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Experiment/Payload Overview

Brief Summary

Test of Midodrine as a Countermeasure Against Post-Flight Orthostatic Hypotension - Short Duration Biological Investigation (Midodrine-SDBI) is a test of the ability of the drug midodrine to reduce the incidence or severity of orthostatic hypotension. If successful, it will be employed as a countermeasure to the dizziness caused by the blood-pressure decrease that many astronauts experience upon returning to the Earth's gravity.

Principal Investigator

Steven Platts, Ph.D., Johnson Space Center, Houston, TX

Co-Investigator(s)/Collaborator(s)

Information Pending

Payload Developer

Johnson Space Center, Human Research Program, Houston, TX

Sponsoring Agency

National Aeronautics and Space Administration (NASA)

Expeditions Assigned

|14|15|16|

Previous ISS Missions

A precursor Supplemental Medical Objective (SMO) for Midodrine has been studied on STS-108, STS-110, STS-111, STS-112, STS-113 and ISS Expedition 5.

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Experiment/Payload Description

Research Summary

• Test of Midodrine as a Countermeasure Against Post-flight Orthostatic Hypotension - Short Duration Biological Investigation (Midodrine-SDBI) is designed to evaluate the effectiveness of the drug midodrine at preventing low blood pressure (hypotension) that some astronauts experience upon returning to Earth.
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• Subjects ingest a dose of Midodrine between Time of Ignition (TIG) and landing. Immediately after exiting the vehicle an operational tilt test will be performed.

Description

Many astronauts experience postflight orthostatic hypotension, a condition where the blood pressure drops when an individual stands up, resulting in presyncope (lightheadedness) or syncope (fainting). Approximately 20-30 percent of crews on short-duration (less than 20 days) missions and 83 percent of crews on long-duration missions experience some degree of orthostatic intolerance after return to Earth. To date, the countermeasures tested, such as fluid loading, the use of lower body negative pressure (LBNP), and Fluronef, have not successfully eliminated postflight orthostatic hypotension.

On Earth, the drug midodrine has been used extensively to treat low blood pressure. Midodrine acts as a vasopressor (raise blood pressure) by causing constriction (tightening) of the blood vessels which leads to an increase in blood pressure. Test of Midodrine as a Countermeasure Against Post-flight Orthostatic Hypotension - Short Duration Biological Investigation (Midodrine-SDBI) studies the effectiveness of midodrine for the treatment of postflight orthostatic hypotension.

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Applications

Space Applications

Orthostatic hypotension (low blood pressure while standing) is a significant problem to astronauts returning from even short-term space flight, and the symptoms are more prevalent with longer-term flights. Often when returning home, an astronaut's body is unable to maintain blood pressure above the heart, which leads to decreased blood flow in the brain, resulting in lightheadedness and even fainting. Currently used countermeasures to the problem, such as increasing blood volume with saline, have not proven completely effective. If effective, postflight midodrine administration may provide a relatively simple method for preventing a significant obstacle to long-term space flight, especially exploratory trips to the Moon and Mars. Astronauts in this study, aside from being test subjects, are also control subjects for studies on Earth, as orthostatic hypotension in astronauts is temporary and they are otherwise healthy.

Earth Applications

In addition to benefits for astronauts, millions of people on Earth suffer from orthostatic hypotension and may benefit from information gained from this experiment.

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Operations

Operational Requirements

Shuttle crewmembers will ingest 10 milligrams of midodrine between Time of Ignition (TIG) and landing.

Operational Protocols

Approximately 90 days before flight, the participants will undergo a drug tolerance test for Midodrine and will participate in a drug familiarization session. An operational tilt test will be conducted 10 days prior to launch, and the participants will complete a brief questionnaire before they leave the testing room.

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Results/More Information

Midodrine has been shown to successfully reduce orthostatic hypotension in patients on Earth, as orthostatic hypotension affects people other than astronauts. To date, this investigation has been performed on some space shuttle crewmembers and on an Expedition 5 crewmember. Further Expeditions will involve testing on more subjects before conclusive results can be determined.

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Related Web Sites

International Space Station Medical Project (ISSMP)

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Publications

Results Publications

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Related Publications

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Images

NASA Image: JSC2004E44665 - Astronaut Leroy Chiao (left), Expedition 10 commander and NASA International Space Station (ISS) science officer, and Russian Federal Space Agency cosmonaut Yuri Shargin (right) undergo physical testing on a mechanized tilt table at crew quarters in Baikonur, Kazakhstan, October 8, 2004, in preparation for launch to ISS. The tilt table is used to condition the crewmembers' cardiovascular system against the effects of weightlessness once on orbit. A similar tilt table will be used for the tilt tests in the Midodrine investigation.
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NASA Image: JSC2005E15226 - View of European Space Agency (ESA) astronaut Roberto Vittori and cosmonaut Sergei K. Krikalev during tilt table tests on April 11, 2005 in Baikonur, Kazakhstan.
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NASA Image: JSC2005E15228 - View of astronaut John L. Phillips during a tilt table test on April 11, 2005, in Baikonur, Kazakhstan.
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Information Provided and Updated by the ISS Program Scientist's Office