List of signs and symptoms of diving disorders
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Diving disorders are medical conditions specifically arising from ambient pressure underwater diving with breathing apparatus. The signs and symptoms of these may present during a dive, on surfacing, or up to several hours after a dive.
The principal conditions are decompression illness (which covers decompression sickness and arterial gas embolism), nitrogen narcosis, high pressure nervous syndrome, oxygen toxicity, and pulmonary barotrauma (burst lung). Although some of these may occur in other settings, they are of particular concern during diving activities.[1]
The disorders are caused by breathing gas at the high pressures encountered at the depth of the water and divers will often breathe a gas mixture different from air to mitigate these effects. Nitrox, which contains more oxygen and less nitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to 34 meters or 112 feet for 32% oxygen).[2] Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis, to avoid the risk of oxygen toxicity, and to reduce work of breathing.[3][4] This is complicated at depths beyond about 150 metres (500 ft), because a helium–oxygen mixture (heliox) then causes high pressure nervous syndrome.[1] More exotic mixtures such as hydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this.[5]
Decompression sickness (DCS) occurs when gas that has been breathed under high pressure dissolves into the body tissues, thus, forming bubbles as the pressure is reduced on ascent from a dive. The results may range from pain in the joints where the bubbles form to blockage of an artery(air bubble)[6] leading to damage to the fatigue, joint and muscle pain, clouded thinking, numbness, weakness, paralysis, rash, poor muscle coordination or balance, paralysis or death. While bubbles can form anywhere in the body, DCS is most frequently observed in the shoulders, elbows, knees, and ankles. Joint pain occurs in about 90% of DCS cases reported to the U.S. Navy, with neurological symptoms and skin manifestations each present in 10% to 15% of cases. Pulmonary DCS is very rare in divers.[7] The table below classifies the effects by affected organ and bubble location.[8]
| DCS type | Bubble location | Clinical manifestations |
|---|---|---|
| Musculoskeletal | Mostly large joints |
|
| Cutaneous | Skin |
|
| Neurologic | Brain |
|
| Neurologic | Spinal cord |
|
| Constitutional | Whole body | |
| Audiovestibular | Inner ear | |
| Pulmonary | Lungs |
|
Arterial gas embolism and pulmonary barotrauma
If the compressed air in a diver's lungs cannot freely escape during an ascent, particularly a rapid one, then the lung tissues may rupture, causing pulmonary barotrauma (PBT). The air may then enter the arterial circulation producing arterial gas embolism (AGE), with effects similar to severe decompression sickness.[9] Although AGE may occur as a result of other causes, it is most often secondary to PBT. AGE is the second most common cause of death while diving (drowning being the most common stated cause of death). Gas bubbles within the arterial circulation can block the supply of blood to any part of the body, including the brain, and can therefore manifest a vast variety of symptoms. The following table presents those signs and symptoms which have been observed in more than ten percent of cases diagnosed as AGE, with approximate estimates of frequency.[10]
| Symptom | Percentage |
|---|---|
| Loss of consciousness | 81 |
| Pulmonary rales or wheezes | 38 |
| Blood in the ear (Hemotympanum) | 34 |
| Decreased reflexes | 34 |
| Extremity weakness or paralysis | 32 |
| Chest pain | 29 |
| Irregular breathing or apnea | 29 |
| Vomiting | 29 |
| Coma without convulsions | 26 |
| Coughing blood (Hemoptysis) | 23 |
| Sensory loss | 21 |
| Stupor and confusion | 18 |
| Vision changes | 20 |
| Cardiac arrest | 16 |
| Headache | 16 |
| Unilateral motor changes | 16 |
| Change in gait or ataxia | 14 |
| Conjunctivitis | 14 |
| Sluggishly reactive pupils | 14 |
| Vertigo | 12 |
| Coma with convulsions | 11 |
Other conditions that can be caused by pulmonary barotrauma include pneumothorax, mediastinal emphysema and interstitial emphysema.
Pneumothorax
Mediastinal emphysema
Interstitial emphysema
Pulmonary interstitial emphysema (PIE) is a relatively rare condition that affects mainly premature babies but can also develop in adults after lung overexpansion.[11]
Nitrogen narcosis
Nitrogen narcosis is a change in consciousness, neuromuscular function, and behavior brought on by breathing compressed inert gasses, most commonly nitrogen. It has also been called depth intoxication, “narks,” and rapture of the deep. It can cause a decrease in the diver's ability to make judgements or calculations. It can also decrease motor skills, and worsen performance in tasks requiring manual dexterity.[12] As depth increases, so does the pressure and hence the severity of the narcosis. The effects may vary widely from individual to individual, and from day to day for the same diver. Because of the perception-altering effects of narcosis, a diver may not be aware of the symptoms, but studies have shown that impairment occurs nevertheless.[13] Since the choice of breathing gas also affects the depth at which narcosis occurs, the table below represents typical manifestations when breathing air.[14]
| Pressure (bar) | Depth (m) | Depth (ft) | Manifestations |
|---|---|---|---|
| 1–2 | 0–10 | 0–33 |
|
| 2–4 | 10–30 | 33–100 |
|
| 4–6 | 30–50 | 100–165 |
|
| 6–8 | 50–70 | 165–230 |
|
| 8–10 | 70–90 | 230–300 |
|
| 10+ | 90+ | 300+ |
|
High pressure nervous syndrome
Helium is the least narcotic of all gases, and divers may use breathing mixtures containing a proportion of helium for dives exceeding about 40 metres (130 ft) deep. In the 1960s it was expected that helium narcosis would begin to become apparent at depths of 300 metres (1,000 ft). However, it was found that different symptoms, such as tremors, occurred at shallower depths around 150 metres (500 ft). This became known as high pressure nervous syndrome, and its effects are found to result from both the absolute depth and the speed of descent. Although the effects vary from person to person, they are stable and reproducible for each individual; the list below summarizes the symptoms observed underwater and in studies using simulated dives in the dry, using recompression chambers and electroencephalography (EEG) monitors.[15]
| Symptom | Notes |
|---|---|
| Impairment | Both intellectual and motor performance are impaired. A 20% decrease in the ability to perform calculations and in manual dexterity is observed at 180 metres (600 ft), rising to 40% at depths of 240 metres (800 ft) |
| Dizziness | Vertigo, nausea, and vomiting may occur in divers at depths of 180 metres (600 ft). Animal studies under more extreme conditions have produced convulsions. |
| Tremors | Tremors of the hands, arms and torso are observed from 130 metres (400 ft) onward. The tremors occur with a frequency in the range of 5–8 hertz (Hz), and their severity is related to the speed of compression; the tremors reduce and may disappear when the pressure has stabilised. |
| EEG changes | At depths exceeding 300 metres (1,000 ft), changes in the electroencephalogram (EEG) are observed; the appearance of theta waves (4–6 Hz) and depression of alpha waves (8–13 Hz). |
| Somnolence | At depths beyond the onset of EEG changes, test subjects intermittently fall asleep, with sleep stages 1 and 2 observed in the EEG. Even when decompressed to shallower depths, the effect continues for 10–12 hours. |
