Modeling of Orthostatic Intolerance During Lower Body Negative Pressure

Postflight orthostatic intolerance (POI) afflicts a significant fraction of male astronauts and nearly all female astronauts when they first stand on Earth after spaceflight. Symptoms include dizziness and fainting, which can impact their abilities to perform critical tasks during the post-landing period. On the Moon or Mars, poor performance or accidents resulting from POI may have potentially catastrophic consequences due to the more hazardous conditions and lack of medical facilities. In addition, the long duration flights necessary to reach Mars may elicit adaptations that increase the risk of POI. Of the many factors that may influence POI, one of the few that may explain the gradual decline in arterial blood pressure experienced by many subjects during stand tests is the loss of blood volume by capillary filtration. Previous simulations suggest that elevated capillary filtration rates distinguish nonfinishers from finishers of stand tests [1, 2]. In this investigation, further computer modeling was undertaken to compare modeled orthostatic response to that of volunteers during graded orthostatic stress (GOS) involving head up tilt (HUT) and lower body negative pressure (LBNP), which reliably produces presyncope and is a candidate training countermeasure for preventing POI.