P2.37 Human-Specific Gravitational Damage of Vascular System

Abstract

Objectives

To present a concept of human-specific gravitational damage of vascular system.

Methods

Application of Newton theory of gravitation to Guytońs cardiovascular(CV) physiology supported by analysis of published research.

Results

In upright posture gravitation creates significant gradient of gravitational potential(GP) across human body. This gradient moves blood downward within CV system. CV system must actively respond to emptying of the upper body in upright posture. Guytońs CV physiology with passively filling heart determines two basic ways to prevent gravitation-induced downward blood shift: 1)low body vasoconstriction squeezing blood to the upper parts — well demonstrated in tilt studies by powerful increase of peripheral vascular resistance during head up tilt(precisely, feet-to-head gradient of GP requires exactly opposite head-to-feet gradient of additional vasoconstriction), 2)water retention to indirectly increase intravascular volume in the upper body — shown in space crews during postflight adaptation. The price is significant elevation of intravascular pressure and mechanical stress on vascular walls. This stress, however, is naturally prevented during walk when activated calf muscle pumps effectively return blood into upper body. From this analysis modern lifestyle with reduced walking and prolonged high upright sitting causes excessive gravitation-induced mechanical stress in vascular system. Mechanical wall stress has been widely shown to promote atherosclerosis in large arteries and hypertrophy/remodeling in small arteries while in severe cases also may cause wall rupture/dissection.

Conclusion

Gravitation may seriously damage human vascular system in modern sitting lifestyle.