Hemodynamics of Miniature Swine during +G sub z Stress with and without Anti-G Support

摘要

Nine unanesthetized, chronically instrumented, female miniature swine (MS) (avg wt, 39.7 kg) were exposed to head-to-tail inertial load (G sub z) levels of +3,+5, and +7 G sub z for 60 s, with and without anti-G-suit inflation. Venous flow (VF) was measured by an electromagnetic flow sensor around the inferior thoracic vena cava at the diaphragm. Central venous pressure (CVP), abdominal venous pressure (AVP), eye-level blood pressure (ELBP) and esophageal pressure (EP ) were also measured before, during, and after G sub z. There was a progressive significant decreased from control of both ELBP (P 0.001) and VF (P 0.05) during the three G sub z exposures, both with and without S-suit inflation. The MS does a spontaneous straining maneuver (cyclic Valsalva) during G sub z with G-suit support. Using EP as aa trigger, the data were grouped as strain or no strain (relaxation). A continuous AVP-to-CVR gradient existed during G-suit inflation, which increased dramatically during no strain with increasing G sub z, and was associated with an increase in VF. Thus, the majority of VF occurred during relaxation between strains, even though relaxation time was shortened as G sub z increased.