In June 2024, the NASA Office of Chief Health and Medical Officer (OCHMO) Standards Team will review the status and progress of research and clinical activities aimed at reducing patent-related decompression sickness (DCS) risks. We hosted an independent evaluation working group. Foramen ovale (PFO) during spaceflight and related ground testing and human subject studies.
Decompression sickness (DCS) is a condition caused by dissolved gases (primarily nitrogen) forming bubbles in the bloodstream and tissues. This typically occurs in conditions where the ambient air pressure drops rapidly, such as in scuba divers, high-altitude aircraft, or other pressurized environments. The generated air bubbles can have various physiological effects, occluding blood vessels, causing inflammation, and damaging tissues, which can result in the symptoms of DCS. NASA currently divides DCS into two categories. Type I DCS is less severe and usually causes musculoskeletal symptoms such as joint or muscle pain or skin rash. Type II DCS is more severe and commonly causes neurological, inner ear, and cardiopulmonary symptoms. The risk of DCS in spaceflight occurs during extravehicular activity (EVA), when astronauts perform missions outside the spacecraft while wearing pressurized suits at a pressure lower than the cabin pressure. DCS mitigation protocols based on strategies to reduce systemic nitrogen loading through a combination of habitat environmental parameters, EVA suit pressure, and breathing gas procedures (pre-breathing protocols) to achieve safe and effective mission operations. Will be implemented. The pathophysiology of DCS is still poorly understood, as cases occur even though no air bubbles are detected, but right-to-left venous gas embolism (VGE) may occur due to several potential mechanisms. These include shunts, one of which is the patent foramen ovale (PFO).
Posted by: Pediatric Pulmonologists Dr. Schochet and Dr. Lee
For additional information, see OCHMO-TB-037 Decompression Sickness (DCS) Risk Reduction Technology Overview.
The PFO is a shunt between the right and left atria of the heart and is a persistent remnant of the physiological communication that exists in the fetal heart. Increased left atrial pressure after birth usually forces the interseptal valve against the septum secundum, leading to permanent fusion of the septum within the first 2 years of life due to the development of fibrous adhesions. Therefore, all humans are born with a PFO, and approximately 75% of PFOs fuse after birth. Of the 25% of the population with non-fused PFOs, up to 6% have what some consider to be large PFOs (> 2 mm). The diameter of the PFO may increase with age. The concern with PFO is that the right-to-left shunt between the atria can allow venous embolic gases to pass (“shunt”) from the right atrium (veins) to the left atrium (arteries), resulting in normal lung The embolic filtration may be bypassed. Venous emboli that obstruct passage into the arterial system. Without filtration, bubbles within the arterial system can cause neurological events such as stroke. Activities that raise right atrial/venous pressure above left atrial/arterial pressure (e.g., Valsalva maneuver, abdominal compressions) can result in more blood and emboli passing through the PFO/shunt.
Posted by: Nuffield Department of Clinical Neuroscience
The purpose of this working group was to review and provide analysis of the status and progress of research and clinical activities aimed at reducing the risk of PFO and DCS problems during spaceflight. Identification of DCS cases during NASA exploration atmospheric ground tests conducted in pressurized chambers led to the prioritization of specific topics for external review. The working group’s main goals include:
Quantify the increased risk associated with the presence of PFOs during decompression protocols utilized during ground tests and spaceflight extravehicular activities, as well as unplanned decompressions (e.g., cabin decompression, EVA suit leaks). We discuss the risks and benefits of PFO screening in astronaut candidates, current crew members, and AV examination subjects. What are the potential risk mitigation measures if PFO appears to pose an increased DCS risk? Recommended research and/or technology developments to inform and/or reduce PFO-related DCS risks? What is it?
The working group met over two days at NASA’s Johnson Space Center and included NASA subject matter experts and stakeholders, as well as external reviewers from fields such as cardiology, low-pressure medicine, spaceflight medicine, and military occupational health. I invited you. During the working group, participants were asked to review past reports and evidence regarding PFO and DCS risks, materials and information regarding NASA’s current experience and practices, case studies and subsequent decision-making processes. The working group culminated in a public forum discussion in which recommendations for current and future practice were presented, which were then summarized in a final summary report. This report is available on the NASA OCHMO Standards Team public website.
Key findings from OCHMO’s independent evaluation include:
In extreme exposure/high risk scenarios, removing individuals with PFO and treating PFO does not necessarily reduce the risk of DCS or create a “safe” environment. The difference may develop over time and reduce the overall risk slightly, but it does not eliminate the risk. There are other physiological factors that contribute to the risk of DCS and may have a greater influence (see Findings section 7.0 Other physiological factors). Based on available evidence and current depressurization exposure risks (based on current NASA protocols and NASA-STD-3001 requirements to limit the risk of DCS), PFO is not recommended for spaceflight or ground test participants. Screening is not recommended. The best strategy to reduce the risk of DCS is to create the safest possible environment in all scenarios through effective pre-breathing protocols, safety, and the ability to rapidly treat DCS if symptoms occur. That’s it. Based on the opinion, no specific studies are needed at this time to further characterize PFO with DCS and high exposure. This is because the risks are low and it is desirable to establish appropriate safety protocols and ensure the availability of treatments both on the ground and in spaceflight. For engineering protocols conducted on the ground, it must be ensured that the same level of processing capacity (processing chamber in the immediate vicinity of the test) is provided as during the research protocol. The ability to treat DCS cases immediately is critical to ensuring subject safety.
The full summary report includes detailed background information, discussion points from the working group, and conclusions and recommendations. The findings from the working group and a summary report of the findings will be used to inform future ground tests and spaceflight operations, with the primary purpose of protecting the health and safety of the crew to ensure overall mission success. Helps inform key stakeholders in the decision-making process.
