Influence of exercise and CO2 on breathing pattern in patients with chronic obstructive lung disease (COLD).

In ten eucapnic patients with chronic obstructive lung disease (COLD) we evaluated the breathing pattern during induced progressive hypercapnia (CO2 rebreathing) and progressive exercise on an ergometric bicycle (30 W/3 min). The time and volume components of the respiratory cycle were measured breath by breath. When compared to hypercapnia, the increase in ventilation (VE) during exercise was associated with a smaller increase in tidal volume (VT) and a greater increase in respiratory frequency (fR). Plots of tidal volume (VT) against both inspiratory time (TI) and expiratory time (TE) showed a greater decrease in both TI and TE during exercise than with hypercapnia. Analysis of VE in terms of flow (VT/TI) and timing (TI/TT) showed VE to increase by a similar increase to that in VT/TI during both exercise and hypercapnia, while TI/TT did not change significantly. When the patients were matched for a given VE (28 l.min-1), exercise induced a smaller increase in VT (p less than 0.05), a greater increase in fR (p less than 0.025); TI (p less than 0.025) and TE (p less than 0.01) were found to be smaller during exercise than hypercapnia. The change in the off-switch mechanism during exercise and hypercapnia could account for our results.