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This is typically secondary to stroke, injury, or cardiac arrest due to heart attack. Most ischemic neurons that die do so due to the activation of chemicals produced during and after ischemia. [2] The ischemic cascade usually goes on for two to three hours but can last for days, even after normal blood flow returns. [3]
The classic symptoms include a slow heart rate due to loss of cardiac sympathetic tone and warm skin due to dilation of the peripheral blood vessels. [20] (This term can be confused with spinal shock which is a recoverable loss of function of the spinal cord after injury and does not refer to the hemodynamic instability.)
Due to sympathetic nervous system activation, blood is diverted away from noncritical organs and tissues to preserve blood supply to vital organs such as the heart and brain. While prolonging heart and brain function, this also leads to other tissues being further deprived of oxygen causing more lactic acid production and worsening acidosis .
Reperfusion injury, sometimes called ischemia-reperfusion injury (IRI) or reoxygenation injury, is the tissue damage caused when blood supply returns to tissue (re-+ perfusion) after a period of ischemia or lack of oxygen (anoxia or hypoxia).
Lactic acidosis is commonly found in people who are unwell, such as those with severe heart and/or lung disease, a severe infection with sepsis, the systemic inflammatory response syndrome due to another cause, severe physical trauma, or severe depletion of body fluids. [3]
Brain ischemia has been linked to a variety of diseases or abnormalities. Individuals with sickle cell anemia, compressed blood vessels, ventricular tachycardia, plaque buildup in the arteries, blood clots, extremely low blood pressure as a result of heart attack, and congenital heart defects have a higher predisposition to brain ischemia in comparison to the average population.
The signs and symptoms of ischemia vary, as they can occur anywhere in the body and depend on the degree to which blood flow is interrupted. [4] For example, clinical manifestations of acute limb ischemia (which can be summarized as the "six P's") include pain, pallor, pulseless, paresthesia, paralysis, and poikilothermia.
Brain failure after clinical death is now known to be due to a complex series of processes called reperfusion injury that occur after blood circulation has been restored, especially processes that interfere with blood circulation during the recovery period. [11] Control of these processes is the subject of ongoing research.