Home Health Matters Risk Factors in Diving

Risk Factors in Diving

By: Dr.Hossam Nasef

1. Patent (Persistent) Foramen Ovale (PFO): During the fetal period, the baby depends entirely on the mother for gas exchange as it cannot yet have it's own respiration. The pulmonary circulation, though still existing, has no role in the babys oxygenation. In a normal pregnancy, the heart and circulatory system of the fetus develop a few openings through which the blood shunts from one side of the heart to the other.

One of these openings (foramena) is the Foramen Ovale existing in the septum (wall) between the two upper chambers of the heart (the Atria). Normally all the openings tend to close at or shortly after birth leading eventually to the build up of the normal circulatory system.

In around 17% of population, the opening between the right and left atria remains open, a situation known as Patent Foramen Ovale (PFO), with minimal or no symptoms at all. During regular diving practice, micro or silent bubbles tend to form in the circulation, namely in the right side of the venous system. This includes the the right heart chambers and the pulmonary arteries.

These bubbles will produce no symptoms in an individual with normal heart septa as these bubbles are eventually filtered out at the lungs as long as the dive profiles regarding times, depths and rates of ascent are kept within permissible levels. In a person with a (PFO) condition who is apparently normal and healthy, after a normal dive(s), the gas bubbles, normally existing in the right (venous) side of the circulation, find their way to the left (arterial) side through this opening, (Paradoxical Emboli) resulting in the risk of Arterial Gas Embolism (AGE) which is a serious condition.

The amount of gas that passes from the right to the left side of the heart through that Foramen Ovale will depend upon: the amount and size of bubbles circulating in the right side, the size of the foramen, and the amount of increase in the right atrial pressure that will push the blood carrying bubbles to the left side.This pressure is normally increased as a result of straining, coughing, sneezing, and the Trendlenberg position “ feet higher than the head”, frequently applied by some people as first aid to DCI cases, and most importantly Valsalva's manoever currently practiced by divers to equalize the middle ears.

Any heart septal defect (including PFO), will carry the risk of a embolism and is an absolute contraindication to diving if discovered early enough before causing serious damage. Unfortunately, this defect in divers is only discovered either accidentally, like during a regular heart checkup or when the diver starts to show signs and symptoms of DCI though carrying out relatively safe dive profiles and procedures. The defect is revealed with the means of echocardiographic studies with bubble contrast tests for the heart, a rather complicated imaging procedure and still beyond most screening recommendations.

2. Dehydration: Dehydration is one of the major predisposing factors in the occurrence of DCI as dehydration leads to an increase in blood viscosity. This condition reduces the normal perfusion of tissues in a way that interferes with the effective elimination of inert gases.

During diving, there is continuous fluid loss due to:

1- Perspiration, especially in hot weather.
2- Humidifying the dry gas that divers breathe by extracting water vapour from the lungs.
3- Immersion increases urine excretion by shifting blood from extremities to the core of the body and giving the stretch receptors the false feeling that the blood volume has increased thus enhancing urine formation. Shifting of blood happens due to closure of the outside blood vessels (to reduce heat loss) and abolishing the orthostatic effect of gravity on circulation.

In general, dehydration can happen as a result of:

1. Inadequate fluid intake with a moderate fluid loss.
2. Drinking dehydrating agents like alcohol and strong coffee and tea.
3. Dehydrating conditions such as diarrhea and vomiting.

As a rule of thumb, drinking plenty of fluids on a diving vacation should be on top of the list of dive briefings.
Divers should as well be advised to avoid drinking dehydrating agents and to avoid diving when suffering from severe diarrhea or vomiting.

Drinking only water will eventually lead to the wash out of salts from the body leading to a status of imbalance in the body electrolytes with the symptoms of tiredness, weakness, dizziness, nausea, and sometimes vomiting.

Divers should be advised to take sufficient rehydrating salts together with drinking enough fluids during their diving vacation, especially in the summer.

3. Sex: It is suggested in medical literature that women are more at risk of DCI. Statistical studies show that the incidence in female dive instructors was 0.02%, whilst in male dive instructors it drops to 0.007%.
No adequate physiological explanation can be found though a number are postulated including: increased body fat, different body fluid dynamics, hormonal influences, differences in limb perfusion and the slight difference in the blood clotting components than males.

4. Obesity: Obesity means an increase in the fat content of the body which increases the tissue mass capable of absorbing more inert gas. ( Nitrogen is 5 times more soluble in fat than in water and non-fatty tissues).
Obesity is measured by the body mass index (Weight, Height, Age, Build and Sex) and studies show that people who are 25% overweight will have a ten-fold chance of occurance of DCI. Australian studies recommend that obese divers should reduce their bottom times for a given depth by somewhere between 25% and 50% of the NDL. Some authors still believe in the action of fat as a good reservoir for nitrogen in cases of short deep single exposures (bounce dives).   

5. High serum cholesterol levels can elevate the incidence of DCI by rendering the blood more viscous and acting on the walls of the blood vessels rendering them narrower and more rigid, reducing perfusion of blood that will interfere with inert gas elimination.

6. Age: After 40 years of age the integrity of the circulatory system, with regards to heart pumping, vessel elasticity and blood dynamics start to deteriorate affecting normal perfusion. This is especialy true for individuals who suffer from high blood pressure or atherosclerosis. Abnormalities and degenerations within joint surfaces also increase the incidence of DCI in the aged, so divers over 40 should start considering much safer dive profiles including their no decompression limits, ascent rates, safety stops and their nitrogen loading.

7. Exercise: Recent studies show that exercise before diving can lead to an increase in the incidence of DCI as it increases bubble formation! Exercise at depth is known to increase the up-take of the inert gas by elevating perfusion, while exercise after diving causes increased bubble formation as the body is practically supersaturated with the inert gas after diving. Exercise before or after diving is a recognized hazard that should be avoided. In the case of a strenuous dive, divers should consider adding more safety to the dive tables regarding decompression procedures.

8. Any underlying condition that hampers the anatomy of the body (like scarring) can form a bubble trap due to the alteration in local tissue perfusion and gas elimination yielding a higher incidence of DCI.

9. Increased carbon dioxide pressures due to exertion or increased breathing resistance because of faulty equipment, will increase nitrogen uptake and loading.

10. Drugs under pressure:Even if the effect of a drug is well understood at sea level, it may be very different in a hyperbaric environment. (Drug-diving interactions are unpredictable). It is highly recommended for somebody who is receiving regular medication to consult a doctor who understands hyperbaric medicine.
It is common knowledge that consuming alcohol on a dive vacation is a most dangerous procedure as, if it is consumed before diving, synergizes with the action of nitrogen on the brain leading to intensifying the narcotic effect. After diving, alcohol consumption can give the false feeling of warmth while possibly leading to the onset of hypothermia.

Finally I would like to emphasize that DCS is mainly dependant on depth, time and rate of ascent violations, but still there is much more to concern ourselves with to remain safe.
Wishing you all safe and enjoyable diving.


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