Reversible airway obstruction: neurohumoral mechanisms and treatment. Lecture on asthma: clinical overview.

Asthma is an airway obstruction which is reversible, either spontaneously or in response to treatment. Repeated peak expiratory flow rate (PEFR) measurements, up to six times daily, allows this characteristic reversibility to be recognised, to guide diagnosis and therapy. Chronic asthmatics may eventually become relatively irreversible, and then appear similar to chronic bronchitics - unless an adequate history is taken. The commonest world-wide allergen is the fecal pellet of the house mite. Modern therapy of asthma starts with inhaled beta 2 agonists, but difficulty in using metered dose inhalers is helped by the 'spacer', or reservoirs (e.g. 'Nebuhaler'). Interaction between slow-release oral theophyllines and beta 2 agonists by inhalation maximises bronchodilatation but minimises tremor. High-dose ipratropium inhalation, as isotonic wet nebulisation with a beta 2 agonist, is useful in acute severe asthma. High doses of inhaled topical steroid are valuable in the difficult asthmatic, but pituitary adrenal suppression occurs if dosage exceeds 1,500 micrograms/day. Cromoglycate and a beta 2 agonist by inhalation can prevent exercise-induced asthma. Long-term oral steroids (never over 10 mg/day) are only used if inhaled therapy (+/- oral slow-release theophyllines) fails. Acute severe asthma needs parenteral steroid, parenteral beta 2 agonist, high-dose beta 2 agonist by inhalation, oxygen and hospital admission. Ventilation is increased in the acute severe asthmatic with hypoxia and low PCO2. In 90 asthmatic deaths surveyed in Britain, half had failed to realise the severity.