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A condition characterized by a low level of dissolved oxygen in an aquatic environment.
Oxygen deficiency; any state wherein a physiologically inadequate amount of oxygen is available to or is utilized by tissue, without respect to cause or degree. Also known as hypoxemia.



(oxygen starvation, oxygen deficiency), the lowering of the oxygen content of the tissues. The pathological condition that arises during hypoxia results from the tissues’ receiving a smaller supply of oxygen than they require (in cases of hypoxemia—lowered oxygen content of the blood). It may also arise when the tissues’ capacity to use oxygen is less than their need for oxygen. Irreversible changes take place in vital organs as a result of hypoxia. The central nervous system, heart muscle, and kidney and liver tissues are the most sensitive to oxygen deficiency.

Various hypoxic states are distinguished according to the classification adopted in 1949 at a conference on hypoxia in Kiev. Hypoxic hypoxia is a form of oxygen deficiency caused by a decrease in the oxygen content of inhaled air (for example, when climbing a mountain), by the difficulty of oxygen penetrating into the blood from the lungs because they are diseased and the air passages are obstructed, and by respiratory disturbances. Hemic hypoxia—which arises when the amount of hemoglobin capable of incorporating oxygen is reduced (decreased oxygen capacity of the blood)—develops after loss of blood, carbon monoxide poisoning, and exposure to radiation. Circulatory hypoxia occurs in cases of circulatory disorders that reduce the amount of blood flowing to the tissues per unit of time. Tissue hypoxia is a form of oxygen deficiency that is associated with changes in the activity of the respiratory enzymes. As a result of these changes the tissues are prevented from using the oxygen present in the blood that bathes them. (Tissue hypoxia develops in cases of disturbances of vitamin metabolism and in certain types of poisoning, such as cyanide.)

Hypoxia may be acute or chronic, depending on the rate at which it intensifies. In acute hypoxia, the functioning of the higher sections of the central nervous system is the first to be affected. In chronic hypoxia, the first to be affected is the functioning of the cardiovascular, respiratory, and circulatory systems. Resistance to hypoxia can be increased by training in a pressure chamber or in the mountains. Under these conditions the body develops a number of adaptive mechanisms, including reflex intensification of respiration and blood circulation, increase in the number of red blood cells as a result of their escaping from the blood depots, and increased hemoglobin content of red blood cells. These adaptations improve the individual’s sense of well-being and increase his work capacity under conditions of oxygen deficiency. It has been found that increased resistance to a given injurious factor simultaneously increases resistance to other adverse influences. For example, as the body becomes more resistant to acute hypoxia, it becomes more resistant to acceleration, ionizing radiation, heat, and great physical exertion.


Barbashova, Z. I. Akklimatizatsiia k gipoksii i ee fiziologicheskie mekhanizmy. Moscow-Leningrad, 1960.
Petrov, I. R. Kislorodnoe golodanie golovnogo mozga. [Leningrad] 1949.



A state of oxygen deficiency in the body sufficient to cause an impairment of body function. It is caused by the reduction in partial pressure of oxygen, inadequate oxygen transport, or the inability of the tissue to use oxygen. In flying, hypoxia is mostly caused by a lower partial pressure of oxygen.
References in periodicals archive ?
Fetal hypoxia and acidosis may develop faster with an abnormal trace when there is scanty thick meconium, IUGR, intrauterine infection with pyrexia and/or pre or post term labour.
Late decelerations are indicators of fetal hypoxia.
1) Prenatal asphyxia and severe, chronic fetal hypoxia are probably present in those disorders.
Introduction of electronic fetal monitoring with a high false positive rate for the detection of fetal hypoxia has also contributed to this rate.
1-6 Meconium spillage due to fetal maturity is a normal physiologic event but fetal hypoxia or increased vagal activity from cord compression may be pathologic reasons.
3) Furthermore, a subsequent meta-analysis of the randomized, controlled trials also showed that electronic fetal monitoring was associated with a significant reduction in perinatal death due to fetal hypoxia (OR, 0.
Failure to manage the situation correctly and relieve fetal hypoxia may lead to perinatal death or morbidity due to meconium aspiration or multi-organ hypoxic damage, especially permanent cerebral injury.
On the other hand, increased activin-A concentrations have been observed in the amniotic fluid of patients who subsequently died of intrauterine fetal hypoxia (20) and in the plasma of hypoxic preterm newborns (12).
Sickle cell trait is associated with previously unreported signs of fetal hypoxia, placental infarcts, and possibly excess risk of fetal demise, according to a study presented in poster form at the annual meeting of the Society for Maternal-Fetal Medicine.
Fetal hypoxia or death can also occur with maternal episodes of headache, palpitations, and diaphoresis related to tumor secretions.
14,15) This results in histopathological changes in placenta and fetal hypoxia leading to IUGR and preterm delivery and fetal death.