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Review of Physiology

Review of Physiology. Physiology - Introduction. Oxygen Toxicity Pulmonary Oxygen Toxicity CNS Oxygen Toxicity Calculating & Tracking Oxygen Toxicity Carbon Dioxide Retention – Hypercapnia Narcosis. Oxygen Toxicity. Oxygen free-radicals Damage Cells Pulmonary Oxygen Toxicity

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Review of Physiology

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  1. Review of Physiology

  2. Physiology - Introduction • Oxygen Toxicity • Pulmonary Oxygen Toxicity • CNS Oxygen Toxicity • Calculating & Tracking Oxygen Toxicity • Carbon Dioxide Retention – Hypercapnia • Narcosis

  3. Oxygen Toxicity • Oxygen free-radicals • Damage Cells • Pulmonary Oxygen Toxicity • CNS Oxygen Toxicity

  4. Oxygen Toxicity • Pulmonary Toxicity • ppO2 > 0.5 bar • Inflammation of Lung Tissue • Reduces area for gaseous exchange • Difficulty breathing • Dry cough • Death • Unlikely • Recompression • Tracking

  5. Tracking Pulmonary Toxicity • Oxygen Tolerance Units (OTU) • REPEX Tables • REPEX Maximum Daily OTU Chart 

  6. Calculating OTUs • OTU Chart • Example: EAN 28, depth: 40m, B.T: 30 minutes • Table 1

  7. Calculating OTUs • Table 2

  8. CNS Oxygen Toxicity • High ppO2 • Relatively short periods • Sudden Onset • Oxygen Free Radicals • Susceptibility Varies • Person to Person • Day to Day • CO2 levels • Activity Levels – Deco ppO2 • Vision Effects • Symptoms – Reduce ppO2

  9. CNS Oxygen Toxicity • ConVENTID • Con – Convulsions • V – Visual disturbances • E – Ears eg. Tinnitus • N – Nausea • T – Twitching of muscles (Particularly facial) • I – Irritability • D – Dizziness A Convulsion May Occur Without Warning

  10. Convulsions • Not in themselves lethal • Tonic Phase • Rigidity • Unconsciousness • Breathing Ceases • Clonic Phase • Spasm • Embolism • Breathing Resumes • Lift Diver

  11. CNS Tracking • NOAA ppO2 Time Limits Table • CNS% = Bottom Time at Depth x 100 NOAA Single Exposure Time for ppO2 at Specific Depth • Recommended Limit – 80% • Dive: B.T. – 30 min ppO2 – 1.4 bar

  12. NOAA ppO2 Time Limits Table • Dive: B.T. – 30 min ppO2 – 1.4 bar • Single Exposure Time for 1.4 bar = 150 min CNS% = (30 x 100)/150 = 20% • No calculations if ppO2 <0.5 bar

  13. CNS% Tracking Table • Speeds up calculation • Dive: B.T. – 30 min ppO2 – 1.4 bar CNS% = 0.67 x 30 = 20.1% ≈ 20%

  14. CNS% Tracking • Example 2 Dive: EAN 100 6 metres 20 minutes ppO2 = FO2 x P = 1.00 x 1.6 = 1.6 bar CNS% per min = 2.22 2.22 x 20 = 44.4 CNS% • Examples 1 & 2 part of same dive • CNS% = 20 + 44 = 64% • Easier to exceed limits with ERN vs. AND

  15. CFT Recommendations • Single Exposure Times • CNS% > 80% Minimum SI = 2 h • Maximum Total Duration Times in 24 h Period • If > 80% Minimum SI = 12 h • Breathing normoxic air • Maximum CNS% - 80%

  16. CNS Tracking – Surface Interval • Example CNS% at end of dive – 64% S.I. – 3h 20 min (200 min) At the end of the dive CNS% = 64% After 90 minutes reduced by 50% = 32% After next 90 minutes reduced by 50% = 16% After next 20 minutes No decrease At the end of the surface interval CNS% = 16% • Added to oxygen load of next dive within 12 h

  17. Carbon Dioxide Retention • Waste Product of Respiration • Increased Production – Reduced Ventilation • Hypercapnia • Physiological Effect – Partial Pressure • 10m (2 Bar) vs. 50m (6 Bar)

  18. Carbon Dioxide Retention • Effects of Hypercapnia • Headache • Anxiety & Confusion • Rapid, shallow breathing • Unconsciousness • Vasodilation • Oxygen Toxicity • Nitrogen Narcosis

  19. Carbon Dioxide Retention • Physical Work • Extra Equipment • Configuration • Buoyancy • Work of Breathing (WOB) • Regulators, Dive suit etc. • Increased WOB, Reduced sensitivity to CO2 • Gas Density • Volume of Gas Ventilated • Exhalation Effort • Physical Condition

  20. Carbon Dioxide Retention • Preventing Hypercapnia • Avoid shallow breathing (Breathe in for 5, out for 7) • Good quality equipment • Well-fitting suit and BCD • Avoid excessive work • Maintain health & physical fitness • Treating Hypercapnia • Stop physical exercise • Take long, slow deep breaths • Ascend • Oxygen

  21. Narcosis • Inert Gases at Increased Partial Pressure • Subjective Feelings • Memory • Manual Dexterity • Reduces shivering and perception of cold • Light levels, temperature, state of mind • Speed of descent • Beware complacency

  22. Narcosis • Personal Variation • Everyone affected • Anaesthetic properties of Nitrogen • Speed of processing information • Accuracy of processing information • Task learning

  23. Narcosis • Exacerbating Factors • Increased CO2 • Fatigue, Anxiety, Alcohol, Sedatives • Adaptation, not immunity

  24. Narcosis • Preventing and Coping • Mentally and physically prepared • Avoid alcohol and drugs • Avoid rapid descents • Avoid hypercapnia • Maintain thermal balance • Sleep • Work-up dives • Task-focussing • Helium – Requires trimix qualification • Ascend in a safe manner

  25. Physiology - Summary • Oxygen Toxicity • Pulmonary Oxygen Toxicity • CNS Oxygen Toxicity • Calculating & Tracking Oxygen Toxicity • Carbon Dioxide Retention – Hypercapnia • Narcosis

  26. Questions?

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