Quantitative assessment of cerebral autoregulation from transcranial Doppler pulsatility: a computer simulation study

Area of Science:

• Neurology
• Biomedical Engineering
• Medical Imaging

Background:

• Transcranial Doppler (TCD) ultrasonography is vital for assessing cerebral autoregulation and cerebrovascular reactivity in neurosurgical patients.
• Beyond mean velocity, TCD velocity pulse amplitude changes during cerebral perfusion pressure (CPP) variations offer insights into autoregulation status.

Purpose of the Study:

• To investigate the relationship between cerebral autoregulation and TCD pulsatility using a mathematical model.
• To develop a new quantitative index for assessing autoregulation strength based on TCD pulsatility.

Main Methods:

• Development of a comprehensive mathematical model of intracranial dynamics and cerebrovascular regulation.
• Simulations were performed varying key parameters: autoregulation strength, CSF outflow resistance, and intracranial elastance.
• Analysis of the relationship between TCD velocity pulse amplitude changes and CPP variations under different autoregulation conditions.

Main Results:

• Velocity pulse amplitude increases with reduced CPP in intact autoregulation, shows modest changes in weak autoregulation, and decreases in impaired autoregulation.
• The relationship between velocity pulse amplitude changes and autoregulation strength is nearly linear and minimally affected by CSF circulation or intracranial elasticity.
• A new quantitative index, G(aut)%, is proposed to assess autoregulation strength.

Conclusions:

• TCD pulsatility, specifically velocity pulse amplitude changes, provides valuable information on cerebral autoregulation status.
• The proposed G(aut)% index offers a reliable method for quantifying autoregulation strength, potentially improving patient management.
• The model demonstrates that TCD pulsatility is a robust indicator of autoregulation, largely independent of other intracranial factors.