Risks of Decompression Sickness and Venous Thromboembolism during Spaceflight and Patent Foramen Ovale Implications

A NASA working group assembled experts to review the latest data on extravehicular activity (EVA) prebreathe testing and decompression sickness (DCS) events, in-flight venous thromboembolism (VTE) occurrences, and patent foramen ovale (PFO) implications as they relate to NASA's Artemis lunar and beyond missions.

The group's recommendations integrate the September 2024 Assessment of Patent Foramen Ovale as Related to Decompression Sickness in the Spaceflight Environment and During Ground Testing (NASA/SP-20240010473), the April 2026 NASA Risk of Venous Thromboembolism in Spaceflight Working Group (NASA/SP-20260005258/REV1), and the updated DCS prevention standard reviewed by the DCS panel in NASA-STD-3001 Volume 2 Human Factors, Habitability, and Environmental Health (NASA-STD-3001 Vol 2 Rev F), with a specific focus on risk-mitigation interventions such as PFO closure.

For ground-based studies, the panel recommended that subjects should no longer be removed from research solely because they have LVGE. Protocols should balance subject safety with population representativeness, and subjects must be fully informed of their LVGE status and any associated risks. On VTE, the consensus was that a PFO is not a major risk factor for VTE formation, nor for complications from an embolism traveling from an initial formation site in the left internal jugular or cerebrum at normoxic or proposed hypoxic space habitats. No changes to astronaut selection criteria regarding PFOs are recommended with respect to VTE.

For DCS, the group found no definitive link between bubble grades and DCS risk at altitude for prebreathe protocols involving partial gravity and ambulation. While minimizing bubbles is desirable, the predictive value of bubble scores for DCS remains uncertain, especially for lunar surface operations. A “small” PFO (Grade 1 or 2) does not pose a significant risk. There were mixed opinions on whether closing or screening out crew members with a “large” PFO (Grade 3 or above) significantly reduces the risk of a venous gas embolism passing to the arterial side and causing a significant mission health event. The group did not recommend universal screening or exclusion of astronauts with large PFOs, but emphasized risk mitigation through protocol design and ongoing data collection; if crews are assessed, they should be informed of their status and offered closure for a large PFO.

Finally, the panel concluded that clear clinical guidance is required regarding medication use for all crewmembers prior to EVAs, specifically addressing the use of aspirin for DCS prevention and pai...