Unit 3 - The Physiology of Diving Nitrox Oxygen: The Good and the Bad Is necessary to sustain life Too high an oxygen level can be just as harmful as too low Oxygen is our life-support gas The primary waste product is carbon dioxide Oxygen and Metabolism
Unit 3 - The Physiology of Diving Nitrox To avoid Oxygen Toxicity we have Partial Pressure Limits The generally accepted limit for nitrox diving is: –1.4 ata PO 2 –1.6 ata PO 2 as a contingency 1.4 ata PO 2 is more than adequate for 99.9% of the dives you may want to accomplish and is the standard at MLML
Unit 3 - The Physiology of Diving Nitrox Physical Effects of High Oxygen Levels Central Nervous System Toxicity –has a wide range of signs and symptoms, the most dramatic being epilepsy-like convulsions –CNS toxicity can result from relatively short exposures to high partial pressures of oxygen Pulmonary Toxicity or Whole Body Toxicity –results from prolonged exposure to elevated partial pressures of oxygen (above about 0.5 atmosphere) –not a concern for recreational nitrox diver
Unit 3 - The Physiology of Diving Nitrox Central Nervous System Toxicity Factors that can increase your susceptibility to CNS oxygen toxicity –heavy exercise, increased carbon dioxide build-up, chilling or hypothermia, and water immersion –One cannot predict oxygen toxicity
Unit 3 - The Physiology of Diving Nitrox Central Nervous System Toxicity continued Central Nervous System Toxicity –The mnemonic acronym ConVENTID is useful for remembering the most obvious of them: Convulsions Visual disturbances Ears Nausea Twitching or Tingling Irritability Dizziness or Dyspnea
Unit 3 - The Physiology of Diving Nitrox Central Nervous System Toxicity continued Central Nervous System Toxicity –Convulsions are the most obvious and most serious signs. –Possible precursors to convulsions are: Visual disturbances, tunnel vision, dazzle or seeing fireflies. Ear ringing, tinnitus, or sounds like an approaching train in a tunnel. Nausea, including vomiting. Twitching, especially of the lips and small facial muscles or the hands, or tingling (paresthesia) especially in the fingers. Irritability, restlessness, euphoria, dysphoria (uneasiness or feelings of impending doom), anxiety, or general confusion. Dizziness and vertigo or dyspnea (difficult or labored breathing).
Unit 3 - The Physiology of Diving Nitrox Managing Oxygen Exposure The best way to avoid oxygen toxicity problems is to stay within correct oxygen exposure limits.
Unit 3 - The Physiology of Diving Nitrox Managing Oxygen Exposure continued NOAA Oxygen Exposure Limits –In addition to a general PO 2 limit, NOAA has oxygen exposure time limits for a range of oxygen partial pressures from 0.6 ata to 1.6 ata –PO 2 =1.4 ata 111 on EAN 32
Unit 3 - The Physiology of Diving Nitrox Avoiding CNS Toxicity CNS toxicity is avoided by abiding by easily managed limits. Remember that the recommended maximum PO 2 for recreational nitrox diving is 1.4 atmospheres, with a PO 2 of 1.6 atmospheres as a contingency amount. Plan your dives and choose a nitrox mix that is appropriate to the dive.
Unit 7 - Knowing What You Breathe Tracking Your Nitrox Cylinder continued Filling Out The Logbook –Once you have analyzed your cylinder and labeled it, you will be asked to complete the permanent Fill Station Logbook and sign that you have received the cylinder. –Enter your name, date, your certification, cylinders serial number, pressure, oxygen mix, maximum operating depth, signature. –Logbook tracks all nitrox cylinders leaving facility. –Logbook verifies that you either analyzed the contents or knew the particulars of the fill when you received your cylinder.