Asthma (Gr. aσθua, from aειυ, to blow), a diseas3 characterized by an extreme difficulty of respiration, which is worse at certain seasons of the year and particular periods of the day, being generally most severe at night. The difficulty of breathing is increased by violent emotions, damp atmosphere, excess of any kind, strong exercise, running, walking quickly, or ascending a flight of stairs. It is also more laborious in a horizontal position, and hence more distress is felt in bed at night; the warmth of the bed also excites increased secretion of the mucous follicles, and this blocks up the air passages more completely, causing paroxysms to be more frequent than during the day. The patient seeks relief by sitting upright in bed, or bending his body forward, and endeavoring to expand the chest mechanically by every possible means. Old persons are more liable to the diease than young. Some writers describe the disease mainly as a nervous affection; others as the result of organic lesion of the heart and blood vessels; while others again attribute it to dilatation of the air vesicles of the lungs. All these and many other complications may exist.

It is now believed that spasmodic asthma is caused by a spasm of the muscular fibres encircling the bronchial tubes, especially the smaller branches. The existence of these fibres is placed beyond a doubt by microscopic examination. In common asthma the lining membrane of the air passages is more or less affected as in chronic bronchitis, but the affection of the mucous membrane extends further down into the lungs, the air cells are more obstructed, and the conformation of the chest itself is often somewhat contracted and defective. The action of the diaphragm is imperfect, as well as that of the walls of the chest; and hence it is that, from want of innervation and free action in these parts, the disease is commonly deemed nervous, as distinguished from chronic bronchitis, which affects the bronchial mucous membrane chiefly. In spasmodic asthma, the nerves are still more deeply implicated; their action seems defective in the respiratory organs, as stammering shows imperfect nervous action in the organs of speech; and in both cases the difficulty is increased by physical or moral excitement.

Chronic asthma seldom shortens life, where patients carefully avoid all violent emotions, exercise, and excess, although spasmodic paroxysms may endanger life at any time where these precautions are neglected. Attacks of spasmodic asthma generally occur during the first sleep, soon after midnight, or very early in the morning. The patient suddenly awakes with a sense of suffocation, tightness of the chest, and difficulty of breathing. The respiration is wheezing and laborious, the shoulders are raised, and every effort made to enlarge the chest. The pulse is usually quick, weak, and irregular; the lower extremities cold. When cough and expectoration come on, the patient is relieved. The spasm, however, may continue half an hour or more, and even as much as three or four hours. - Asthma is often complicated with diseases of the heart or with chronic bronchitis, acting as a source of permanent congestion, predisposing the parts to be more easily thrown into a state of spasm. Sometimes severe attacks of dry catarrh are aggravated by spasm, as in the "bronchial asthma" of Andral. - The most common consequences or concomitants of the disease are chronic inflammation and dilatation of the bronchi; emphysema and oedema of the lungs; haemoptysis; tubercular deposits; hypertrophy and dilatation of the cavities of the heart; effusions into the pericardium, the pleura, and sometimes congestion and effusions in the head, giving rise to coma or apoplexy.

The treatment of the paroxysm consists in administering narcotics and antispasmodics, to be given if possible as soon as the first sensations are felt. Strong coffee, laudanum, and ether are among the best; and stramonium smoked as tobacco is often very useful, but should be used with caution where the heart is diseased. Those medicines are most effectual which produce expectoration.