Rapidly adapting receptors in acute heart failure and their impact on dyspnea.

Acute heart failure is associated with dyspnea that is usually defined as difficulty in breathing that is accompanied by an element of distress. It is commonly associated with an increase in the rate of ventilation, wheezing, an increase in airway secretions and cough. This review examines the reflexes which generate these responses with particular reference to the role of rapidly adapting receptors (RAR) in the airways. The essential feature of acute heart failure is an increase in pulmonary extravascular fluid volume. Small acute increases in extravascular fluid volume in the airways activate the RAR. With larger increases both the RAR and the C-fiber receptors in the airways and the alveoli are activated. Activation of RAR causes a reflex increase in respiratory rate, tracheal tone and mucus secretion from the airways. It is suggested that the RAR play a significant role in monitoring changes in the extravascular fluid volume of the airways and mediate the respiratory reflexes associated with acute heart failure.