Also called expiration, this is the act of breathing air from the lungs out through the bronchi, trachea, mouth and nose. (See also RESPIRATION.)
The explosive nature of coughing results in a spray of droplets into the surrounding air and, if these are infective, hastens the spread of colds (see COLD, COMMON) and INFLUENZA. Coughing is, however, a useful reaction, helping the body to rid itself of excess phlegm (mucus) and other irritants. The physical e?ort of persistent coughing, however, can itself increase irritation of the air passages and cause distress to the patient. Severe and protracted coughing may, rarely, fracture a rib or cause PNEUMOTHORAX. Coughs can be classi?ed as productive – when phlegm is present – and dry, when little or no mucus is produced.
Most coughs are the result of common-cold infections but a persistent cough with yellow or green sputum is indicative of infection, usually bronchitis, and sufferers should seek medical advice as medication and postural drainage (see PHYSIOTHERAPY) may be needed. PLEURISY, pneumonia and lung CANCER are all likely to cause persistent coughing, sometimes associated with chest pain, so it is clearly important for people with a persistent cough, usually accompanied by malaise or PYREXIA, to seek medical advice.
Treatment Treatment of coughs requires treatment of the underlying cause. In the case of colds, symptomatic treatment with simple remedies such as inhalation of steam is usually as e?ective as any medicines, though ANALGESICS or ANTIPYRETICS may be helpful if pain or a raised temperature are among the symptoms. Many over-the-counter preparations are available and can help people cope with the symptoms. Preparations may contain an analgesic, antipyretic, decongestant or antihistamine in varying combinations. Cough medicines are generally regarded by doctors as ine?ective unless used in doses so large they are likely to cause sedation as they act on the part of the brain that controls the cough re?ex.
Cough suppressants may contain CODEINE, DEXTROMETHORPHAN, PHOLCODINE and sedating ANTIHISTAMINE DRUGS. Expectorant preparations usually contain subemetic doses of substances such as ammonium chloride, IPECACUANHA, and SQUILL (none of which have proven worth), while demulcent preparations contain soothing, harmless agents such as syrup or glycerol.
A list of systemic cough and decongestant preparations on sale to the public, together with their key ingredients, appears in the British National Formulary.... cough
Static lung volumes and capacities can be measured: these include vital capacity – the maximum volume of air that can be exhaled slowly and completely after a maximum deep breath; forced vital capacity is a similar manoeuvre using maximal forceful exhalation and can be measured along with expiratory ?ow rates using simple spirometry; total lung capacity is the total volume of air in the chest after a deep breath in; functional residual capacity is the volume of air in the lungs at the end of a normal expiration, with all respiratory muscles relaxed.
Dynamic lung volumes and ?ow rates re?ect the state of the airways. The forced expiratory volume (FEV) is the amount of air forcefully exhaled during the ?rst second after a full breath – it normally accounts for over 75 per cent of the vital capacity. Maximal voluntary ventilation is calculated by asking the patient to breathe as deeply and quickly as possible for 12 seconds; this test can be used to check the internal consistency of other tests and the extent of co-operation by the patient, important when assessing possible neuromuscular weakness affecting respiration. There are several other more sophisticated tests which may not be necessary when assessing most patients. Measurement of arterial blood gases is also an important part of any assessment of lung function.... pulmonary function tests
Causes The cause of fever is the release of fever-producing proteins (pyrogens) by phagocytic cells called monocytes and macrophages, in response to a variety of infectious, immunological and neoplastic stimuli. The lymphocytes (see LYMPHOCYTE) play a part in fever production because they recognise the antigen and release substances called lymphokines which promote the production of endogenous pyrogen. The pyrogen then acts on the thermoregulatory centre in the HYPOTHALAMUS and this results in an increase in heat generation and a reduction in heat loss, resulting in a rise in body temperature.
The average temperature of the body in health ranges from 36·9 to 37·5 °C (98·4 to 99·5 °F). It is liable to slight variations from such causes as the ingestion of food, the amount of exercise, the menstrual cycle, and the temperature of the surrounding atmosphere. There are, moreover, certain appreciable daily variations, the lowest temperature being between the hours of 01.00 and 07.00 hours, and the highest between 16.00 and 21.00 hours, with tri?ing ?uctuations during these periods.
The development and maintenance of heat within the body depends upon the metabolic oxidation consequent on the changes continually taking place in the processes of nutrition. In health, this constant tissue disintegration is exactly counterbalanced by the consumption of food, whilst the uniform normal temperature is maintained by the adjustment of the heat developed, and of the processes of exhalation and cooling which take place, especially from the lungs and skin. During a fever this balance breaks down, the tissue waste being greatly in excess of the food supply. The body wastes rapidly, the loss to the system being chie?y in the form of nitrogen compounds (e.g. urea). In the early stage of fever a patient excretes about three times the amount of urea that he or she would excrete on the same diet when in health.
Fever is measured by how high the temperature rises above normal. At 41.1 °C (106 °F) the patient is in a dangerous state of hyperpyrexia (abnormally high temperature). If this persists for very long, the patient usually dies.
The body’s temperature will also rise if exposed for too long to a high ambient temperature. (See HEAT STROKE.)
Symptoms The onset of a fever is usually marked by a RIGOR, or shivering. The skin feels hot and dry, and the raised temperature will often be found to show daily variations – namely, an evening rise and a morning fall.
There is a relative increase in the pulse and breathing rates. The tongue is dry and furred; the thirst is intense, while the appetite is gone; the urine is scanty, of high speci?c gravity and containing a large quantity of solid matter, particularly urea. The patient will have a headache and sometimes nausea, and children may develop convulsions (see FEBRILE CONVULSION).
The fever falls by the occurrence of a CRISIS – that is, a sudden termination of the symptoms – or by a more gradual subsidence of the temperature, technically termed a lysis. If death ensues, this is due to failure of the vital centres in the brain or of the heart, as a result of either the infection or hyperpyrexia.
Treatment Fever is a symptom, and the correct treatment is therefore that of the underlying condition. Occasionally, however, it is also necessary to reduce the temperature by more direct methods: physical cooling by, for example, tepid sponging, and the use of antipyretic drugs such as aspirin or paracetamol.... fever
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