Breathing pattern assessment in normocapnic and hypercapnic patients in chronic obstructive pulmonary disease

Thirty-six patients, 24 normocapnic (mean age +/- SD: 60 +/- 10) and 12 hypercapnic (mean age +/- SD: 64 +/- 9) were compared with a control group (10 volunteers, mean age +/- SD: 46 +/- 8) for the following patterns of respiratory drive and respiratory timing: (1) mean inspiratory flow (Vt/Ti); (2) mouth occlusion pressure 100 ms after the onset of inspiration (P 0.1) and minute ventilation (Ve); (3) inspiratory duty cycle Ti/Tt). The data suggest COPD "respiratory patterns" which may be characterized by the following features: (1) increased mean inspiratory flow (Vt/Ti); (2) increased P 0.1 (in absolute values), P 0.1/Ve and P 0.1/Vt/Ti; (3) reduction in inspiratory duty cycle (Ti/Tt). Changes are more evident in inspiratory duty cycle among hypercapnic pts. When respiratory obstruction becomes worse and hypercapnia appears, the Ti/Tt decrease could be explained by a reduction in diaphragm muscle work, that can prevent the failure of diaphragmatic contractility.