<P> Respiration is controlled by centres in the medulla, which influence the rate of breathing and the depth of each breath . This is influenced by the blood level of carbon dioxide, as determined by central and peripheral chemoreceptors located in the central nervous system and carotid and aortic bodies, respectively . Hypoxia occurs when the breathing center doesn't function correctly or when the signal is not appropriate: </P> <Ul> <Li> Strokes, epilepsy and cervical neck fractures can all damage the medullary respiratory centres that generates rhythmic impulses and transmit them along the phrenic nerve to the diaphragm, the muscle that is responsible for breathing . </Li> <Li> A decreased respiratory drive can also be the result of metabolic alkalosis, a state of decreased carbon dioxide in the blood </Li> <Li> Central sleep apnea . During sleep, the breathing centers of the brain can pause their activity, leading to prolonged periods of apnea with potentially serious consequences . </Li> <Li> Hyperventilation followed by prolonged breath - holding . This hyperventilation, attempted by some swimmers, reduces the amount of carbon dioxide in the lungs . This reduces the urge to breathe . However, it also means that falling blood oxygen levels are not sensed, and can result in hypoxemia . </Li> </Ul> <Li> Strokes, epilepsy and cervical neck fractures can all damage the medullary respiratory centres that generates rhythmic impulses and transmit them along the phrenic nerve to the diaphragm, the muscle that is responsible for breathing . </Li> <Li> A decreased respiratory drive can also be the result of metabolic alkalosis, a state of decreased carbon dioxide in the blood </Li>

Causes of low oxygen levels in arterial blood