The frequency response of cerebral autoregulation

Area of Science:

• Neuroscience
• Physiology
• Biomedical Engineering

Background:

• Cerebrovascular autoregulation's frequency-response is poorly understood.
• Optimal methods for assessing autoregulation using arterial blood pressure (ABP) modulation are unknown.

Purpose of the Study:

• To determine the frequency-response of cerebrovascular autoregulation.
• To identify the optimal ABP modulation frequency for measuring autoregulation and differentiating its states.

Main Methods:

• Neonatal swine underwent positive end-expiratory pressure (PEEP) modulation at various frequencies (0.75-6 cycles/min).
• Arterial blood pressure (ABP) and intracranial pressure (ICP) were measured above and below the lower limit of autoregulation (LLA).
• Phase lag between ABP and ICP quantified vascular reactivity at different frequencies.

Main Results:

• Cerebrovascular reactivity was observed at frequencies below 2 cycles/min.
• A significant phase shift between ABP and ICP indicated intact autoregulation above LLA, while no shift indicated impaired autoregulation below LLA.
• A 60-second wave (1 cycle/min) demonstrated 100% sensitivity and specificity in distinguishing autoregulation states, fitting a high-pass filter model with a cutoff at 1.8 cycles/min.

Conclusions:

• Cerebrovascular autoregulation is band-limited, with reactivity to ABP changes occurring for sustained variations (≥30 seconds).
• A modulation frequency of 1 cycle/min (60-second wave) is optimal for assessing cerebrovascular autoregulation.
• This method effectively differentiates intact from impaired autoregulation in a neonatal swine model.