Since 4500 BC, humans have engaged in free (breath-hold) diving to obtain food and substances from shallow ocean floors at depths of 100 ft or more. Humans, always ready for new inventions and exploring new areas, created several equipments to make water exploration possible. The invention of SCUBA was one of the biggest inventions. Scuba diving (“scuba” originally being an acronym for Self Contained Underwater Breathing Apparatus, although now widely considered a word in its own right) is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons. Unlike early diving, which relied exclusively on air pumped from the surface, scuba divers carry their own source of breathing gas (usually compressed air), allowing them greater freedom than with an air line. Both surface supplied and scuba diving allow divers to stay underwater significantly longer than with breath-holding techniques as used in snorkeling and free-diving.
Scuba diving has become more popular nowadays and the number of recreational divers has also increased significantly. However, diving is not without risk and a good understanding of the changes in water to the human body is important before one plans to dive.
UNDERWATER PRESSURE VS HUMAN BODY
The deeper down under water, the higher the pressure is. Direct effects of increasing pressure occur only on the gas filled spaces in the body. The human body is primarily made of water, which is non-compressible and transmits pressure evenly. However, the gases in hollow organs – lungs, middle ear, sinuses, poorly filled teeth, bowels and those dissolved in the blood – are at the mercy of pressure changes.
Have you ever dived underwater and felt that your lungs shrunk? Well they actually do. For every 10 metres of descent, the pressure increases by one atmosphere (atm), therefore, the total lung volume during a breath-hold dive at 10 metres is 1/2 that at the surface. At 20 metres it is 1/3, at 30 metres it is 1/4 and at 40 metres it is 1/5. On surfacing these figures are reversed, however, when breathing compressed gases as in diving, the mass of gas in the lungs is increased to fill the normal volume. Now when the diver ascends, the lungs need time to adjust with the pressure changes and will need to let the gas out. If the diver ascends too fast, the lung volume will increase rapidly, causing pressure trauma or baro-trauma. A simple way to imagine this is by imagining your lungs as a balloon. Imagine what will happen if there is too much air in the balloon, the same thing will happen with your lungs.
The air that we breathe contains 21% of oxygen. Although oxygen is known for its importance to one’s life, 100% oxygen can cause oxygen toxicity and be hazardous. During descent, the partial pressure increases, causing the amount of oxygen dissolved in the body to increase. At a certain level, the normal 21% oxygen in compressed air contained in the tank can cause oxygen toxicity as caused by inhaling 100% oxygen. For this reason, sometimes deep divers use specialized mixtures that replace nitrogen with helium and allow for varying percentages of oxygen depending on depth.
Nitrogen makes up approximately 78% of atmospheric air we breathe, so normally it is present in the human lungs but does not dissolve in the blood. When descending, nitrogen’s partial pressure also increases, this means it will easily dissolve in blood. When ascending the nitrogen will dissolve out from blood back to its gas form and fill hollow organs. Problems occur if the diver ascends too fast. Nitrogen will return to its gas form and cause “bubbles”. These bubbles can get stuck in the joints, or more fatally in the circulation and cause an emboli, which can lead to a stroke, heart attack, etc.
All changes above can lead to a series of symptoms known as decompression sickness, which can range from mild to serious health problems. Mostly, the treatment is by creating a similar pressure condition making the ascend more tolerable for the body, ie. by the hyperbaric chamber.
Although decompression sickness may sound scary, many technical advances have been made to prevent these complications, so nowadays diving can be considered a safe activity. However, other things that need to be considered are pre-existing diseases which cannot tolerate the changes that happen during diving.
Serious Contraindications to Diving
These medical conditions are generally regarded as not fit to dive:
- Epilepsy: An epileptic fit underwater normally means certain death by drowning, however, if an epileptic has been fit free for many years and they have not been on medication for 5 years, diving can be considered after a doctor’s evaluation.
- Lung Problems: with the pressure changes causing large changes in the volume of air, especially at shallow depths, the lungs are particularly important in diving medicine. Any lung condition that causes a restriction in air coming out of the lungs or a weakness in the structure of the lung is considered not fit to dive. Such conditions may be bullae (large air sacs), severe asthma, chronic obstructive pulmonary disease (emphysema) and certain types of lung surgery. Spontaneous pneumothorax (burst lung) occur in people (usually young men) that have weaknesses in their lung and are normally not fit to dive.
- Severe heart disease: this includes congenital heart defects, severe valve problems and some ‘holes in the heart’. Severe ischaemic heart disease especially when not fully controlled or residual heart problems after heart attacks may be a problem too.
- Neurological Problems: Progressive neurological problems such as severe MS, Parkinson’s, and motor neurone disease tend to stop people diving. The reason is these diseases may include inability to control motoric movements, which can cause many problems underwater.
- Heart Rhythm problems: any sort of heart rhythm or electrical problem of the heart that causes a person to feel funny, black out or collapse would be a contraindication.
- Perforated eardrum, grommets, severe vertigo: diving with perforated eardrums could lead to a nasty middle ear infection and even meningitis. Severe dizziness could be very dangerous underwater.
- Blood disorders: This includes severe bleeding disorders (e.g. haemophilia), and blood cancers (leukaemias).
- Severe mental health problems: Schizophrenia, mixed bipolar disorders, depression (in acute stages), personality disorders etc. are unlikely to be fit to dive due to the stresses and potential dangers of instability in the water (to both the diver and the buddy).
- Drug abuse: Active drug abusers are definitely not fit to dive. This could include drugs such as cannabis and alcohol.
The safest way to determine fitness to dive is to see a doctor who is familiar with medical conditions related to diving. The doctor might need to perform tests to determine your lung condition (by spirometry), heart condition (by ECG, treadmill), and a neuro exam (might include an EEG).
When you do get certified to dive, do not forget to follow the instructor’s advice and dive with only reputable dive companies.