Problems in Oxygen Transport

At high altitude (above about 8000 ft), both atmospheric pressure and the partial pressure of oxygen are lower than at sea level. A person who ascends quickly can develop acute mountain sickness (AMS), with symptoms such as headache, shortness of breath, nausea, dizziness and palpitations, because haemoglobin cannot bind oxygen as effectively at this lower pO2. Given time, the body makes long-term adjustments: the kidneys step up production of the hormone erythropoietin, which stimulates the bone marrow to make more red blood cells, increasing the blood's overall oxygen-carrying capacity so that the same volume of blood can deliver more oxygen despite the lower pO2 in the air.

Diving deep underwater creates the opposite kind of problem - increasing pressure. As a diver descends, rising water pressure compresses the lungs and raises the partial pressure of the gases within them. This can actually help push extra oxygen into circulation, but it also drives more nitrogen into the blood, which can cause nitrogen narcosis (a state resembling intoxication) at depth. If a diver then ascends to the surface too quickly, the dissolved nitrogen comes out of solution while still in the blood and forms bubbles - a condition called decompression sickness, or 'the bends'. Small bubbles are usually harmless, but larger ones can lodge in small capillaries, blocking blood flow or pressing on nerves, causing joint and muscle pain and, in severe cases, neurological problems including stroke. …