Peripheral vascular reflexes elicited during lower body negative pressure

Area of Science:

• Cardiovascular Physiology
• Human Physiology
• Autonomic Nervous System Regulation

Background:

• Understanding the interplay between thermal and baroreflexes is crucial for cardiovascular regulation.
• Peripheral venous responses to baroreceptor unloading during gravitational stress require further investigation.

Purpose of the Study:

• To investigate the interaction of thermal reflexes and baroreflexes on human forearm vasomotor and venomotor control.
• To test if peripheral veins are responsive to baroreceptor unloading during gravitational stress.

Main Methods:

• Lower body negative pressure (LBNP) from 10 to 50 mm Hg was applied at ambient temperatures of 28°C and 37°C.
• Measurements included arterial and central venous pressures, heart rate, forearm venous volume, forearm venous pressure, and forearm blood flow in 12 volunteers.
• Analysis focused on changes in forearm venous compliance and vascular resistance relative to central venous pressure changes.

Main Results:

• Central venous pressure decreased significantly at 10 mm Hg LBNP.
• Arterial systolic and pulse pressures decreased significantly above 30 mm Hg LBNP.
• Forearm venous compliance decreased and vascular resistance increased with LBNP, with responses significantly amplified between 30 and 50 mm Hg LBNP.

Conclusions:

• Unloading of cardiopulmonary mechanoreceptors stimulates increases in forearm vasomotor and venomotor tone.
• Arterial baroreceptor unloading further enhances these reflex responses, indicating a coordinated autonomic control during gravitational stress.