Decompression sickness (DCS) is an occupational hazard as long as extravehicular activity (EVA) is performed at suit pressure less than tissue inert gas tension. Efforts to eliminate DCS in astronauts through engineering control of the habitat atmosphere to minimize atmospheric nitrogen partial pressure will reduce the probability of DCS and severity of symptoms related to evolved gas. Prudent planning requires that DCS treatment resources be provided for Exploration Class missions where EVAs will be numerous, energetic, and a return to definitive medical care is not possible.
Effective treatment to achieve a high symptom resolution is when treatment starts shortly after a symptom is recognized. Effective treatment is through the application of pressure during repressurization to the habitat pressure, an increase in habitat pressure, additional pressurization from the suit above habitat pressure, and the use of 100% oxygen (O2) breathing to accelerate the natural process of bubble dissolution. Combinations of both treatment pressure and 100% O2 breathing through time to achieve greater than or equal to 0.75 symptom resolution at the lower 95% confidence interval is proposed as a requirement to establish treatment resources that assures a successful treatment outcome for Exploration Class EVAs. Adjunctive pharmaceutical and supportive critical care therapy are also necessary, even given a low probability of serious DCS. This study had the following specific aims:
- Consolidate data on factors that provide for effective hypobaric DCS treatment from the NASA Hypobaric Decompression Sickness Database.
- Assemble these data into an NASA Hypobaric DCS Treatment Database.
- Create a statistical model on the probability of effective treatment given inputs on factors that influence effective treatment.
- Consolidate data on interventions that provide for effective hypobaric DCS treatment from published literature and from the Wright-Patterson Air Force Research Laboratory Decompression Sickness Research Database into the NASA Hypobaric DCS Treatment Database.
- Evaluate the initial statistical model (NASA data only) against data from literature and the Air Force database.
- Optimize the model using all available data.
- Evaluate the use of an available bubble growth index (BGI) model as a DCS treatment model and compare to statistical DCS treatment model.
- Deliver to NASA a draft quantitative model(s) for astronaut DCS treatment.
- Document the relevant data, literature reports, and treatment model(s).
- Communicate findings to a wider audience in the event there are applications outside of NASA.
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The Hypobaric DCS Treatment Model links a decrease in computed bubble volume from increased pressure (delta P), increased oxygen (O2) partial pressure, and passage of time during treatment to the probability of symptom resolution symptom resolution. The decrease in volume is realized in two stages: a) during compression of the offending gas phase (Boyle’s Law) and b) during subsequent dissolution of the gas phase by the O2 window. The symptom resolution during re-pressurization was modeled as a log logistic function of pressure difference and two other explanatory variables while accounting for multiple symptoms within subjects. The investigators used data on 154 symptoms from 119 subjects with DCS in 47 different denitrogenation protocols (969 exposures) to fit the model.
The best DCS estimated model is symptom resolution, where increased pressure difference; AMB = 1 if ambulation took place during part of the altitude exposure, otherwise AMB = 0; and Ts is the elapsed time in minutes from the start of altitude exposure to recognition of a DCS symptom.
Conkin J, Abercromby AFJ, Dervay JP, Feiveson AH, Gernhardt ML, Norcross JR, Ploutz-Snyder R, and Wessel JH 3rd. Hypobaric decompression sickness treatment model. Aerospace Medicine and Human Performance..
2015. June; 86(6):508-17. [DOI]
Conkin J, Abercromby AFJ, Dervay JP, Feiveson AH, Gernhardt ML, Norcross J, Ploutz-Snyder R, and Wessel JH 3rd. Probabilistic assessment of treatment success for hypobaric decompression sickness. Houston, Texas: NASA Johnson Space Center, 2014. NASA Technical Publication NASA/TP-2014-218561. [NTRS]
Body mass index
Bubble growth index
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Symptom onset time
Symptoms resolved but then reoccurred
Symptoms resolved at altitude
Symptoms resolved at site pressure
Symptoms resolved on repressurization
Symptoms resolved, percent
Symptons resolved after hyperbaric oxygen
Time from ascent
Time from depress
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