RESPIRATORY LOAD COMPENSATION DURING HYPERCAPNIC VENTILATORY RESPONSE IN PULMONARY-EMPHYSEMA

The purpose of this study is to examine the relationship between mechanical factors and the load compensation during hypercapnia in emphysema. In 36 clinically stable patients, we conducted pulmonary function tests and hypercapnic ventilatory response (HCVR) tests with and without inspiratory flow-resistive loading (IRL) (17 cm H2O/L/s). The mean value of HCVR significantly decreased with IRL, while that of the mouth occlusion pressure (P0.1) response increased. Regardless of IRL, the HCVR values were correlated with FEV(1)/FVC and airway resistance. The load compensation, evaluated by the ratio of the HCVR value and the P0.1 response before and after IRL, was inversely correlated with percent FRC (r= -0.38, r= -0.39: both p<0.05). Breathing pattern analysis at the end-tidal pressure of carbon dioxide of 55 mm Hg elicited the decrease of (tidal volume/inspiratory time (VT/TI) and the increase of TI and TI/TTOT. Although the absolute changes of VT and f were inconsistent among subjects, each relative ratio before and after IRL was correlated again with percent FRC (r= -0.46, r=0.44: both p<0.01). Therefore, the position of the inspiratory muscles at the onset of inspiration may influence the load compensation during hypercapnia in emphysema.