LACK OF VENTILATORY THRESHOLD IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

We investigated whether the ventilatory threshold (VET) could be detec ted in 25 patients with severe chronic obstructive pulmonary disease ( COPD). Exercise on a treadmill was performed until symptom-limited max imum oxygen uptake (V-O2SL) was obtained. VET was absent in 14 patient s (56%, VET(-) group) and present in the others (44%, VET(+) group). B asal pulmonary functions and dyspnea index (V-E,V-SL/MVV) were not dif ferent between the two groups. Endurance time and exercise tolerance ( V-O2SL/bw) were significantly less in VET(-) than in VET(+). In the fo rmer group, Pa-O2, and pH at maximal exercise decreased and Pa-CO2 inc reased significantly, but HCO3- did not change compared with the corre sponding values before exercise. In the latter group, Pa(CO2)at maxima l exercise increased significantly, and pH and HCO3- decreased signifi cantly compared with the values before exercise, but Pa-O2 did not. Th e changes in Pa-O2 and Pa-CO2, were not different between the two grou ps, but changes in pH and HCO3- in VET(+) were greater than those in V ET(-). These results suggest that the absence of VET in some COPD pati ents indicates a lower exercise capacity without producing metabolic a cidosis. This may be caused by rapidly developing dyspnea.