Vertical shift in cerebral autoregulation curve: a graded head-up tilt study

Area of Science:

• Neuroscience
• Physiology
• Aerospace Medicine

Background:

• Cerebral autoregulation normally maintains constant cerebral blood flow (CBF) across a mean arterial blood pressure (MABP) range of 60-150 mmHg.
• Recent studies suggest shifts in the autoregulation curve, contradicting classical theory.
• Head-up tilt (HUT) studies are used to investigate cerebrovascular responses, including potential applications for astronauts.

Purpose of the Study:

• To investigate potential shifts in the cerebral autoregulation curve using a graded head-up tilt protocol.
• To evaluate cerebrovascular and cardiovascular responses during head-up tilt in healthy volunteers.
• To provide preliminary data for protocols applicable to astronauts returning from spaceflight.

Main Methods:

• A graded head-up tilt (HUT) study involving 9 healthy volunteers (5 female, 4 male).
• Participants were tilted to 30, 60, and 90 degrees for 5 minutes each.
• Cerebrovascular and cardiovascular parameters, including middle cerebral artery mean flow velocity (MFV) via transcranial Doppler, MABP, and heart rate (HR), were continuously monitored.

Main Results:

• Mean arterial blood pressure (MABP) and MFV showed significant decreases at 60 and 90 degrees of tilt.
• These decreases in MFV occurred despite MABP remaining within the typical autoregulation range (60-150 mmHg).
• Heart rate (HR) significantly increased from baseline at all tilt angles (30, 60, and 90 degrees).

Conclusions:

• The observed trend of decreasing MFV, even with stable MABP within autoregulation limits, suggests a downward shift in the cerebral blood flow plateau.
• These findings support previous research indicating dynamic shifts in cerebral autoregulation.
• The study provides valuable preliminary data for understanding cerebrovascular adaptation and developing countermeasures for spaceflight.