Carbon dioxide respiratory response during positive inspiratory pressure in COPD patients

The aim of this study was to compare the effect of inspiratory pressure support (IPS) on the respiratory CO2 response in 13 stable COPD patients and in 13 normal subjects. Without IPS, the slopes of the ventilatory response to CO2 were lower in the patients than in the normal subjects (mean +/- SEM, 0.82 +/- 0.19 vs. 1.69 +/- 0.31 l.min-1.mmHg-1). When IPS was applied, both groups showed, at any level of end-tidal CO2 pressure, an increase in ventilation due to an increase in tidal volume (VT) associated with a decrease in occlusion pressure (P0.1). In addition, respiratory parameters (VE, VT, P0.1, inspiratory flow) were insensitive to CO2 as long as PETCO2 remained below a threshold which was slightly above the eupneic value. However, above this CO2-threshold, no differences in slopes were observed between the IPS and control conditions in either group, except for a decrease in the P0.1 slope during IPS in the COPD patients. In conclusion, IPS induced similar respiratory changes during CO2 response in stable COPD patients and in normal subjects. Above the eupneic value, IPS did not change the slope of the ventilatory response to CO2.