Cardiovascular Consequences of Weightlessness Promote Advances in Clinical and Trauma Care

Abstract

Cardiovascular adaptations driven by exposure to weightlessness cause some astronauts to experience orthostatic intolerance upon return to Earth. Maladaptations of spaceflight that lead to hemodynamic instability are temporary, and therefore astronauts provide for researchers a powerful model to study cardiovascular dysfunction in terrestrial patients. Orthostatic intolerance in astronauts is linked to changes in the autonomic control of cardiovascular function, and so patients that suffer neurocardiogenic syncope may benefit from a greater understanding of the effects of spaceflight on the autonomic nervous system. In addition, appropriate autonomic compensation is fundamental to the maintenance of stable arterial pressures and brain blood flow in patients suffering traumatic bleeding injuries. The application of lower body negative pressure (LBNP), an experimental procedure used widely in aerospace physiology, induces autonomic and hemodynamic responses that are similar to actual hemorrhage and therefore may emerge as a useful experimental tool to simulate hemorrhage in humans. Observations that standing astronauts and severely injured patients are challenged to maintain venous return has contributed to the development of an inspiratory impedance threshold device that serves as a controlled "Mueller maneuver" and has the potential to reduce orthostatic intolerance in returning astronauts and slow the progression to hemorrhagic shock in bleeding patients. In this review, we focus on describing new concepts that have arisen from studies of astronauts, patients, and victims of trauma, and highlight the necessity of developing the capability of monitoring medical information continuously and remotely. Remote medical monitoring will be essential for long-duration space missions and has the potential to save lives on the battlefield and in the civilian sector.

Validation of a computational platform for the analysis of the physiologic mechanisms of a human experimental model of hemorrhage

“…Researchers at the USAISR and others have pioneered the use of LBNP as a model to study the effects of hypovolemia in conscious humans 17,30,31. Previous studies have shown that changes in hemodynamics and autonomic responses produced by sequential LBNP are comparable to hemorrhage produced in large animals or mild to moderate blood removal in humans 17,30–33. While the model produces changes in CO and MAP that appear to be similar to actual clinical hemorrhage, there is still much to be explored regarding the physiologic mechanisms of microvascular perfusion and tissue oxygenation.…”

Microgravity Induces Pelvic Bone Loss through Osteoclastic Activity, Osteocytic Osteolysis, and Osteoblastic Cell Cycle Inhibition by CDKN1a/p21

“…Conversely, during spaceflight, gravity-generated forces are absent and the mechanical stimulation of tissues is greatly diminished. Direct and immediate physiological responses to microgravity-induced mechanical unloading include adaptive losses of bone [1], [2], [3], [4], [5], [6] and muscle mass [7], [8], [9], [10], and alterations in cardiovascular function [11], [12], [13], [14]. Because of practical reasons, most space biological animal research has focused on the short-term effects of spaceflight, and thus our understanding of long-term effects of microgravity exposure is very limited.…”

Health Risks of Space Exploration: Targeted and Nontargeted Oxidative Injury by High-Charge and High-Energy Particles

“…Microgravity leads to bone loss (153). Like ionizing radiation, it alters physiological functions (60,265) and contributes to oxidative stress (153). Interestingly, analyses of urinary excretion before, during, and after long-duration space flight (4-9 months) on the Russian space station MIR and short-duration missions on the shuttle revealed opposite results in-flight and post-flight.…”