NASA-STD-3001 Technical Brief

Relevant Technical

Requirements

Orthostatic

Intolerance

OCHMO-TB-019

Rev B

NASA-STD-3001Volume 1, Rev C

[V1 3003] In-Mission Preventive HealthCare

NASA-STD-3001Volume 2, Rev D

[V2 6109] Water Quantity

[V2 7038] Physiological Countermeasures 

Capability

[V2 7040] PhysiologicalCountermeasure

Operations

[V2 7042] Orthostatic Intolerance 

Countermeasures

Executive Summary

Orthostatic intolerance (OI) is an 

abnormal response observed during 

return to a gravitational environment 

after microgravity exposure. It is 

triggered by upright positioning and is 

caused by an inability to maintain

arterial blood pressure and cerebral 

perfusion. It can result in presyncope 

and, ultimately, syncope (i.e., loss of

consciousness).

Specifically in the spaceflight 

community, OI is a major concern when 

crewmembers are re- introduced to 

gravity after landing due to decreased 

plasma volume and sympathetic

nervous system dysfunction. OI must 

also be considered for standing or 

upright crew experiencing acceleration 

loads. A variety of countermeasures 

can be implemented to mitigate OI 

symptoms.

Fluid loading prior to reentry is animportant

countermeasure to decreaseOI

Source: NASA
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

When a crewmember enters a microgravity environment, a large number of physiological

changes occur, including a significant shift in bodily fluids. Below is a chronological

representation of fluid shifts within the body of a spaceflight crewmember:

A: crewmember is on Earth; usual distribution of fluid while standing – fluid pooled 

in the lower body

B: crewmember arrives in microgravity; distribution of fluid is more towards the upper

body and head due to absence of gravity and hydrostatic gradient

C: crewmember adapts to the microgravity environment (<2 days) by reducing circulating

(intravascular) fluid volume by around 15%, redistribution of fluid to extracellular space

D: crewmember returns to Earth; diminished intravascular fluid volume coupled with

gravitational gradient pooling fluids in the lower extremities leads to reduced venous

return, decreased cardiac output, and OI symptoms

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 2

Background
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

Several countermeasures can be utilized to lessen the effects of OI, with the main strategy

being increasing venous return or intravascular fluid volume. Examples include:

• Inflight exercise – aerobic or resistance; used to counteract the cardiac and muscular

deconditioning accrued throughout the mission.

• Fluid loading & salt intake – increased intake of water with sodium chloride the day

prior to landing via broth or water + salt tablets; increases intravascular volume

• Current protocols include the intake of 24-48 oz of NaCl-water solution before

deorbit, depending on bodyweight

• Compression garments – promote venous

return via lower extremity compression; improved

venous return reduces light-headedness and

pre-syncope risk. Examples include the anti-G suit

(AGS; left picture), gradient compression garments 

(GCG; right picture)

• AGS provides a maximal compression of

~75 mmHg with differential settings

• GCGs have a greater pressure in the lower

leg (~55 mmHg) that gradually decreases

throughout the upper leg (~30 mmHg) and

abdomen (~20 mmHg) to maintain arterial 

blood pressure and mitigate tachycardia

• Cooling garments – to reduce the heat load 

experienced by the crew which, in turn, reduces peripheral vasodilation and further 

fluid redistribution to extravascular space; may have small effects akin to compression

garments

• Pharmaceutical options – while some data suggests benefits of pharmaceutical

intervention for the reduction of OI symptoms (e.g., midodrine, octreotide), the data is

limited and associated pharmaceutical effects or adverse sequelae currently limit

widespread use of such medications during spaceflight

• Artificial gravity – via short radius centrifugation – shown efficacy in bedrest studies, 

but unknown in spaceflight

These countermeasures have individual variability, but all present limitations.

In order to fully protect the crew, several methods should be used in

combination to reduce the risk of OI.

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 3

Application
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

• Cephalad (headward) fluid shifts occur when the crew enters microgravity

• Bed rest studies suggest fluid redistribution

occurs within 2 days of transition to

microgravity

• 6 ̊ head-down tilt bed rest studies

have produced similar plasma

volume reduction (4-17%) to those

seen in microgravity

• Apollo program noted decrease in

crewmember intravascular volume after

spaceflight via bodyweight measurements

• Head-down tilt bed rest studies have

confirmed (via MRI and EKG) cardiac atrophy occurs within 2 weeks

• Studies also confirm autonomic dysfunction, including decreased baroreflex

sensitivity

• Large norepinephrine differences are seen between presyncopal and non-presyncopal

hypovolemic test subjects

• Presyncopal subjects had circulating norepinephrine values similar to

normovolemic subjects, but non-presyncopal subjects had values ~3x those of

normovolemic subjects

• There are differences in OI incidence between males and females. Females generally

experience increased symptoms

during tilt tests and are more

prone to OI in the field. The

figure (right) highlights

sex-based differences in OI

symptoms seen before and

after prolonged bed rest.

Approximately 50% of

female subjects became

presyncopal within 10 

minutes of 30 ̊ tilt.

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 4

Reference Data
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

Back-Up

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 5
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

Major Changes Between Revisions

Original  Rev A

• Updated information to be consistent with NASA-STD-3001

Volume 1 Rev C and Volume 2 Rev D.

Original  Rev A

• Updated information to be consistent with NASA-STD-3001

Volume 1 Rev B and Volume 2 Rev C.

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 6
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

Referenced Technical Requirements

NASA-STD-3001 Volume 1 Revision C

[V1 3003] In-Mission Preventive Health Care All programs shall provide training, in-mission capabilities, 

and resources to monitor physiological and psychosocial well-being and enable delivery of in-mission 

preventive health care, based on epidemiological evidence-based probabilistic risk assessment (PRA),

individual crewmember needs, clinical practice guidelines, flight surgeon expertise, historical review, 

mission parameters, and vehicle derived limitations. These analyses consider the needs and limitations

of each specific vehicle and design reference mission (DRM) with particular attention to parameters such 

as mission duration, expected return time to Earth, mission route and destination, expected radiation

profile, concept of operations, and more. In-mission preventive care includes, but is not limited to: (see 

NASA-STD-3001 Volume 1 Rev C for full technical requirement).

NASA-STD-3001 Volume 2 Revision D

[V2 6109] Water Quantity The system shall provide a minimum water quantity as specified in Table 6.3-

1—Water Quantities and Temperatures, for the expected needs of each mission, which should be 

considered mutually independent.

[V2 7038] Physiological Countermeasures Capability The system shall provide countermeasures to meet

crew bone, muscle, sensorimotor, thermoregulation, and aerobic/cardiovascular requirements defined in

NASA-STD-3001, Volume 1.

[V2 7040] Physiological Countermeasure Operations The physiological countermeasure system design

shall allow the crew to unstow supplies, perform operations, and stow items within the allotted

countermeasure schedule.

[V2 7042] Orthostatic Intolerance Countermeasures The system shall provide countermeasures to

mitigate the effects of orthostatic intolerance when transitioning from weightlessness to gravity

environments and during Gz (head-to-foot) vehicle accelerations defined in the sustained acceleration

limits.

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 7

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-019

Orthostatic Intolerance

Reference List

NASA Office of the Chief Health & Medical Officer(OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for referenceonly.

It does not supersede or waive existing Agency, Program, or Contractrequirements.

12/01/2023

Rev B 8

1. Evidence Report: Risk of Orthostatic Intolerance During Re-exposure to Gravity – HRP,HHCE.

https://humanresearchroadmap.nasa.gov/Evidence/other/ORTHO.pdf

2. Space Operations Medical Support Training Course – Space Mission Operations Division

3. Risk of Orthostatic Intolerance during Re-exposure to Gravity – Stuart Lee (Human Systems Risk Board

presentation on 9/12/2019)