Causes And Effects Of Strokes Biology Essay
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Stroke is defined as "A neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours".
- WHO (1970)
A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain. This can be due to ischemia caused by thrombosis or embolism or due to a hemorrhage. As a result, the affected area of the brain is unable to function, leading to inability to move one or more limbs on one side of the body, inability to understand or formulate speech or inability to see one side of the visual field (Donnan GA, Fisher M. May 2008).
PREVALANCE AND INCIDENCE:
Stroke could soon be the most common cause of death worldwide (Murray CJ, Lopez AD 1997). Stroke is currently the second leading cause of death in the Western world, ranking after heart disease and before cancer (Donnan GA, Fisher M, May 2008)and it causes 10% of deaths worldwide (World Health Organization. 2004) .
It has been noted that stroke incidence may vary considerably from country to country. The prevalence of stroke in India was estimated as 203 per 100,000 populations above 20 years, amounting to a total of about 1 million cases. Stroke represented 1.2% of total deaths in India (PK Sethi Neurosciences Today 2002).
Men are 1.25 times more likely to suffer strokes than women(PK Sethi Neurosciences Today 2002), yet 60% of deaths from stroke occur in women (Villarosa, Linda, Ed.1993).
Strokes can be classified into two major categories: ischemic and hemorrhagic. Ischemia is due to interruption of the blood supply, while hemorrhage is due to rupture of a blood vessel or an abnormal vascular structure. 80% of strokes are due to ischemia; the remainders are due to hemorrhage (Donnan GA, Fisher M. May 2008).
In an ischemic stroke, blood supply to a part of the brain is decreased, leading to dysfunction of the brain tissue in that area. The four reasons responsible for ischemic stroke are thrombosis, embolism (Donnan GA, Fisher M. May 2008), systemic hypoperfusion (Shuaib A, Hachinski VC .September 1991) and venous thrombosis (Stam J. 2005).
Intracranial hemorrhage is the accumulation of blood anywhere within the skull vault.
Intracerebral hemorrhage (ICH) is bleeding directly into the brain tissue, forming a gradually enlarging haematoma.
High blood pressure, High blood cholesterol levels, Diabetes, Cigarette smoking (Hankey GJ. August 1999), Heavy alcohol consumption (Reynolds K, Lewis B, Nolen JD, et al .2003) , drug use, (Sloan MA, 1991), lack of physical activity, obesity, unhealthy diet (American Heart Association.2007) and Atrial fibrillation.
When the flow of blood in an artery supplying the brain is interrupted for more than a few seconds, brain cells can die, causing permanent damage. An interruption can be caused by either blood clots or bleeding in the brain. Most strokes are due to blood clots that blocks the blood flow to brain. Bleeding into the brain occurs if a blood vessel ruptures or if there is a significant injury (Ay H; Furie KL. 2005).
A common cause of stroke is atherosclerosis. Fatty deposits and blood platelets collect on the walls of the arteries, forming plaques. Over time, the plaques slowly begin to block the flow of blood. The plaque itself may block the artery enough to cause a stroke (Ay H; Furie KL. 2005).
The plaque causes the blood to flow abnormally, which leads to a blood clot. A clot can stay at the site of narrowing and prevent blood flow to all of the smaller arteries it supplies. In other cases, the clot can travel and wedge into a smaller vessel (Ay H; Furie KL. 2005).
Strokes caused by embolism are most commonly caused by heart disorders. An embolism may originate in a major blood vessel as it branches off the heart. A clot can also form elsewhere in the body for any number of reasons, and then travel to the brain, causing a stroke (Ay H; Furie KL. 2005).
Arrhythmias of the heart, such as atrial fibrillation, can be associated with this type of stroke and may contribute to clot formation. Other causes of embolic stroke include endocarditis, or use of a mechanical heart valve. A clot can form on the artificial valve, break off, and travel to the brain (Ay H; Furie KL. 2005).
BLEEDING IN THE BRAIN:
A second major cause of stroke is bleeding in the brain. This can occur when small blood vessels in the brain become weak and burst. Some people have defects in the blood vessels of the brain that make this more likely. The flow of blood after the blood vessel ruptures damages brain cells (Ay H; Furie KL. 2005).
Ischemic stroke occurs due to a loss of blood supply to part of the brain, initiating the ischemic cascade. Brain tissue ceases to function if deprived of oxygen for more than 60 to 90 seconds and after a few hours will suffer irreversible injury possibly leading to death of the tissue. Atherosclerosis may disrupt the blood supply by narrowing the lumen of blood vessels leading to a reduction of blood flow, by causing the formation of blood clots within the vessel (National Institute of Neurological Disorders and Stroke.1999).
Embolic infarction occurs when emboli formed elsewhere in the circulatory system, typically in the heart as a consequence of atrial fibrillation, or in the carotid arteries. These break off, enter the cerebral circulation, then lodge in and occlude brain blood vessels (National Institute of Neurological Disorders and Stroke.1999).
Hemorrhagic strokes results in tissue injurys by causing compression of tissues from an expanding hematomas. This can distort and injure the tissues. In addition, the pressure may lead to a loss of blood supply to affected tissue with resulting infarction, and the blood released by brain hemorrhage appears to have direct toxic effects on brain tissue and vasculature (National Institute of Neurological Disorders and Stroke.1999).
SIGNS AND SYMPTOMS:
A stroke symptom typically starts suddenly, over seconds to minutes, and in most cases don't progress further. The symptoms depend on the area of the brain affected. The more extensive the area of brain affected, more the functions that are likely to be lost (National Institute of Neurological Disorders and Stroke.1999).
A sudden development of one or more of the following indicates a stroke:
Paresis or paralysis of any part of the body, Numbness, tingling, or decreased sensation, Changed or diminished vision, Language difficulties, including slurred speech, inability to speak, inability to understand speech, difficulty in reading or writing, Swallowing difficulties or drooling, Loss of memory, Vertigo, Loss of balance or coordination, Personality changes, Mood/emotion changes, Drowsiness, lethargy, or loss of consciousness, Uncontrollable eye movements or eyelid drooping.
If the area of the brain affected contains one of the three prominent Central nervous system pathways-the spinothalamic tract, corticospinal tract, and dorsal column, symptoms may include hemiplegia and muscle weakness of the face, numbness, reduction in sensory or vibratory sensation.
In most cases, the symptoms affect only one side of the body. The defect in the brain is usually on the opposite side of the body depending on which part of the brain is affected. In addition to the above CNS pathways, the brainstem also consists of the 12 cranial nerves. Hence a stroke affecting the brain stem can produce symptoms relating to deficits in the cranial nerves. The symptoms are altered smell, taste, hearing, or vision, drooping of eyelid and weakness of ocular muscles, decreased reflexes like gag, swallow and pupil reactivity to light, decreased sensation and muscle weakness of the face, balance problems and nystagmus,altered breathing and heart rate,weakness in sternocleidomastoid muscle with inability to turn head to one side,weakness in tongue.
If the cerebral cortex is involved, the CNS pathways can again be affected, but also can produce the symptoms like aphasia, apraxia, visual field defect, memory deficits, hemineglect, disorganized thinking, confusion, hypersexual gestures ,anosognosia (Bamford JM 2000).
When the cerebellum is involved, the patient may have the symptoms like Trouble walking, altered movement, coordination, Vertigo and disequilibrium (Bamford JM 2000).
Loss of consciousness, headache, and vomiting usually occurs more often in hemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing on the brain.
The techniques which were used to diagnose the stroke are neurological examination, CT scans or MRI scans, Doppler ultrasound, and arteriography. The diagnosis of stroke itself is clinical, with assistance from the imaging techniques. Imaging techniques also assist in determining the subtypes and cause of stroke. There is yet no commonly used blood test for the stroke diagnosis itself, though blood tests may be of help in finding out the likely cause of stroke (Hill M 2005).
Screening for high blood pressure at least every two years, regular cholesterol check up, treat high blood pressure, diabetes, high cholesterol and heart disease, follow a low-fat diet, quit smoking, exercise regularly, lose weight if you are over weight, avoid excessive alcohol use (Goldstein LB, Adams R, Alberts MJ et al. 2006).
Treatment of ischemic stroke:
Pharmacologic thrombolysis with the drug tissue plasminogen activator (tPA), Mechanical thrombectomy and anticoagulants.
Treatment of hemorrhagic stroke:
Patients with intracerebral hemorrhage require neurosurgical evaluation to detect and treat the cause of the bleeding, although many may not need surgery. Patients are monitored and their blood pressure, blood sugar, and oxygenation are kept at optimum levels.
The rehabilitation techniques commonly used were Rood's Sensorimotor Approach, Knott's and Voss Proprioceptive Neuromuscular Facilitation, Brunnstrom's Movement Therapy, Bobath's Neuro Developmental Therapy, Motor Relearning Programme, Bimanual Rapid Alternating Movement, Motor Imagery Therapy, Robot Assisted Movement Therapy, Functional Electrical Stimulation, Bilateral Isokinetic Training, Cyclic Electrical Neuromuscular Stimulation, Biofeedback etc.
The results of stroke vary widely depending on size and location of the lesion (Stanford Hospital & Clinics.2005). Dysfunctions correspond to areas in the brain that have been damaged. Disability affects 75% of stroke survivors enough to decrease their employability (Coffey C. Edward.2000). Stroke can affect patients physically, mentally, emotionally, or a combination of the three. 30 to 50% of stroke survivors suffer post stroke depression, which is characterized by lethargy, irritability, sleep disturbances, lowered self esteem, and withdrawal. Depression can reduce motivation and worsen outcome (Senelick Richard C.1994).
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