Assessing the influence of postural and respiratory changes on the functional brain-heart axis communication.

The brain-heart axis regulates cardiovascular and cerebral function through bidirectional neural communication, integrating autonomic reflexes such as respiratory sinus arrhythmia and postural blood pressure regulation. Despite a growing body of literature, the quantitative dynamics of brain-heart interplay (BHI) underlying respiratory and baroreflex-mediated changes to postural challenges remain incompletely understood. This study aims to elucidate this relationship by investigating postural and controlled respiratory changes. Seventeen healthy volunteers (average age: 22 ± 1.83 years) participated in the study, performing a 5-min resting state in both supine and upright positions, with breathing patterns categorized as either spontaneous or slow-paced (6 cycles/min). Throughout the experiment, we recorded high-density electroencephalography (EEG), arterial blood pressure, and electrocardiogram signals to derive RR interval series and calculate baroreflex sensitivity (BRS). Results indicate that postural changes reduced the power of EEG delta (δ) oscillations and cardiac vagal activity while enhancing EEG beta (β) and gamma (γ) oscillations and increasing diastolic blood pressure. Slow-paced breathing amplified EEG beta (β) and gamma (γ) oscillations but reduced sympathovagal activity. Finally, the upright position enhanced bidirectional BHI information transfer while weakening the functional coupling between BRS and BHI. In contrast to slow-paced breathing, spontaneous breathing is characterized by negative heart-brain correlations in both the high- and low-frequency bands across all EEG spectral bands. These findings underscore the contributions of respiratory sinus arrhythmia and baroreflex-mediated cardiovascular regulation to BHI, demonstrating that both postural and respiratory changes influence BHI directionality and autonomic cardiovascular regulation.NEW & NOTEWORTHY This study demonstrates that posture and respiration significantly modulate brain-heart interplay. Cortical and neurocardiovascular dynamics exhibited frequency-dependent adaptations to gravitational and respiratory changes. Directional neural-cardiac coupling revealed condition-specific afferent pathways linked to baroreflex modulation and descending influences on blood pressure control. These findings underscore the marked physiological sensitivity of brain-heart pathways, offering new insights into autonomic and neurocardiovascular regulation.