Breathlessness and mouth occlusion pressure in patients with chronic obstruction of the airways.

In order to evaluate the hypothesis that the sensation of dyspnea is due to an "inappropriate relationship between length and tension" in the respiratory musculature, studies were performed in 24 patients with chronic obstruction of the airways. They were divided into two groups solely on the basis of subjective and objective presence or absence of breathlessness and dyspnea at rest. Spirometric tests and body plethysmography were performed in each patient. The ventilatory pattern at rest was recorded and repeated measurements of mouth occlusion pressure were made. It is concluded that breathlessness in patients with airways obstruction is not associated with major differences in arterial blood gases or in VO2, VE, f or the pattern of individual breaths; there is a greater degree of airway obstruction and increased inspiratory neuromuscular drive. The minute ventilation achieved for a given inspiratory neuromuscular output, which may be considered analogous to the length-tension relationship of the respiratory musculature, is significantly decreased. These results are in accordance with the theory of mechanical inappropriateness as a cause of dyspnea.