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Dive Tables & Decompression Theory

Dive Tables & Decompression Theory. What We Will Cover. Blood Supply and Tissue Compartments Tissue Half-Times Tissue Tolerance Tissue Behaviour During Dives Predisposing Factors to DCS Nitrogen Uptake Nitrogen Pressure Gradient Basic Bubble Theory Deep Decompression Stops.

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Dive Tables & Decompression Theory

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  1. Dive Tables & Decompression Theory

  2. What We Will Cover • Blood Supply and Tissue Compartments • Tissue Half-Times • Tissue Tolerance • Tissue Behaviour During Dives • Predisposing Factors to DCS • Nitrogen Uptake • Nitrogen Pressure Gradient • Basic Bubble Theory • Deep Decompression Stops

  3. What We Will Cover • Dive Table Development • Buehlmann Tables: • Definitions • Rules • Worked Examples • Special Circumstances

  4. Blood Supply & Compartments • Nitrogen Absorption Dependant on Tissue Blood Supply • Fast Tissues have a High Blood Flow • Slow Tissues have a Low Blood Flow • Exercise and Blood Flow to Organs • Increases for Heart, Lungs, Chest Area • Decreases for Kidneys, Stomach & Liver

  5. Body Tissue Groups Type # Half-Time for N2 - Mins Corresponding Organs & Body Tissue Group F A S T 1 2 3 4 5 4 8 12.5 18.5 27 Blood Brain, Central Nervous System Spinal Cord M E D I U M 6 7 8 9 10 38.3 54.3 77 109 146 Skin Skin, Muscles S L O W 11 12 13 14 15 16 187 239 305 390 498 635 Muscles, Bones, Joints Bones, Joints

  6. Tissue Saturation and Desaturation

  7. Tissue Tolerance • Body Tissue can Tolerate Increased Pressure • Rapid Reduction in Pressure => Problems • Haldane: Half the Pressure if Fine • M-Value: Max Permissible Excess Pressure • Doppler Studies: • Fast Tissue ratio: 2.3 to 1 • Slow Tissues ration 1.3 to 1 • Controlled Ascent and Stops

  8. Desaturation C.N.S. Skin, Muscles 12.2 minute half life 37 minute half life 4 minute half life 1.0 22’ 3 m 1.3 7’ 6 m 1.6 Pressure reduction tolerance [bar] • Tissues with shorter half times govern deeper stops. • Tissues with longer half times govern shallower stops. 4’ 9 m 1.9 2’ 12 m 2.2 20 30 40 50 60 70 Time - minutes

  9. Tissue Behaviour During Dives • First Dive • Fast Tissues Absorb and Release Nitrogen Quickly • Slow Tissues Absorb and Release Nitrogen Slowly • Repetitive Dive • Nitrogen Still in Slow Tissues • Intensive Diving can Cause a Build Up • Take 12 Hour Break Every Third Day • No Flying for 24 Hours

  10. Predisposing DCS Factors • Time • Increase Nitrogen Uptake • BT < 45 mins, statistically safer • Depth • Increase Pressue, More Nitrogen Uptake • Dives > 30m show increase risk of DCS • Ascent Rate • Fast Ascent - Dangerous • Multiple Ascents • Sawtooth Profile

  11. Predisposing DCS Factors • Repetitive Diving • More DCS Incidents Occur • Already have Excess Nitrogen • Any Micro bubbles Present will Increase in Size • Pulmonary Shunt May Occur • Cold • Nitrogen More Soluble • Vasoconstriction • Diuresis and Dehyrdation • Diver Rewarms: Nitrogen Less Soluble; Vasodilation

  12. Predisposing DCS Factors • Carbon Dioxide Levels (Hypercapnia) • Vasodilation • Increase Bubble Size • Exercise • Increase Blood Flow • Increase Breathing Rate • Ascent - Reduced Blow Flow and Elimination • Dehydration • Reduced Blood Volume • Clotting • Previous DCS • Higher Rate Statistically • Damaged Tissue - Slower Release of Nitrogen

  13. Predisposing DCS Factors • Altitude • Atmospheric Pressure < 1 bar • Patent Foramen Ovale (PFO) • Blood Flow from Right Atrium to Left • Venous Bubbles Enters Arterial Circulation • Unfitness and Fatigue • Nitrogen Removal from Tissues is Slower • Obesity • Solubility • Circulation

  14. Predisposing DCS Factors • Age • Reduced Circulation Efficiency • Obesity • Illness • Reduced Fitness • Circulatory or Repiratory • Stress • Adrenaline - Increased Breathing Rate and Circulation • Increases Diver Error • Alcohol, Drugs and Nitrogen Narcosis • More Mistakes Made • Alcohol Causes Dehyration • Affects of Drugs Unknown at Depth

  15. Nitrogen Uptake • Depth • Time at Depth • Tissue Type: Fast vs Slow • Fat • Blood Flow • Cold • Exercise

  16. Nitrogen Pressure Gradient • Difference Between ppN2 of Body Tissue and Inhaled Gas • Descent: Air (Hi) - Blood (Mid) - Tissue (Lo) • During Dive: N2 Accumulates but O2 Metabolised • Ascent: Tissue (Hi) - Blood (Mid) - Air (Lo) • N2 Leaves Blood (Lungs) / Replaced by O2 • N2 Leaves Tissues to the Blood. • Cycle Continues • 100% O2 Increases Gradient Between Inside and Outside of Bubble -> Decreases in Size

  17. Basic Bubble Theory • Micro Nuclei - Seeds • Micro Bubbles -> DCS Bubbles • Crushing Forces acting on a bubble include: • Ambient Pressure • Tissue pressure exerted on bubble • Surface tension • Bubbles grow if Crushing Forces < Pressure inside bubble • Bubbles shrink if Crushing Forces > Pressure inside bubble

  18. Pulmonary/Vascular Shunt • Micro bubble formation more common • Occur after most dives • Bubbles delay outgassing due to vascular shunt • Most pronounced after surfacing • Can persist for up to 90 minutes • Always do a minimum 2 hour surface interval

  19. Deep Decompression Stops • Also known as Pyle Stops • Series of Deep Stops of 1 or 2 minutes • Half way pressure point between bottom and first stop. • Reduces Bubble Formation and Growth • Limits gas freed from solution. • Keeps Pressure inside bubble high causes bubbles to shrink • CMAS and CFT have ratified Deep Decompression Stop tables

  20. Dive Table Development • Haldane: Sheep • Caisson Worker Observations • Injuries -> DCS Type 1 • US Navy • 94% Safe - Primarily military use • Buehlmann • Doppler Testing

  21. Definitions • Bottom Time • Depth • Ascent Rate • Safety Stop • No Decompression Limit (N.D.L.) • Decompression Stop Time (Stops)

  22. Definitions • Repetitive Dive • Repetitive Group (R.G.) • Surface Interval (S.I.) • Residual Nitrogen Time (R.N.T.)

  23. Definitions 1. Depth 30 mts 2. Bottom Time A-B (15 mins) 3. Ascent Rate 10m/min 4. Ascent Time B-C (2 mins) 5. Safety Stop C-D (3 mins) 6. Dive Duration A-E (21 mins) 7. No Decompression Limit 30m N.D.L. = 17 mins

  24. Rules • Ascent Rate • Intermediate Depth • Intermediate Time • Strenuous/Cold Dives • Safety Stop • Maximum Depth • Stage Decompression

  25. Air Diving Decompression Table Learn the No-Decompression Limits (NDL)

  26. Repetitive Dive Table

  27. Rules Deeper Dive First For a Repetitive Dive to an Intermediate Depth Use shallower depth for R.N.T. and deeper depth for N.D.L.

  28. Example Dive to 27m for 17mins R.G. = C Surface interval = 2 hours (R.G. = A) 2nd dive 20m = intermediate depth \ Apply rule (shallower for R.N.T.) = 18m column So 18m/column A = R.N.T. of 14min For N.D.L. of dive 2 apply rule (deeper) = 21m N.D.L. of 21m = 34 Max N.D.L. for 2nd dive is 34 - 14 = 20mins

  29. Example 1: 15 mts for 59 mins RG = Surface interval 15 mins RG = What is maximum NDL for a second dive to 15 mts.? NDL for 15 mts. mins Less RNT for RG C at 15 mts. -___ mins Maximum NDL for 2nd dive mins

  30. Example 2: Working dive to 28 mts for 10 mins RG = Surface interval 2 hours RG = What is maximum NDL for a repetitive dive to 20 mts.? Max NDL for 20 mts (21 mts) mins Less RNT for RG A at 18 mts -___ mins Maximum NDL for 2nd dive mins

  31. Example 3: 24 mts for 19 mins RG = Surface interval 2 hrs RG = 2nd dive to 22 mts, actual time 23 mins Decompression stops: mins at mts 3rd dive planned to 15 mts after a surface interval of 1 hour. What is max time at this depth? RG at end of 2nd dive = RG at end of surface interval = Max NDL for 15 mts mins Less RNT for RG C at 15 mts. -___ mins Maximum NDL for 3rd dive mins

  32. Example 4: 36 mts for 10 mins RG = Surface interval 2 hours 30 mins To what depth can a diver return for a dive of duration 30 mins? RG at end of surface interval = Scan range of depths: Depth NDL RNT Max Time Allowed 15 mts 18 mts 21 mts

  33. Extraordinary Situations Slowed Ascent Add additional ascent time to bottom time Shortened/Omitted Decompression & Emergency Ascents • Give 100% O2 • Observe Victim & Buddy - Contact Coast Guard • If signs of D.C.S or Barotrauma - Remove to Chamber • No diving for 24 hours

  34. Intensive Diving • 12 hr break every 3 days • Dive sequence to get shallower during day

  35. Flying After Diving • Cabin Pressure • 0.73 - 0.85 Bar • After Intensive Diving • Stop 24 hrs Before Flying • After Decompression Diving • Stop 24 Hours Before Flying

  36. Surface Interval (SI) A 2 hours Minimum is recommended to facilitate efficient out-gassing

  37. Summary • Blood Supply and Tissue Compartments • Tissue Half-Times • Tissue Tolerance • Tissue Behaviour During Dives • Predisposing Factors to DCS • Nitrogen Uptake • Nitrogen Pressure Gradient • Basic Bubble Theory • Deep Decompression Stops

  38. Summary • Dive Table Development • Buehlmann Tables: • Definitions • Rules • Worked Examples • Special Circumstances

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