The use of exercise testing and other methods in the investigation of dyspnea.

The sensation of effort is increased when the tension developed by active muscle is increased or when the muscle is weak; similar factors contribute to the sense of respiratory effort that constitute the symptoms of dyspnea. Exercise testing enables systematic loading of the respiratory muscles to be studied; the components of the ventilatory responses to exercise may be quantified in terms of the pattern and timing of breathing and of inspiratory flow and volume. The associated sensation of respiratory effort may then be related to the tension developed by respiratory muscles and to their strength.