Drive and Performance of the Ventilatory Apparatus in Chronic Obstructive Lung Disease

Abstract

Mechanical performance of the ventilatory apparatus (lungs and chest wall) and drive from the respiratory center were independently assessed in patients with chronic obstructive lung disease and normal subjects. Performance was abnormal in all the patients but more noticeably in those with hypercapnia. Drive, assessed from changes in the electromyogram of the diaphragm during rebreathing, was abnormally low only in patients with hypercapnia (average arterial-blood P CO ₂ of 61 mmHg); the integrated electromyographic activity increased an average of 1.7 units/mmHg of arterial-blood P CO ₂ whereas in other patients and in normal subjects, it increased 24 and 18 units respectively. These results suggest that mechanical alterations of lungs and chest wall have a fundamental role in the buildup of CO₂ retention in chronic obstructive lung disease. However, once hypercapnia appears, decreased respiratory-center drive is also important and becomes predominant with marked CO₂ retention. Mechanical and central factors in the treatment of respiratory failure must be distinguished.