High altitudes have reduced amounts of oxygen and, consequently, the partial pressure of oxygen in tissues reduces in hypoxic environments. At sea level, the concentration of oxygen is approximately 21 percent and at an altitude of 4000 m, it is reduced by about 40 percent. Symptoms of altitude sickness include headache, nausea, dizziness and shortness of breath. Higher elevations may lead to the loss of bodily fluids from blood vessels due to decreased pressure and cause death.
PO2 Levels and Altitude
The partial pressure of oxygen (PO2) in the blood increases during acclimatization to higher altitudes. A study published in the November 2004 issue of the "American Journal of Physiology" investigated the effects of altitude on oxygen levels in participants living at below sea level in Denmark. The test subjects were acclimated over an 8-week period to altitudes of 4,100 meters. The researchers tested their blood oxygen levels at the beginning of the study and at two- and six-week periods. The study found that PO2 levels increased from an average basal level of 61 to 69 at two weeks and 72 at eight weeks. The study further compared the Danish participants to individuals living at the higher altitudes and found that PO2 levels were similar in both groups by the end of the investigation.
Acclimating to High Altitudes
The April 2002 issue of the "Journal of Applied Physiology" included a study that compared the PO2 levels in Danish lowlanders to a group of participants from La Paz, Bolivia at altitudes of 5,260 meters. The study found that after a nine-week period, the arterial oxygen saturation levels climbed to 77 percent in the Danish participants. However, the study concluded that the PO2 levels in the lowland group remained below those of the Bolivian nationals.
Hypoxia and Brain Function
Hypoxia is a state of reduced oxygen, which occurs at high altitudes. A study published in the January 2007 issue of "Clinical Neurophysiology" described the effects of various hypoxic levels on brain activity. The researchers recorded PO2 levels, respiration and brain waves by use of an EEG at three levels of induced barometric pressure. The study found that brain function diminished at lower oxygen levels, but were restored along with PO2. The study concluded that neuronal function was inhibited by lower oxygen levels.
Hyperventilation, or rapid breathing, occurs in hypoxic environments to maintain proper oxygen levels. A study published in the summer 2009 issue of "High Altitude Medicine and Biology" investigated the effects of hyperventilation on restoring PO2 levels in participants exercising in hypoxic environments. The study found that severe hypoxia inhibited the maximal oxygen uptake and reduced the amount of oxygen reaching muscle tissue. The authors concluded, however, that humans have a reserve of oxygen in muscle tissue that can be accessed during exercise in hypoxic environments.