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Test of Midodrine as a Countermeasure Against Postflight Orthostatic Hypotension (SMO 006)

Following exposure to space flight, upright posture can result in an inability to maintain adequate arterial pressure and cerebral perfusion (orthostatic or postural hypotension). This may result in presyncope (lightheadedness) or syncope (loss of consciousness) during reentry or egress. A significant number of astronauts experience orthostatic hypotension and presyncope during upright posture. The severity of this problem increases with the length of the space flight mission, as seen in approximately 20% of short-duration and 83% of long-duration crewmembers. It is expected that orthostatic hypotension will be severe on exploration class missions.

To date, available countermeasures (LBNP, fluid loading, Florinef) have not eliminated postflight orthostatic hypotension. This study was designed to evaluate a new pharmacologic countermeasure for protection from postflight orthostatic hypotension. Investigators were studying the ability of the drug Midodrine to reduce the incidence and/or severity of orthostatic hypotension in astronauts returning to Earth. The subject pool included subjects who experience presyncope as well as those who do not. Midodrine is a selective alpha-1 adrenergic agonist that is used clinically to treat orthostatic hypotension. It is almost completely absorbed after oral administration and is hydrolyzed enzymatically to its active metabolite, desglymidodrine, which has a bioavailability of 93%. Midodrine acts by increasing vaso- and venoconstriction, thereby decreasing peripheral venous capacity and blood pooling, but does not pass the blood-brain barrier and therefore has no central stimulant effects. The effect of midodrine as an alpha-adrenergic agonist may be particularly protective of orthostatic tolerance in astronauts who become presyncopal on landing day due to inadequate release of norepinephrine.

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Adrenergic alpha-Agonists
Arterial pressure
Blood pressure
Cardiac output
Cardiovascular system
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Data Information
Data Availability
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Blood flow
Blood pressure
Electrocardiogram (ECG)
Heart rate
Orthostatic intolerance
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
Expedition 16 10/10/2007 04/19/2008 192 days
Expedition 17 04/08/2008 10/23/2008 198 days
STS-116 12/09/2006 12/22/2006 13 days
STS-118 08/08/2007 08/21/2007 13 days
STS-120 10/23/2007 11/07/2007 15 days
STS-122 02/07/2008 02/20/2008 13 days

Human Research Program (HRP) Human Research Roadmap (HRR) Information
Crew health and performance is critical to successful human exploration beyond low Earth orbit. The Human Research Program (HRP) investigates and mitigates the highest risks to human health and performance, providing essential countermeasures and technologies for human space exploration. Risks include physiological and performance effects from hazards such as radiation, altered gravity, and hostile environments, as well as unique challenges in medical support, human factors, and behavioral health support. The HRP utilizes an Integrated Research Plan (IRP) to identify the approach and research activities planned to address these risks, which are assigned to specific Elements within the program. The Human Research Roadmap is the web-based tool for communicating the IRP content.

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Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Pamela A. Bieri
Institutional Support
National Aeronautics and Space Administration (NASA)
Alternate Experiment Name
Midodrine Short
Midodrine Long
SDBI_1503 S
Proposal Date