Static autoregulation in humans: a review and reanalysis

Area of Science:

• Physiology
• Neurology
• Cardiovascular Science

Background:

• Cerebral autoregulation (CA) describes the relationship between mean arterial pressure (MAP) and cerebral blood flow (CBF).
• Understanding the static relationship between MAP and CBF is crucial for assessing brain health.
• This review synthesizes current knowledge on the static MAP-CBF relationship.

Purpose of the Study:

• To conduct an up-to-date literature review on the static relationship between MAP and CBF.
• To analyze the autoregulatory capacity of the cerebral circulation under varying MAP conditions.

Main Methods:

• A comprehensive literature search was performed, analyzing 40 studies with 49 experimental protocols in healthy adults (18-65 years).
• Studies with less than 5% change in MAP, hypoxia, hyperoxia, or unstable conditions were excluded.
• Cerebral blood flow (CBF) data were adjusted for partial pressure of arterial CO2 (PaCO2) in a subset of studies.

Main Results:

• The regression coefficient for CBF changes during MAP decreases (0.82±0.77) differed significantly from MAP increases (0.21±0.47; p<0.001).
• After adjusting for PaCO2, this significant difference in slopes was lost (increased MAP: 0.64±1.16; decreased MAP: 0.39±0.30; p=0.60).

Conclusions:

• Cerebral circulation demonstrates greater autoregulatory activity in response to increases in MAP compared to decreases.
• The observed hysteresis in cerebral autoregulation is not statistically significant after correction for PaCO2.
• These findings highlight the complex interplay between MAP, CBF, and CO2 in cerebral autoregulation.