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Related Experiment Videos

A probabilistic model of hypobaric decompression sickness based on 66 chamber tests

J Conkin1, K V Kumar, M R Powell

  • 1Space Biomedical Research Institute, NASA/Johnson Space Center/SD5, Houston, TX.

Aviation, Space, and Environmental Medicine
|February 1, 1996
PubMed
Summary

The NASA tissue ratio (TR) model

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Area of Science:

  • Physiology
  • Aerospace Medicine
  • Biophysics

Background:

  • The NASA tissue ratio (TR) model assumes constant probability of decompression sickness (P(DCS)) under specific conditions.
  • This model's P(DCS) is constant if the ratio of nitrogen pressure in the 360-minute half-time compartment (P1N2) to ambient pressure (P2) remains the same.
  • Existing models may not accurately reflect P(DCS) across varied decompression scenarios.

Purpose of the Study:

  • To test the hypothesis that P(DCS) is better described by TRs that decrease as P2 decreases.
  • To evaluate the efficacy of a modified TR model compared to the standard TR model.
  • To investigate the impact of exercise on P(DCS).

Main Methods:

  • Utilized data from 66 NASA and USAF hypobaric chamber tests involving 1075 exposures and 211 DCS cases.
Keywords:
NASA Center JSCNASA Discipline Environmental Health

Related Experiment Videos

  • Employed survival analysis techniques to fit probability models.
  • Compared a standard TR model with a modified TR model incorporating exercise and fitted parameters.

    • Main Results:

    • The modified TR model, including exercise, significantly improved the log likelihood (-663) compared to the standard TR model (-801).
    • P(DCS) was better described by TRs that decrease as P2 decreases, contradicting the constant P(DCS) assumption.
    • Exercise at ambient pressure was found to increase P(DCS).

    Conclusions:

    • The modified TR model provides a superior description of decompression "dose" across a wider range of conditions than the standard TR.
    • Findings support the need for decompression models where TR decreases with decreasing ambient pressure.
    • Exercise is a significant factor increasing DCS risk during decompression.