Factors determining the ventilatory response to carbon dioxide in chronic obstructive airways disease.

1. The ventilatory response to carbon dioxide was measured in a group of patients with chronic obstructive airways disease using a rebreathing method. 2. The slope of the carbon dioxide response curve was obtained by plotting the ventilation at successive half minutes against the corresponding mean end tidal Pco,. 3. The slope of the carbon dioxide response curve was positively correlated with (a) the FEVl and (b) the reciprocal of the resting arterial Pco,, both these correlations being statistically significant. 4. Reference to FEV, alone could explain more than 80% of the variation in the slope of the CO, response curve. This explained variation was not significantly improved by the additional consideration of the resting arterial Pco,. 5. It was suggested that whatever the underlying complex mechanisms that determine the response to COz, the FEVl can be used as an empirical factor for the prediction of this response in patients with chronic obstructive airways disease.