Assessment of DCS-related PFO in the spaceflight environment and during ground testing – NASA

In June 2024, the NASA Office of the Chief Health and Medical Officer (OCHMO) Standards Team hosted an independent evaluation working group to review the status and progress of research and clinical activities aimed at patent decompression sickness. (DCS) is to reduce the risk. Foramen ovale (PFO) during spaceflight and associated ground testing and human subjects studies.

Decompression sickness (DCS) is a condition that results in bubbles of dissolved gases (mainly nitrogen) forming in the blood and tissues. It is commonly experienced in situations where there is a rapid drop in ambient pressure, such as scuba divers, high-altitude aviation, or in other pressurized environments. The gas bubbles produced have various physiological effects and can obstruct blood vessels, stimulate inflammation and damage tissue, resulting in the symptoms of DCS. NASA currently classifies DCS into two types: Type I DCS, which is less severe, usually causes musculoskeletal symptoms including joint or muscle pain, or skin rashes. Type II DCS is more severe and usually results in neurological, inner ear, and cardiopulmonary symptoms. The risk of DCS in spaceflight presents during extravacuolar activities (EVAs) in which astronauts perform mission tasks outside the spaceflight vehicle while wearing a pressurized suit at a pressure lower than cabin pressure. A DCS mitigation protocol based on strategies to reduce systemic nitrogen load by combining habitat environmental parameters, EVA suit pressure, and breathing gas procedures (pre-breath protocol) to achieve safe and efficient mission operations. are implemented through The pathophysiology of DCS is not yet fully elucidated because cases occur despite the absence of detectable gas bubbles but involves right-to-left shunting of venous gas emboli (VGE) through several possible mechanisms. included, one of which is the patent foramen ovale (PFO).

by: Dr. Shushe and Dr. Lai, pediatric pulmonologists

Reference OCHMO-TB-037 Decompression Sickness (DCS) Risk Reduction Technical Brief for additional information.

A PFO is a shunt between the right atrium and left atrium of the heart, a permanent remnant of the anatomical communication in the fetal heart. An increase in left atrial pressure after birth usually forces the interseptal valve against the septum secundum and within the first 2 years of life, the septae permanently fuse due to fibrous adhesions. Thus, all humans are born with a PFO and approximately 75% of PFOs fuse after childbirth. For the 25% of the population whose PFOs do not fuse, ~6% have what some consider a large PFO (> 2 mm). PFO diameter may increase with age. The concern with PFOs is that with a right-to-left shunt between the atria, venous emboli gas can move from the right atrium (venous) to the left atrium (arterial) (the “shunt”), thereby bypassing normal lung filtration. goes Venous emboli that block the passage of the arterial system. Without filtration, bubbles in the arterial system can lead to neurological events such as stroke. Any activity that increases right atrium/venous pressure over left atrium/arterial pressure (eg Valsalva maneuver, abdominal compression) may further activate blood and/or emboli in the PFO/shunt.

by: Nuffield Department of Clinical Neurosciences

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. Cases of DCS identified during ground testing of NASA exploration environments in pressurized chambers led to the prioritization of a given subject for external review. The main objectives of the working group include:

1. Quantify any increased risk associated with the presence of a PFO as well as unplanned decompressions (eg, cabin depression, EVA suit leak) during decompression protocols used in ground testing and spaceflight EVA.
2. Explain the risks and benefits of PFO screening in astronaut candidates, current crew members, and chamber test subjects.
3. What are potential risk reduction measures that can be considered if a person is considered to be at increased risk for DCS due to a PFO?
4. What research and/or technology development is recommended that may help inform and/or reduce the risk of PFO-related DCS?

The working group took place over two days at NASA’s Johnson Space Center and included NASA subject matter experts and stakeholders, as well as external reviewers from the fields of cardiology, hypobaric medicine, spaceflight medicine, and military occupational health. Invited. During the working group, participants were asked to review past reports and evidence on the risk of PFOs and DCS, materials and information on current NASA experience and practices, and case studies and subsequent decision-making processes. The working group culminated in an open forum where recommendations for current and future practices were presented and subsequently summarized in a final summary report, which is publicly available on the NASA OCHMO Standards Team. Website.

The following are key findings from OCHMO’s independent evaluation:

1. In the high-exposure/high-risk scenario, treating PFOs by excluding individuals with PFOs does not necessarily reduce the risk of DCS or create a ‘safer’ environment. This may make an incremental difference and slightly reduce the overall risk but does not make the risk zero. There are other physical factors that also contribute to the risk of DCS that may have a greater effect (see 7.0 Other Physical Factors in the Fusing section).
2. Based on the available evidence and the risk of current decompression exposures (based on current NASA protocols and requirements of NASA-STD-3001 to limit the risk of DCS), screen any spaceflight or ground test participants for PFOs. is not recommended. The best strategy to reduce the risk of DCS is to create the safest environment possible in every scenario, through effective pre-breath protocols, safety, and the ability to treat DCS quickly when symptoms appear.
3. Based on opinion, no specific research is currently needed to further characterize PFOs with DCS and altitude exposure, a priority to establish low-risk and appropriate safe protocols and the availability of treatment in both ground and spaceflight. Due to ensure.
4. For engineering protocols conducted on land, it must be ensured that the same level of treatment capacity (treatment chamber in the vicinity of the testing area) is provided as during research protocols. The ability to treat a DCS case quickly is critical to ensuring the safety of test subjects.

The full summary report includes detailed background information, working group discussion points, and conclusions and recommendations. A summary report of the working group’s findings and results to inform key stakeholders in the decision-making process for future ground testing and spaceflight operations with the primary goal of crew health and safety to ensure overall mission success. I will help.