List of signs and symptoms of diving disorders

Last updated January 24, 2024

Diving disorders are medical conditions specifically arising from underwater diving. 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 depth, 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 about 40 metres (130 ft)). 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 and to avoid the risk of oxygen toxicity. 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.^[2]

Decompression sickness

Decompression sickness (DCS) occurs when gas, which has been breathed under high pressure and dissolved into the body tissues, forms 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 leading to damage to the nervous system, 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.^[3] The table below classifies the effects by affected organ and bubble location.^[4]

Signs and symptoms of decompression sickness
DCS type	Bubble location	Clinical manifestations
Musculoskeletal	Mostly large joints	Localised deep pain, ranging from mild to excruciating; sometimes a dull ache, but rarely a sharp pain Pain aggravated by active and passive motion of the joint Pain which may be reduced by bending the joint to find a more comfortable position Pain occurring immediately on surfacing or up to many hours later
Cutaneous	Skin	Itching, usually around the ears, face, neck, arms, and upper torso Sensation of tiny insects crawling over the skin (formication) Mottled or marbled skin or subcutaneous crepitation, usually around the shoulders, upper chest and abdomen, with itching Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema)
Neurologic	Brain	Altered sensation, paresthesia (tingling or numbness), hyperesthesia (increased sensitivity) Confusion or memory loss (amnesia) Visual abnormalities Unexplained mood or behaviour changes Seizures, unconsciousness
Neurologic	Spinal cord	Ascending weakness or paralysis in the legs Girdling abdominal or chest pain Urinary incontinence and fecal incontinence
Constitutional	Whole body	Headache Unexplained fatigue Generalised malaise, poorly localised aches
Audiovestibular	Inner ear	Loss of balance Dizziness, vertigo, nausea, vomiting Hearing loss
Pulmonary	Lungs	Dry persistent cough Burning chest pain under the sternum, aggravated by breathing Shortness of breath

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.^[5] 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.^[6]

Signs and symptoms of arterial gas embolism
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.

Nitrogen narcosis

Narcosis can produce tunnel vision, making it difficult to read multiple gauges. Console-narc.jpg — Narcosis can produce tunnel vision, making it difficult to read multiple gauges.

Nitrogen narcosis is caused by the pressure of dissolved gas in the body and produces impairment to the nervous system. This results in alteration to thought processes and 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. 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.^[7] Since the choice of breathing gas also affects the depth at which narcosis occurs, the table below represents typical manifestations when breathing air.^[8]

Signs and symptoms of narcosis
Pressure (bar)	Depth (m)	Depth (ft)	Manifestations
1–2	0–10	0–33	Unnoticeable small symptoms, or no symptoms at all
2–4	10–30	33–100	Mild impairment of performance of unpracticed tasks Mildly impaired reasoning Mild euphoria possible
4–6	30–50	100–165	Delayed response to visual and auditory stimuli Reasoning and immediate memory affected more than motor coordination Calculation errors and wrong choices Idea fixation Overconfidence and sense of well-being Laughter and loquacity which may be overcome by self-control Anxiety (common in cold murky water)
6–8	50–70	165–230	Sleepiness, impaired judgment, confusion Hallucinations Severe delay in response to signals, instructions and other stimuli Occasional dizziness Uncontrolled laughter, hysteria Terror in some
8–10	70–90	230–300	Poor concentration and mental confusion Stupefaction with some decrease in dexterity and judgment Loss of memory, increased excitability
10+	90+	300+	Hallucinations Increased intensity of vision and hearing (Hyperesthesia) Sense of impending blackout, euphoria, dizziness Manic or depressive states A sense of levitation and disorganisation of the sense of time Changes in facial appearance Unconsciousness, death

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 summarises the symptoms observed underwater and in studies using simulated dives in the dry, using recompression chambers and electroencephalography (EEG) monitors.^[9]

Signs and symptoms of HPNS
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.

Oxygen toxicity

Although oxygen is essential to life, in concentrations greater than normal it becomes toxic, overcoming the body's natural defences (antioxidants), and causing cell death in any part of the body. The lungs and brain are particularly affected by high partial pressures of oxygen, such as are encountered in diving. The body can tolerate partial pressures of oxygen around 0.5 bars (50 kPa; 7.3 psi) indefinitely, and up to 1.4 bars (140 kPa; 20 psi) for many hours, but higher partial pressures rapidly increase the chance of the most dangerous effect of oxygen toxicity, a convulsion resembling an epileptic seizure.^[10] Susceptibility to oxygen toxicity varies dramatically from person to person, and to a much smaller extent from day to day for the same diver.^[11] Prior to convulsion, several symptoms may be present – most distinctly that of an aura.

During 1942 and 1943, Professor Kenneth W Donald, working at the Admiralty Experimental Diving Unit, carried out over 2,000 experiments on divers to examine the effects of oxygen toxicity. To date, no comparable series of studies has been performed. In one seminal experiment, Donald exposed 36 healthy divers to 3.7 bars (370 kPa; 54 psi) of oxygen in a chamber, equivalent to breathing pure oxygen at a depth of 27 metres (90 ft), and recorded the time of onset of various signs and symptoms. Five of the subjects convulsed, and the others recovered when returned to normal pressure following the appearance of acute symptoms. The table below summarises the results for the relative frequency of the symptoms, and the earliest and latest time of onset, as observed by Donald. The wide variety of symptoms and large variability of onset between individuals typical of oxygen toxicity are clearly illustrated.^[12]

Signs and symptoms of oxygen toxicity observed in 36 subjects
Signs and symptoms	Frequency	Earliest onset (minutes)	Latest onset (minutes)
Lip-twitching	25	6	67
Vertigo	5	9	62
Convulsion	5	20	33
Nausea	4	6	62
Spasmodic respiration	3	16	17
Dazed	2	9	51
Syncope	2	15	16
Epigastric aura	2	18	23
Arm twitch	2	21	62
Dazzle	2	51	96
Diaphragmatic spasm	1	7	7
Tingling	1	9	9
Confusion	1	15	15
Inspiratory predominance^{[note 1]}	1	16	16
Amnesia	1	21	21
Drowsiness	1	26	26
Fell asleep	1	51	51
Euphoria	1	62	62
Vomiting	1	96	96

Note

↑ Normally, breathing in takes less time than breathing out; inspiratory predominance is a reversal of this.

Related Research Articles

Nitrox refers to any gas mixture composed of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater diving, nitrox is normally distinguished from air and handled differently. The most common use of nitrox mixtures containing oxygen in higher proportions than atmospheric air is in scuba diving, where the reduced partial pressure of nitrogen is advantageous in reducing nitrogen uptake in the body's tissues, thereby extending the practicable underwater dive time by reducing the decompression requirement, or reducing the risk of decompression sickness.

<span class="mw-page-title-main">Nitrogen narcosis</span> Reversible narcotic effects of respiratory nitrogen at elevated partial pressures

Narcosis while diving is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high pressure. The Greek word νάρκωσις (narkōsis), "the act of making numb", is derived from νάρκη (narkē), "numbness, torpor", a term used by Homer and Hippocrates. Narcosis produces a state similar to drunkenness, or nitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 metres (98 ft).

Heliox is a breathing gas mixture of helium (He) and oxygen (O₂). It is used as a medical treatment for patients with difficulty breathing because this mixture generates less resistance than atmospheric air when passing through the airways of the lungs, and thus requires less effort by a patient to breathe in and out of the lungs. It is also used as a breathing gas diluent for deep ambient pressure diving as it is not narcotic at high pressure, and for its low work of breathing.

Decompression sickness is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.

Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes. Historically, the central nervous system condition was called the Paul Bert effect, and the pulmonary condition the Lorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen toxicity is a concern for underwater divers, those on high concentrations of supplemental oxygen, and those undergoing hyperbaric oxygen therapy.

Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tension or shear, either directly by an expansion of the gas in the closed space or by pressure difference hydrostatically transmitted through the tissue. Tissue rupture may be complicated by the introduction of gas into the local tissue or circulation through the initial trauma site, which can cause blockage of circulation at distant sites or interfere with the normal function of an organ by its presence. The term is usually applied when the gas volume involved already exists prior to decompression. Barotrama can occur during both compression and decompression events.

Decompression Illness (DCI) comprises two different conditions caused by rapid decompression of the body. These conditions present similar symptoms and require the same initial first aid. Scuba divers are trained to ascend slowly from depth to avoid DCI. Although the incidence is relatively rare, the consequences can be serious and potentially fatal, especially if untreated.

Gas blending for scuba diving is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox. Use of these gases is generally intended to improve overall safety of the planned dive, by reducing the risk of decompression sickness and/or nitrogen narcosis, and may improve ease of breathing.

Diving medicine, also called undersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how relationships of a diver's fitness to dive affect a diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determine fitness to dive.

High-pressure nervous syndrome is a neurological and physiological diving disorder which can result when a diver descends below about 500 feet (150 m) using a breathing gas containing helium. The effects experienced, and the severity of those effects, depend on the rate of descent, the depth and the percentage of helium.

Diving disorders, or diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides into conditions caused by exposure to ambient pressures significantly different from surface atmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities.

In diving and decompression, the oxygen window is the difference between the partial pressure of oxygen (P_O₂) in arterial blood and the P_O₂ in body tissues. It is caused by metabolic consumption of oxygen.

Peter B. Bennett was the founder and a president and CEO of the Divers Alert Network (DAN), a non-profit organization devoted to assisting scuba divers in need. He was a professor of anesthesiology at Duke University Medical Center, and was the Senior Director of the Center for Hyperbaric Medicine and Environmental Physiology at Duke. Bennett is recognized as a leading authority on the effects of high pressure on human physiology.

<span class="mw-page-title-main">Latent hypoxia</span> Lung gas and blood oxygen concentration sufficient to support consciousness only at depth

Latent hypoxia is a condition where the oxygen content of the lungs and arterial blood is sufficient to maintain consciousness at a raised ambient pressure, but not when the pressure is reduced to normal atmospheric pressure. It usually occurs when a diver at depth has a lung gas and blood oxygen concentration that is sufficient to support consciousness at the pressure at that depth, but would be insufficient at surface pressure. This problem is associated with freediving blackout and the presence of hypoxic breathing gas mixtures in underwater breathing apparatus, particularly in diving rebreathers.

In physiology, isobaric counterdiffusion (ICD) is the diffusion of different gases into and out of tissues while under a constant ambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The term inert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gas diving and anesthesiology.

Hypobaric decompression or altitude decompression is the reduction in ambient pressure below the normal range of sea level atmospheric pressure. Altitude decompression is the natural consequence of unprotected elevation to altitude, while hypobaric decompression is due to intentional or unintentional release of pressurization of a pressure suit or pressurized compartment, vehicle or habitat, and may be controlled or uncontrolled, or the reduction of pressure in a hypobaric chamber.

The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure, and involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs,, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.

Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.

The science of underwater diving includes those concepts which are useful for understanding the underwater environment in which diving takes place, and its influence on the diver. It includes aspects of physics, physiology and oceanography. The practice of scientific work while diving is known as Scientific diving. These topics are covered to a greater or lesser extent in diver training programs, on the principle that understanding the concepts may allow the diver to avoid problems and deal with them more effectively when they cannot be avoided.

Inner ear decompression sickness, (IEDCS) or audiovestibular decompression sickness is a medical condition of the inner ear caused by the formation of gas bubbles in the tissues or blood vessels of the inner ear. Generally referred to as a form of decompression sickness, it can also occur at constant pressure due to inert gas counterdiffusion effects.

References

1 2 Brubakk, Alf O.; Neuman, Tom S, eds. (2003). "9: Pressure Effects". Bennett and Elliott's physiology and medicine of diving (5th Revised ed.). United States: Saunders Ltd. pp. 265–418. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Abraini, JH; Gardette-Chauffour, MC; Martinez, E; Rostain, JC; Lemaire, C (1994). "Psychophysiological reactions in humans during an open sea dive to 500 m with a hydrogen-helium-oxygen mixture". Journal of Applied Physiology. American Physiological Society. 76 (3): 1113–8. doi:10.1152/jappl.1994.76.3.1113. ISSN 8750-7587. PMID 8005852 . Retrieved 1 March 2009.
↑ Powell, Mark (2008). Deco for Divers. Southend-on-Sea: Aquapress. p. 70. ISBN 978-1-905492-07-7.
↑ Francis, T James R; Mitchell, Simon J (2003). "10.6: Manifestations of Decompression Disorders". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th Revised ed.). United States: Saunders Ltd. pp. 578–99. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Neuman, Tom S (2003). "10.5: Arterial Gas Embolism and Pulmonary Barotrauma". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. pp. 557–8. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Neuman, Tom S (2003). "10.5: Arterial Gas Embolism and Pulmonary Barotrauma". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. pp. 568–71. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Bennett, Peter B; Rostain, Jean Claude (2003). "9.2: Inert Gas Narcosis". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. p. 301. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Lippmann, John; Mitchell, Simon J (2005). "Nitrogen narcosis". Deeper into Diving (2nd ed.). Victoria, Australia: J L Publications. p. 105. ISBN 0-9752290-1-X. OCLC 66524750.
↑ Bennett, Peter B; Rostain, Jean Claude (2003). "9.3: The High Pressure Nervous Syndrome". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. pp. 323–8. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Clark, James M; Thom, Stephen R (2003). "9.4: Oxygen under pressure". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. pp. 358–360. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Clark, James M; Thom, Stephen R (2003). "9.4: Oxygen under pressure". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders Ltd. p. 376. ISBN 0-7020-2571-2. OCLC 51607923.
↑ Donald, Kenneth W (1947). "Oxygen poisoning in man — part I". British Medical Journal. 1 (4506): 667–72. doi:10.1136/bmj.1.4506.667. PMC 2053251 . PMID 20248086.