Underwater Medicine

Underwater Medicine: Physical Principles of Diving

• Boyle's Law states the volume of gas is inversely proportional to pressure if the temperature is constant.
• In seawater, pressure increases approximately 1 atm for every 10 meters (33 feet) of depth.
• Boyle's Law relates to barotrauma injuries caused by pressure changes.
• Gas-filled spaces, like those in the sinuses or lungs, are crushed as a diver descends.
• The greatest risk is often at shallow depths where rapid pressure changes occur.
• Henry's Law states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas.
• Henry's Law applies to decompression sickness, which is caused by the formation of nitrogen bubbles in tissues.

Barotrauma

• Barotrauma affects gas-filled spaces, with the middle ear being most common.
• Middle ear, sinuses and lungs can be affected by barotrauma.
• Symptoms of barotrauma appear rapidly, often during or shortly after a pressure change.
• Treatment for barotrauma includes lying down, administering 100% oxygen, and IV fluids.
• Rupture of the lungs from barotrauma is rare, but has potentially fatal consequences.
• Tympanic membrane bows inwards with increasing external pressure
• Failure to equalize pressure on both sides of the tympanic membrane can result in bleeding and rupture.
• Risks include an URI (upper respiratory infection), hay fever/Eustachian tube dysfunction and excessive pressure on the Eustachian tube
• Symptoms include pain, fullness, or deafness.
• Signs include hemorrhage of the tympanic membrane.
• Treatment involves decongestants and/or antibiotics
• Ruptured tympanic membrane is an absolute contraindication to diving.
• Inner ear barotrauma is a possibility, assess hearing loss, tinnitus, vertigo and ataxia.
• Audiogram is required for further investigation of inner ear barotrauma.
• Inner ear barotrauma is from rupture of round/oval window causing perilymph fistula.
• Symptoms of inner ear barotrauma can include tinnitus, vertigo, ataxia, disorientation, and sensorineural hearing loss
• Treatment includes rest, avoidance of increases in intracranial pressure, and ENT referral
• Sinus barotrauma is often caused by nasal congestion leading to bleeding into the sinus cavity.
• Airflow into the sinus during descent causes relative negative pressure, resulting in rupture and bleeding into sinus cavity.
• Signs and symptoms of Sinus barotrauma are presents as blood in the face mask and pain with descent.
• Red wavelengths don't penetrate depth so blood not noticed by the diver.
• Sinus barotrauma can be treated decongestants +/- antibiotics.
• Pulmonary barotrauma is the 2nd most common cause of death while diving (after drowning).
• Alveolar wall rupture is caused by air trapping, failure to exhale or breath holding on ascent and air-trapping lung conditions such as asthma.
• Asthma is an absolute contraindication to diving.
• Pulmonary barotrauma: air can get trapped in the alveolus expands or by mucous plugs during ascent.
• Systemic complication: air embolism causing cerebral air embolism (CAGE).
• Symptoms for cerebral air embolism include a range of neurological features, usually within minutes of the dive ending.
• Clinical signs for cerebral air embolism: can change with moving bubbles in the brain.
• Management includes lying down flat, administering 100% oxygen, IV fluids (cautious of cerebral edema) and sedative.
• Urgent recompression is essential, along with monitoring via ECG for arrhythmias.
• Dental barotrauma involves pain in teeth due to volume changes in cavities, may need dental review.
• Mask squeeze happens when divers wear goggles that prevent nose equalization, causing facial tissue trauma which is prevented by letting air into mask.

Decompression Sickness

• Caused by nitrogen bubbles precipitate out of dissolved gas in tissues when pressure decreases while ascending.
• Can lead to direct mechanical damage and activation of inflammatory pathways.
• Can occur despite using decompression tables.
• Risk factors: fatigue, flown, dehydration, cold, longer/deeper dives, obesity and injuries.
• Symptoms: lethargy, fatigue.
• Symptoms also depend of bubble location
• Intravascular symptoms: vessel damage and clotting.
• Neurological symptoms: cord.
• Respiratory: chokes.
• Musculoskeletal: bends.
• Cutaneous: silent decompression sickness.
• Treatment: Rest, 100% O2, IV fluids, IDC, recompression chamber.
• Treatment: Don't use steroids, anticoagulants, plasma expanders or steroids.
• It is not possible to transfer by air with a plane unless flying below 300m.
• If recovered after recompression, there should be no diving or flying in 1 month.

Nitrogen Narcosis

• N2 acts like a narcotic at >30m depths.
• Martini's law: every 30m is like drinking 1 glass of Martini in consumption.
• Symptoms: lightheaded, poor concentration/judgment.
• Symptoms relieved by ascending.
• First sign may be seizure.
• Tolerance can develop.
• Treatment: only dive to 30-40m using compressed air, use helium for deeper dives.

Oxygen Toxicity

• Military applications often involve using 100% oxygen.
• Exposure to PO2 318-1500mmHg produces severe CNS and lung effects.
• High PIO2 causes more O2 to dissolve, resulting in less unbound O2.
• High O2 impairs CO2 offloading, causing vasoconstriction.
• High risk if below 6m with high VO2.
• Visual distortion, rapid/shallow breathing, and convulsions can occur.
• Free radicals cause these effects.
• Can affect nervous system at 1.6 bar.
• May have prodromal disturbances such tinnitus.
• Irritation of respiratory system leads to microdamage and pneumonia.

Osteonecrosis

• A potential risk associated with diving, but is not discussed further in the provided text.
• More information is needed to provide detailed notes on this condition.

Recognising Risks of Diving with Pre-existing Medical Conditions

• Asthma can be OK for diving if asymptomatic
• Asthma must be managed with out medication and have had no medication for 5 years
• Asthma must normal lung function/CXR, and have negative hypertonic saline test.
• For potential divers must be over 14 years old.
• Divers must be physically and mentally mature.
• It is recommended to have a CVS and respiratory health check if over 45yrs.
• divers must be fit and be able to swim 200m unassisted in 5 minutes.
• Risks for divers include smoking and obesity.
• Risks for divers include recent eye surgery, patent foramen ovale (refer to cariologist).
• Systemic examination checks include vision for the ability to locate dive boat and the buddy.
• ENT exam for Eustachian tube function and baseline audiometry.
• ENT tests are not contraindicative tests.
• Dental examination is to check completely filled caries and if the diver can retain regulator
• CNS: checks included modified sharpened Rhomberg to look for neurological problems.
• CVS: listen for murmur and PFO.
• BP less than 150/95.
• Lungs: to check for asthma.
• GIT: to ensure there is no herniation of the bowl that will cause rejection.
• MSK: if they can hold equipment or move as planned.

Investigations

• Lung function tests consist of doing a FVC at least 4L Male, 3L female, FEV1 >80% predicted, FEV1/FVC >75%, Audiogram and ECG +/- exercise stress test
• Risk Advice make sure they Advice on equalizing middle ear.
• Asthma a relative contraindication due increased risk of air trapping, and bronchospasm (cold air, sea water, etc).
• Asthma a 2x risk of decompression sickness.
• Baseline risk only 1/200,000.
• Need full workup and pulmonary function testing (+/- saline challenge).
• To be fit, must have well controlled infrequent attacks asthma
• It is general to not recommend the above
• .Diabetes is relative contraindication for recreational diving insulin-dependent. Hypoglycemia symptoms blunted during diving.
• Divers cannot eat underwater.
• Guideline for these patients needs to be more lenient now if they well controlled
• If a diabetic MUST dive, they should use buddy up and Utilise a diabetic dive programme generally shallower.

Contraindications to diving

• Epilepsy, Valvular disease and shunts: inl PFO, VSD, Respiratory disease, Middle ear/ENT issues, Bowel problems w risk of air trapping (some colostomy bags), Pregnancy: fetus can get bent and cannot know, Psychiatric disorder, surgery, dental work, fractures and Any conditions that change blood flow increases N2 delivery

Recompression Units and Hyperbaric Chambers

• Recompression chambers and hyperbaric units and give 02 via a mask to patients

Altitude: Physiological Responses

• Normal air composition, but reduced partial pressures (reduced pO2) --> hypobaric hypoxia.
• Hypoxia causes: increased RR, reduced PaCO2, respiratory alkalosis, and left shift in the Hb curve.
• Stroke volume is reduced with reduces heart contractility, filling time and preload.
• There is an increase HR, but a decrease HR max, higher arterial pressure and reduced in Plasma volume.
• Increase Hb to help O2 intake (initially due to dieresis and later due to erythropoiesis).
• Body temp is increased for acclimation to help O2 distribution.
• Hypoxia contributes to the disease because there less blood and increased cerebral vasodilation and raised ICP --> cerebral edema => sympathetic vasoconstriction and increased capilarty permeability--> pulmonary edema.
• Huma response to altitude --> acclimatisation, evolutionary adaptation and maladaptive response (AMS, HAPE, HACE) and 4 main responses
• Ventilatory and Pulmonary vascular response (behaves unlike any other vascular system in the body) and Erythrocytosis all contribute to the Humas response.
• Can' directly measure the oxygen PAO2 = [FIO2 x (PATM – PH20)] - (PACO2/R)
• Ventilation is causes hypoxia, that results in deceases in CO2, also causes respiratory alkalosis and Paritial renal compensation occurs with kidneys excreting HCO3-
• Ventilation helps increase increase to increase HR.
• CO returns too normal because HR is staying high and stroke volume is reduced.
• Increase in EPO and Hb and a increase Angiogenesis due to VEGF helps the CVS
• Exercise response increases VO2 max and decreases 1000m above 1500m.
• Increase BMR so there for there for are you have decreases appetite.

Muscle

• Help switch for oxidative to glycolytic metabolism. Muscle also increase in Increase mitrochondria, myoglobin and capillary and increases fibre ration to help for with altitude. You body goes Tachycardia, Hyperventilation, Exertional dyspnoea, Increased micturition, Insomnia, nocutonral waking and Peripheral facial and muscle edema is the overall effect or altitude. Body then as decreases PO2 the patient has to come down the mountain because if the type 1 cells are to low they wont get enough 03 so they will have a dereased reaction time to certain things.

Hypoxia and induced factors

• As decreases 02 results in change in ventilation.
• The is then and over or under regulation of regulators that helps give what cells needs.
• There are different amounts of oxygen to what different blood types can tolorate and with less oxygen they will try to work with less