Muscle oxygen saturation increases during head-up tilt-induced (pre)syncope

Area of Science:

• Physiology
• Cardiovascular Research
• Autonomic Function

Background:

• Central hypovolemia can lead to hypotension.
• The role of muscle vasodilation in this response is not fully understood.

Purpose of the Study:

• To investigate the role of muscle vasodilatation in hypotension during central hypovolemia.
• To examine muscle oxygenation (SmO2) during head-up tilt (HUT)-induced presyncope.

Main Methods:

• Twenty healthy males underwent passive 50° HUT.
• Muscle oxygenation (SmO2), skin blood flow (SkBF), cerebral oxygenation (ScO2), and middle cerebral artery mean blood flow velocity (MCAvmean) were measured.
• Hemodynamic parameters including mean arterial pressure (MAP) and cardiac output (CO) were monitored.

Main Results:

• Presyncope was associated with decreased MAP, stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR).
• Cerebral oxygenation (ScO2) and MCAvmean decreased significantly.
• Muscle oxygenation (SmO2) increased, while skin oxygenation (SskinO2) and skin blood flow (SkBF) decreased.

Conclusions:

• Head-up tilt (HUT)-induced hypotension is linked to reduced cerebral perfusion.
• Increased muscle oxygenation (SmO2) during presyncope, despite reduced skin blood flow (SkBF), supports a significant role for muscle vasodilation in HUT-induced hypotension.