Theoretical Analysis of the Mechanisms of a Gender Differentiation in the Propensity for Orthostatic Intolerance After Spaceflight
- Paper number
IAC-08.A1.2.3
- Author
Dr. Richard Summers, University of Mississippi, United States
- Coauthor
Dr. Thomas Coleman, University of Mississippi, United States
- Coauthor
Dr. Steven Platts, National Aeronautics and Space Administration Johnson Space Center, United States
- Coauthor
Dr. Janice Meck, National Aeronautics and Space Administration Johnson Space Center, United States
- Year
2008
- Abstract
Purpose: A tendency to develop reentry orthostasis after a prolonged exposure to microgravity is a common problem among astronauts. The problem is 5 times more prevalent in female astronauts as compared to their male counterparts. The mechanisms responsible for this gender differentiation are poorly understood despite many detailed and complex investigations directed toward an analysis of the physiologic control systems involved. In this study, a series of computer simulation studies using a mathematical model of cardiovascular functioning were performed to examine the proposed hypothesis that this phenomenon could be explained by basic physical forces acting through the simple common anatomic differences between men and women. Methodology: The hypothesis was examined through a systems analysis approach using the well validated cardiovascular portion of the NASA Digital Astronaut Project. The computer model contains over 4000 parameters that describe the detailed interaction of multiple aspects of the circulatory system as determined by basic hydraulics as well as neural, endocrine and metabolic control mechanisms. The female gender differences were simulated by a 15 percent caudal shift in the longitudinal center of gravity of the model’s anatomic structure with a resulting relative increase in the proportional mass in the lower body compartment. However, no additional gender distinctions were otherwise incorporated in the physiologic functioning of the model. Results: In the computer simulations, the circulatory components and hydrostatic gradients of the model were allowed to adapt to the physical constraints of microgravity. After a simulated period of two weeks in microgravity, the model parameters were returned to the conditions of earth’s gravity and a recreation of the standard postflight tilt test protocol was performed. The model output of vital signs during the simulated test revealed a 32 percent larger drop in mean arterial pressure in the females as compared to the corresponding males. These differences in pressure changes with tilt were also associated with an increased tendency for syncope in the females. Conclusions: A systems analysis using the NASA Digital Astronaut demonstrated that a 15 percent lowering of the longitudinal center of gravity in the anatomic structure of the model was all that was necessary to prevent the physiologic compensatory mechanisms from overcoming the propensity for reentry orthostasis leading to syncope. This information may be important in countermeasure development.
- Abstract document
- Manuscript document
IAC-08.A1.2.3.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.