Curtin University of Technology
Skip to content
Link to Curtin homepage
Curtin School of Physiotherapy

Scuba Diving - Physiology and Common Medical Conditions

Proposition for Debate - by Karen Carmichael (Otago, NZ)

Contents

Statement of the Topic

Scuba Diving - Physiology and Common Medical Conditions

Introduction

SCUBA refers to self-contained underwater breathing apparatus. Jacques Cousteau and Emile Gagnon first pioneered it in 1943. Initially scuba was primarily used in the navy and in commercial operations, such as pearl diving. However there has been a growing recreational trend over the last 20-30 years. Although the precise number of recreational scuba divers is difficult to estimate, it is believed that in the USA alone there may be between 4 or 5 million scuba divers with an additional 200,000 divers trained each year (McCardle et al 1996, p. 527). With large numbers of people diving it is inevitable that injuries and fatalities will occur, especially in a high-risk sport like scuba diving. Morgan (1995) estimated that between 3 to 9 deaths per 100 000 divers occurs annually in the US alone (although these estimates are subject to question). It is therefore important that medical professionals that deal with scuba divers understand the mechanisms behind diving injuries, their presentations, as well as the physiological changes that occur with scuba diving and potential problems that these changes may cause.

Scuba Equipment

Scuba diving requires specialist equipment to allow us to breathe underwater. The most vital piece of equipment is the main scuba system, which consists of a pressurized tank (either steel of aluminium), which is traditionally worn on the back. The regulator allows the air to be delivered to the diver at the same pressure as the ambient pressure; it consists of a first stage, which is connected to the tank and the second stage or mouthpiece. These vary between manufacturers. Also connected to the first stage is a high-pressure line, to which the submersible pressure gauge or dive computer is attached. There is commonly a second mouthpiece available for emergencies. The tank is usually attached to the diver via a buoyancy compensation device (BCD); this is an inflatable vest that is used by the diver to control buoyancy in the water. Weights attached via a weight belt, or incorporated, by quick release pockets into the BCD are also used to control buoyancy.

Due to the thermal properties of water a wetsuit or drysuit is used to reduce heat loss during diving. Gloves and boots, usually made of neoprene are also worn in many instances. Fins are used to aid in propulsion through the water. These come in varying sizes, shapes and materials. A mask is worn to aid in visibility, and a snorkel is often used to breathe while at the surface.

As can be imagined when a diver is completely geared up, significant stress can be applied to the musculoskeletal system, before the diver enters the water.

Physics of Diving

Scuba diving consists of breathing air (a mixture of various gases, mostly oxygen and nitrogen) through varying depths. Gas responds according to the laws of physics in certain ways depending on the pressure it is subject to. As a diver goes deeper the ambient pressure increases. At sea level the pressure is described as one atmosphere, for every 10 metres below sea level, this increases; therefore at 10 metres the pressure is 2 Atmospheres (i.e. it has doubled), at 20 metres it is 3 Atmospheres and so on. Thus the greatest changes in pressure occur in the first 10 metres (McCardle et al 1996).

To understand how the properties of gas change with pressure, several laws are used.

Boyle's Law states:

p1V1 = p2V2

That is, that the volume of gas is inversely related to the pressure, so as the pressure increases the volume decreases and vice versa.

Henry's Law describes the solubility of gases in liquids. The solubility depends mainly on the ambient pressure of the gas in contact with the liquid and on the partial pressure of a particular gas component. Because the human body consists mainly of water, the solubility of gases in water plays an essential role in the uptake and release of inert gases by the body's tissues, that is the deeper someone dives the more gas is dissolved in the body, until it reaches equilibrium or saturation. (Lettnin 1999 pp. 35-36, Smith 1996). Saturation diving is normally the realm of commercial divers who may live at depth for extended periods.

On-gassing refers to process of the high-pressure inert gas (nitrogen), being breathed into the lungs and then dissipated throughout the body (via the blood circulation) loading the tissues with dissolved nitrogen. The gas is moving from a higher pressure to a lower pressure. The deeper the diver goes and the longer the diver remains at that depth, the more gas is dissolved, until equilibrium is reached, that is saturation. On ascent, going from a higher to a lower pressure the gas must escape to maintain equilibrium. This process is known as off-gassing. If this occurs too rapidly then the gas will dissolve out of the tissues forming bubbles, this is the basis for decompression sickness. It seems however it may be the size of the bubble that is the problem. Doppler monitoring has shown that small bubbles are present as part of the normal off-gassing process, however when the ascent is too fast the bubble grows too large and can no longer be transported around the body, thus causing the symptoms seen in decompression illness. Symptoms vary depending on where the bubbles lodge (Taylor 2000). Carturan et al (2000) studied bubble formation in divers ascending from 35 metres and found that an ascent rate of 9m/min gave a much lower bubble grade than a rate of 17m/min which is recommended as safe in some tables (PADI allows for an ascent rate of 18m/min).

Another problem occurs due to Boyle's Law. As a diver descends the volume of the gas is decreased in response to the increasing pressure, the converse is true as the diver ascends, with the volume of gas increasing as the pressure decreases. Barotrauma, trauma caused by a change in pressure, can occur in any anatomical space, which is filled with gas. This includes the middle ear, sinuses, teeth and lungs. Barotrauma of the middle ear is the most common form seen in diving, with barotrauma to the lungs being the most serious (Smith 1996).

Physiological effects of Diving

Scuba diving takes us into an alien world, a world we're not designed very well to live in. Divers are exposed to environmental conditions not found in other activities, these include increased ambient pressure, raised partial pressure of oxygen, increased resistance to movement, added weight and drag of diving equipment, cold stress and a higher breathing resistance (Doubt 1996). Therefore there are various physiological effects that occur when we enter the water. Breathing through scuba equipment increases the resistance of breathing; this can place increased strain on the respiratory system. An adaptive response to the stress of the added breathing resistance is an attempt to reduce minute ventilation (VE). A lower VE for a given VO2 means that the respiratory efficiency has improved (Doubt 1996). It may be that the decrease in VE is the physiologic response to the higher inspired oxygen content due to the increase in partial pressure of oxygen at depth. One of the results of this change in respiration may be hypoventilation with an increase in end-tidal CO2, these divers are known as CO2 retainers (Doubt 1996).

Due to the increase in respiratory resistance, at heavy workloads a sense of dyspnea may be felt. It may be that the regulator is unable to meet the demands required of it. Under these conditions it is possible that the diver will panic and take dangerous action, such as a rapid ascent or omission of decompression requirements (Doubt 1996, Edmonds et al 1997). It is therefore important that divers be educated about this, so that regulators can be brought that meet the demand of the diver's style of diving, or that if they encounter this condition, the diver is able to recognise it and take safe and appropriate action.

Divers are commonly immersed in cold water; this has certain physiologic effects. Temperature regulation becomes more difficult, hence the need for an appropriate exposure suit. Doubt (1996) reports that immersion in cold water can cause hyperventilation, however this normally subsides within several minutes. However he states that: "VEmay remain elevated relative to warmer conditions, even in the presence of moderate levels of exercise." This appears to be contrary to the findings of Whipp and Wasserman (1970) who found that there was no significant difference in VE after exercise in hypothermic conditions. Any increase in VE is important because it will shorten the duration of the dive, and may also result in hyperventilation. Other effects of a decrease in temperature are an increased desire to urinate (Edmonds et al 1997), shivering, temporary sinus arrhythmias, and an increase in VO2 (helps to generate more body heat). Due to shivering and other mechanisms used to conserve or generate body heat, such as a shut down of peripheral circulation, there can be a decrease in aerobic efficiency (Doubt 1996), and loss of strength and co-ordination, because of the decrease in the blood flow to the deep muscle (Doubt 1991) this can be dangerous in diving, where the inability to react to a situation could be life threatening.

Cold-water immersion can have quite marked effects on the cardiovascular system. As noted above cardiac arrhythmias are more frequent in the cold and sudden incapacity and death of divers soon after entering cold water has been reported; this has often been noted to occur in older divers, some with previous histories of cardiac problems (Doubt 1991, Doubt 1996, Edmonds et al 1997). During cold water immersion there is an increase in sympathetic nervous system activity, causing a decrease in heart rate, the heart may also have to work against a greater load due to the shut down of the peripheral circulation (Doubt 1991, Doubt 1996, Edmonds et al 1997). Another factor, which can increase the risk of cardiac failure in divers, is the diving reflex. This is present in mammals such as whales to enable them to dive to depth for long periods of time; it is also present in humans to a lesser extent. The heart rate is slowed due to vagal stimulation, and the sympathetic nervous system constricts the blood flow to the skin and other organs, in humans this can cause a rise in blood pressure, but minimal or no fall in cardiac output, thus increasing rather than reducing the work of the heart (Edmonds et al 1997).

The energy cost of diving can be quite high. Scuba equipment does not tend to be streamlined and can have considerable drag, especially when bulky items, such as cameras, catch bags and reels are added. The main mechanism of propulsion is through the legs, with efficiency improved by the addition of fins. Overhead arm action is impractical due to the surrounding water resistance. The speed, at which a diver swims, has been shown to affect the energy requirement. The experience level of the diver also affects their VO2, with beginners having a higher VO2 than experienced, regular divers. It has also been found that female divers have lower energy costs than male divers, at all skill levels. Another factor, which influences energy cost, is the body position in the water, a horizontal position is found to reduce the drag, and therefore the energy cost of diving (Pendergast et al 1996)

Decompression Sickness (DCS)

Decompression sickness or the bends as it is commonly known, has been a problem faced by divers since at least the 1800's. It was a major killer of commercial divers. For example the Pearl Divers of Broome, rarely lived beyond the age of 40, due to the devastating effects of this condition. In the early 20th century Dr JS Haldane derived mathematical decompression tables to overcome this problem (Edmonds 1997). Research is still continuing into this area and luckily much more is known about this condition now, along with the advent of dive tables and recompression chambers the numbers of deaths has declined. Although every year scuba divers still need recompression therapy or die from the effects of DCS. Morgan (1995) reports that between 600-900 divers are treated for decompression illness (DCI), which includes DCS every year. (DCI also includes Arterial Gas Embolism (AGE)).

As mentioned above DCS results from the formation of bubbles in the blood or body tissues. It appears that different people have different susceptibilities to DCS. Various conditions in the diver or in his surroundings may cause him to absorb an excessive amount of inert gas (usually nitrogen), or inhibit the elimination of the dissolved gas during normal controlled decompression. Some of the factors that may affect a person's susceptibility to DCS are: depth, adaptation to a depth, age, obesity, dehydration, hang-overs, exhaustion, cold, strenuous exercise, gender (females > males) rapid and multiple ascents, repetitive dives and flying after diving (Edmonds 1997). As bubbles form they may transit the venous system, enter the pulmonary circulation and cause pulmonary vascular occlusion: or they may transit a right to left cardiac communication (atrial defect, patent foramen ovale (up to 33% of population)) and result in arterial embolisation (Bove 1996). The US Navy Diver's Handbook (Thalman 1995), describes two types of DCS. Type I (also called pain-only DCS) includes skin symptoms, lymph nod swelling, and joint and/or muscle pain and is not life threatening. Bubbles are present in the tissues, but they do not appear to enter the body through the blood stream or the lungs (Bove 1996). Type II DCS (or serious DCS) includes symptoms involving the CNS, respiratory system, or circulatory system. This may become life threatening. The brain contains large amounts of lipid in the form of myelin, which surrounds the nerves. This has a high solubility for nitrogen and other inert gases used in diving (such as helium and hydrogen) and therefore the brain and spinal cord are more at risk of bubble formation on ascent (Bove 1996).

Musculoskeletal pain from Type I DCS is usually described as a deep-seated, boring "toothache like" pain, often associated with a joint. There is some thought that injured joints are more susceptible to DCS (Edmonds 1997). The pain is usually not affected by movement, and is always present at rest, with an increasing intensity over time (Smith 1996, Thalman 1995). Trunk and abdominal pain is more serious as this may be a precursor of more serious symptoms observed in Type II DCS (Smith 1996, Thalman 1995). Skin symptoms usually manifest as intense itching, which may progress on to a rash, and lymph involvement presents as a painful swelling of individual or regional lymph nodes. In Type II DCS symptoms may affect any of the five main functions of the brain: 1) sensation: numbness and tingling are frequent symptoms, 2) movement: the strength or co-ordination may be affected, 3) higher brain function: cognition, consciousness, orientation, speech and memory, 4) autonomic functions: problems with control of breathing, heart function and bladder or bowel problems, 5) reflexes (Edmonds et al 1997). Pulmonary symptoms may also be observed; if profuse intravascular bubbling (chokes) occurs, symptoms may develop due to congestion of the lung circulation. This manifests as chest pain aggravated by inspiration, and/or an irritating cough, with an increased respiratory rate, loss of consciousness. Death may occur if recompression is not begun as soon as possible (Thalman 1996). Fatigue, out of proportion to the work of the dive is also a common symptom of DCS (Edmonds 1997).

DCS usually occurs within a short period of time following a dive, from Thalman (1995), 42% occurs within one hour, 60% within three hours, 83% within eight hours and 98% occurs within 24 hours. Smith (1996) reported similar times, although he reported 95% occurring within 6 hours. So in diagnosis the time factor can play a major role, anything presenting after 24-48 hours is unlikely to be DCS.

Arterial Gas Embolism (AGE)

AGE and DCS are commonly reported together as DCI, because symptoms may be similar and treatment for both is essentially the same with 100% oxygen given as soon as possible and recompression therapy. AGE however may cause rapid deterioration, so must be treated as an extreme emergency. AGE is a result of Boyle's Law (see above) as the diver ascends, air in the lungs expands, and unless this air has an outlet, barotrauma will result. This may occur in even shallow depths of less than 10 metres, as this is where the pressure changes are the greatest. The repercussions of this barotrauma may be an arterial gas embolism, pneumothorax, mediastinal emphysema, and subcutaneous emphysema (Thalman 1995, Smith 1996). Arterial gas embolism is the most serious and may be fatal, especially if it reaches the heart or brain.

Musculoskeletal Effects

There are several musculoskeletal complaints that occur in the diving population. Most of the studies have shown these are more common in commercial and Navy divers than in the sport diving population, and appear to be related to frequency and type of dive profile.

One of these conditions is known as Osteobaric Necrosis (or Dysbaric Osteonecrosis). This is defined as: "Death of a portion of bone that is thought to be caused by nitrogen embolisation 'blockage' of the blood vessels in divers." The pathogenesis isn't fully understood, but it is thought to occur in one of four ways:

The lesion begins as an asymptomatic finding on x-ray. It can progress to involve the joint, resulting in fractures and disintegration of the joint surface. It eventually leads to joint degeneration (Campbell E 2000a, Edmonds 1997). The condition was first noted in 1888, and the radiographic appearance described first in 1911 (Ohta and Matsunaga 1974). Edmonds (1997) classifies the lesions into two types: A, which is near the joint surface (juxta-articular), and B, which is remote from the joint surface. Typically the lesions are found in the long bones: humerus, femur and tibia (Campbell E 2000a, Ohta and Matsunaga 1974). The predisposing factors are: age greater than 30 years, inadequate decompressions, experimental dives, deep dives, decompression sickness and long duration dives. MRI can be used to pick up the lesions early (Edmonds 1997). It should be remembered when treating divers with high risk factors that this is a possibility with undiagnosed joint pain, and should be investigated, to try and pick it up in the early stages.

Another musculoskeletal problems that has been reported to be associated with diving, is a higher incidence of cervical intervertebral disc lesions. Reul et al (1995) did a study looking at the incidence of central nervous system lesions and cervical disc herniation in amateur divers with long histories of scuba diving. They found that a significantly larger proportion of the divers had degenerated intervertebral discs than the controls, they suggested that gas microbubbles might account for the observed degenerative changes of the cervical disc. There does not seem to be any literature implying that lumbar or thoracic discs are also susceptible. Another study by Hoiberg (1986) reported in Roos (1989) found that Navy divers who had no history of DCS had significantly more hospitalisations for neurologic diseases and joint disorders than matched controls. However as Roos (1989) goes on to observe, there is a deficit of other studies to endorse this finding in the general sport-diving population, who normally dive less frequently than Navy divers.

Another musculoskeletal problem that appears to be associated with scuba diving is temporomandibular joint dysfunction (TMJD). Hobson (1991) suggests that TMJD may be due to either an occlusion imbalance or over-exertion of the joint and muscles, resulting in pain. It has been suggested that the use of a diving mouthpiece can result in local inflammation of the TMJ. Hobson (1991) found that mouthpieces examined, exacerbated, pre-existing TMJ pain in most cases. This is important because TMJD while being uncomfortable may also be a precursor to middle ear problems, giving vertigo and disorientation, potentially hazardous conditions while diving. Hobson (1996) went on to look at mouthpieces and airways efficiency. He found that a mouthpiece with an interdental bite platform of 4mm gave the greatest comfort, along with the most efficient airway.

Conclusion

It can be seen that there are many physiological effects that occur when entering the water. Scuba equipment enables divers to enter this realm with relative ease. However the underwater environment, while being beautiful and unique can be potentially harmful or deadly to divers. Some of the difficulties that may be encountered from a physiological point of view are:

An increased resistance to movement caused by the drag of water, making propulsion through the water difficult, resulting in an increased energy cost. Heat loss can occur rapidly in water, with other effects such as an increase in minute ventilation, a decrease in heart rate and possible risk of arrhythmias, a decrease in peripheral circulation, along with lower muscle temperatures and core temperatures. Respiratory efficiency is impaired due to the scuba equipment, and this can give a sense of dyspnea at higher work loads which may induce panic, a potentially lethal state of mind while diving. There is also the effect on the body of breathing gas at increased pressures with the risk of DCS or AGE. As well, specific musculoskeletal problems can be encountered, in the diving population.

It is therefore important that medical professionals recognise these physiological effects and other conditions, so that diving specific conditions may be recognised and the appropriate action taken as soon as possible. It is vital divers are educated on the importance of remaining fit and that they have regular check-ups so that potential problems can be caught before a disaster strikes. More and more people are learning to dive, and so it is likely that more medical professionals will be confronted with diving related problems, or are in the situation where they need to advise a diver whether or not they can continue to dive, or changes to make their diving safer. Information on the stresses and physiological responses to diving is therefore important to have. It also appears that maybe education on the need to be fit and in good physical condition is not conveyed strongly enough to divers. With the industry pushing to get as many divers as possible in the water. Maybe stricter guidelines on education and screening of potential and present divers are necessary?

References

Bove AA (1996)
Medical aspects of sport diving. Medicine and Science in Sports and Exercise 28(5):591-595.
Campbell E (Ed.) (2000a)
Dysbaric Osteonecrosis. Diving Medicine Online. URL: http://scuba-doc.com/Dysost.htm: accessed 19 October 2000.
Campbell E (Ed.) (2000b)
Physical fitness for scuba diving. Diving Medicine Online. URL: http://www.scuba-doc.com/physfit.htm: accessed 19 October 2000.
Carturan D, Boussuges A, Molenat F, Burnet H, Fondarai J and Gardette B (2000)
Ascent rate and circulating venous bubbles in recreational diving. International Journal of Sports Medicine 21:459-462.
Doubt TJ (1996)
Cardiovascular and thermal responses to SCUBA diving. Medicine and Science in Sports and Exercise 28(5):581-585.
Doubt TJ (1991)
Physiology of exercise in the cold. Sports Medicine 11(6):367-381.
Edmonds C, McKenzie B and Thomas R (1997)
Diving Medicine for Scuba Divers (2nd ed.) Melbourne: JL Publications.
Hobson RS (1991)
Temporomandibular dysfunction syndrome associated with scuba diving mouthpieces. British Journal of Sports Medicine 25(1):49-51.
Hobson RS (1996)
Airway efficiency during the use of SCUBA diving mouthpieces. British Journal of Sports Medicine 30: 145-147.
Lettnin HKJ (1999)
International textbook of Mixed Gas Diving. Flagstaff: Best Publishing Company.
McCardle WD, Katch FI and Katch VL (1996)
Exercise Physiology. (4th ed.) Baltimore: Williams and Wilkins.
Morgan WP (1995)
Anxiety and panic in recreational scuba divers. Sports Medicine 20(6):398-421.
Ohta Y and Matsunaga H (1974)
Bone lesions in divers. The Journal of Bone and Joint Surgery 56B(1):3-16.
Pendergast DR, Tedesco M, Nawrocki DM and Fisher NM (1996)
Energetics of underwater swimming with SCUBA. Medicine and Science in Sports and Exercise 28(5):573-580.
Reul J, Weis J, Jung A, Willmes K and Thron A (1995)
Central nervous system lesions and cervical disc herniations in amateur divers. Lancet 345(8962):1403-1405.
Roos R (1989)
Are the risks of sport scuba diving being underestimated? The Physician and Sportsmedicine 17(7):132-142.
Smith DJ (1996)
Diagnosis and management of diving accidents. Medicine and Science in Sports and Exercise 28(5):587-590.
Taylor R (2000)
Blood and bubbles. Sydney: Australian Scuba Diver, May/June 2000 pp.18-19.
Thalman ED (Ed) (1995)
US Navy Diver's Handbook. Flagstaff: Best Publishing Company.
Whipp BF and Wasserman K (1970)
Effect of body temperature on the ventilatory response to exercise. Respiratory Physiology 87:354.

Exercise Physiology Educational Resources 2000