the amount of blood ejected from each ventricle on each contraction, which can be affected by medication, exercise, decreases in the volume of circulating blood, or heart anomalies. In a healthy adult, stroke volume is estimated at 70 ml.
Causes Blood supply to the brain may be interrupted by arteries furring up with ATHEROSCLEROSIS (which is accelerated by HYPERTENSION and DIABETES MELLITUS, both of which are associated with a higher incidence of strokes) or being occluded by blood clots arising from distant organs such as infected heart valves or larger clots in the heart (see BLOOD CLOT; THROMBOSIS). Hearts with an irregular rhythm are especially prone to develop clots. Patients with thick or viscous blood, clotting disorders or those with in?amed arteries – for example, in SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) – are particularly in danger of having strokes. Bleeding into the brain arises from areas of weakened blood vessels, many of which may be congenital.
Symptoms Minor episodes due to temporary lack of blood supply and oxygen (called TRANSIENT ISCHAEMIC ATTACKS OR EPISODES (TIA, TIE)) are manifested by short-lived weakness or numbness in an arm or leg and may precede a major stroke. Strokes cause sudden weakness or complete paralysis of the muscles controlled by the part of the brain affected, as well as sensory changes (e.g. numbness or tingling). In the worst cases these symptoms and signs may be accompanied by loss of consciousness. If the stroke affects the area of the brain controlling the larynx and throat, the patient may suffer slurring or loss of speech with di?culty in initiating swallowing. When the face is involved, the mouth may droop and the patient dribble. Strokes caused by haemorrhage may be preceded by headaches. Rarely, CVAs are complicated by epileptic ?ts (see EPILEPSY). If, on the other hand, numerous small clots develop in the brain rather than one major event, this may manifest itself as a gradual deterioration in the patient’s mental function, leading to DEMENTIA.
Investigations Tests on the heart or COMPUTED TOMOGRAPHY or ultrasonic scans (see ULTRASOUND) on arteries in the neck may indicate the original sites of distantly arising clots. Blood tests may show increased thickness or tendency to clotting, and the diagnosis of general medical conditions can explain the presence of in?amed arteries which are prone to block. Special brain X-rays show the position and size of the damaged brain tissue and can usually distinguish between a clot or infarct and a rupture of and haemorrhage from a blood vessel in the brain.
Management It is better to prevent a stroke than try to cure it. The control of a person’s diabetes or high blood pressure will reduce the risk of a stroke. Treatment with ANTICOAGULANTS prevents the formation of clots; regular small doses of aspirin stop platelets clumping together to form plugs in blood vessels. Both treatments reduce the likelihood of minor transient ischaemic episodes proceeding to a major stroke.
Once the latter has occurred, there is no e?ective treatment to reduce the damage to brain tissue. Function will return to the affected part of the body only if and when the brain recovers and messages are again sent down the appropriate nerves. Simple movements are more likely to recover than delicate ones, and sophisticated functions have the worst outlook. Thus, movement of the thigh may improve more easily than ?ne movements of ?ngers, and any speech impairment is more likely to be permanent. A rehabilitation team can help to compensate for any disabilities the subject may have. Physiotherapists maintain muscle tone and joint ?exibility, whilst waiting for power to return; occupational therapists advise about functional problems and supply equipment to help patients overcome their disabilities; and speech therapists help with diffculties in swallowing, improve the clarity of remaining speech or o?er alternative methods of communication. District nurses or home helps can provide support to those caring for victims of stroke at home. Advice about strokes may be obtained from the Stroke Association.... stroke
Heat collapse is characterised by fatigue, giddiness, and temporary loss of consciousness. It is accompanied by HYPOTENSION and BRADYCARDIA; there may also be vomiting and muscular cramps. Urinary volume is diminished. Recovery is usual.
Heat exhaustion is characterised by increasing weakness, dizziness and insomnia. In the majority of sufferers, sweating is defective; there are few, if any, signs of dehydration. Pulse rate is normal, and urinary output good. Body temperature is usually 37·8–38·3 °C.
Heat cramps (usually in the legs, arms or back, and occasionally involving the abdominal muscles) are associated with hard physical work at a high temperature. Sweating, pallor, headache, giddiness and intense anxiety are present. Body temperature is only mildly raised.
Heat hyperpyrexia is heralded by energy loss and irritability; this is followed by mental confusion and diminution of sweating. The individual rapidly becomes restless, then comatose; body temperature rises to 41–42 °C or even higher. The condition is fatal unless expertly treated as a matter of urgency.
Treatment With the ?rst two syndromes, the affected individual must be removed immediately to a cool place, and isotonic saline administered – intravenously in a severe case. The fourth syndrome is a medical emergency. The patient should be placed in the shade, stripped, and drenched with water; fanning should be instigated. He or she should be wrapped in a sheet soaked in cool water and fanning continued. When rectal temperature has fallen to 39 °C, the patient is wrapped in a dry blanket. Immediately after consciousness returns, normal saline should be given orally; this usually provokes sweating. The risk of circulatory collapse exists. Convalescence may be protracted and the patient should be repatriated to a cool climate. Prophylactically, personnel intended for work in a tropical climate must be very carefully selected. Adequate acclimatisation is also essential; severe physical exertion must be avoided for several weeks, and light clothes should be worn. The diet should be light but nourishing, and ?uid intake adequate. Those performing hard physical work at a very high ambient temperature should receive sodium chloride supplements. Attention to ventilation and air-conditioning is essential; fans are also of value.... heat stroke
About 80 per cent of patients survive an acute stroke and they are at risk of a further episode within a few weeks and months; about 10 per cent in the ?rst year and 5 per cent a year after that. HYPERTENSION, smoking, HYPERLIPIDAEMIA and raised concentration of blood sugar, along with OBESITY, are signi?cant pointers to further strokes and preventive steps to reduce these factors are worthwhile, although the reduction in risk is hard to assess. Even so, the affected person should stop smoking, greatly reduce alcohol intake, check for and have treated diabetes, reduce weight and exercise regularly. In any case, a diet rich in fresh fruit and vegetables and low in fat and salt, exercise and the avoidance of smoking may reduce the risk of having a ?rst stroke.
The evidence is inconclusive that patients with ischaemic stroke should be treated with antihypertensives. Furthermore, neither the starting blood pressure nor the best drug regimen or its starting time are generally agreed. Studies on the most e?ective methods of preventing and treating stroke are continuing; meanwhile available evidence suggests that an active approach to prevention of primary and secondary hypertension will bene?t patients and usually be cost-e?ective.... ischaemic stroke
Normal values for a 60 kg man are (in ml):
Total lung capacity (TLC) The volume of air that can be held in the lungs at maximum inspiration.
Tidal volume (TV) The volume of air taken into and expelled from the lungs with each breath.
Inspiratory reserve volume (IRV) The volume of air that can still be inspired at the end of a normal quiet inspiration.
Expiratory reserve volume (ERV) The volume of air that can still be expired at the end of a normal quiet expiration.
Residual volume (RV) The volume of air remaining in the lungs after a maximal expiration.
Vital capacity (VC) The maximum amount of air that can be expired after a maximal inspiration.
Functional residual capacity (FRC) The volume of air left in the lungs at the end of a normal quiet expiration.... lung volumes
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