1 / 20

Decompression

Decompression. Decompression - Introduction. Nitrogen Depth & Time Safe Ascent Various Theories Varying Permeability Model (VPM) Reduced Gradient Bubble Model (RGBM) Gradient Factors. General Theory. Inert Gas Partial Pressure Supersaturation Slow & Fast Tissues M-Values

fadhila
Download Presentation

Decompression

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Decompression

  2. Decompression - Introduction • Nitrogen • Depth & Time • Safe Ascent • Various Theories • Varying Permeability Model (VPM) • Reduced Gradient Bubble Model (RGBM) • Gradient Factors

  3. General Theory • Inert Gas • Partial Pressure • Supersaturation • Slow & Fast Tissues • M-Values • Tissue Compartments • Leading Tissues • Avoid Exceeding M-Value

  4. General Theory • Supersaturation • Gradient • PP of dissolved inert gas in a tissue (High) • Ambient pressure of gas in alveoli (Low) • Steep Gradient • Faster Decompression • Level of supersaturation nearer to M-Value • Greater risk of DCS • Lower Gradient • Slower Decompression • Less risk of DCS • Balance

  5. General Theory • Haldanian Models Empirical • Bubbles cause DCS • Silent Bubbles – Doppler • Newer theories look at bubble formation • Algorithms • Deep stops – Attempt to limit bubble formation • Dissolved gas and free gas • Bubble Models • Varying Permeability Model (VPM) • Reduced Gradient Bubble Model (RGBM)

  6. General Theory • Ideally inert gas remains in solution • Bubbles • Damage tissue • Clog up pulmonary capillary bed • Bubble Nuclei

  7. Physics of the Bubble Pgas – Partial Pressure of Gas in the Bubble Ptension – Surface Tension Pamb – Ambient Pressure Ptissue – Tension from surrounding Tissue PGas PTension Pamb PTissue

  8. Physics of the Bubble • Reducing Forces > Expanding Forces – Bubble Shrinks • Expanding Forces > Reducing Forces – Bubble Expands • Equilibrium • Gases diffuse into and out of Bubble • Partial Pressure in bubble = Tissue Tension outside bubble • At Depth • pp inert gas in bubble is high • pp of dissolved gas in tissue is low • Reduces bubble size • Deep stops beneficial

  9. Oxygen Window • Inherent Unsaturation • Oxygen metabolised • CO2 highly soluble • Gas tension lower than in arterial blood • Aids removal of gas from bubbles • Zero Supersaturation • Nitrogen Supersaturation no greater than Inherent Unsaturation • Ambient Pressure not exceeded

  10. Gas Elimination • Low partial pressure of inert gas in alveoli • Achieved at Shallower Depths • M – Values create ceiling • Low FN2 in breathing mix • Rich Mix on Ascent • Decompression Schedules • Deep Stops reduce bubble formation • Shallow stops remove dissolved inert gas • Balance

  11. Bubble Models • Varying Permeability Model • Gas Nuclei • Surfactant Skin • Skins permeable at low ambient pressure • Gas diffusion reduced at high ambient pressure • Bubble growth and contraction varies with pressure • Critical total volume of bubbles

  12. Varying Permeability Model • Bubble Growth • Tissue tension vs. Bubble pressure Pb = Pamb + S/r Pb – Bubble Pressure, Pamb – Ambient pressure S – Constant based on bubble skin, r – Bubble radius • Larger bubbles limit permitted tissue tension • Need to know bubble size

  13. VPM – Bubble Size • Ambient pressure • Dissolved gas tissue tension • Fast tissues – More dissolved gas- Larger bubbles • Speed of descent, tissue type, breathing mixture

  14. VPM – Bubble Size • Fast Descent – Lower tissue tension • Increased crushing pressure – smaller bubble • Bubble crushing & growth calculated for differing tissue tensions & bubble sizes • Higher ambient pressure – smaller bubbles – Less decompression? • Increased amount of dissolved gas increases decompression obligation • Volume of bubbles on ascent limited to theoretical critical value

  15. Bubble Models • Reduced Gradient Bubble Model (RGBM) • Oxygen window included in algorithm • Assumes a distribution of bubble nuclei • Calculations based on limiting total volume • Assumes bubble skins permeable at all pressures • Contrary to VPM • Considers bubbles in slow compartments • Eliminated over several days • Repetitive, Multi-Day diving • Conservative no-stop times – Doppler measurements

  16. Bubble Models Gradient Factors M-Value Line GF 20% Inert Gas Pressure in Tissue Compartment Ambient Pressure Line Gradient Factor Line GF 80% Ambient Pressure

  17. Bubble Models – Gradient Factors • M-Value Line • Theoretical limit for avoiding DCS • 100% permitted supersaturation • Tissue Tension = Ambient Pressure • 0% supersaturation • Limit level of supersaturation – Gradient Factor eg. Level of supersaturation of 80% - GF 80 • Different conservatism at different depths • GF Low (Eg. 20%) • GF High (Eg. 80%) • GF 20/80

  18. Bubble Models – Gradient Factors • GF Low • Generates Deep Stops • Reduce microbubbles • Fast Tissues offgassing • Slow Tissues ongassing • Longer deco stops at shallower depths • Gas supply • Gradient Factors • Which to use? • Personal Decision

  19. Summary • Nitrogen • Depth & Time • Safe Ascent • Various Theories • Varying Permeability Model (VPM) • Reduced Gradient Bubble Model (RGBM) • Gradient Factors

  20. Questions?

More Related