Lack of linear correlation between dynamic and steady-state cerebral autoregulation

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Gerontology

Background:

• Cerebral autoregulation (CA) is crucial for maintaining stable brain blood flow despite fluctuations in systemic blood pressure.
• Understanding the relationship between dynamic (dCA) and steady-state (sCA) CA measurements is essential for accurate interpretation in research and clinical settings.
• Previous assumptions suggested a correlation between dCA and sCA, influencing measurement choices.

Purpose of the Study:

• To investigate the relationship between dynamic and steady-state cerebral autoregulation indices in healthy older adults.
• To assess the inter-individual variability in both dynamic and steady-state CA measures within a healthy elderly population.

Main Methods:

• Steady-state CA was assessed by analyzing the slope of cerebrovascular resistance (CVR) changes in response to mean blood pressure (BP) changes induced by pharmacological infusions (sodium nitroprusside/phenylephrine).
• Dynamic CA was evaluated using transfer function analysis (gain and phase) and the autoregulatory index (ARI) from spontaneous BP oscillations and transient BP changes.
• Measurements included cerebral blood flow (CBF) at the internal carotid and vertebral arteries, and CBF velocity at the middle cerebral artery in 28 healthy older adults.

Main Results:

• No significant linear correlations were found between steady-state CA indices and dynamic CA indices.
• Correlations were observed within steady-state measures (e.g., Slope-CVR_VA with Slope-CVRi_MCA) and within dynamic measures (e.g., ARI_SNP with ARI_PhE and ARI_Baseline).
• Significant inter-individual variability in both dCA and sCA efficiency was observed, ranging from low to high autoregulation.

Conclusions:

• The findings challenge the assumption of a direct correlation between dynamic and steady-state cerebral autoregulation measures.
• The significant inter-individual variability underscores the need for careful selection of CA assessment methods based on specific research or clinical goals.
• Neither dynamic nor steady-state measures alone may fully represent overall cerebral autoregulation functioning.