Hypoxia is a condition in which the body or a region of the body is deprived of an adequate oxygen supply at the tissue level. or may be used as a synonym for hypoxic hypoxia, which occurs when there is insufficient oxygen in the breathing gas to oxygenate the blood to a level that will adequately support normal metabolic processes,
Localized hypoxia
thumb|Vascular ischemia of the toes with characteristic cyanosis
Hypoxia that is localized to a region of the body, such as an organ or a limb, is usually the consequence of ischemia, the reduced perfusion to that organ or limb, and may not necessarily be associated with general hypoxemia. A locally reduced perfusion is generally caused by an increased resistance to flow through the blood vessels of the affected area.
Ischemia is a restriction in blood supply to any tissue, muscle group, or organ, causing a shortage of oxygen. The corneas are not perfused and get their oxygen from the atmosphere by diffusion. Impermeable contact lenses form a barrier to this diffusion, and therefore can cause damage to the corneas. Symptoms may include irritation, excessive tearing and blurred vision. The sequelae of corneal hypoxia include punctate keratitis, corneal neovascularization and epithelial microcysts. In order to support continuous growth and proliferation in challenging hypoxic environments, cancer cells are found to alter their metabolism. Furthermore, hypoxia is known to change cell behavior and is associated with extracellular matrix remodeling and increased migratory and metastatic behavior.
In systemic tissues, oxygen again diffuses down a concentration gradient into cells and their mitochondria, where it is used to produce energy in conjunction with the breakdown of glucose, fats, and some amino acids.
Altitude
Atmospheric pressure reduces with altitude and proportionally, so does the oxygen content of the air.
Anemia
Hemoglobin plays a substantial role in carrying oxygen throughout the body,
In most tissues of the body, the response to hypoxia is vasodilation. By widening the blood vessels, the tissue allows greater perfusion.
By contrast, in the lungs, the response to hypoxia is vasoconstriction. This is known as hypoxic pulmonary vasoconstriction, or "HPV", and has the effect of redirecting blood away from poorly ventilated regions, which helps match perfusion to ventilation, giving a more even oxygenation of blood from different parts of the lungs.
The resulting tumor vasculature is often abnormal in structure and function — characterized by irregular vessel diameters, increased permeability, and poor perfusion — which further perpetuates local hypoxia and genomic instability. This feedback loop enhances the tumor’s adaptive potential and resistance to therapies such as radiotherapy and chemotherapy, both of which rely on adequate oxygenation to maximize cytotoxic effects.
In addition to promoting angiogenesis, HIF signaling also supports metabolic reprogramming toward anaerobic glycolysis, enhances the expression of matrix metalloproteinases (MMPs) that degrade extracellular matrix components, and increases the expression of adhesion molecules that facilitate tumor invasion and metastatic dissemination.
Together, these mechanisms make hypoxia-induced angiogenesis a central hallmark of malignant progression and a major therapeutic target in oncology. Agents that block VEGF signaling (such as bevacizumab) or inhibit HIF-1α activity are currently used or under investigation to counteract tumor angiogenesis and improve treatment outcomes.
Diagnosis
Physical examination and history
Hypoxia can present as acute or chronic.
Acute presentation may include dyspnea (shortness of breath) and tachypnea (rapid, often shallow, breathing). Severity of symptom presentation is commonly an indication of severity of hypoxia. Tachycardia (rapid pulse) may develop to compensate for low arterial oxygen tension. Stridor may be heard in upper airway obstruction, and cyanosis may indicate severe hypoxia. Neurological symptoms and organ function deterioration occur when the oxygen delivery is severely compromised. In moderate hypoxia, restlessness, headache and confusion may occur, with coma and eventual death possible in severe cases.
Treatment and management
Treatment and management depend on circumstances. For most high altitude situations the risk is known, and prevention is appropriate. At low altitudes hypoxia is more likely to be associated with a medical problem or an unexpected contingency, and treatment is more likely to be provided to suit the specific case. It is necessary to identify persons who need oxygen therapy, as supplemental oxygen is required to treat most causes of hypoxia, but different oxygen concentrations may be appropriate.
Hypoxia that leads to impaired judgment, delayed reactions, or loss of consciousness can indirectly contribute to fatal outcomes in situations where the immediate cause of death is secondary. This has been documented in underwater diving accidents, where hypoxia can cause confusion or unconsciousness before drowning occurs; in high-altitude mountaineering, where it contributes to exposure, hypothermia, and falls; and in aviation, where pilots of unpressurized aircraft or performers in aerobatic maneuvers may lose control of the aircraft following hypoxic incapacitation.
Epidemiology
Hypoxia is a common disorder but there are many possible causes.
Potentially life-threatening hypoxemia is common in critically ill patients.
Hypoxia related to underdeveloped lung function is also a frequent complication of premature birth. In preterm infants, incomplete maturation of the alveoli and insufficient production of surfactant can lead to respiratory distress syndrome, resulting in systemic oxygen deprivation. In the United States, intrauterine hypoxia and birth asphyxia together were ranked as the tenth leading cause of infant mortality in recent national statistics.
Silent hypoxia
Silent hypoxia (also known as happy hypoxia)
Etymology
Hypoxia is formed from the Greek roots υπo (hypo), meaning under, below, and less than, and oξυ (oxy), meaning acute or acid, which is the root for oxygen.
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