How many squat-stand manoeuvres to assess dynamic cerebral autoregulation?

Area of Science:

• Physiology
• Neurology
• Biomedical Engineering

Background:

• Squat-stand manoeuvres (SSMs) are utilized to assess dynamic cerebral autoregulation by inducing blood pressure (BP) changes.
• However, SSMs are physically demanding, posing challenges for older individuals and limiting the number of repetitions possible.

Purpose of the Study:

• To determine the minimum number of SSMs required to achieve satisfactory coherence for reliable dynamic cerebral autoregulation assessment.
• To minimize the physical workload for participants, particularly older adults.

Main Methods:

• Twenty subjects performed SSMs at 0.05 Hz, with measurements including end-tidal CO2, cerebral blood flow velocity, heart rate, BP, and squat depth.
• Transfer function analysis was used to estimate coherence and the autoregulation index (ARI) at different numbers of SSMs (3, 6, 9, 12, 15).

Main Results:

• Coherence reached satisfactory levels (0.93 ± 0.05) after just three SSMs and peaked at 0.95 ± 0.02 after 12.
• The autoregulation index (ARI) showed a consecutive decrease with more manoeuvres, while intra-subject variability for ARI remained consistent.
• Coherence was significantly enhanced in a repeat visit, indicating improved reliability with familiarization.

Conclusions:

• The findings suggest that a reduced number of SSMs may be acceptable for designing protocols when participant tolerance is limited.
• However, it is emphasized that fewer manoeuvres should be used cautiously, and a full protocol is generally preferred for robust assessment.
• Further validation at a different frequency (0.10 Hz) is recommended to confirm the generalizability of these findings.