Arterial diameter during central volume depletion in humans

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function

Background:

• Head-up tilt is a common method to induce central volume depletion.
• Presyncope results from cardiovascular adjustments to reduced central volume.
• Serotonergic pathways may influence vascular tone.

Purpose of the Study:

• To investigate the role of the radial artery in vascular control during head-up tilt-induced central volume depletion.
• To examine the effect of methysergide, a serotonin receptor antagonist, on tilt tolerance and cardiovascular responses.

Main Methods:

• High-frequency ultrasound was used to measure radial artery diameter in healthy subjects during 50-degree head-up tilt.
• Thoracic electrical impedance was monitored to assess central volume changes.
• Cardiac output, heart rate, mean arterial pressure, and total peripheral resistance were measured.
• A double-blind, randomized design was employed with methysergide or placebo pretreatment.

Main Results:

• Head-up tilt induced central volume depletion, decreased cardiac output, and increased heart rate, mean arterial pressure, and total peripheral resistance.
• Presyncopal symptoms were associated with a reduction in heart rate, mean arterial pressure, and total peripheral resistance.
• Radial artery diameter decreased during tilt and increased preceding presyncope, indicating vascular resistance changes.
• Methysergide reduced resting arterial diameters but did not alter tilt tolerance or cardiovascular responses.

Conclusions:

• The radial artery plays a role in vascular resistance adjustments during central volume depletion.
• Vascular control during tilt-induced presyncope is independent of the investigated serotonergic influence.
• Serotonergic pathways may influence resting arterial tone.