Ischemia is one of the most studied medical conditions. It is associated with various infectious and non-infectious medical conditions. The term ischemia is derived from the Greek word Icheim (restrain) referring to the lack of blood supply to a respective tissue. The occurrence of ischemia in the body triggers many biochemical abnormalities in the body therefore creating insufficiency of metabolites to the tissue.
Studies indicate that almost fifty percent of deaths around the world happen because of ischemia. The most prevalent forms of ischemia are associated with the cardiovascular system and brain. Ischemia progresses itself in to metabolic disorders such as hypoxia. Hypoxia is a fatal condition in which there is oxygen deficiency to the cells causing cellular damage and death. The predisposing factors for hypoxia may include blockage of arteries in a respective circulatory region preventing the blood supply. Ischemia gradually results in tissue necrosis and damage to blood vessels restricting the flow of blood into the tissues.
Biochemical changes such as accumulation of metabolized waste products occur as a result of ischemia in relation to conditions such as embolism, atherosclerosis, thrombosis and compression. This metabolic waste accumulation eventually leads to increase in toxin levels in the body. Cell death is one of the main outcomes of ischemia. The complications of ischemia range from reversible forms to irreversible forms depending on the type of organ damage.
Physiological studies indicate the significance of parenchyma cells in the occurrence of ischemia. Parenchyma cells located in each organ have a specific threshold. In the cardiac muscle, the threshold levels are 20-30 min whereas in the neural cells it is only 3-4 min. Parenchyma cells are more prone to damage than the cells of the stoma and hence the difference in these threshold values indicate the exact etiology of ischemia.
Ischemia occurring in the cardiac region is predominantly because of the hypoxia present in the sub endocardial region. Simultaneously in the central nervous system, it is because of the watershed infarcts. Hence the effect of ischemia is directly proportional to the micro vascular anatomy of the organ systems. Another form of ischemia is silent ischemia. It is an asymptomatic condition often found in people who are old, women and have a history of diabetes. Silent ischemia does not present any visible clinical signs of illness, however through diagnostic examinations such as electrocardiogram and stress testing; the insufficient blood supply to the cardiac muscle can be identified.
Acute mesenteric ischemia is caused due to inadequate blood flow the the mesentery artery and results in tissue hypoxemia. Symptoms such as acute abdominal pain, nausea, diarrhea and vomiting are noticed. Some feel acute pain on eating - 'abdominal angina'. The narrowed mesenteric artery is usually a result of chronic atherosclerosis. Anticoagulation and vasodilation are resorted to. Often surgery is done to treat mesenteric ischemia due to embolus or thrombosis.
Ischemia is treated by administering blood thinning drugs such as aspirin. This is done to prevent the clot formation in the blood vessels. Temporary opening of the arterial walls is done by using nitro-glycerine medication. Since ischemia is the precursor for the occurrence of tachycardia, beta blockers are used to relax the heart muscle. Other medications include calcium channel blockers and cholesterol lowering drugs.
The body needs a specific amount of Oxygen to function normally and when this amount is lowered the body experiences hypoxia. Hypoxia literally means lack of oxygen for effective ventilation.
Hypoxemia refers to a state of abnormally low level of Oxygen in the blood.
Anoxia refers to the condition of absence of Oxygen supply to an organ or tissue
Anoxemia refers to the condition where the blood stream contains below normal amount of Oxygen.
Hypoxia is primarily classified into:
Generalized hypoxia: affects the entire body, may occur in normal healthy people when they scale high altitudes.
Local hypoxia: affects one particular region of the body.
When the level of oxygen in the blood reduces, it leads to the condition. People suffering from conditions like ischemia or blockage/constriction of blood vessels may suffer from hypoxia. In general when people travel from low to high altitudes, they may face this problem as the oxygen level depletes with altitude.
Any condition wherein the body is deprived of oxygen can lead to hypoxia. Major causes that lead to the condition include:
Types of hypoxia
Hypemic hypoxia: Obstruction in the ability of the blood to deliver oxygen, caused by carbon monoxide poisoning.
Anemic Anoxia: Occurs due to a decrease in the hemoglobin or RBC making it too little for the blood to carry oxygen. Anemia may be the result of iron deficiency, hemorrhage or shortened life span of RBC owing to an autoimmune disease.
Histotoxic: When the required amount of oxygen reaches the body part, however it does not utilize it because of its reduced ability, it is called as histotoxic hypoxia. Cyanide poisoning, for example, incapacitates a cellular enzyme essential for oxygen utilization. Other causes include: Alcohol, narcotics, acetone, formaldehyde and some anesthetic agents.
Hypoxic: Also called as Hypoxemic Anoxia: When the body does not receive the required amount of oxygen it leads to low partial pressure of oxygen in the blood thus leading to hypoxic hypoxia. The oxygen pressure of the blood which gets supplied to other body tissues is too low to push and flood the hemoglobin with oxygen. High altitude has lower density of air and lower pressure of oxygen than at sea level. Altitude Sickness occurs because the partial pressure of oxygen decreases with altitude. Hypoxemia is the direct result of lower oxygen in the high altitude which translates to lower level oxygen in the blood.
Stagnant: Obstruction of blood that carries oxygen. It can be due to exposure to cold, diseases which stifle blood circulation to the extremities or ergot poisoning.
Pulse Oximetry, a non invasive test is useful to diagnose Hypoxia. A blood test like serum lactate test can show elevated levels of lactic acid - the result of starvation of oxygen in tissues. The normal level of lactic acid is less than 2 mmol/L. However an increase in lactic acid alone does not indicate hypoxia and some form of Anoxia does not increase the lactic acid concentration. Symptoms may be dangerous on the onset and may include the following:
Some types of Hypoxia cannot be prevented. Treatment depends on the severity of the condition and the appearance of the clinical symptoms. Treatment may include the following:
Paraplegia is sensory or motor disorder in the lower extremities of the body. The impairment is due to damage caused as a result of congenital deformities or trauma and spinal injuries. The effects of paraplegia are predominantly seen in the thoracic, lumbar and sacral region. The damage caused as a result of paraplegia can lead to other issues such as monoplegia (dysfunction of one organ), paralysis and some times fecal incontinence and impotence.
Spastic paraplegia and flaccid paraplegia are two important forms of the disease which are differentiated based on the location. Flaccid paraplegia is associated with the lesion caused in the spinal cord; which in turn causes two significant forms of myelopathies compressive and non-compressive respectively. The compressive form of paraplegia occurs because of the destruction of the spinal cord due to pressure exerted on it. In most cases the pressures caused are because of underlying medical conditions such as neoplasms, degenerative spinal disease or hematoma. The compressive forms are predominantly located in extradural and subdural regions causing extra medullary and intramedullary complications such as neurofibroma and meningioma.
The lesions caused affect the spinal arteries causing ischemia eventually leading to tissue necrosis in the respective region. This leads to the development of edema in the spinal region causing compression and damage. Because of increased pressure, paraplegia can initiate complications such as pneumonia, pressure sores which are decubitus in origin. Often the pain associated with paraplegia radiates in the region of nerve damage. Vitamin B 12 deficiency also leads to the occurrence of paraplegia of non compressive origin.
Bibliography / Reference
Collection of Pages - Last revised Date: July 21, 2018