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The ventriculo-arterial coupling ratio during transient Gz events
C D Offerdahl1, D L Ewert, R P Crisman
1Dept. Electrical Engineering, College of Engineering and Architecture, North Dakota State University, Fargo 58105, USA.
Biomedical Sciences Instrumentation
|January 1, 1995
Summary
The ratio of systemic arterial compliance and total peripheral resistance to heart period (tau/T) is not constant during rapid onset +Gz acceleration in baboons. Cardiovascular control systems adjust this ratio in response to G-force stress.
Area of Science:
- Cardiovascular Physiology
- Aerospace Medicine
- Biomedical Engineering
Background:
- The ratio tau/T (total peripheral resistance * systemic arterial compliance / heart period) is a constant in mammals at rest, ensuring adequate coronary perfusion.
- Understanding cardiovascular responses to stress is crucial for human health and safety.
Purpose of the Study:
- To investigate if the tau/T ratio remains constant under rapid onset +Gz acceleration.
- To test the hypothesis that the cardiovascular control system maintains this ratio during G-force exposure.
Main Methods:
- Four baboons were exposed to 10-second rapid onset +Gz profiles.
- Aortic pressure and flow were recorded beat-by-beat.
- Total peripheral resistance (Rp) and systemic arterial compliance (SAC) were calculated using a 2-element windkessel model; heart period (T) was derived from heart rate.
Main Results:
- The tau/T ratio showed minimal increase at +2 Gz but increased dramatically at +3 and +5 Gz.
- This deviation was caused by significant increases in peripheral resistance and heart rate changes during Gz exposure.
- The ratio returned to baseline levels shortly after Gz stress removal.
Conclusions:
- The hypothesis that the tau/T ratio is held constant during rapid onset +Gz acceleration was disproven.
- The observed changes in tau/T reflect baroreceptor reflex responses to decreased aortic pressure during G-force stress.
- The cardiovascular system actively modulates vascular resistance and heart rate to manage G-force effects.