatory overactivation under impaired cerebrovascular control.