Decompression Sickness

1. Decompression Sickness Dr. Emilia ZainalAbidin EOH3202

2. Pressure • Definition – pressure is force acting on a unit area • Pressure = Force/Area • Unit of pressure • 1 atmosphere = 29.9 inches (760 mm) of Hg = 33 feet (10.08 m) of seawater = 101.3 kilopascals (kPa) = 14.7 pounds per suare inch (psi)

3. Composition of Gases in Atmosphere

4. Dalton’s Law Dalton's Law states that the total pressure of a gas is equal to the sum of pressures of its individual components. At sea level the total air pressure is 1 atm. or 760 mm Hg. Of this total air pressure, 21% (or .21) is from oxygen, 78% (.78) from nitrogen, and 1% (.01) from other gases. The percentage of an individual gas times the total air pressure gives the pressure of that component gas. Thus, at sea level: • Pressure nomenclature • Absolute pressure, ambient pressure, atmospheric pressure, hydrostatic pressure, partial pressure, design pressure

5. What happens to inhaled air at depth? • At depth all pressure increase • Doubling of ambient air pressure occurs at just 33 feet • Tripling of ambient air pressure at 66 feet • Boyle’s Law and Diving

6. Boyle’s Law • The mechanical responses to changes in pressure are in accordance with Boyle's Law, which states that a volume of gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant.

7. Henry’s Law • The amount of gas in solution is proportional to the partial pressure of that gas over the solution • As the pressure of the gas above a solution increases, the amount of that gas dissolved in the solution increases • Reverse is also true, as the pressure of the gas above a solution decreases, the amount of gas dissolved in the solution decreases and forms a “bubble” of gas within the solution

8. Henry’s Law Illustration Low pressure equilibrium Low concentration Double the pressure equilibrium Double the concentration

9. How does the increased pressure at depth affect gas in the body? • The increased pressure of each gas component at depth means that more of each gas will dissolve into the blood and body tissues, a physical effect predicted by Henry's Law • Inhaled gases are in close contact with blood entering the lungs • Hence, the greater the partial pressure of any inhaled gas, the more that gas will diffuse into the blood.

10. Hyperbaric work environment • Hyperbaric work environment (work below sea level pressure or in aquatic environment) • Together, Boyle's and Henry's laws explain when happens when compressed air is breathed • 1) inhaled PO2 and PN2 increase and • 2) the amount of nitrogen and oxygen entering the blood and tissues also increase. • Potential hazards: • Mechanical effects • Inert gas narcosis – physical and mental disturbances when breathing gas contains inert gas under pressure • Effects of CO2 accumulation – refer next slide • Oxygen toxicity – hyperoxia • Decompression sickness

11. Inspiration and expiration • Inspiration: When atmospheric pressure is greater than within the lungs, air flows from outside into the lungs. • Expiration: When pressure in the lungs is greater than the atmospheric pressure, air moves from the lungs to the outside. • If surrounding pressure is high, CO2 could not be exhaled thus CO2 accumulated

12. When does decompression sickness happens? • A diver ascends from a dive • A worker who is doing underwater logging • A worker comes out of a pressurized caisson, or out of a mine, which has been pressurized to keep water out • An unpressurized aircraft flies upwards • The cabin pressurisation system of an aircraft fails. • Divers flying in any aircraft after diving • Pressurized aircraft are not risk-free, since the cabin pressure is not maintained at sea-level pressure

13. Decompression sickness • Decompression sickness(DCS) or diver's disease • Describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation • The bends, or caisson disease • DCS most commonly refers to a specific type of underwater diving hazard but may be experienced in other depressurisation events such as caisson working, flying in unpressurised aircraft.

14. Symptoms of decompression sickness • Bends -

15. Symptoms of decompression sickness

16. Symptoms of decompression sickness

17. Body cavities with trapped gases • When the gases in cavities can't equalize with the ambient environment, the gas is considered to be "trapped" • Lungs • Middle ear - Middle ear squeezes occur because of obstruction of the eustachian tube. • Sinuses - If openings of sinuses are obstructed equalization of pressure becomes difficult • Tooth cavities - mechanically imperfect fillings • Stomach and intestines- gases in the stomach and intestines expand during ascent

18. Factors predisposing to decompression sickness • Ill health • Old age • Obesity • Exercise/exertion • Drugs • Alcohol • Cold • Hypoxia • Previous exposure to decompression – several unpressurized flights or scuba before flight

19. Hypobaric work environment • Work in conditions with reduced pressure – above sea level • For example • Aviation • Space industry As altitude increases, excess nitrogen will begin to try to escape the body to the lower pressure outside. This results in decompression sickness, which can be very painful and even deadly. • Potential hazards • Reduction in partial pressure of oxygen • Decompression sickness

20. Manifestation of decompression sickness at 28000 feet altitude • Bends – joint pains 74% • Creeps – skin rash 7% • Chokes – chest discomfort 5% • Staggers – neurological complaints 1% • Visual disturbances 2% • Reduced awareness/comfusion 9%

21. Dalton’s Law and hypoxia % saturation of hemoglobin varies with changes in partial pressure of alveolar oxygen at various altitudes

22. CNS effects of increasing hypoxia • Feeling tired, sleepy • Euphoria • Impairment of judgement • Dulling of thoughts • Light-headedness • Tingling of hands and feet • Pallor of skin, cyanosis • In-coordination of limbs and disorientation • Falling of vision • Semi-consciousness • Unconsciousness

23. Time of useful consciousness with increasing altitude

24. Role of occupational health professional • Advice on health effects of pressure changes • Treatment of pressure related complications • Medical selection of workers to be engaged in work in hypobaric or hyperbaric environments • Periodic medical examination of diving or aviation personnel • Certification of invalidity for air travel

25. Middle Ear: Preventions • Valsalva maneuver Valsalva maneuver is performed by closing the mouth, pinching the nostrils closed and blowing air through the nose. This will force air up the eustachian tube and into the middle ear. • Make sure you are in good health with no upper respiratory or sinus problems. • swallowing, • yawning, or • tensing the muscles of the throat; this will allow the pressure to equalize

26. Sinus: Preventions Equalization of pressure to relieve pain in the sinuses is best accomplished by use of: • the Valsalva procedure, and/or inhalants. • Reversing the direction of pressure change as rapidly as possible may be necessary to clear severe sinus blocks.

27. GI tract: Preventions • Watch what you eat before you fly. • Staying away from foods you know cause you discomfort or pain in the gastrointestinal tract. Some of the foods that more commonly disagree with individuals are: onions, cabbage, raw apples, radishes, dried beans, cucumbers, melons-or any food that you know causes you problems.

28. Thank you