Acute asthma is characterized by dyspnea and commonly also by troublesome cough.
Air passing through multiple narrowed airways makes polyphonic musical sounds called wheezing that are most apparent on expiration when intrathoracic airways narrow. Inspiratory effort to overcome airway obstruction causes retraction of the soft tissues of the thorax. Intercostal retractions alone suggest only mildly increased respiratory effort while substernal and suprasternal retractions indicate substantially increased work of breathing and is generally accompanied by use of accessory muscles of respiration. Hypoxemia is commonly present, initially from mismatching of ventilation and perfusion but may also result from hypoventilation with hypercapnia. Death can occur unexpectedly from these sudden attacks or from progressive respiratory failure during prolonged episodes that are inadequately treated.