The arterial baroreflex and inherent G tolerance

Area of Science:

• Cardiovascular Physiology
• Aerospace Medicine
• Human Physiology

Background:

• High G tolerance is crucial for maintaining arterial pressure (AP) under gravitational load.
• The arterial baroreflex plays a key role in regulating AP during G exposure.
• Understanding baroreflex function in individuals with varying G tolerance is essential for safety and performance.

Purpose of the Study:

• To investigate differences in carotid baroreflex responses between subjects with high (H group) and low (L group) G tolerance.
• To test the hypothesis that higher G tolerance is associated with stronger arterial baroreflex responses.
• To evaluate open-loop carotid baroreflex responses using the neck pressure (NP) method.

Main Methods:

• Carotid baroreflex testing was performed on 16 subjects (8 in H group, 8 in L group).
• Measurements included heart rate and arterial pressure (AP) in supine and upright postures.
• The neck pressure method was used to assess open-loop baroreflex responses.

Main Results:

• No significant differences were found in the maximum slopes of carotid baroreflex curves between groups.
• The H group showed a greater increase in systolic and mean AP to hypotensive stimuli in the upright position compared to the L group.
• The L group exhibited increased latency in AP response to stimuli in the upright posture versus supine.

Conclusions:

• The ability for reflexive vasoconstriction and the speed of vascular baroreflex responses during orthostatic stress are linked to higher G-onset-rate (GOR) tolerance.
• These findings highlight the importance of vascular baroreflex function in determining G tolerance.
• Individual differences in baroreflex regulation may explain variations in tolerance to high G environments.