Orthostatic intolerance
Overview
Post-space flight orthostatic intolerance (PSOI) is a medical condition experienced by astronauts after returning from space to Earth's gravity. PSOI refers to the inability of the body to maintain adequate blood pressure when transitioning from a horizontal position to an upright stance, which can cause dizziness, lightheadedness, and fainting.[1]
Pathophysiology
During spaceflight, the human body adapts to the microgravity environment by altering its physiological systems, particularly the cardiovascular system. In normal gravity conditions on Earth, the body relies on gravity-dependent processes such as venous return and blood pressure regulation. However, in microgravity, these processes are disrupted leading to a reduction of plasma volume, cardiac atrophy, and a decrease in baroreceptor sensitivity.[2]
Upon returning to Earth's gravity, the body struggles to re-establish its normal cardiovascular functions, resulting in orthostatic intolerance, which can persist for several days up to several weeks post-flight. The inability to maintain adequate blood pressure and blood flow when standing upright leads to symptoms such as dizziness, lightheadedness, and fainting.[3]
Risk Factors
- Duration of spaceflight: Longer missions are associated with a higher incidence of PSOI.
- Age: Older individuals tend to be more susceptible to PSOI.
- Sex: Females are at a greater risk for developing PSOI compared to males.
- Physical fitness: Individuals with lower levels of physical fitness have a higher likelihood of experiencing PSOI.
Symptoms
Common symptoms include:
- Dizziness or lightheadedness when standing up
- Fainting or near-fainting
- Headaches
- Fatigue
- Nausea and vomiting
- Increased heart rate and blood pressure when standing up
Diagnosis
Diagnosis of PSOI is primarily based on the individual's reported symptoms and medical history. Physical examination, including assessment of vital signs (blood pressure, pulse, and respiration) in supine and upright positions, may be performed to evaluate orthostatic changes.
Treatment
There is no definitive cure for PSOI, but several interventions can help alleviate its symptoms:
- Fluid intake: Drinking plenty of fluids before, during, and after spaceflight can help maintain adequate hydration levels.
- Gradual re-adaptation: Slowly transitioning from horizontal to upright positions upon return to Earth can reduce the risk of developing PSOI.
- Medications Options:
- Fludrocortisone 0.1-0.2 mg per day, starting 1-2 days before re-entry to Earth's gravity dose can be increased to 0.3-0.4 mg per day if needed
- Midodrine 2.5-5 mg orally, 3 times a day and increased to 10 mg, 3 times a day, if needed [4]
Prevention
Strategies include:
- Pre-flight training: Astronauts undergo specific exercise regimens before spaceflight to improve cardiovascular fitness.
- In-flight exercise: Regular exercise during spaceflight, such as using the advanced resistive exercise device (ARED), can help maintain cardiovascular function.
- Post-flight rehabilitation: Physical conditioning programs are implemented after return from space to gradually re-adapt the body to Earth's gravity.
See also
References
- ↑ Thornton WE, Moore TP. (1987) Space Motion Sickness and Space Adaptation Syndrome. NASA Technical Paper 2873.
- ↑ Clement G. (2003) Fundamentals of Space Medicine. Springer, New York.
- ↑ Convertino VA. (1991) Physiological changes associated with space travel. Medicine and Science in Sports and Exercise, 23(2): 191-206.
- ↑ Hemodynamic Effects of Midodrine After Space Flight in Astronauts Without Orthostatic Hypotension. https://ntrs.nasa.gov/citations/20080033572