PHYSIOLOGY of DEEP-SEA DIVING and OTHER HYPERBARIC CONDITIONS

1. PHYSIOLOGY of DEEP-SEA DIVING and OTHER HYPERBARIC CONDITIONS

2. Relationship of pressure to sea depth

3. Relationship of pressure to sea depth • Boyle’s law:The volume to which a given quantity of gas is compressed is inversely proportional to the pressure. • 1 lt air, at 33 feet beneath the sea, half a liter • Actual volume versus sea-level volume

4. Hyperbaric Physiology • For every increase of hydrostatic pressure equivalent to 33 feet of seawater, a pressure increase of 1 atm is present. • Eg. When the chamber is at the equivalent of 66 feet of sea water it is at 3 atmospheres absolute • 2 atm of hydrostatic pressure and 1 atm outside the chamber (if at sea level) • Boyle’s law: at a constant temperature the volume of a gas is inversely proportional to the absolute pressure to which it is subjected.

5. Hyperbaric Physiology

6. Nitrogen Narcosis at High Nitrogen Pressures • Percentage of N2 in the air (4/5) • At sea-level, N2 has no significant effect on bodily function • At high pressures, it can cause varying degree of narcosis • Symptoms of narcosis appear about 120 feet • N2 narcosis beyond 250 feet • Lipid solubility in neuron membranes and physical effect on altering ionic conductance

7. Oxygen Toxicity at High Pressures • Effect of very high PO2 on blood oxygen transport • When the PO2 in the blood rises above 100 mmHg, the amount of O2 dissolved in the water of the blood increases markedly • Large amount of O2 is dissolved, in addition to that bound with hemoglobin • Effect of high alveolar PO2 on tissue PO2 • Extremely high pressure PO2 delivery to the tissues • Hemoglobin-oxygen buffer system, safe range of PO2 between 20 and 60 mmHg

8. Oxygen Toxicity at High Pressures

9. Acute Oxygen Poisoning • High alveolar oxygen pressure • Extremely high tissue PO2 can be detrimental • Breathing O2 at 4 atmospheres pressure of O2 (about 3000 mmHg) will cause brain seizures followed by coma within 30-60 minutes • Other symptoms include nausea, muscle twitchings • Dizziness, disturbance of vision, irritability and disorientation • Excessive intracellular oxidation as a cause of nervous system oxygen toxicity • Oxidizing Free Radicals

10. Acute Oxygen Poisoning • Most of the acute lethal effects of oxygen toxicity are caused by brain dysfunction • Chronic oxygen poisoning causes pulmonary disability • No nervous system effects after exposure to oxygen • Development of lung passageway congestion, pulmonary edema and edema 12h after exposure to 1 atmosphere O2 • Damage to the linings of the bronchi and alveoli

11. CO2 toxicity at great depths in the sea • If the diving gear functions properly, the diver has no problem due to CO2 toxicity • Depth alone does not increase PCO2 in the alveoli • As long as the diver breaths a normal tidal volume • Improper diving gear, accummulation of CO2 • The diver can tolerate PCO2 of up to 80 mmHg • Beyond that it becomes intolerable • Negative tissue metabolic effects of high PCO2 • Development of respiratory acidosis, lethargy, narcosis and finally anaesthesia

12. Decompression Sickness • Air consists of approximately 79% nitrogen • Inert (not physiologically active) • As the diver takes on pressure (descends) the nitrogen is compressed and driven into the tissues. • On ascent, as the pressure decreases N2 comes out of the tissue and returns to solution

13. Decompression Sickness • Most of these nitrogen bubbles are harmlessly filtered out by the lungs • However • If the nitrogen bubbles are too numerous or grow too quickly the diver will develop “the bends”

14. Hyperbaric Physiology

15. Decompression of the diver • When a person breaths air under high pressure for a long time, the amount of N2 dissolved in the body fluids increases • Eventually tissue PN2 increases and becomes equal to the PN2 in the breathing air • Because N2 is not metabolized in the body, it remains in the tissues until the PN2 in the alveoli is decreased back to some lower level • This removal takes hours to occur • Decompression sickness

16. Volume of dissolved N2 at different depths • N2 is highly lipid soluble • It is dissolved both in the body water and fat of the body • If the person remains at a deep level for several hours, both the body water and fat become saturated with N2 • 0 feet 1 lt; 33 ft 2 lt; 100 ft 4 lt; 300 ft 10 lt • Decompression sickness: (Bends, Dysbarism, Caisson Disease, Diver’s Paralysis) • Development of N2 bubles in the body fluids, intracellularly or extracellularly • Decompression sickness

17. Volume of dissolved N2 at different depths

18. Symptoms of Decompression Sickness • Small bubbles block smallest vessels • The bubbles may coalesce and affect larger vessels • Development of tissue ischemia • Symptoms of pain in the joints and muscles of the legs • “bending” in 85-90% of patients with decompression sickness (DS) • In 5 – 10 % of people with DS, nervous symptoms develop (dizziness, unconsciousness, paralysis) • In 2%, patients may develop “chokes” caused by massive numbers of microbubbles plugging the capillaries of the lungs, development of pulmonary edema

19. Hyperbaric Medicine • Hyperbaric means "relating to, producing, operating, or occurring at pressures higher than normal atmospheric pressure.” • Initially used to treat victims of the Spanish Influenza • Later treated many maladies including hypertension, diabetes, syphillis and cancer

20. Hyperbaric Physiology • Take home point: • Hyperbaric therapy increases the partial pressure of oxygen • Saturates the hemoglobin and plasma • Dramatically increases the driving force for oxygen diffusion

21. Diving related injuries • Decompression Sickness (DCS): • refers to a spectrum of clinical illnesses that result from the formation of small bubbles of nitrogen gas in the blood and tissues

22. Decompression Sickness • How do you prevent the bends? • Slow, controlled ascents • No greater than 30 feet per minute • Observing “no decompression” time limits on dives • However, divers may do everything by the book and still get bent • Inherent risk

23. Nitrogen elimination from the body • Decompression tables • Slow ascension of the diver, elimination of N2 • About 2/3 of N2 is liberated in about 1 to 6 hours • Decompression tables have been prepared by the U.S. Navy • A diver who has been breathing air and has been on the sea bottom for 60 minutes at a depth of 190 feet is decompressed according to the following schedule: 10 minutes at 50 feet depth 17 minutes at 40 feet depth 19 minutes at 30 feet depth 50 minutes at 20 feet depth 84 minutes at 10 feet depth

24. Hyperbaric Physiology • The administration of oxygen at a pressure greater than atmospheric pressure at sea level • To achieve hyperbaric pressure the patient is placed in the chamber, which is then pressurized with air. • The absolute pressure is the sum of the atmospheric and hydrostatic pressure as measured in the chamber

25. Tank decompression and treatment of DS • Tank decompression is very important in patients in whom symptoms of DS develop minutes to several hours after they have returned to the surface • The diver is recompressed immediately to a deep level

26. Saturation Diving and Use of Helium-Oxygen Mixtures in Deep Dives • Divers working at 250 to 1000 ft frequently live in a large compression tank for days or weeks • This keeps the tissues and fluids of the body saturated with gases • After this saturation diving, decompression bubbles do not occur • In very deep dives, helium is usually used in the gas mixture instead of N2 • Helium has less narcotic effect • It less dissolves in body fluids • Low density of He keep the airway resistance for breathing at a minimum

27. SCUBA Diving • Self Contained Underwater Breathing Apparatus • 1943, Jacques Cousteau • Compressed air tank • Buoyancy compensator (BC) • Regulator • Weight belt • Mask, snorkel • fins