RELATIONSHIP OF RESTING LUNG-MECHANICS AND EXERCISE PATTERN OF BREATHING IN PATIENTS WITH CHRONIC OBSTRUCTIVE LUNG-DISEASE

To investigate the influence of resting pulmonary mechanics on the pat tern of breathing during exercise in chronic obstructive pulmonary dis ease (COPD), we studied 29 patients with moderate to severe COPD (FEV1 50 +/- 20 percent predicted), and 10 normal subjects. Lung mechanics were studied using esophageal balloon technique and body-box. Incremen tal exercise testing was performed to exhaustion. As minute ventilatio n (VE) increases, COPD patients with the highest pulmonary resistance (RL) or lowest elastic recoil pressure (PL), used a greater tidal volu me/vital capacity ratio (VT/VC) than the COPD patients with more norma l RL or lowest PL. To describe the breathing pattern during exercise, an exponential constant (K) describes the rates of increase in VT/VC r atio with increasing VE, calculated according to the equation VT=VC(1- e(-KVE)). The K values achieved by COPD patients were higher than in n ormal subjects. In addition, K value correlated negatively with the re sting FEV1 and FVC of COPD patients. When COPD patients were grouped a ccording to their K values, it was revealed that patients with high K values generated greater VT/VC ratio and also have the most abnormal r esting lung mechanics. These results suggest that the exercise breathi ng pattern in COPD patients is significantly influenced by the degree of impairment of resting lung mechanics.