Effect of chronic lung disease on the perception of added inspiratory loads.

The perceived magnitude of externally added loads to breathing was estimated in 10 normal subjects and 10 patients with chronic lung disease (5 obstructive, 5 interstitial disorders) to determine if chronic mechanical abnormalities of the respiratory system are accompanied by changes in the perception of dyspnea. Flow rates and tidal volumes were varied to assess the effect of altered patterns of breathing. With added resistive loads, the perceived magnitude increased as both resistance and the flow rate increased. With elastic loads the perceived magnitude increased as both elastance and tidal volume increased. In all subjects, perceived magnitude of added loads was most directly related to the inspiratory pressure used to overcome the load. Although the exponent for the power function relationship between perceived magnitude and the physical magnitude of the load was affected by the subject's age, there was no difference between the patients studied and the age-matched normal subjects. The results indicate that the sensation associated with added loads to breathing is the same in patients with chronic lung disease as in normal subjects. Also, they suggest that the altered pattern of breathing in patients with chronic lung disease is a behavioral adaptation to minimize respiratory distress.