Decompression Sickness Dr. Emilia Zainal Abidin EOH3202

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)

Composition of Gases in Atmosphere Component Composition Symbol Volume percent Nitrogen Oxygen Argon Neon Helium Hydrogen Others N O A Ne He H (Co, Kr, Xe, etc) 78.094 20.948 0.934 0.001818 0.000524 0.00005 0.01

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

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 Air 760 mm Hg 14.7 psi 1 atm Sea 33 ft 1520 mm Hg 29.4 psi 2 atm Sea 66 ft 2280 mm Hg 44.1 psi 3 atm Sea 99 ft 3040 mm Hg 58.8 psi 4 atm Sea 132 ft 3800 mm Hg 73.5 psi 5 atm

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.

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

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

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.

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

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

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

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.

Symptoms of decompression sickness Bends - DCS Type Bubble Location Signs & Symptoms (Clinical Manifestations) BENDS Mostly large joints of the body (elbows, shoulders, hip, wrists, knees, ankles) Localized deep pain, ranging from mild (a "niggle") to excruciating. Sometimes a dull ache, but rarely a sharp pain. Active and passive motion of the joint aggravates the pain. The pain may be reduced by bending the joint to find a more comfortable position. If caused by altitude, pain can occur immediately or up to many hours later.

Symptoms of decompression sickness CHOKES Lungs Burning deep chest pain (under the sternum) Pain is aggravated by breathing Shortness of breath (dyspnea) Dry constant cough SKIN BENDS Skin Itching usually around the ears, face, neck arms, and upper torso Sensation of tiny insects crawling over the skin Mottled or marbled skin usually around the shoulders, upper chest and abdomen, with itching Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema)

Symptoms of decompression sickness NEUROLOGIC Brain Confusion or memory loss Headache Spots in visual field (scotoma), tunnel vision, double vision (diplopia), or blurry vision Unexplained extreme fatigue or behaviour changes Seizures, dizziness, vertigo, nausea, vomiting and unconsciousness may occur Spinal Cord Abnormal sensations such as burning, stinging, and tingling around the lower chest and back Symptoms may spread from the feet up and may be accompanied by ascending weakness or paralysis Girdling abdominal or chest pain Peripheral Nerves Urinary and rectal incontinence Abnormal sensations, such as numbness, burning, stinging and tingling (paresthesia) Muscle weakness for twitching

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

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

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

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%

Dalton’s Law and hypoxia Ambient air Partial pressure Alveolar air Nitrogen 600 mm Hg 570 mm Hg Oxygen 160 mm Hg 103 mm Hg Carbon dioxide 40 mm Hg Water vapour 47 mm Hg Total 760 mm Hg % saturation of hemoglobin varies with changes in partial pressure of alveolar oxygen at various altitudes

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

Time of useful consciousness with increasing altitude Rapid disconnect of O2 systems Moderate activity Sitting activity 22,000 5 minutes 10 minutes 25,000 2 minutes 3 minutes 30,000 45 seconds 1 ¼ minutes 35,000 30 seconds 40,000 18 seconds

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

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

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.

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.

Thank you