What is Hypoxia?

what is hypoxia, hyperbaric oxygen therapy

Hypoxia can be a dangerous, even life-threatening state for our cells and tissues. To sustain the life we have an absolute and continual need for the oxygen, necessary to produce energy for our cells' survival and reproduction.

Illness often comes as a direct result of inadequate blood supply to our cells where life is actually occurs. Acute oxygen deficit in damaged tissues may promote the hypoxia which is often caused by severe injuries, chronic diseases, insufficient oxygen available to the lungs, some environmental or toxic factors. The different causes of hypoxia usually determine the type of hypoxia.

Systemic oxygen delivery is the product of CaO2, and cardiac output. Even when CaO2, is normal, tissue oxygenation may be inadequate if cardiac function is impaired. The latter is commonly encountered both in the intensive care unit (as with cardiac failure or the application of excessive positive end-expiratory pressure) and in the ambulatory care setting (as with chronic congestive heart failure).260

Physiologic Responses to Hypoxia

JBS Haldane is said to have remarked that a lack of oxygen not only stops the machine but also wrecks the machinery. The correctness of this observation is manifestly apparent with acute, severe hypoxia as encountered in cardiopulmonary arrest or severe hypoxemic acute respiratory failure.260

In the 1960s it was shown that a PO2 of at least 18 mm Hg is necessary to sustain mitochondrial function, and to generate adenosine triphosphate, which is essential for all major cellular biochemical functions. Cellular hypoxia may be defined as a state in which convective or diffusive oxygen transport fails to meet the tissue demand for oxygen and when the rate of adenosine triphosphate synthesis becomes limited by the oxygen supply.

Decreases in oxygen supply set in motion adaptive mechanisms designed to maintain cellular activity at a minimum acceptable level; the failure of these mechanisms results in cellular dysfunction and can lead to irreversible cell damage.260 Learn about Aerobic Cellular Respiration...

Hypoxia Types And Causes

Hypoxia types are often determined by specific causes of oxygen deprivation in each individual case. Lack of oxygen may occur in specific area of the body such as brain (cerebral hypoxia), sites of non healing wounds, tumors, or it can affect the body in general. Among the common sub types of hypoxia are the following:

  • Anemic hypoxia: due to a decreased concentration of functional hemoglobin or a reduced number of red blood cells, as seen in anemia and hemorrhage;
  • Hypoxic hypoxia: resulting from a defective mechanism of oxygenation in the lungs, as caused by a low tension of oxygen, abnormal pulmonary function, airway obstruction, or a right-to-left shunt in the heart;
  • Ischemic hypoxia: tissue hypoxia characterized by tissue oligemia and caused by arteriolar obstruction or vasoconstriction;
  • Oxygen affinity hypoxia: due to reduced ability of hemoglobin to release oxygen;
  • Stagnant hypoxia: tissue hypoxia characterized by intravascular stasis due to impairment of venous outflow or decreased arterial inflow.260

Other terms are also used to describe more sub types of oxygen deprivation. Among them are:

  • Cerebral Hypoxia (Brain Hypoxia) develops when our brain receives less oxygen than required to sustain its metabolic requirements. Among all cells in our body, the brain cells are most sensitive to the oxygen deprivation. Five minutes without oxygen is enough for the brain cell to start dying. Cerebral Hypoxia that lasts for that or longer time can cause seizures, coma or even brain death. Awareness of Cerebral Hypoxia symptoms is crucial because it is a medical emergency and every moment is critical to a meaningful survival. Read more about Cerebral Hypoxia...
  • Histotoxic Hypoxia develops when body is getting enough oxygen, but it cannot use it sufficiently due to physiological problems at a cellular level. Thus due to a disruption of oxidative phosphorylation enzymes activity, tissue cells are unable to use the oxygen effectively. Excessive drinking of alcohol or narcotics, can also produce Histotoxic Hypoxia. In other cases histotoxic hypoxia can be developed by a person exposed to poisoning chemicals or gases in poorly ventilated or insufficiently controlled areas. In such cases hemoglobin’s abilities to bind, transport and release oxygen are inhibited by poisoning gas. Read more about Histotoxic Hypoxia...
  • Chronic Hypoxia can result either from a number of medical conditions such as any disease associated with chronic blood loss, cardiac disorders, chronic pulmonary diseases, or from adjustment to high altitudes after moving from the sea level. Conditions promoting chronic hypoxia gradually induce degradation in tissue oxygenation levels leading to a physiological stresses that influence multiple body systems. In patients with chronic lung diseases chronic hypoxia can induce a decreased arterial vessel density due to the fibrosis or destruction often associated with development of the disease. Read more about Chronic Hypoxia...
  • Tissue Hypoxia is a condition in which tissue cells experience inadequate oxygen utilization due to a number of causes such as decreased partial pressure of oxygen (PO2) in a given tissue. Endotoxins associated with sepsis or other critical conditions may also inhibit cellular metabolism and decrease oxygen consumption. Cellular utilization of oxygen may be inhibited by some metabolic poisons, such as cyanide. Releasing various toxins and/or mediators one organ affected by tissue hypoxia can lead indirectly to a dysfunction or even failure of other organs. Read more about Tissue Hypoxia...

If you prefer to learn more about Hypoxia by reading a well written textbook, we recommend a selection of good books... Providing a detail overview of hypoxia, its symptoms and types, the recommended books address the distinctive problems that lack fo oxygen presents to vulnerable organs such as the kidney, liver, heart and brain.

Symptoms of Hypoxia

The symptoms of Hypoxia can differ from person to person and can depend on many factors among which are severity of the condition and underlaying cause of hypoxia. Sometimes it’s even hard to recognize the symptoms. Awareness of hypoxia and its association to the one of the following symptoms is of great importance:

  • Behavior/personality changes
  • Confusion
  • Cyanosis
  • Dizziness
  • Euphoria
  • Inattentiveness
  • Motor in-coordination
  • Nausea
  • Poor judgment
  • Rapid breathing
  • Sensation of air hunger

The effects of oxygen deprivation may range from subtle to deadly, particularly in situations where sound judgment, reasoning and physical coordination are required. The awareness of this is especially important among some professionals like aviators. Often, the person affected will not likely notice the symptoms of hypoxia. As the severity of oxygen dificiency increases the symptoms grow worse increasing associated risks.

hypoxic hypoxia, aircraft
Photo courtesy of "Visions by Sorenson"

One manifestation of hypoxia, particularly important to pilots results from the decreasing amounts of oxygen available on ascent in the atmosphere. This deficiency is known as hypoxic hypoxia or altitude hypoxia.

At sea level the percentage composition of the atmosphere remains the same, approximately 78% nitrogen, 21% oxygen and 1% inert gases. As one takes off and climbs higher in an unpressurized aircraft, an increasingly greater oxygen deficit will be experienced. Reduced atmospheric pressure results in fewer oxygen molecules per volume in the air. This reduced oxygen supply may eventually result in the symptoms of hypoxia.

The body, however, has several adaptation mechanisms. First, the rate and depth of breathing increase in order to deliver more oxygen to the lungs. Then, the pulse rate increases as the heart pumps blood faster in order to increase the delivery of oxygen to the tissues. There is a limit, however, on how far these adaptations can be taken, and eventually, supplemental oxygen will be required to make up for the deficit.

Studies performed at the FAA’S Civil Aeromedical Institute, have shown that pilots flying in unpressurized airplanes at altitudes between 8,000 and 12,000 feet without supplemental oxygen, make more procedural errors than pilots who are well oxygenated. Pilots not receiving oxygen at altitude also made more errors on descent and approach because the effects of hypoxia at altitude have residual impact later on - a sort of “hypoxia hangover.”

Hyperbaric oxygen (HBO2) significantly increases the oxygen diffusion driving force, thus increasing oxygen availability to tissues. This helps to correct negative effects of hypoxia and restore normal tissue oxygenation.

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