By This Hour Science Desk
NASA’s Office of the Chief Health and Medical Officer has brought together several unsettled spaceflight health questions—decompression sickness, venous thromboembolism and patent foramen ovale—under a single set of recommendations for Artemis-era missions. The panel’s central message is restrained: it does not identify patent foramen ovale, or PFO, as a major driver of clot formation in the circumstances it reviewed, and it does not call for broad screening or exclusion of astronauts on the basis of the condition.
That conclusion does not amount to a declaration that all PFO-related concerns have been resolved. The group found uncertainty in two areas that matter for operational planning: how well bubble grades predict decompression sickness during particular prebreathe protocols, and whether closing or screening out crew members with a large PFO would meaningfully reduce the chance of a serious mission health event. Its response was to emphasize protocol design, informed decisions where crew are assessed, clinical guidance and further data collection rather than a universal medical rule.
The review was conducted in relation to Artemis missions, which NASA describes as lunar and beyond. It considered data on testing before extravehicular activity, or EVA; decompression sickness events; in-flight venous thromboembolism, or VTE; and the implications of PFO. NASA said the work integrated earlier assessments of PFO and decompression sickness, a prior VTE working group’s work, and an updated standard for preventing decompression sickness.
Selection policy and individual assessment are separate questions
The panel’s conclusion on VTE is specific. It said the presence of a PFO was not a major risk factor for VTE formation, nor for embolic complications involving an initial formation site in the left internal jugular vein or the cerebrum, under normoxic or proposed hypoxic habitat conditions. On that basis, it recommended no changes to astronaut-selection criteria concerning PFO status with respect to VTE.
That recommendation addresses selection in relation to clot risk; it should not be read as a blanket judgment about every conceivable health consequence of a PFO during human spaceflight. NASA’s summary separately addresses the possibility of a venous gas embolism moving to the arterial side. The distinction is important because the working group’s concerns involved more than one mechanism and more than one operational setting.
The group concluded that a small PFO—described as Grade 1 or 2—does not pose a significant risk. It did not recommend universal PFO screening, and it did not endorse excluding astronauts found to have a large PFO. Those positions place the emphasis on managing mission conditions and collecting evidence rather than on automatically treating PFO status as a bar to flight.
Yet the panel did not treat every PFO finding as interchangeable. Where crew members are assessed for PFO, it recommended that they be informed of the result and that closure be offered when a large PFO is identified. That is a conditional recommendation for people who have already been assessed, not a recommendation to test everybody or to require a procedure.
NASA’s account also records mixed opinions over whether closing or screening out crew with a large PFO, defined as Grade 3 or above, significantly lowers the risk that a venous gas embolism could cross to the arterial side and cause a significant health event. The mixed view is material. Offering closure after an assessment is not evidence that closure has been shown to prevent mission health events, and the panel did not present it that way.
Bubble scores do not settle decompression risk
The working group also examined the relationship between bubble grades and decompression sickness at altitude in prebreathe protocols that involve partial gravity and ambulation. It found no definitive link. While minimizing bubbles was considered desirable, the panel said the ability of bubble scores to predict decompression sickness remained uncertain, particularly for lunar surface operations.
That finding bears directly on how evidence from testing is used. The panel recommended that ground-based studies no longer remove participants from research solely because of the presence of left ventricular gas emboli, identified by NASA as LVGE. Instead, study protocols should balance safety against the need for a population that represents the people the research is intended to inform. Participants should also be told of their LVGE status and associated risks.
The recommendation does not dismiss the presence of bubbles as irrelevant. NASA’s summary makes clear that the group favors minimizing them. But it rejects a simpler inference: that a bubble grade by itself can definitively forecast whether decompression sickness will occur under the reviewed conditions. The difference between an indicator worth minimizing and a score with established predictive value is central to the panel’s reasoning.
For Artemis planning, that leaves a practical burden on prebreathe procedures. A protocol cannot rely on a bubble score alone as a decisive proxy for clinical risk if the score’s relationship to decompression sickness is unsettled in partial-gravity and ambulatory settings. The group instead points toward risk mitigation embedded in the protocol itself, alongside continuing data collection.
NASA’s description of the review links that focus to an updated decompression-sickness prevention standard. The available summary does not detail any specific change to a prebreathe schedule, nor does it quantify the level of risk associated with any proposed procedure. It therefore supports a conclusion about the limits of the present evidence, not a comparison of particular EVA preparations.
Medication policy is part of the safety question
One of the panel’s more concrete operational requests concerns medication before, during and after EVAs. It said clear clinical guidance is needed for all crew members. The request specifically includes aspirin in connection with decompression-sickness prevention and pain relief, as well as guidance on pain medicines that may be used before or after an EVA.
The group identified acetaminophen, ibuprofen, naproxen and celecoxib among the analgesics that could mask symptoms of decompression sickness. Its recommendation is not, in the material available, a directive that any of those medicines be used or avoided in every circumstance. Rather, NASA says the panel wants protocols to confront the problem explicitly: medication decisions can affect both pain management and the recognition of symptoms that matter to decompression-sickness care.
This aspect of the review fits the broader approach taken across the recommendations. Rather than treating a single test result or an individual anatomical finding as a complete answer, the panel focuses on the decisions surrounding an EVA: how personnel are prepared, how research subjects are handled, what medical information crew receive, and how symptoms may be interpreted after activity outside the spacecraft.
That does not establish that medication masking has caused a spaceflight incident, nor does NASA’s summary make such a claim. The point is prospective and procedural. The panel sees a need for clinical guidance because the potential for symptom masking could complicate the evaluation of decompression sickness.
The limits of the record matter for Artemis planning
The NASA account portrays the recommendations as an integration of previous working-group outcomes and current review, rather than as a final settlement of every disputed question. Its firmest conclusions are narrow: small PFOs were judged not to pose a significant risk; PFO was not considered a major VTE risk factor in the habitat conditions examined; and PFO status did not warrant changes to selection criteria for VTE.
The same account preserves important limits. It says there is no definitive bubble-grade link for the specified prebreathe setting. It records mixed opinions on the benefit of closure or exclusion for large PFOs. And it favors ongoing collection of information. Taken together, those positions argue against presenting the recommendations as proof that PFO closure prevents a serious event, or as proof that a large PFO carries no operational concern.
They also explain why the recommendations can appear, at first glance, to pull in different directions. No universal screening and no selection exclusion are population-level approaches. Informing assessed crew of their results and offering closure for a large PFO are individual-level options. The former does not erase the latter, and the latter does not create a universal screening mandate.
NASA has not, in the supplied material, set out a timetable for putting these recommendations into practice, named a new selection standard, or described which future studies will be used to narrow the uncertainties. Nor does the available account provide outcome data showing that any particular intervention reduces decompression sickness, VTE or embolic complications in Artemis operations.
The report has not been independently corroborated. This article is based on NASA’s account of its working group and the limited source material supplied for review; the underlying data, deliberations and recommendations have not been independently examined here. The appropriate reading is therefore one of calibrated confidence: the agency has described a risk-management framework, but several of the medical questions it highlights remain open.
For further context on this subject, see Researchers Reportedly Used Claude in Effort That Reached OpenAI Account and GitHub Data.
Reporting notes
What is confirmed: The panel advised against PFO-based selection changes for VTE and against universal PFO screening or exclusion.
Why this matters: The recommendations separate astronaut-selection policy from individual risk-management choices while identifying unresolved medical evidence.
What remains unclear: Bubble-score prediction and the benefit of closure or exclusion for large PFOs remain unsettled in the supplied account. This report is based on one source and has not been independently corroborated.
