Short Title: Hypoxia
Last Published:
07/30/21 01:05:31 PM (Central)
Element: Human Health Countermeasures (HHC)
HRP Risk Status: Inactive [no current ongoing research]
Inactive Rationale
While Exploration Atmosphere research and operational development is of high importance, much of this work is now funded by organizations other than HRP, in a collaborative joint effort with HRP as a stakeholder. Details of the work that is already being done (or planned to be done) may be found in the comprehensive NASA technical paper “Integrated Extravehicular Activity Human Research and Testing Plan” (NASA/TP-2019-220232). The impact of using the exploration atmosphere (8.2 psi/34% O2) on various physiological systems has been previously evaluated and summarized in an evidence report. No physiological concerns have been identified, however, the effects of such as atmosphere on the development of SANS is unknown. As part of HRP’s new strategy, that question will be addressed in a future study that will combine head-down tilt bedrest with exposure to the exploration atmosphere. This planned study is captured in the SANS science strategy, and the former gap ExAtm1 has been merged into the new gap SANS-201.
Inactive Documentation:
No Inactive Documentation Available
Risk Ratings and Dispositions per Design Reference Mission (DRM) Category
| DRM Categories | Mission Type and
Duration | Operations | Long-Term Health |
| LxC | Risk Disposition * | LxC | Risk Disposition * |
| Low Earth Orbit | Short
(<30 days) | 3x1 | Accepted with Monitoring | 3x1 | Accepted |
Long
(30 days-1 year) | 3x1 | Accepted with Monitoring | 3x2 | Requires Mitigation |
| Lunar Orbital | Short
(<30 days) | 3x1 | Accepted with Monitoring | 3x1 | Accepted |
Long
(30 days-1 year) | 3x1 | Accepted with Monitoring | 3x2 | Requires Mitigation |
Lunar Orbital
+ Surface | Short
(<30 days) | 3x1 | Accepted with Monitoring | 3x1 | Accepted |
Long
(30 days-1 year) | 3x1 | Accepted with Monitoring | 3x2 | Requires Mitigation |
| Mars | Preparatory
(<1 year) | 3x2 | Accepted with Monitoring | 3x2 | Requires Mitigation |
Mars Planetary
(730-1224 days) | 3x2 | Accepted with Monitoring | 3x2 | Requires Mitigation |
Given that future human exploration missions require a robust, flexible Extravehicular Activity (EVA) architecture not provided with existing approved operational prebreathe protocols, but that might be met by the use of a reduced pressure cabin atmosphere enabling staged denitrogenation, there is a possibility that this atmosphere could result in compromised health and performance to the crewmember due to exposure to mild hypobaric hypoxia.
The exploration atmosphere [8.2 psia]/34% O2) was selected by the Exploration Atmospheres Working Group (EAWG) because it was considered to be a mildly hypoxic atmosphere with acceptable flammability risk and low O2 prebreathe (PB) overhead to maintain acceptable DCS risk while facilitating efficient EVA operations. The 8.2/34 environment (PI O2 = 128 mmHg) is physiologically similar in terms of O2 availability to the nominal shuttle and ISS staged decompression atmosphere of 10.2 psia / 26.5% O2 (PI O2 = 127 mmHg). Both of these environments provide a hypoxic dose approximately by an equivalent air altitude of 4000 ft. The staged atmosphere was used on 40 different shuttle missions for durations of 1 to 8 days. Of most concern are the potential effects on the increased intracranial pressure, visual impairment, cognitive performance, sensorimotor dysfunction, oxidative damage and sleep quality. Other areas of focus include incidence and treatment of transient acute mountain sickness (AMS), development of new exercise countermeasure protocols and effective food preparation at 8.2 psia. Per HLS requirements, the original 7 day limit in NASA-STD-3001 for mildly hypoxic environments was extended to 30 days with monitoring because it was shown to improve the net risk posture for flight crew health and performance. With an agreement on what monitoring is required, this 30 day duration could be extended to indefinite with monitoring for all missions other than Mars, which will need additional assessment due to the long transit in microgravity prior to use of staged denitrogenation environments.
Decreased levels of O2 to the body’s organs and systems affects all physiological functions. However, the 8.2 psia and /34% O2 environment induces only mild hypoxic stress, which healthy individuals can tolerate well on Earth. For example, millions of people live at altitudes higher than 4000 ft. and even more people experience mild transient hypoxia during airplane flights at 5000-8000 ft. However, additive effects of an 8.2 psia and 34% O2 environment and other spaceflight factors, such as microgravity, elevated CO2, mission stress, space radiation, and cycling between mild hypoxia and mild hyperoxia during EVA, might impair human health and performance, although this has not been established.
With 8.2 psia and 34% O2 becoming the baseline for exploration missions, we need to understand how varying periods of exposure to this level of hypobaric hypoxic stress affects the astronaut. Using data from past shuttle flights that operated at a mild hypobaric hypoxic environment for short durations of time, we plan to evaluate how the increased hypobaric stress contributes to the overall physiological stress associated with this engineered environment, however, the data from Shuttle is limited and exploration scenarios could vary significantly from our Shuttle experience. In addition, an inflight surveillance program may need to be developed to understand if and how this mild hypobaric hypoxia affects astronauts for increased durations of time.