Abstracts from Plenary Speakers

s from Plenary Speakers K-01 Spaceflight and the cardiovascular system: surprises, paradoxes and implications for future deep space missions P Norsk Universities Space Research Association & NASA For many years, the effects of sudden weightlessness (0 G) on cardiac distension and central venous pressure (CVP) were discussed in the aerospace community. It puzzled researchers that CVP compared to the 1-G supine position decreased during the initial hours of spaceflight, when at the same time left atrial diameter increased (Buckey et al. 1996). By measuring oesophageal pressure as an estimate of interpleural pressure, it was later shown during brief periods of 0 G induced by parabolic flights that this pressure decreases more than CVP does (Videbaek & Norsk 1997). Thus, transmural CVP is increased during 0 G, which distends the cardiac chambers. Because transmural CVP is increased, stroke volume increases according to the law of Frank–Starling leading to an increase in cardiac output, which for months in space is maintained increased to levels, which are 35 % above those in the 1-G seated posture (Norsk et al 2015). Simultaneously, systemic vascular resistance is decreased inducing a decrease in 24-hour ambulatory blood pressure of 10 mm Hg. The paradox is that sympathetic nervous activity is still unchanged in space and at the level observed in the upright seated 1-G posture. Thus, the mechanisms for the simultaneous (1) high sympathetic nervous activity, (2) central blood volume expansion, (3) 35 % increase in cardiac output,( 4) systemic vasodilatation and (5) ambulatory blood pressure reduction need to be explored. These features have implications for understanding cardiovascular health during future long-duration deep space missions. Acta Physiol 2017, 219 (Suppl. 710), 3 © 2017 The Authors. Acta Physiologic © 2017 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd 3 Acta Physiol 2017, 219 (Suppl. 710), 3