It is characterised by paroxysms of dyspnoea accompanied by wheezing resulting from temporary narrowing of the bronchi by muscle spasm, mucosal swelling or viscid secretion. Obstruction of may smaller bronchi by the secretion causes respiratory embarrassment.
In most cases it starts either in childhood or in middle age. Generally the patient also suffers from other allergic disorders like allergic rhinitis or eczema. Family history is often positive. Wide range of allergens can cause asthma. In intrinsic asthma external antigens play no part. Common allergens are dust, smoke, pollens, congress-grass, cold weather or eatables, sour food etc., Anything under the sun can cause allergy. Previous exposure to antigen stimulates formation of antibody(IgE) and a type I antigen-antibody reaction in the bronchi may follow further exposure to specific antigen. This releases histamine, bradykinin and slow release substance which promote bronchial constriction and an inflammatory reaction of allergic type in the bronchial mucosa. Fish, eggs, milk, wheat may reach the bronchi via blood stream to cause similar effects. Non protein substances like drugs may cause asthma by forming haptens, emotional stress or strenuous work may also provoke asthmatic attack.
Paroxysms of sudden onset preceded by feeling of tightness in chest, upright posture. In chronic asthma there may be continuous wheeze and breathlessness on exertion. Here may be associated chronic bronchitis.
In some patients the attack may occur only in the night. This is called nocturnal asthma.
During acute attack the patient may be restless, agitated, sweating, breathing through lips with a prolonged expiration and using accessory muscles of respiration. Wheezing may be audible and patient may have census. Wheeze decreases as airflow diminishes. This decrease in wheeze may wrongly be interpreted as sign of improvement. Cyanosis, tachypnoea, tachycardia and completely silent chest suggest serious condition and hence necessity of hospitalisation.