Difference Between Hypoxia and Ischemia

Key Difference – Hypoxia vs Ischemia

Hypoxia and Ischemia are both diseases caused due to the insufficiency of oxygen supply in the body, but there is a difference between hypoxia and ischemia. Thekey differencebetween these two diseases is that theHypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supplywhileIschemia is a reduction of blood supply to tissues, causing a limitation of oxygen andglucoserequired for themetabolism.

What is Hypoxia?

Hypoxia can be classified as eithergeneralized(affecting the whole body) orlocalized(affecting a single region of the body).Hypoxia is different from hypoxemia. Hypoxia refers to a state in which the oxygen supply is insufficient for the demand, whereas hypoxemia refers to states that have low arterial oxygen concentration. Complete deprivation of oxygen supply is called “anoxia.”

Generalized hypoxiacan occur in healthy people at a high altitude where oxygen concentration of the air is low. It causesaltitude sickness causing potentially fatal outcomessuch ashigh altitudepulmonary edema(HAPE) andhigh altitude cerebral edema由于缺氧损伤(HACE)。缺氧也可以occurred in healthy people when breathing mixtures of gasses with a low oxygen concentration, e.g. Diving deep underwater (Deep sea divers). Sometimes mild and non-damaging intermittent hypoxia is used intentionally for altitude training to improve athletic performance by adaptation of both thesystemicand cellular bio environments.

Hypoxia can be aserious complication of preterm birthin the neonate due to immature lungs. Lungs of the human fetus mature toward the latter part of the pregnancy. To minimize this complication, infant at risk of hypoxia are often placed inside an incubator which is capable of maintaining continuous positive airway pressure to prevent lung collapse.

What is Ischemia?

Ischemia is caused by problems with thecirculatory systemcausingdamage or dysfunction of oxygen sensitive tissues. Most tissues cannot survive more than few minutes without a continuous oxygen supply. Lack of oxygen leads to a process known asIschemic cascade. The damage is caused by the accumulation of metabolic waste products, damage to cell membranes,mitochondrial(powerhouse of the cell) dysfunction. This leads to leakage of or activation of autolyzing and proteolytic enzymes causing damage to the cell and surrounding tissues. The sudden restoration of blood supply to an ischemic tissue can lead to increased damage by a process calledreperfusion injurywhich can be more harmful than the initial ischemic damage. Reintroduction of blood supply brings more oxygen back to the damaged tissues. It causes a greater production of oxygen free radicals and reactive oxygen species that in turn damage cells and tissues. As asecondary complication, it increases calcium concentration inside cells causingfatalcardiac arrhythmiasand alsoincreased cellular damageby activating many proteolytic enzymes.Heart ischemialeads toheart attacksandbrain ischemialeads tostrokes. Any organ of the body can get ischemia damage due to inadequate oxygen supply to meet the continuous demand for cellular metabolism.

What is the Difference Between Hypoxia and Ischemia?

Definition of Hypoxia and Ischemia

Hypoxia:Hypoxia refers to a state where the oxygen supply is insufficient for the demand.

Ischemia:Ischemia is damage or dysfunction of oxygen sensitive tissues due to reduction of blood supply.

Causes and Complications of Hypoxia and Ischemia

Cause

Hypoxia:Causes of Hypoxia can be the high altitude where oxygen concentration of the air is low, breathing mixtures of gasses with a low oxygen concentration, etc.

Ischemia:Ischemia is caused by problems with the circulatory system.

Complications

Hypoxia:Hypoxia damage can cause fatal outcomes such as high altitude pulmonary edema and high altitude cerebral edema. It can also cause preterm birth complications.

Ischemia:Complications of Ischemia include heart attacks, strokes, reperfusion injury and the fatal cardiac arrhythmias can be a secondary complication.

Characteristics ofHypoxia and Ischemia

Reversibility

Hypoxia:Hypoxia can be reversed when the oxygen supply is restored.

Ischemia:Ischemia is potentially reversible when the blood supply is restored. However, oxygen sensitive tissues such as brain and heart may not recover unless the blood supply is restored rapidly.

Pathophysiological basis

Hypoxia:Hypoxia can be physiological such as in exercise.

Ischemia:Ischemia is almost always pathological.

Distribution

Hypoxia:Hypoxia can affect the whole body (generalized) or a single region of the body (localized).

Ischemia:Ischemia affects one part of the body (local) in most of the cases.

Image Courtesy:

“Cynosis” by James Heilman, MD – Own work.(CC BY-SA 3.0)viaWikimedia Commons

“Heart inferior wall infarct” by Patrick J. Lynch, medical illustrator – Patrick J. Lynch, medical illustrator. (CC BY-SA 3.0) viaWikimedia Commons