Middle cerebral artery diameter changes during rhythmic handgrip exercise in humans.

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Medical Imaging

Background:

• Transcranial Doppler (TCD) sonography estimates cerebral blood flow assuming constant arterial diameter.
• Exercise increases arterial pressure via sympathetic activation, potentially altering cerebral artery diameter.

Purpose of the Study:

• To investigate if handgrip exercise alters the cross-sectional area of large cerebral arteries.
• To assess the in vivo response of the middle cerebral artery (MCA) diameter during exercise.

Main Methods:

• High-resolution 7 Tesla magnetic resonance imaging (MRI) was used to measure MCA cross-sectional area.
• Twenty healthy subjects performed rhythmic handgrip exercise at 60% maximum voluntary contraction.
• MCA cross-sectional area changes were analyzed using mixed-effects modeling.

Main Results:

• MCA cross-sectional area significantly decreased by 2.1% during handgrip exercise (p=0.01).
• Heart rate increased by 11% (p<0.001) while end-tidal CO2 remained constant (p=0.10).

Conclusions:

• Rhythmic handgrip exercise induces in vivo vasoconstriction of the MCA.
• Sympathetic activation during exercise leads to a decrease in large cerebral artery diameter.
• Assumptions of constant arterial diameter in TCD exercise studies should be re-evaluated.