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Physiology of underwater diving Immersion in water and exposure to cold water and high pressure have physiological effects on the diver which limit the depths and duration possible in ambient pressure diving.
Breath-hold endurance is a severe limitation, and breathing at high ambient pressure adds further complications, both directly and indirectly. Technological solutions have been developed which can greatly extend depth and duration of human ambient pressure dives, and allow useful work to be done underwater.
Physiological response to water immersion Immersion of the human body in water affects the circulationrenal systemfluid balanceand breathing, because the external hydrostatic pressure of the water provides support against the internal hydrostatic pressure of the blood.
This causes a blood shift from the extravascular tissues of the limbs into the chest cavity,  and fluid losses known as immersion diuresis compensate for the blood shift in hydrated subjects soon after immersion. Stroke volume is not greatly affected by immersion or variation in ambient pressure, Thesis bootcamp melbourne slowed heartbeat reduces the overall cardiac output, particularly because of the diving reflex in breath-hold diving.
This may occur during higher intensity exercise while immersed or submerged. The immediate shock of the cold causes involuntary inhalation, which if underwater can result in drowning.
The cold water can also cause heart attack due to vasoconstriction;  the heart has to work harder to pump the same volume of blood throughout the body, and for people with heart disease, this additional workload can cause the heart to go into arrest.
A person who survives the initial minute after falling into cold water can survive for at least thirty minutes provided they do not drown.
The ability to stay afloat declines substantially after about ten minutes as the chilled muscles lose strength and co-ordination. It is exhibited strongly in aquatic mammals seals ottersdolphins and muskrats and also exists Thesis bootcamp melbourne other mammals, including humans.
Diving birdssuch as penguinshave a similar diving reflex. As this internal oxygen supply reduces, the animal experiences an increasing urge to breathe caused by buildup of carbon dioxide and lactate in the blood,  followed by loss of consciousness due to central nervous system hypoxia.
If this occurs underwater, it will drown. This is accelerated by exertion, which uses oxygen faster, or by hyperventilation, which reduces the carbon dioxide level in the blood. Lower carbon dioxide levels increase the oxygen-haemoglobin affinity, reducing availability of oxygen to brain tissue towards the end of the dive Bohr effect ; they also suppress the urge to breathe, making it easier to hold the breath to the point of blackout.
This can happen at any depth. The partial pressure of oxygen at depth may be sufficient to maintain consciousness but only at that depth and not at the reduced pressures nearer the surface.
When diving, the pressure differences which cause the barotrauma are changes in hydrostatic pressure. In this case the pressure difference causes a resultant tension in the surrounding tissues which exceeds their tensile strength. Besides tissue rupture, the overpressure may cause ingress of gases into the tissues and further afield through the circulatory system.
This can cause blockage of circulation at distant sites, or interfere with the normal function of an organ by its presence. Physiology of decompression Provision of breathing gas at ambient pressure can greatly prolong the duration of a dive, but there are other problems that may result from this technological solution.
Absorption of metabolically inert gases is increased as a function of time and pressure, and these may both produce undesirable effects immediately, as a consequence of their presence in the tissues in the dissolved state, such as nitrogen narcosis and high pressure nervous syndrome  or cause problems when coming out of solution within the tissues during decompression.
These range from the toxic effects of oxygen at high partial pressure,  through buildup of carbon dioxide due to excessive work of breathing, increased dead space or inefficient removal, to the exacerbation of the toxic effects of contaminants in the breathing gas due to the increased concentration at high pressures.
Visibility underwater is reduced because light passing through water attenuates rapidly with distance, leading to lower levels of natural illumination. Underwater objects are also blurred by scattering of light between the object and the viewer, resulting in lower contrast.
These effects vary with the wavelength of the light, and the colour and turbidity of the water. The human eye is optimised for air vision, and when it is immersed in direct contact with water, visual acuity is adversely affected by the difference in refractive index between water and air.
Provision of an airspace between the cornea and the water can compensate, but causes scale and distance distortion. Artificial illumination can improve visibility at short range. A narrow field of vision caused by a small viewport in a helmet results in greatly reduced stereoacuity,  and an apparent movement of a stationary object when the head is moved.
Sound from an underwater source can propagate relatively freely through body tissues where there is contact with the water as the acoustic properties are similar. When the head is exposed to the water, some sound is transmitted by the eardrum and middle ear, but a significant part reaches the cochlea independently, by bone conduction.
When wearing a helmet, hearing sensitivity is similar to that in surface air, as it is not greatly affected by the breathing gas or chamber atmosphere composition or pressure. The combination of instability, equipment, neutral buoyancy and resistance to movement by the inertial and viscous effects of the water encumbers the diver.
Cold causes losses in sensory and motor function and distracts from and disrupts cognitive activity. The ability to exert large and precise force is reduced. Underwater, some of these inputs may be absent or diminished, making the remaining cues more important.
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