DYSPNOEA

Dyspnoea is an abnormal awareness of breathing occurring either at rest or at an unexpectedly low level of exertion. It is a major symptom of many cardiac disorders, particularly left heart failure, but its mechanisms are complex. In acute pulmonary oedema and orthopnoea, dyspnoea is due mainly to the elevated left atrial pressure that characterizes left heart failure. This produces a corresponding elevation of the pulmonary capillary pressure and increases transudation into the lungs, which become oedematous and stiff. The extra effort required to ventilate the stiff lungs causes dyspnoea. In exertional dyspnoea, however, other mechanisms apart from changes in left atrial pressure are also important.